Merge pull request #5 from fix/excel-multiline-tsv

Fix #6: 変換時の暗黙的なデータ欠落を防止

.gitea/workflows/ci.yml

@@ -39,6 +39,12 @@ jobs:
       - name: Run tests
         run: go test ./...
 
+      - name: Run vet
+        run: go vet ./...
+
+      - name: Check reachable vulnerabilities
+        run: go run golang.org/x/vuln/cmd/govulncheck@v1.6.0 ./...
+
       - name: Build
         run: go build ./cmd/dataxl
 

.gitea/workflows/release.yml

@@ -30,6 +30,12 @@ jobs:
       - name: Run tests
         run: go test ./...
 
+      - name: Run vet
+        run: go vet ./...
+
+      - name: Check reachable vulnerabilities
+        run: go run golang.org/x/vuln/cmd/govulncheck@v1.6.0 ./...
+
       - name: Build release archives
         env:
           RELEASE_TAG: ${{ inputs.tag }}

README.md

@@ -18,7 +18,7 @@ TSVへ変換したり、Excelからコピーした表を再び構造化データ
 
 ## インストール
 
-Go 1.24以上が必要です。
+Go 1.25以上が必要です。
 
 ```sh
 go install git.rumginger.org/agent/dataxl/cmd/dataxl@latest
@@ -111,6 +111,45 @@ id	items[0].qty	items[0].sku	user.name
 逆方向の変換では、`user.name` や `items[0].sku` のような列名から入れ子の
 map/arrayを復元します。
 
+列パスは `.` でmapのキー、`[n]` で0始まりの配列indexを表します。たとえば
+`orders[0].items[1].sku` は、最初の注文に含まれる2番目の商品の `sku` です。
+
+`.`、`[`、`]` を含むmapキーや空のmapキーはJSON文字列を使ったbracket記法で
+表します。たとえば `{"build.target": {"x[y]": 1}}` は
+`["build.target"]["x[y]"]` という列名になります。
+
+同じ行に `user` と `user.name` のような競合する列がある場合や、同名ヘッダーが
+複数ある場合はエラーにします。どちらかの値だけを採用して正常終了することは
+ありません。
+
+## セル値の型推定
+
+CSV、TSV、XLSXから構造化形式へ戻す際は、セル文字列を次の順で推定します。
+
+- 空文字は空文字列
+- `true` / `false` はboolean
+- 通常の整数は64-bit integer
+- 小数点または指数表記を含む数値は64-bit floating point
+- それ以外は文字列
+
+郵便番号や商品コードを想定し、`00123` や `-01` のようなゼロ埋め値は文字列のまま
+保持します。セルの前後空白も文字列の一部として保持し、` 42 ` のような値を数値に
+変換しません。日付、時刻、`null` は自動推定しません。
+
+## データ欠落を防ぐ検証
+
+- JSON入力はUTF-8として検証し、1つの値と後続空白だけを許可します。2つ目の値、
+  不正な後続データ、object内の重複キーは、値を置換・無視せずエラーにします。
+- YAML streamに複数文書がある場合は、順序を保った配列としてすべて変換します。
+- UTF-8 BOM付きCSV/TSVでは先頭のBOMをencoding markerとして除去します。
+- CSV/TSVはUTF-8として検証し、ヘッダーより列数が多い行をエラーにします。
+- 空ヘッダー列に値がある場合、重複ヘッダー、復元時に型が競合する列パスは
+  エラーにします。
+- scalar fieldを1つも持たないrecordは表で表現できないため、空行へ変換して
+  record数を失う代わりにエラーにします。空のrecord listは空の表へ変換できます。
+- `rows`、`records`、`items` を行配列として展開するのは、それがオブジェクト唯一の
+  キーである場合だけです。同階層のmetadataを破棄しません。
+
 ## CLIオプション
 
 - `-i`: 入力ファイル。省略時はstdin。
@@ -119,12 +158,17 @@ map/arrayを復元します。
 - `-to`: 出力形式。`json`, `yaml`, `toml`, `csv`, `tsv`, `xlsx`。
 - `-sheet`: XLSXの読み書きに使うシート名。既定値は `Sheet1`。
 - `-pretty`: JSONなどの構造化出力を整形するか。既定値は `true`。
+- `-version`: バージョンを表示して終了します。
 
 ## 現在の制約
 
 - 表形式では1行目をヘッダーとして扱います。
 - XLSXは指定した1シートのみ読み書きします。
 - セル値の型推定は、空文字、真偽値、整数、小数、文字列の範囲です。
+- 空のmap/arrayは表側で `{}` / `[]` と表示されますが、逆変換時は文字列になります。
+- structured形式の `null` と表形式の空文字は同じ空セルになります。
+- top-level scalarやscalar配列は表側で `value` 列を使うため、逆変換時は
+  `value` キーを持つレコードになります。
 - 複雑なExcel書式や数式の保持は目的外です。
 
 ## 開発者向け情報

cmd/dataxl/conversion.go

@@ -0,0 +1,79 @@
+package main
+
+import (
+	"fmt"
+	"path/filepath"
+	"strings"
+)
+
+// convert routes data through either the structured-value or table internal
+// representation. Keeping this matrix in one place makes format adapters
+// independent from CLI and file I/O concerns.
+func convert(input []byte, from, to, sheet string, pretty bool) ([]byte, error) {
+	switch {
+	case isTabular(from) && isTabular(to):
+		t, err := parseTable(input, from, sheet)
+		if err != nil {
+			return nil, err
+		}
+		return encodeTable(t, to, sheet)
+	case isTabular(from):
+		t, err := parseTable(input, from, sheet)
+		if err != nil {
+			return nil, err
+		}
+		records, err := tableToRecords(t)
+		if err != nil {
+			return nil, err
+		}
+		return encodeStructured(records, to, pretty)
+	case isTabular(to):
+		value, err := parseStructured(input, from)
+		if err != nil {
+			return nil, err
+		}
+		t := valueToTable(value)
+		if len(t.Header) == 0 && len(t.Rows) > 0 {
+			return nil, fmt.Errorf("structured value has records but no scalar fields to represent as a table")
+		}
+		return encodeTable(t, to, sheet)
+	default:
+		value, err := parseStructured(input, from)
+		if err != nil {
+			return nil, err
+		}
+		return encodeStructured(value, to, pretty)
+	}
+}
+
+func normalizeFormat(format string) string {
+	format = strings.ToLower(strings.TrimPrefix(strings.TrimSpace(format), "."))
+	switch format {
+	case "yml":
+		return "yaml"
+	case "xlsm", "xls":
+		return "xlsx"
+	default:
+		return format
+	}
+}
+
+func inferFormat(path string) string {
+	if path == "" || path == "-" {
+		return ""
+	}
+	return normalizeFormat(filepath.Ext(path))
+}
+
+func validateFormat(format string) error {
+	switch format {
+	case "json", "yaml", "toml", "csv", "tsv", "xlsx":
+		return nil
+	default:
+		return fmt.Errorf("unsupported format %q", format)
+	}
+}
+
+func isTabular(format string) bool {
+	return format == "csv" || format == "tsv" || format == "xlsx"
+}

cmd/dataxl/conversion_matrix_test.go

@@ -0,0 +1,64 @@
+package main
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestConversionMatrixPreservesRepresentativeTable(t *testing.T) {
+	formats := []string{"json", "yaml", "toml", "csv", "tsv", "xlsx"}
+	records := []any{
+		map[string]any{
+			"active": true,
+			"id":     int64(1),
+			"name":   "Alice",
+			"note":   "  first line\nsecond line  ",
+		},
+		map[string]any{
+			"active": false,
+			"id":     int64(2),
+			"name":   "ボブ",
+			"note":   "comma, tab\t and quote \"",
+		},
+	}
+	want := valueToTable(records)
+
+	fixtures := make(map[string][]byte, len(formats))
+	for _, format := range formats {
+		var (
+			data []byte
+			err  error
+		)
+		if isTabular(format) {
+			data, err = encodeTable(want, format, "Sheet1")
+		} else {
+			data, err = encodeStructured(records, format, true)
+		}
+		if err != nil {
+			t.Fatalf("build %s fixture: %v", format, err)
+		}
+		fixtures[format] = data
+	}
+
+	for _, from := range formats {
+		for _, to := range formats {
+			t.Run(from+"_to_"+to, func(t *testing.T) {
+				converted, err := convert(fixtures[from], from, to, "Sheet1", true)
+				if err != nil {
+					t.Fatalf("convert %s -> %s: %v", from, to, err)
+				}
+				normalized, err := convert(converted, to, "tsv", "Sheet1", false)
+				if err != nil {
+					t.Fatalf("normalize %s output through TSV: %v", to, err)
+				}
+				got, err := parseTable(normalized, "tsv", "Sheet1")
+				if err != nil {
+					t.Fatalf("parse normalized TSV: %v", err)
+				}
+				if !reflect.DeepEqual(got, want) {
+					t.Fatalf("%s -> %s table = %#v, want %#v", from, to, got, want)
+				}
+			})
+		}
+	}
+}

cmd/dataxl/data_integrity_test.go

@@ -0,0 +1,373 @@
+package main
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"reflect"
+	"strings"
+	"testing"
+)
+
+func TestDelimitedInputPreservesCellWhitespace(t *testing.T) {
+	tests := []struct {
+		format string
+		input  string
+	}{
+		{format: "csv", input: "name,note\nAlice,  keep both sides  \n"},
+		{format: "tsv", input: "name\tnote\nAlice\t  keep both sides  \n"},
+	}
+	for _, tc := range tests {
+		t.Run(tc.format, func(t *testing.T) {
+			got, err := convert([]byte(tc.input), tc.format, "json", "Sheet1", false)
+			if err != nil {
+				t.Fatal(err)
+			}
+			var records []map[string]any
+			if err := json.Unmarshal(got, &records); err != nil {
+				t.Fatal(err)
+			}
+			if value := records[0]["note"]; value != "  keep both sides  " {
+				t.Fatalf("note = %#v, want surrounding whitespace preserved", value)
+			}
+		})
+	}
+}
+
+func TestDelimitedInputStripsUTF8BOMFromHeader(t *testing.T) {
+	tests := []struct {
+		format    string
+		delimiter string
+	}{
+		{format: "csv", delimiter: ","},
+		{format: "tsv", delimiter: "\t"},
+	}
+	for _, tc := range tests {
+		t.Run(tc.format, func(t *testing.T) {
+			input := "\ufeffname" + tc.delimiter + "active\nAlice" + tc.delimiter + "true\n"
+			got, err := convert([]byte(input), tc.format, "json", "Sheet1", false)
+			if err != nil {
+				t.Fatal(err)
+			}
+			var records []map[string]any
+			if err := json.Unmarshal(got, &records); err != nil {
+				t.Fatal(err)
+			}
+			want := []map[string]any{{"name": "Alice", "active": true}}
+			if !reflect.DeepEqual(records, want) {
+				t.Fatalf("records = %#v, want %#v", records, want)
+			}
+		})
+	}
+}
+
+func TestRecordsFromValuePreservesWrapperSiblings(t *testing.T) {
+	for _, wrapper := range []string{"items", "records", "rows"} {
+		t.Run(wrapper, func(t *testing.T) {
+			value := map[string]any{
+				"metadata": "keep me",
+				wrapper:    []any{map[string]any{"id": json.Number("1")}},
+			}
+			got := recordsFromValue(value)
+			want := []any{value}
+			if !reflect.DeepEqual(got, want) {
+				t.Fatalf("records = %#v, want complete object %#v", got, want)
+			}
+		})
+	}
+}
+
+func TestRecordsFromValueUnwrapsSoleWrapper(t *testing.T) {
+	rows := []any{map[string]any{"id": json.Number("1")}}
+	for _, wrapper := range []string{"items", "records", "rows"} {
+		t.Run(wrapper, func(t *testing.T) {
+			if got := recordsFromValue(map[string]any{wrapper: rows}); !reflect.DeepEqual(got, rows) {
+				t.Fatalf("records = %#v, want sole wrapper rows %#v", got, rows)
+			}
+		})
+	}
+}
+
+func TestParseStructuredRejectsTrailingJSONValue(t *testing.T) {
+	_, err := parseStructured([]byte(`{"first":1} {"second":2}`), "json")
+	if err == nil || !strings.Contains(err.Error(), "multiple JSON values") {
+		t.Fatalf("error = %v, want multiple JSON values", err)
+	}
+}
+
+func TestParseStructuredRejectsDuplicateJSONKeys(t *testing.T) {
+	for _, input := range []string{
+		`{"id":1,"id":2}`,
+		`{"nested":{"name":"first","name":"second"}}`,
+	} {
+		if _, err := parseStructured([]byte(input), "json"); err == nil || !strings.Contains(err.Error(), "duplicate JSON object key") {
+			t.Fatalf("error = %v for %s, want duplicate-key error", err, input)
+		}
+	}
+}
+
+func TestParseStructuredRejectsInvalidJSONUTF8(t *testing.T) {
+	input := []byte{'{', '"', 'k', 'e', 'y', '"', ':', '"', 0xff, '"', '}'}
+	if _, err := parseStructured(input, "json"); err == nil || !strings.Contains(err.Error(), "not valid UTF-8") {
+		t.Fatalf("error = %v, want UTF-8 error", err)
+	}
+}
+
+func TestJSONParserPreservesEmptyArrayAndLargeNumber(t *testing.T) {
+	largeNumber := strings.Repeat("9", 400)
+	for _, input := range []string{"[]", `{"value":` + largeNumber + `}`} {
+		got, err := convert([]byte(input), "json", "json", "Sheet1", false)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if string(got) != input {
+			t.Fatalf("JSON = %s, want %s", got, input)
+		}
+	}
+}
+
+func TestParseStructuredPreservesEveryYAMLDocument(t *testing.T) {
+	got, err := parseStructured([]byte("first: 1\n---\nsecond: 2\n"), "yaml")
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := []any{
+		map[string]any{"first": 1},
+		map[string]any{"second": 2},
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("documents = %#v, want %#v", got, want)
+	}
+}
+
+func TestParseStructuredAllowsTrailingWhitespace(t *testing.T) {
+	for _, tc := range []struct {
+		format string
+		input  string
+	}{
+		{format: "json", input: "{\"name\":\"Alice\"}\n\t  "},
+		{format: "yaml", input: "name: Alice\n\n"},
+	} {
+		t.Run(tc.format, func(t *testing.T) {
+			if _, err := parseStructured([]byte(tc.input), tc.format); err != nil {
+				t.Fatalf("valid input rejected: %v", err)
+			}
+		})
+	}
+}
+
+func TestWrapperSiblingsSurviveJSONTSVRoundTrip(t *testing.T) {
+	input := []byte(`{"metadata":"keep me","items":[{"id":1},{"id":2}]}`)
+	tsv, err := convert(input, "json", "tsv", "Sheet1", false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if lines := bytes.Count(tsv, []byte{'\n'}); lines != 2 {
+		t.Fatalf("TSV has %d lines, want header plus one complete-object row:\n%s", lines, tsv)
+	}
+	for _, column := range []string{"items[0].id", "items[1].id", "metadata"} {
+		if !bytes.Contains(tsv, []byte(column)) {
+			t.Fatalf("TSV missing %q:\n%s", column, tsv)
+		}
+	}
+
+	restored, err := convert(tsv, "tsv", "json", "Sheet1", false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var records []map[string]any
+	if err := json.Unmarshal(restored, &records); err != nil {
+		t.Fatal(err)
+	}
+	if got := fmt.Sprint(records[0]["metadata"]); got != "keep me" {
+		t.Fatalf("metadata = %q after round trip", got)
+	}
+}
+
+func TestDelimitedInputRejectsRowsWiderThanHeader(t *testing.T) {
+	_, err := convert([]byte("a,b\n1,2,3\n"), "csv", "json", "Sheet1", false)
+	if err == nil || !strings.Contains(err.Error(), "row 2 has 3 fields") {
+		t.Fatalf("error = %v, want wider-row error", err)
+	}
+}
+
+func TestDelimitedInputRejectsInvalidUTF8(t *testing.T) {
+	input := []byte{'n', 'a', 'm', 'e', '\n', 0xff, '\n'}
+	_, err := convert(input, "csv", "json", "Sheet1", false)
+	if err == nil || !strings.Contains(err.Error(), "not valid UTF-8") {
+		t.Fatalf("error = %v, want UTF-8 error", err)
+	}
+}
+
+func TestDelimitedSingleEmptyCellRowRoundTrip(t *testing.T) {
+	want := table{Header: []string{"value"}, Rows: [][]string{{""}}}
+	for _, format := range []string{"csv", "tsv"} {
+		t.Run(format, func(t *testing.T) {
+			encoded, err := encodeTable(want, format, "Sheet1")
+			if err != nil {
+				t.Fatal(err)
+			}
+			got, err := parseTable(encoded, format, "Sheet1")
+			if err != nil {
+				t.Fatal(err)
+			}
+			if !reflect.DeepEqual(got, want) {
+				t.Fatalf("round trip = %#v, want %#v; encoded %q", got, want, encoded)
+			}
+		})
+	}
+}
+
+func TestStructuredRecordsWithoutScalarFieldsAreRejectedForTables(t *testing.T) {
+	for _, input := range []string{`{}`, `[{}]`} {
+		for _, format := range []string{"csv", "tsv", "xlsx"} {
+			t.Run(format+"_"+input, func(t *testing.T) {
+				_, err := convert([]byte(input), "json", format, "Sheet1", false)
+				if err == nil || !strings.Contains(err.Error(), "no scalar fields") {
+					t.Fatalf("error = %v, want unrepresentable-table error", err)
+				}
+			})
+		}
+	}
+}
+
+func TestEmptyRecordListCanRoundTripThroughDelimitedFormats(t *testing.T) {
+	for _, format := range []string{"csv", "tsv"} {
+		t.Run(format, func(t *testing.T) {
+			tabular, err := convert([]byte(`[]`), "json", format, "Sheet1", false)
+			if err != nil {
+				t.Fatal(err)
+			}
+			got, err := convert(tabular, format, "json", "Sheet1", false)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if string(got) != `[]` {
+				t.Fatalf("round trip = %s, want []", got)
+			}
+		})
+	}
+}
+
+func TestTableToRecordsRejectsColumnsThatWouldLoseData(t *testing.T) {
+	tests := []struct {
+		name  string
+		table table
+		want  string
+	}{
+		{
+			name:  "duplicate header",
+			table: table{Header: []string{"id", "id"}, Rows: [][]string{{"1", "2"}}},
+			want:  "duplicate header",
+		},
+		{
+			name:  "blank header with value",
+			table: table{Header: []string{"id", ""}, Rows: [][]string{{"1", "orphan"}}},
+			want:  "header is blank",
+		},
+		{
+			name:  "parent and child conflict",
+			table: table{Header: []string{"user", "user.name"}, Rows: [][]string{{"Alice", "Bob"}}},
+			want:  "expected an object",
+		},
+		{
+			name:  "object and array conflict",
+			table: table{Header: []string{"value.name", "value[0]"}, Rows: [][]string{{"Alice", "Bob"}}},
+			want:  "expected an array",
+		},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			_, err := tableToRecords(tc.table)
+			if err == nil || !strings.Contains(err.Error(), tc.want) {
+				t.Fatalf("error = %v, want one containing %q", err, tc.want)
+			}
+		})
+	}
+}
+
+func TestNestedArraysSurviveJSONTSVRoundTrip(t *testing.T) {
+	input := []byte(`{"matrix":[[1,2],[3,4]]}`)
+	tsv, err := convert(input, "json", "tsv", "Sheet1", false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	restored, err := convert(tsv, "tsv", "json", "Sheet1", false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var got []map[string]any
+	if err := json.Unmarshal(restored, &got); err != nil {
+		t.Fatal(err)
+	}
+	want := []map[string]any{{
+		"matrix": []any{
+			[]any{float64(1), float64(2)},
+			[]any{float64(3), float64(4)},
+		},
+	}}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("round trip = %#v, want %#v\nTSV:\n%s", got, want, tsv)
+	}
+}
+
+func TestDelimiterKeysSurviveJSONTSVRoundTrip(t *testing.T) {
+	input := []byte(`{"a.b":{"x[y]":1,"":2},"plain":3}`)
+	tsv, err := convert(input, "json", "tsv", "Sheet1", false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	parsed, err := parseTable(tsv, "tsv", "Sheet1")
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, header := range []string{`["a.b"][""]`, `["a.b"]["x[y]"]`, "plain"} {
+		if !containsString(parsed.Header, header) {
+			t.Fatalf("TSV missing escaped header %q:\n%s", header, tsv)
+		}
+	}
+	restored, err := convert(tsv, "tsv", "json", "Sheet1", false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var got []map[string]any
+	if err := json.Unmarshal(restored, &got); err != nil {
+		t.Fatal(err)
+	}
+	want := []map[string]any{{
+		"a.b":   map[string]any{"x[y]": float64(1), "": float64(2)},
+		"plain": float64(3),
+	}}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("round trip = %#v, want %#v\nTSV:\n%s", got, want, tsv)
+	}
+}
+
+func containsString(values []string, target string) bool {
+	for _, value := range values {
+		if value == target {
+			return true
+		}
+	}
+	return false
+}
+
+func TestParsePathRejectsMalformedHeaders(t *testing.T) {
+	tooDeep := "root" + strings.Repeat(".child", maxPathTokens)
+	for _, path := range []string{
+		"a..b",
+		"a[-1]",
+		"a[foo]",
+		"a[0",
+		"a]",
+		`["unterminated]`,
+		fmt.Sprintf("a[%d]", maxArrayIndex+1),
+		tooDeep,
+	} {
+		t.Run(path, func(t *testing.T) {
+			if _, err := parsePath(path); err == nil {
+				t.Fatalf("parsePath(%q) succeeded", path)
+			}
+		})
+	}
+}

cmd/dataxl/doc.go

@@ -0,0 +1,7 @@
+// Package main implements the dataxl command-line converter.
+//
+// Conversion uses two internal representations: structured Go values for
+// JSON/YAML/TOML and table for CSV/TSV/XLSX. Nested structured values cross the
+// boundary through dotted and indexed column paths such as user.name and
+// items[0].sku.
+package main

cmd/dataxl/fuzz_test.go

@@ -0,0 +1,90 @@
+package main
+
+import (
+	"encoding/json"
+	"reflect"
+	"strings"
+	"testing"
+	"unicode/utf8"
+)
+
+func FuzzPathKeyRoundTrip(f *testing.F) {
+	for _, seed := range []string{"name", "", "a.b", "x[y]", "日本語", " leading ", "quote\"slash\\"} {
+		f.Add(seed)
+	}
+	f.Fuzz(func(t *testing.T, key string) {
+		if !utf8.ValidString(key) {
+			t.Skip()
+		}
+		for _, prefix := range []string{"", "root"} {
+			path := appendPathKey(prefix, key)
+			tokens, err := parsePath(path)
+			if err != nil {
+				t.Fatalf("parse generated path %q: %v", path, err)
+			}
+			last := tokens[len(tokens)-1]
+			if last.isIndex || last.key != key {
+				t.Fatalf("path %q decoded final token %#v, want key %q", path, last, key)
+			}
+		}
+	})
+}
+
+func FuzzParseJSON(f *testing.F) {
+	for _, seed := range [][]byte{
+		[]byte(`{"name":"Alice","items":[1,2,null]}`),
+		[]byte(`{"duplicate":1,"duplicate":2}`),
+		[]byte(`[]`),
+		[]byte(`{"a":1} {"b":2}`),
+		{0xff},
+	} {
+		f.Add(seed)
+	}
+	f.Fuzz(func(t *testing.T, input []byte) {
+		if len(input) > 64*1024 {
+			t.Skip()
+		}
+		value, err := parseStructured(input, "json")
+		if err != nil {
+			return
+		}
+		encoded, err := json.Marshal(value)
+		if err != nil {
+			t.Fatalf("marshal accepted value: %v", err)
+		}
+		if !json.Valid(encoded) {
+			t.Fatalf("parser returned value that encoded as invalid JSON")
+		}
+	})
+}
+
+func FuzzDelimitedTableRoundTrip(f *testing.F) {
+	for _, seed := range []string{
+		"plain",
+		"  surrounding spaces  ",
+		"comma, tab\t quote\"",
+		"first line\nsecond line",
+		"日本語と絵文字🌙",
+	} {
+		f.Add(seed)
+	}
+	f.Fuzz(func(t *testing.T, value string) {
+		if !utf8.ValidString(value) || strings.Contains(value, "\r\n") {
+			t.Skip()
+		}
+		want := table{Header: []string{"value"}, Rows: [][]string{{value}}}
+		for _, format := range []string{"csv", "tsv"} {
+			encoded, err := encodeTable(want, format, "Sheet1")
+			if err != nil {
+				t.Fatalf("encode %s: %v", format, err)
+			}
+			got, err := parseTable(encoded, format, "Sheet1")
+			if err != nil {
+				t.Fatalf("parse %s: %v", format, err)
+			}
+			if !reflect.DeepEqual(got, want) {
+				t.Fatalf("%s round trip = %#v, want %#v", format, got, want)
+			}
+		}
+	})
+}

cmd/dataxl/main.go

@@ -1,25 +1,18 @@
 package main
 
 import (
-	"bytes"
-	"encoding/csv"
-	"encoding/json"
-	"errors"
 	"flag"
 	"fmt"
 	"io"
 	"os"
-	"path/filepath"
+	"runtime/debug"
-	"regexp"
-	"sort"
-	"strconv"
 	"strings"
-
-	"github.com/BurntSushi/toml"
-	"github.com/xuri/excelize/v2"
-	"gopkg.in/yaml.v3"
 )
 
+var buildVersion = "dev"
+
+// options contains CLI concerns only. Conversion functions receive explicit
+// arguments so they can be reused and tested without constructing a FlagSet.
 type options struct {
 	inFile  string
 	outFile string
@@ -27,11 +20,7 @@ type options struct {
 	to      string
 	sheet   string
 	pretty  bool
-}
+	version bool
-
-type table struct {
-	Header []string
-	Rows   [][]string
 }
 
 func main() {
@@ -42,6 +31,30 @@ func main() {
 }
 
 func run(args []string, stdin io.Reader, stdout, stderr io.Writer) error {
+	opt, err := parseOptions(args, stderr)
+	if err != nil {
+		return err
+	}
+	if opt.version {
+		_, err := fmt.Fprintln(stdout, "dataxl", resolvedVersion())
+		return err
+	}
+	if err := opt.resolveFormats(); err != nil {
+		return err
+	}
+
+	input, err := readInput(opt.inFile, stdin)
+	if err != nil {
+		return err
+	}
+	output, err := convert(input, opt.from, opt.to, opt.sheet, opt.pretty)
+	if err != nil {
+		return err
+	}
+	return writeOutput(opt.outFile, stdout, output)
+}
+
+func parseOptions(args []string, stderr io.Writer) (options, error) {
 	var opt options
 	fs := flag.NewFlagSet("dataxl", flag.ContinueOnError)
 	fs.SetOutput(stderr)
@@ -51,6 +64,7 @@ func run(args []string, stdin io.Reader, stdout, stderr io.Writer) error {
 	fs.StringVar(&opt.to, "to", "", "output format: json, yaml, toml, csv, tsv, xlsx")
 	fs.StringVar(&opt.sheet, "sheet", "Sheet1", "worksheet name for xlsx input/output")
 	fs.BoolVar(&opt.pretty, "pretty", true, "pretty-print structured output")
+	fs.BoolVar(&opt.version, "version", false, "print version and exit")
 	fs.Usage = func() {
 		_, _ = fmt.Fprintln(stderr, `Usage:
   dataxl -from yaml -to tsv -i input.yaml -o output.tsv
@@ -66,16 +80,26 @@ Notes:
   converting back to json/yaml/toml.`)
 	}
 	if err := fs.Parse(args); err != nil {
-		return err
+		return options{}, err
 	}
 	if fs.NArg() != 0 {
-		return fmt.Errorf("unexpected arguments: %s", strings.Join(fs.Args(), " "))
+		return options{}, fmt.Errorf("unexpected arguments: %s", strings.Join(fs.Args(), " "))
+	}
+	return opt, nil
 }
 
-	input, err := readInput(opt.inFile, stdin)
+func resolvedVersion() string {
-	if err != nil {
+	if buildVersion != "dev" {
-		return err
+		return buildVersion
 	}
+	info, ok := debug.ReadBuildInfo()
+	if ok && info.Main.Version != "" && info.Main.Version != "(devel)" {
+		return info.Main.Version
+	}
+	return buildVersion
+}
+
+func (opt *options) resolveFormats() error {
 	opt.from = normalizeFormat(opt.from)
 	opt.to = normalizeFormat(opt.to)
 	if opt.from == "" {
@@ -85,60 +109,12 @@ Notes:
 		opt.to = inferFormat(opt.outFile)
 	}
 	if opt.from == "" || opt.to == "" {
-		return errors.New("both -from and -to are required when a format cannot be inferred from file names")
+		return fmt.Errorf("both -from and -to are required when a format cannot be inferred from file names")
 	}
 	if err := validateFormat(opt.from); err != nil {
 		return err
 	}
-	if err := validateFormat(opt.to); err != nil {
+	return validateFormat(opt.to)
-		return err
-	}
-
-	var out []byte
-	// Use table as the common representation whenever either side is a
-	// spreadsheet-like format. Structured formats can then share the same
-	// flatten/restore path for CSV, TSV, and XLSX.
-	if isTabular(opt.from) && isTabular(opt.to) {
-		t, err := parseTable(input, opt.from, opt.sheet)
-		if err != nil {
-			return err
-		}
-		out, err = encodeTable(t, opt.to, opt.sheet)
-		if err != nil {
-			return err
-		}
-	} else if isTabular(opt.from) {
-		t, err := parseTable(input, opt.from, opt.sheet)
-		if err != nil {
-			return err
-		}
-		records := tableToRecords(t)
-		out, err = encodeStructured(records, opt.to, opt.pretty)
-		if err != nil {
-			return err
-		}
-	} else if isTabular(opt.to) {
-		value, err := parseStructured(input, opt.from)
-		if err != nil {
-			return err
-		}
-		t := valueToTable(value)
-		out, err = encodeTable(t, opt.to, opt.sheet)
-		if err != nil {
-			return err
-		}
-	} else {
-		value, err := parseStructured(input, opt.from)
-		if err != nil {
-			return err
-		}
-		out, err = encodeStructured(value, opt.to, opt.pretty)
-		if err != nil {
-			return err
-		}
-	}
-
-	return writeOutput(opt.outFile, stdout, out)
 }
 
 func readInput(path string, stdin io.Reader) ([]byte, error) {
@@ -155,459 +131,3 @@ func writeOutput(path string, stdout io.Writer, data []byte) error {
 	}
 	return os.WriteFile(path, data, 0o644)
 }
-
-func normalizeFormat(format string) string {
-	format = strings.ToLower(strings.TrimPrefix(strings.TrimSpace(format), "."))
-	switch format {
-	case "yml":
-		return "yaml"
-	case "xlsm", "xls":
-		return "xlsx"
-	default:
-		return format
-	}
-}
-
-func inferFormat(path string) string {
-	if path == "" || path == "-" {
-		return ""
-	}
-	return normalizeFormat(strings.TrimPrefix(filepath.Ext(path), "."))
-}
-
-func validateFormat(format string) error {
-	switch format {
-	case "json", "yaml", "toml", "csv", "tsv", "xlsx":
-		return nil
-	default:
-		return fmt.Errorf("unsupported format %q", format)
-	}
-}
-
-func isTabular(format string) bool {
-	return format == "csv" || format == "tsv" || format == "xlsx"
-}
-
-func parseStructured(input []byte, format string) (any, error) {
-	var value any
-	switch format {
-	case "json":
-		dec := json.NewDecoder(bytes.NewReader(input))
-		dec.UseNumber()
-		if err := dec.Decode(&value); err != nil {
-			return nil, err
-		}
-	case "yaml":
-		if err := yaml.Unmarshal(input, &value); err != nil {
-			return nil, err
-		}
-		value = normalizeYAML(value)
-	case "toml":
-		var m map[string]any
-		if err := toml.Unmarshal(input, &m); err != nil {
-			return nil, err
-		}
-		value = m
-	default:
-		return nil, fmt.Errorf("format %q is not structured", format)
-	}
-	return value, nil
-}
-
-func encodeStructured(value any, format string, pretty bool) ([]byte, error) {
-	switch format {
-	case "json":
-		if pretty {
-			return json.MarshalIndent(value, "", "  ")
-		}
-		return json.Marshal(value)
-	case "yaml":
-		return yaml.Marshal(value)
-	case "toml":
-		m, ok := value.(map[string]any)
-		if !ok {
-			m = map[string]any{"rows": value}
-		}
-		var b bytes.Buffer
-		err := toml.NewEncoder(&b).Encode(m)
-		return b.Bytes(), err
-	default:
-		return nil, fmt.Errorf("format %q is not structured", format)
-	}
-}
-
-func normalizeYAML(value any) any {
-	switch v := value.(type) {
-	case map[string]any:
-		out := make(map[string]any, len(v))
-		for key, child := range v {
-			out[key] = normalizeYAML(child)
-		}
-		return out
-	case map[any]any:
-		out := make(map[string]any, len(v))
-		for key, child := range v {
-			out[fmt.Sprint(key)] = normalizeYAML(child)
-		}
-		return out
-	case []any:
-		for i := range v {
-			v[i] = normalizeYAML(v[i])
-		}
-	}
-	return value
-}
-
-func parseTable(input []byte, format, sheet string) (table, error) {
-	switch format {
-	case "csv":
-		return readDelimited(input, ',')
-	case "tsv":
-		return readDelimited(input, '\t')
-	case "xlsx":
-		f, err := excelize.OpenReader(bytes.NewReader(input))
-		if err != nil {
-			return table{}, err
-		}
-		defer f.Close()
-		rows, err := f.GetRows(sheet)
-		if err != nil {
-			return table{}, err
-		}
-		return rowsToTable(rows), nil
-	default:
-		return table{}, fmt.Errorf("format %q is not tabular", format)
-	}
-}
-
-func readDelimited(input []byte, comma rune) (table, error) {
-	r := csv.NewReader(bytes.NewReader(input))
-	r.Comma = comma
-	r.FieldsPerRecord = -1
-	r.TrimLeadingSpace = comma == ','
-	rows, err := r.ReadAll()
-	if err != nil {
-		return table{}, err
-	}
-	return rowsToTable(rows), nil
-}
-
-func rowsToTable(rows [][]string) table {
-	if len(rows) == 0 {
-		return table{}
-	}
-	width := 0
-	for _, row := range rows {
-		if len(row) > width {
-			width = len(row)
-		}
-	}
-	header := padRow(rows[0], width)
-	body := make([][]string, 0, len(rows)-1)
-	for _, row := range rows[1:] {
-		body = append(body, padRow(row, width))
-	}
-	return table{Header: header, Rows: body}
-}
-
-func padRow(row []string, width int) []string {
-	out := make([]string, width)
-	copy(out, row)
-	return out
-}
-
-func encodeTable(t table, format, sheet string) ([]byte, error) {
-	switch format {
-	case "csv":
-		return writeDelimited(t, ',')
-	case "tsv":
-		return writeDelimited(t, '\t')
-	case "xlsx":
-		return writeXLSX(t, sheet)
-	default:
-		return nil, fmt.Errorf("format %q is not tabular", format)
-	}
-}
-
-func writeDelimited(t table, comma rune) ([]byte, error) {
-	var b bytes.Buffer
-	w := csv.NewWriter(&b)
-	w.Comma = comma
-	if err := w.Write(t.Header); err != nil {
-		return nil, err
-	}
-	for _, row := range t.Rows {
-		if err := w.Write(row); err != nil {
-			return nil, err
-		}
-	}
-	w.Flush()
-	return b.Bytes(), w.Error()
-}
-
-func writeXLSX(t table, sheet string) ([]byte, error) {
-	f := excelize.NewFile()
-	defaultSheet := f.GetSheetName(0)
-	if sheet == "" {
-		sheet = "Sheet1"
-	}
-	if defaultSheet != sheet {
-		if err := f.SetSheetName(defaultSheet, sheet); err != nil {
-			return nil, err
-		}
-	}
-	rows := append([][]string{t.Header}, t.Rows...)
-	for r, row := range rows {
-		for c, value := range row {
-			cell, err := excelize.CoordinatesToCellName(c+1, r+1)
-			if err != nil {
-				return nil, err
-			}
-			if err := f.SetCellValue(sheet, cell, value); err != nil {
-				return nil, err
-			}
-		}
-	}
-	if len(t.Header) > 0 {
-		// The generated workbook is meant for editing, so keep the header row
-		// visible and visually distinct.
-		end, _ := excelize.CoordinatesToCellName(len(t.Header), 1)
-		style, _ := f.NewStyle(&excelize.Style{Font: &excelize.Font{Bold: true}})
-		_ = f.SetCellStyle(sheet, "A1", end, style)
-		_ = f.SetPanes(sheet, &excelize.Panes{
-			Freeze:      true,
-			Split:       false,
-			XSplit:      0,
-			YSplit:      1,
-			TopLeftCell: "A2",
-			ActivePane:  "bottomLeft",
-		})
-	}
-	var b bytes.Buffer
-	if err := f.Write(&b); err != nil {
-		return nil, err
-	}
-	return b.Bytes(), nil
-}
-
-func valueToTable(value any) table {
-	records := recordsFromValue(value)
-	flatRows := make([]map[string]string, 0, len(records))
-	seen := map[string]bool{}
-	var header []string
-	for _, record := range records {
-		flat := map[string]string{}
-		flatten("", record, flat)
-		for key := range flat {
-			if !seen[key] {
-				seen[key] = true
-				header = append(header, key)
-			}
-		}
-		flatRows = append(flatRows, flat)
-	}
-	// Stable column ordering keeps generated CSV/TSV/XLSX diffs predictable.
-	sort.Strings(header)
-	rows := make([][]string, 0, len(flatRows))
-	for _, flat := range flatRows {
-		row := make([]string, len(header))
-		for i, key := range header {
-			row[i] = flat[key]
-		}
-		rows = append(rows, row)
-	}
-	return table{Header: header, Rows: rows}
-}
-
-func recordsFromValue(value any) []any {
-	switch v := value.(type) {
-	case []any:
-		return v
-	case map[string]any:
-		// Common wrapper keys let TOML and object-shaped inputs represent a
-		// table without adding a format-specific flag.
-		for _, key := range []string{"rows", "records", "items"} {
-			if rows, ok := v[key].([]any); ok {
-				return rows
-			}
-		}
-		return []any{v}
-	default:
-		return []any{v}
-	}
-}
-
-// flatten converts nested values into spreadsheet-safe column paths such as
-// user.name and items[0].sku.
-func flatten(prefix string, value any, out map[string]string) {
-	switch v := value.(type) {
-	case map[string]any:
-		if len(v) == 0 && prefix != "" {
-			out[prefix] = "{}"
-			return
-		}
-		keys := make([]string, 0, len(v))
-		for key := range v {
-			keys = append(keys, key)
-		}
-		sort.Strings(keys)
-		for _, key := range keys {
-			childPrefix := key
-			if prefix != "" {
-				childPrefix = prefix + "." + key
-			}
-			flatten(childPrefix, v[key], out)
-		}
-	case []any:
-		if len(v) == 0 && prefix != "" {
-			out[prefix] = "[]"
-			return
-		}
-		for i, child := range v {
-			flatten(fmt.Sprintf("%s[%d]", prefix, i), child, out)
-		}
-	default:
-		if prefix == "" {
-			prefix = "value"
-		}
-		out[prefix] = scalarString(v)
-	}
-}
-
-func scalarString(value any) string {
-	switch v := value.(type) {
-	case nil:
-		return ""
-	case json.Number:
-		return v.String()
-	case string:
-		return v
-	case bool:
-		return strconv.FormatBool(v)
-	case int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, float32, float64:
-		return fmt.Sprint(v)
-	default:
-		data, err := json.Marshal(v)
-		if err != nil {
-			return fmt.Sprint(v)
-		}
-		return string(data)
-	}
-}
-
-// tableToRecords restores each row by interpreting header cells as path
-// expressions. Empty headers are ignored so spare spreadsheet columns are safe.
-func tableToRecords(t table) []map[string]any {
-	var records []map[string]any
-	for _, row := range t.Rows {
-		record := map[string]any{}
-		for i, header := range t.Header {
-			header = strings.TrimSpace(header)
-			if header == "" || i >= len(row) {
-				continue
-			}
-			setPath(record, header, parseCell(row[i]))
-		}
-		records = append(records, record)
-	}
-	return records
-}
-
-// parseCell keeps spreadsheet round trips useful while avoiding broad type
-// inference that could surprise users editing IDs or codes.
-func parseCell(s string) any {
-	s = strings.TrimSpace(s)
-	if s == "" {
-		return ""
-	}
-	if s == "true" {
-		return true
-	}
-	if s == "false" {
-		return false
-	}
-	if i, err := strconv.ParseInt(s, 10, 64); err == nil {
-		return i
-	}
-	if f, err := strconv.ParseFloat(s, 64); err == nil && strings.ContainsAny(s, ".eE") {
-		return f
-	}
-	return s
-}
-
-var pathTokenRE = regexp.MustCompile(`([^\.\[\]]+)|\[(\d+)\]`)
-
-// setPath creates maps and slices as needed for dotted and indexed header
-// paths. Invalid intermediate shapes are left unchanged instead of guessing.
-func setPath(root map[string]any, path string, value any) {
-	tokens := parsePath(path)
-	if len(tokens) == 0 {
-		return
-	}
-	var cur any = root
-	for i, token := range tokens {
-		last := i == len(tokens)-1
-		nextIsIndex := !last && tokens[i+1].isIndex
-		if token.isIndex {
-			continue
-		}
-		m, ok := cur.(map[string]any)
-		if !ok {
-			return
-		}
-		if last {
-			m[token.key] = value
-			return
-		}
-		if _, ok := m[token.key]; !ok {
-			if nextIsIndex {
-				m[token.key] = []any{}
-			} else {
-				m[token.key] = map[string]any{}
-			}
-		}
-		if nextIsIndex {
-			slice, _ := m[token.key].([]any)
-			index := tokens[i+1].index
-			for len(slice) <= index {
-				if i+2 < len(tokens) && !tokens[i+2].isIndex {
-					slice = append(slice, map[string]any{})
-				} else {
-					slice = append(slice, nil)
-				}
-			}
-			m[token.key] = slice
-			if i+2 == len(tokens) {
-				slice[index] = value
-				return
-			}
-			if slice[index] == nil {
-				slice[index] = map[string]any{}
-			}
-			cur = slice[index]
-			i++
-			continue
-		}
-		cur = m[token.key]
-	}
-}
-
-type pathToken struct {
-	key     string
-	index   int
-	isIndex bool
-}
-
-func parsePath(path string) []pathToken {
-	matches := pathTokenRE.FindAllStringSubmatch(path, -1)
-	tokens := make([]pathToken, 0, len(matches))
-	for _, m := range matches {
-		if m[1] != "" {
-			tokens = append(tokens, pathToken{key: m[1]})
-			continue
-		}
-		index, _ := strconv.Atoi(m[2])
-		tokens = append(tokens, pathToken{index: index, isIndex: true})
-	}
-	return tokens
-}

cmd/dataxl/main_test.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"os"
 	"path/filepath"
+	"reflect"
 	"strings"
 	"testing"
 )
@@ -66,6 +67,36 @@ func TestTSVToJSONRestoresPaths(t *testing.T) {
 	}
 }
 
+func TestTSVToJSONAcceptsExcelMultilineCells(t *testing.T) {
+	// Excel's clipboard format uses CRLF between records and quotes cells that
+	// contain line breaks. Quotes inside a quoted cell are doubled.
+	input := strings.NewReader("id\tdescription\tnote\r\n" +
+		"1\t\"first line\r\nsecond line\"\t\"She said \"\"hello\"\".\"\r\n" +
+		"2\tsingle line\tplain\r\n")
+	var out bytes.Buffer
+	var errOut bytes.Buffer
+	if err := run([]string{"-from", "tsv", "-to", "json"}, input, &out, &errOut); err != nil {
+		t.Fatalf("run failed: %v\nstderr: %s", err, errOut.String())
+	}
+
+	var records []map[string]any
+	if err := json.Unmarshal(out.Bytes(), &records); err != nil {
+		t.Fatalf("invalid json: %v\n%s", err, out.String())
+	}
+	if len(records) != 2 {
+		t.Fatalf("record count = %d, want 2", len(records))
+	}
+	if got := records[0]["description"]; got != "first line\nsecond line" {
+		t.Fatalf("description = %#v, want multiline cell", got)
+	}
+	if got := records[0]["note"]; got != `She said "hello".` {
+		t.Fatalf("note = %#v, want embedded quotes", got)
+	}
+	if got := records[1]["description"]; got != "single line" {
+		t.Fatalf("second description = %#v, want single line", got)
+	}
+}
+
 func TestJSONToXLSXAndBack(t *testing.T) {
 	dir := t.TempDir()
 	xlsxPath := filepath.Join(dir, "data.xlsx")
@@ -88,6 +119,119 @@ func TestJSONToXLSXAndBack(t *testing.T) {
 	}
 }
 
+func TestResolveFormatsFromFileExtensions(t *testing.T) {
+	opt := options{inFile: "input.YML", outFile: "output.XLSM"}
+	if err := opt.resolveFormats(); err != nil {
+		t.Fatal(err)
+	}
+	if opt.from != "yaml" || opt.to != "xlsx" {
+		t.Fatalf("resolved formats = %q -> %q, want yaml -> xlsx", opt.from, opt.to)
+	}
+}
+
+func TestVersionFlagDoesNotRequireFormats(t *testing.T) {
+	oldVersion := buildVersion
+	buildVersion = "v9.8.7-test"
+	t.Cleanup(func() { buildVersion = oldVersion })
+
+	var out bytes.Buffer
+	var errOut bytes.Buffer
+	if err := run([]string{"-version"}, nil, &out, &errOut); err != nil {
+		t.Fatalf("run failed: %v\nstderr: %s", err, errOut.String())
+	}
+	if got, want := out.String(), "dataxl v9.8.7-test\n"; got != want {
+		t.Fatalf("version output = %q, want %q", got, want)
+	}
+}
+
+func TestConvertStructuredToStructured(t *testing.T) {
+	got, err := convert([]byte("name: Alice\nactive: true\n"), "yaml", "json", "Sheet1", false)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(got) != `{"active":true,"name":"Alice"}` {
+		t.Fatalf("JSON = %s", got)
+	}
+}
+
+func TestRowsToTablePadsRaggedRows(t *testing.T) {
+	got, err := rowsToTable([][]string{{"a", "b"}, {"1"}, {"2", "3"}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := table{
+		Header: []string{"a", "b"},
+		Rows:   [][]string{{"1", ""}, {"2", "3"}},
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("table = %#v, want %#v", got, want)
+	}
+}
+
+func TestParseCellConservativeInference(t *testing.T) {
+	tests := map[string]any{
+		"":        "",
+		"true":    true,
+		"42":      int64(42),
+		"3.14":    3.14,
+		"00123":   "00123",
+		"1e3":     1000.0,
+		"Alice":   "Alice",
+		" 42 ":    " 42 ",
+		" true ":  " true ",
+		" Alice ": " Alice ",
+	}
+	for input, want := range tests {
+		if got := parseCell(input); !reflect.DeepEqual(got, want) {
+			t.Errorf("parseCell(%q) = %#v, want %#v", input, got, want)
+		}
+	}
+}
+
+func TestSetPathRejectsConflictingShape(t *testing.T) {
+	t.Run("parent scalar before child", func(t *testing.T) {
+		record := map[string]any{}
+		if err := setPath(record, "user", "Alice"); err != nil {
+			t.Fatal(err)
+		}
+		if err := setPath(record, "user.name", "Bob"); err == nil {
+			t.Fatal("conflicting child path succeeded")
+		}
+		if got := record["user"]; got != "Alice" {
+			t.Fatalf("user = %#v, want original scalar", got)
+		}
+	})
+
+	t.Run("child before parent scalar", func(t *testing.T) {
+		record := map[string]any{}
+		if err := setPath(record, "user.name", "Bob"); err != nil {
+			t.Fatal(err)
+		}
+		if err := setPath(record, "user", "Alice"); err == nil {
+			t.Fatal("conflicting parent path succeeded")
+		}
+		want := map[string]any{"name": "Bob"}
+		if got := record["user"]; !reflect.DeepEqual(got, want) {
+			t.Fatalf("user = %#v, want original nested value %#v", got, want)
+		}
+	})
+}
+
+func TestSetPathRestoresNestedArrays(t *testing.T) {
+	record := map[string]any{}
+	if err := setPath(record, "orders[0].items[1].sku", "B-002"); err != nil {
+		t.Fatal(err)
+	}
+
+	orders := record["orders"].([]any)
+	order := orders[0].(map[string]any)
+	items := order["items"].([]any)
+	item := items[1].(map[string]any)
+	if item["sku"] != "B-002" {
+		t.Fatalf("nested sku = %#v, want B-002", item["sku"])
+	}
+}
+
 type ioDiscard struct{}
 
 func (ioDiscard) Write(p []byte) (int, error) { return len(p), nil }

cmd/dataxl/path.go

@@ -0,0 +1,317 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+type parsedColumn struct {
+	header string
+	index  int
+	tokens []pathToken
+}
+
+// tableToRecords interprets non-empty headers as path expressions. A blank
+// header is safe only when every cell below it is also blank; otherwise there
+// is no key under which the value can be preserved.
+func tableToRecords(t table) ([]map[string]any, error) {
+	columns := make([]parsedColumn, 0, len(t.Header))
+	seen := make(map[string]int)
+	for columnIndex, header := range t.Header {
+		if header == "" {
+			for rowIndex, row := range t.Rows {
+				if columnIndex < len(row) && row[columnIndex] != "" {
+					return nil, fmt.Errorf(
+						"row %d column %d contains data but its header is blank",
+						rowIndex+2, columnIndex+1,
+					)
+				}
+			}
+			continue
+		}
+		if firstIndex, exists := seen[header]; exists {
+			return nil, fmt.Errorf(
+				"duplicate header %q in columns %d and %d",
+				header, firstIndex+1, columnIndex+1,
+			)
+		}
+		seen[header] = columnIndex
+		tokens, err := parsePath(header)
+		if err != nil {
+			return nil, fmt.Errorf("invalid header %q in column %d: %w", header, columnIndex+1, err)
+		}
+		columns = append(columns, parsedColumn{header: header, index: columnIndex, tokens: tokens})
+	}
+
+	records := make([]map[string]any, 0, len(t.Rows))
+	for rowIndex, row := range t.Rows {
+		record := make(map[string]any)
+		for _, column := range columns {
+			cell := ""
+			if column.index < len(row) {
+				cell = row[column.index]
+			}
+			if err := setPathTokens(record, column.tokens, parseCell(cell)); err != nil {
+				return nil, fmt.Errorf("row %d header %q: %w", rowIndex+2, column.header, err)
+			}
+		}
+		records = append(records, record)
+	}
+	return records, nil
+}
+
+// parseCell deliberately performs narrow inference. In particular, strings
+// with surrounding whitespace and zero-padded identifiers remain strings.
+func parseCell(s string) any {
+	if s == "" {
+		return ""
+	}
+	if s == "true" {
+		return true
+	}
+	if s == "false" {
+		return false
+	}
+	// Preserve zero-padded identifiers such as postal codes and product codes.
+	leadingZero := len(s) > 1 && s[0] == '0'
+	negativeLeadingZero := len(s) > 2 && s[0] == '-' && s[1] == '0'
+	if i, err := strconv.ParseInt(s, 10, 64); err == nil && !leadingZero && !negativeLeadingZero {
+		return i
+	}
+	if f, err := strconv.ParseFloat(s, 64); err == nil && strings.ContainsAny(s, ".eE") {
+		return f
+	}
+	return s
+}
+
+type pathToken struct {
+	key     string
+	index   int
+	isIndex bool
+}
+
+const (
+	maxPathTokens = 256
+	maxArrayIndex = 10_000
+)
+
+// parsePath accepts dotted keys, zero-based array indices, and JSON-quoted map
+// keys in brackets. Quoted keys make delimiters and empty keys unambiguous:
+// user.name, items[0].sku, and settings["build.target"] are all valid.
+func parsePath(path string) ([]pathToken, error) {
+	if path == "" {
+		return nil, fmt.Errorf("path is empty")
+	}
+
+	var tokens []pathToken
+	var err error
+	position := 0
+	if strings.HasPrefix(path, `["`) {
+		var key string
+		key, position, err = parseQuotedKey(path, position)
+		if err != nil {
+			return nil, err
+		}
+		tokens = append(tokens, pathToken{key: key})
+	} else {
+		var key string
+		key, position, err = parseBareKey(path, position)
+		if err != nil {
+			return nil, err
+		}
+		tokens = append(tokens, pathToken{key: key})
+	}
+
+	for position < len(path) {
+		switch path[position] {
+		case '.':
+			position++
+			key, next, err := parseBareKey(path, position)
+			if err != nil {
+				return nil, err
+			}
+			tokens = append(tokens, pathToken{key: key})
+			position = next
+		case '[':
+			if position+1 < len(path) && path[position+1] == '"' {
+				key, next, err := parseQuotedKey(path, position)
+				if err != nil {
+					return nil, err
+				}
+				tokens = append(tokens, pathToken{key: key})
+				position = next
+				continue
+			}
+			index, next, err := parseIndex(path, position)
+			if err != nil {
+				return nil, err
+			}
+			tokens = append(tokens, pathToken{index: index, isIndex: true})
+			position = next
+		default:
+			return nil, fmt.Errorf("unexpected character %q at byte %d", path[position], position)
+		}
+	}
+	if len(tokens) > maxPathTokens {
+		return nil, fmt.Errorf("path has %d elements; maximum is %d", len(tokens), maxPathTokens)
+	}
+	return tokens, nil
+}
+
+func parseBareKey(path string, position int) (string, int, error) {
+	start := position
+	for position < len(path) && !strings.ContainsRune(".[]", rune(path[position])) {
+		position++
+	}
+	if position == start {
+		return "", position, fmt.Errorf("map key is empty at byte %d", start)
+	}
+	return path[start:position], position, nil
+}
+
+func parseQuotedKey(path string, position int) (string, int, error) {
+	if position+1 >= len(path) || path[position] != '[' || path[position+1] != '"' {
+		return "", position, fmt.Errorf("quoted key expected at byte %d", position)
+	}
+	quoteStart := position + 1
+	escaped := false
+	quoteEnd := -1
+	for i := quoteStart + 1; i < len(path); i++ {
+		switch {
+		case escaped:
+			escaped = false
+		case path[i] == '\\':
+			escaped = true
+		case path[i] == '"':
+			quoteEnd = i
+			i = len(path)
+		}
+	}
+	if quoteEnd == -1 {
+		return "", position, fmt.Errorf("unterminated quoted key at byte %d", position)
+	}
+	if quoteEnd+1 >= len(path) || path[quoteEnd+1] != ']' {
+		return "", position, fmt.Errorf("quoted key at byte %d is missing closing ]", position)
+	}
+	var key string
+	if err := json.Unmarshal([]byte(path[quoteStart:quoteEnd+1]), &key); err != nil {
+		return "", position, fmt.Errorf("invalid quoted key at byte %d: %w", position, err)
+	}
+	return key, quoteEnd + 2, nil
+}
+
+func parseIndex(path string, position int) (int, int, error) {
+	digitsStart := position + 1
+	digitsEnd := digitsStart
+	for digitsEnd < len(path) && path[digitsEnd] >= '0' && path[digitsEnd] <= '9' {
+		digitsEnd++
+	}
+	if digitsEnd == digitsStart {
+		return 0, position, fmt.Errorf("array index is empty or invalid at byte %d", position)
+	}
+	if digitsEnd >= len(path) || path[digitsEnd] != ']' {
+		return 0, position, fmt.Errorf("array index at byte %d is missing closing ]", position)
+	}
+	index, err := strconv.Atoi(path[digitsStart:digitsEnd])
+	if err != nil {
+		return 0, position, fmt.Errorf("array index at byte %d is out of range: %w", position, err)
+	}
+	if index > maxArrayIndex {
+		return 0, position, fmt.Errorf("array index %d exceeds maximum %d", index, maxArrayIndex)
+	}
+	return index, digitsEnd + 1, nil
+}
+
+// appendPathKey adds a map key to a column path. Keys containing path
+// delimiters (and the empty key) use JSON bracket notation so round trips do
+// not confuse literal key content with structure.
+func appendPathKey(prefix, key string) string {
+	segment := key
+	quoted := key == "" || strings.ContainsAny(key, ".[]")
+	if quoted {
+		encoded, _ := json.Marshal(key) // Go strings always have a JSON representation.
+		segment = "[" + string(encoded) + "]"
+		return prefix + segment
+	}
+	if prefix == "" {
+		return segment
+	}
+	return prefix + "." + segment
+}
+
+// setPath creates maps and slices while walking a dotted/indexed header.
+// Conflicting shapes return an error instead of discarding a column value.
+func setPath(root map[string]any, path string, value any) error {
+	tokens, err := parsePath(path)
+	if err != nil {
+		return err
+	}
+	return setPathTokens(root, tokens, value)
+}
+
+func setPathTokens(root map[string]any, tokens []pathToken, value any) error {
+	if len(tokens) == 0 || tokens[0].isIndex {
+		return fmt.Errorf("path must start with a map key")
+	}
+	_, err := setPathValue(root, tokens, value)
+	return err
+}
+
+func setPathValue(current any, tokens []pathToken, value any) (any, error) {
+	if len(tokens) == 0 {
+		return value, nil
+	}
+	token := tokens[0]
+	if token.isIndex {
+		var values []any
+		switch typed := current.(type) {
+		case nil:
+			values = []any{}
+		case []any:
+			values = typed
+		default:
+			return nil, fmt.Errorf("expected an array at index [%d], found %T", token.index, current)
+		}
+		for len(values) <= token.index {
+			values = append(values, nil)
+		}
+		if len(tokens) == 1 {
+			if values[token.index] != nil {
+				return nil, fmt.Errorf("path conflicts with an existing array value at index [%d]", token.index)
+			}
+			values[token.index] = value
+			return values, nil
+		}
+		child, err := setPathValue(values[token.index], tokens[1:], value)
+		if err != nil {
+			return nil, err
+		}
+		values[token.index] = child
+		return values, nil
+	}
+
+	var object map[string]any
+	switch typed := current.(type) {
+	case nil:
+		object = make(map[string]any)
+	case map[string]any:
+		object = typed
+	default:
+		return nil, fmt.Errorf("expected an object before key %q, found %T", token.key, current)
+	}
+	if len(tokens) == 1 {
+		if _, exists := object[token.key]; exists {
+			return nil, fmt.Errorf("path conflicts with an existing value at key %q", token.key)
+		}
+		object[token.key] = value
+		return object, nil
+	}
+	child, err := setPathValue(object[token.key], tokens[1:], value)
+	if err != nil {
+		return nil, err
+	}
+	object[token.key] = child
+	return object, nil
+}

cmd/dataxl/structured.go

@@ -0,0 +1,206 @@
+package main
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"unicode/utf8"
+
+	"github.com/BurntSushi/toml"
+	"gopkg.in/yaml.v3"
+)
+
+// parseStructured decodes a format into maps, slices and scalar Go values.
+// json.Number is retained so large JSON integers do not pass through float64.
+func parseStructured(input []byte, format string) (any, error) {
+	var value any
+	switch format {
+	case "json":
+		// encoding/json replaces malformed UTF-8 inside strings with U+FFFD.
+		// Reject it up front so a successful conversion never changes bytes
+		// silently.
+		if !utf8.Valid(input) {
+			return nil, fmt.Errorf("JSON input is not valid UTF-8")
+		}
+		dec := json.NewDecoder(bytes.NewReader(input))
+		dec.UseNumber()
+		var err error
+		value, err = decodeJSONValue(dec)
+		if err != nil {
+			return nil, err
+		}
+		_, err = decodeJSONValue(dec)
+		switch {
+		case errors.Is(err, io.EOF):
+		case err == nil:
+			return nil, fmt.Errorf("multiple JSON values are not supported")
+		default:
+			return nil, fmt.Errorf("invalid trailing JSON data: %w", err)
+		}
+	case "yaml":
+		dec := yaml.NewDecoder(bytes.NewReader(input))
+		var documents []any
+		for {
+			var document any
+			err := dec.Decode(&document)
+			if errors.Is(err, io.EOF) {
+				break
+			}
+			if err != nil {
+				return nil, err
+			}
+			documents = append(documents, normalizeYAML(document))
+		}
+		switch len(documents) {
+		case 0:
+			value = nil
+		case 1:
+			value = documents[0]
+		default:
+			// A YAML stream is an ordered sequence of documents. Representing it
+			// as a slice preserves every document for conversion to other formats.
+			value = documents
+		}
+	case "toml":
+		var m map[string]any
+		if err := toml.Unmarshal(input, &m); err != nil {
+			return nil, err
+		}
+		value = normalizeTOML(m)
+	default:
+		return nil, fmt.Errorf("format %q is not structured", format)
+	}
+	return value, nil
+}
+
+// decodeJSONValue builds a generic structured value directly from decoder
+// tokens so duplicate object keys can be rejected before a map overwrites one.
+func decodeJSONValue(dec *json.Decoder) (any, error) {
+	token, err := dec.Token()
+	if err != nil {
+		return nil, err
+	}
+	delimiter, isDelimiter := token.(json.Delim)
+	if !isDelimiter {
+		return token, nil
+	}
+
+	switch delimiter {
+	case '{':
+		object := make(map[string]any)
+		for dec.More() {
+			keyToken, err := dec.Token()
+			if err != nil {
+				return nil, err
+			}
+			key, ok := keyToken.(string)
+			if !ok {
+				return nil, fmt.Errorf("JSON object key has unexpected type %T", keyToken)
+			}
+			if _, exists := object[key]; exists {
+				return nil, fmt.Errorf("duplicate JSON object key %q", key)
+			}
+			child, err := decodeJSONValue(dec)
+			if err != nil {
+				return nil, err
+			}
+			object[key] = child
+		}
+		if _, err := dec.Token(); err != nil {
+			return nil, err
+		}
+		return object, nil
+	case '[':
+		array := make([]any, 0)
+		for dec.More() {
+			child, err := decodeJSONValue(dec)
+			if err != nil {
+				return nil, err
+			}
+			array = append(array, child)
+		}
+		if _, err := dec.Token(); err != nil {
+			return nil, err
+		}
+		return array, nil
+	default:
+		return nil, fmt.Errorf("unexpected JSON delimiter %q", delimiter)
+	}
+}
+
+func encodeStructured(value any, format string, pretty bool) ([]byte, error) {
+	switch format {
+	case "json":
+		if pretty {
+			return json.MarshalIndent(value, "", "  ")
+		}
+		return json.Marshal(value)
+	case "yaml":
+		return yaml.Marshal(value)
+	case "toml":
+		m, ok := value.(map[string]any)
+		if !ok {
+			// TOML has no top-level array, so preserve it under a documented key.
+			m = map[string]any{"rows": value}
+		}
+		var b bytes.Buffer
+		err := toml.NewEncoder(&b).Encode(m)
+		return b.Bytes(), err
+	default:
+		return nil, fmt.Errorf("format %q is not structured", format)
+	}
+}
+
+// normalizeYAML converts yaml.v3's possible map[any]any values into the
+// string-keyed maps used by the rest of the conversion pipeline.
+func normalizeYAML(value any) any {
+	switch v := value.(type) {
+	case map[string]any:
+		out := make(map[string]any, len(v))
+		for key, child := range v {
+			out[key] = normalizeYAML(child)
+		}
+		return out
+	case map[any]any:
+		out := make(map[string]any, len(v))
+		for key, child := range v {
+			out[fmt.Sprint(key)] = normalizeYAML(child)
+		}
+		return out
+	case []any:
+		for i := range v {
+			v[i] = normalizeYAML(v[i])
+		}
+	}
+	return value
+}
+
+// BurntSushi/toml represents arrays of tables as []map[string]any instead of
+// []any. Normalize that concrete container so wrapper detection, flattening,
+// and format-to-format conversions use the same structured representation.
+func normalizeTOML(value any) any {
+	switch v := value.(type) {
+	case map[string]any:
+		out := make(map[string]any, len(v))
+		for key, child := range v {
+			out[key] = normalizeTOML(child)
+		}
+		return out
+	case []map[string]any:
+		out := make([]any, len(v))
+		for i, child := range v {
+			out[i] = normalizeTOML(child)
+		}
+		return out
+	case []any:
+		out := make([]any, len(v))
+		for i, child := range v {
+			out[i] = normalizeTOML(child)
+		}
+		return out
+	default:
+		return value
+	}
+}

cmd/dataxl/table.go

@@ -0,0 +1,291 @@
+package main
+
+import (
+	"bytes"
+	"encoding/csv"
+	"encoding/json"
+	"fmt"
+	"sort"
+	"strconv"
+	"unicode/utf8"
+
+	"github.com/xuri/excelize/v2"
+)
+
+// table is the common representation for CSV, TSV and XLSX. Rows are padded
+// to Header width when read, which keeps subsequent conversions rectangular.
+type table struct {
+	Header []string
+	Rows   [][]string
+}
+
+func parseTable(input []byte, format, sheet string) (table, error) {
+	switch format {
+	case "csv":
+		return readDelimited(input, ',')
+	case "tsv":
+		return readDelimited(input, '\t')
+	case "xlsx":
+		f, err := excelize.OpenReader(bytes.NewReader(input))
+		if err != nil {
+			return table{}, err
+		}
+		defer f.Close()
+		rows, err := f.GetRows(sheet)
+		if err != nil {
+			return table{}, err
+		}
+		return rowsToTable(rows)
+	default:
+		return table{}, fmt.Errorf("format %q is not tabular", format)
+	}
+}
+
+func readDelimited(input []byte, comma rune) (table, error) {
+	// Spreadsheet applications commonly prefix UTF-8 CSV/TSV exports with a
+	// BOM. It is an encoding marker, not part of the first column name.
+	input = bytes.TrimPrefix(input, []byte{0xEF, 0xBB, 0xBF})
+	if !utf8.Valid(input) {
+		return table{}, fmt.Errorf("delimited input is not valid UTF-8")
+	}
+	r := csv.NewReader(bytes.NewReader(input))
+	r.Comma = comma
+	r.FieldsPerRecord = -1
+	rows, err := r.ReadAll()
+	if err != nil {
+		return table{}, err
+	}
+	return rowsToTable(rows)
+}
+
+func rowsToTable(rows [][]string) (table, error) {
+	if len(rows) == 0 {
+		return table{}, nil
+	}
+	width := len(rows[0])
+	for rowIndex, row := range rows[1:] {
+		if len(row) > width {
+			return table{}, fmt.Errorf(
+				"row %d has %d fields but the header has %d",
+				rowIndex+2, len(row), width,
+			)
+		}
+	}
+	header := padRow(rows[0], width)
+	body := make([][]string, 0, len(rows)-1)
+	for _, row := range rows[1:] {
+		body = append(body, padRow(row, width))
+	}
+	return table{Header: header, Rows: body}, nil
+}
+
+func padRow(row []string, width int) []string {
+	out := make([]string, width)
+	copy(out, row)
+	return out
+}
+
+func encodeTable(t table, format, sheet string) ([]byte, error) {
+	switch format {
+	case "csv":
+		return writeDelimited(t, ',')
+	case "tsv":
+		return writeDelimited(t, '\t')
+	case "xlsx":
+		return writeXLSX(t, sheet)
+	default:
+		return nil, fmt.Errorf("format %q is not tabular", format)
+	}
+}
+
+func writeDelimited(t table, comma rune) ([]byte, error) {
+	var b bytes.Buffer
+	w := csv.NewWriter(&b)
+	w.Comma = comma
+	writeRecord := func(row []string) error {
+		if len(row) == 1 && row[0] == "" {
+			// encoding/csv writes this record as a bare empty line, which its
+			// Reader intentionally skips. Quote the field so the row survives a
+			// table-to-table round trip.
+			w.Flush()
+			if err := w.Error(); err != nil {
+				return err
+			}
+			b.WriteString("\"\"\n")
+			return nil
+		}
+		return w.Write(row)
+	}
+	if err := writeRecord(t.Header); err != nil {
+		return nil, err
+	}
+	for _, row := range t.Rows {
+		if err := writeRecord(row); err != nil {
+			return nil, err
+		}
+	}
+	w.Flush()
+	return b.Bytes(), w.Error()
+}
+
+func writeXLSX(t table, sheet string) ([]byte, error) {
+	f := excelize.NewFile()
+	defer f.Close()
+	defaultSheet := f.GetSheetName(0)
+	if sheet == "" {
+		sheet = "Sheet1"
+	}
+	if defaultSheet != sheet {
+		if err := f.SetSheetName(defaultSheet, sheet); err != nil {
+			return nil, err
+		}
+	}
+	rows := append([][]string{t.Header}, t.Rows...)
+	for rowIndex, row := range rows {
+		for columnIndex, value := range row {
+			cell, err := excelize.CoordinatesToCellName(columnIndex+1, rowIndex+1)
+			if err != nil {
+				return nil, err
+			}
+			if err := f.SetCellValue(sheet, cell, value); err != nil {
+				return nil, err
+			}
+		}
+	}
+	if err := styleHeader(f, sheet, len(t.Header)); err != nil {
+		return nil, err
+	}
+	var b bytes.Buffer
+	if err := f.Write(&b); err != nil {
+		return nil, err
+	}
+	return b.Bytes(), nil
+}
+
+// styleHeader applies editing conveniences without trying to preserve or
+// emulate arbitrary workbook formatting.
+func styleHeader(f *excelize.File, sheet string, width int) error {
+	if width == 0 {
+		return nil
+	}
+	end, err := excelize.CoordinatesToCellName(width, 1)
+	if err != nil {
+		return err
+	}
+	style, err := f.NewStyle(&excelize.Style{Font: &excelize.Font{Bold: true}})
+	if err != nil {
+		return err
+	}
+	if err := f.SetCellStyle(sheet, "A1", end, style); err != nil {
+		return err
+	}
+	return f.SetPanes(sheet, &excelize.Panes{
+		Freeze: true, YSplit: 1, TopLeftCell: "A2", ActivePane: "bottomLeft",
+	})
+}
+
+func valueToTable(value any) table {
+	records := recordsFromValue(value)
+	flatRows := make([]map[string]string, 0, len(records))
+	seen := make(map[string]bool)
+	var header []string
+	for _, record := range records {
+		flat := make(map[string]string)
+		flatten("", record, flat)
+		for key := range flat {
+			if !seen[key] {
+				seen[key] = true
+				header = append(header, key)
+			}
+		}
+		flatRows = append(flatRows, flat)
+	}
+	// Stable column ordering makes generated files and their diffs predictable.
+	sort.Strings(header)
+	rows := make([][]string, 0, len(flatRows))
+	for _, flat := range flatRows {
+		row := make([]string, len(header))
+		for i, key := range header {
+			row[i] = flat[key]
+		}
+		rows = append(rows, row)
+	}
+	return table{Header: header, Rows: rows}
+}
+
+func recordsFromValue(value any) []any {
+	switch v := value.(type) {
+	case []any:
+		return v
+	case map[string]any:
+		// A sole wrapper key lets object-shaped formats such as TOML carry row
+		// arrays. If siblings exist, unwrapping would silently discard them, so
+		// preserve the complete object as one table record instead.
+		if len(v) == 1 {
+			for _, key := range []string{"rows", "records", "items"} {
+				if rows, ok := v[key].([]any); ok {
+					return rows
+				}
+			}
+		}
+		return []any{v}
+	default:
+		return []any{v}
+	}
+}
+
+// flatten converts nested values to column paths such as user.name and
+// items[0].sku. Empty maps and arrays use explicit textual markers; these are
+// visible to editors but currently return as strings when converted back.
+func flatten(prefix string, value any, out map[string]string) {
+	switch v := value.(type) {
+	case map[string]any:
+		if len(v) == 0 && prefix != "" {
+			out[prefix] = "{}"
+			return
+		}
+		keys := make([]string, 0, len(v))
+		for key := range v {
+			keys = append(keys, key)
+		}
+		sort.Strings(keys)
+		for _, key := range keys {
+			childPrefix := appendPathKey(prefix, key)
+			flatten(childPrefix, v[key], out)
+		}
+	case []any:
+		if len(v) == 0 && prefix != "" {
+			out[prefix] = "[]"
+			return
+		}
+		for i, child := range v {
+			flatten(fmt.Sprintf("%s[%d]", prefix, i), child, out)
+		}
+	default:
+		if prefix == "" {
+			prefix = "value"
+		}
+		out[prefix] = scalarString(v)
+	}
+}
+
+func scalarString(value any) string {
+	switch v := value.(type) {
+	case nil:
+		return ""
+	case json.Number:
+		return v.String()
+	case string:
+		return v
+	case bool:
+		return strconv.FormatBool(v)
+	case int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, float32, float64:
+		return fmt.Sprint(v)
+	default:
+		data, err := json.Marshal(v)
+		if err != nil {
+			return fmt.Sprint(v)
+		}
+		return string(data)
+	}
+}

cmd/dataxl/testdata/fuzz/FuzzDelimitedTableRoundTrip/5838cdfae7b16cde

@@ -0,0 +1,2 @@
+go test fuzz v1
+string("")

docs/architecture.md

@@ -12,17 +12,22 @@
 - table -> structured
 - table -> table
 
-## Format Adapters
+## Source Layout
 
-各形式の処理は `cmd/dataxl/main.go` の以下の関数に集約しています。
+実装は `cmd/dataxl` package内で責務別に分割しています。
 
-- `parseStructured`
+- `main.go`: CLI option、stdin/stdout、ファイル入出力
-- `encodeStructured`
+- `conversion.go`: 変換経路の選択、形式名の正規化・推定
-- `parseTable`
+- `structured.go`: JSON/YAML/TOML adapter
-- `encodeTable`
+- `table.go`: CSV/TSV/XLSX adapter、table model、flatten
+- `path.go`: セル値の型推定、列パスのparse、unflatten
 
-現在はCLIが小さいため単一ファイルに置いています。形式やオプションが増えたら、
+`convert` はファイル入出力から独立しているため、CLIを経由せず変換matrixをテストできます。
-`internal/format` や `internal/table` へ分割する余地があります。
+形式固有処理は `parseStructured` / `encodeStructured` または
+`parseTable` / `encodeTable` に閉じ込めます。
+
+現状は単一commandだけが利用するため同じpackageに置いています。別commandやlibrary APIから
+再利用する段階になったら、安定させたい境界を見極めたうえで `internal` packageへ移します。
 
 ## Table Model
 
@@ -35,7 +40,8 @@ type table struct {
 }
 ```
 
-CSV/TSV/XLSXの読み込みでは、短い行を空文字で埋めて列数を揃えます。
+CSV/TSV/XLSXの読み込みでは、短い行を空文字で埋めて列数を揃えます。ヘッダーより
+長い行は、名前のない値を破棄しないようエラーにします。
 XLSXの書き出しではヘッダーを太字にし、1行目を固定します。
 
 ## Flattening
@@ -44,6 +50,7 @@ structured -> table では、入れ子のmap/arrayを列パスへ展開します
 
 - map: `user.name`
 - array: `items[0].sku`
+- delimiterを含むmap key: `settings["build.target"]`
 - top-level scalar: `value`
 
 列順は安定性を優先してソートしています。Excel上で列の位置が変わっても、
@@ -79,6 +86,38 @@ items[0].sku
 - 小数または指数表記: float64
 - その他: string
 
+ゼロ埋め整数と前後に空白があるセルは、IDや文字列を壊さないためstringとして
+保持します。複数列が同じパスで異なる中間型を要求する場合はエラーにし、入力列を
+黙って捨てません。
+
+### Path grammar
+
+現在の列パスは次の要素を扱います。
+
+```text
+path       = first-key, { map-child | quoted-key | array-index };
+first-key  = bare-key | quoted-key;
+map-child  = ".", bare-key;
+quoted-key = "[", JSON-string, "]";
+array-index = "[", digit, { digit }, "]";
+```
+
+実例は `user.name`、`items[0].sku`、`orders[0].items[1].qty` です。map keyに
+`.`、`[`、`]` が含まれる場合や空文字の場合は、`["build.target"]` や `[""]` の
+ようなJSON quoted keyを使います。連続したarray indexも扱うため、
+`matrix[0][1]` を復元できます。入力サイズに対して過大なmemory allocationを
+起こさないよう、pathは最大256要素、array indexは最大10000です。
+
+## Structured input integrity
+
+- JSON inputはUTF-8として検証します。decoderは最初の値の後まで読み、空白以外の
+  後続データを拒否します。object keyもtoken単位で読み、重複を拒否します。
+- YAML decoderはstream終端まで読み、複数文書を順序付きsliceとして保持します。
+- `rows`、`records`、`items` wrapperはオブジェクト唯一のキーである場合だけ
+  table rowsとして展開します。
+- recordが存在するのにscalar fieldが1つもないstructured valueは、表へ変換すると
+  record数を失うため拒否します。空のrecord listは空の表として扱います。
+
 ## TOML Output
 
 TOMLはトップレベル配列を直接表せないため、表からTOMLへ出力する場合など、
@@ -90,4 +129,11 @@ TOMLはトップレベル配列を直接表せないため、表からTOMLへ出
 - `gopkg.in/yaml.v3`: YAML読み書き
 - `github.com/BurntSushi/toml`: TOML読み書き
 
-Go 1.24以上を前提にしています。
+Go 1.25以上を前提にしています。
+
+## Error handling
+
+- 未対応形式、decode失敗、workbook/sheet操作失敗は呼び出し元へerrorを返します。
+- CSV/TSVのinvalid UTF-8、headerより長い行、値を持つ空header列を拒否します。
+- path復元中の重複header、構文エラー、型競合は変換全体をerrorにします。
+- XLSXのstyle・pane設定も通常の変換errorとして扱い、不完全なworkbookを成功扱いしません。

docs/development.md

@@ -2,7 +2,7 @@
 
 ## Requirements
 
-- Go 1.24 or later
+- Go 1.25 or later
 
 ## Setup
 
@@ -51,6 +51,16 @@ The current tests cover:
 - YAML -> TSV flattening
 - TSV -> JSON path restoration
 - JSON -> XLSX -> JSON round trip
+- structured -> structured conversion without CLI/file I/O
+- extension normalization and format inference
+- short table row padding and wider-row rejection
+- conservative cell type inference, including zero-padded identifiers
+- whitespace and UTF-8 BOM preservation rules
+- invalid UTF-8, duplicate keys, and trailing-data rejection for JSON
+- multi-document YAML streams and empty-record table boundaries
+- wrapper arrays with sibling metadata
+- duplicate, blank, malformed, and conflicting headers
+- nested arrays and JSON-quoted path keys
 
 When adding a new format or path rule, add tests around both directions where
 possible.
@@ -62,14 +72,18 @@ Gitea Actions workflows live under `.gitea/workflows`.
 - `ci.yml`: runs on pushes to `main`, pull requests, and manual dispatch.
 - `release.yml`: runs on `v*` tag pushes and manual dispatch with a `tag` input.
 
-The CI workflow checks formatting, runs tests, builds the CLI, and performs a
+The CI workflow checks formatting, runs tests and `go vet`, scans reachable
-small YAML -> TSV -> JSON smoke test.
+vulnerabilities with `govulncheck`, builds the CLI, and performs a small
+YAML -> TSV -> JSON smoke test.
 
 The release workflow runs tests, cross-builds release archives for Linux,
 macOS, and Windows on amd64/arm64, writes `checksums.txt`, creates or reuses a
 Gitea Release, and uploads the generated assets. It uses the built-in
 `${{ secrets.GITEA_TOKEN }}` provided by Gitea Actions.
 
+Release binaries receive their tag through the `main.buildVersion` linker
+variable. Verify an extracted native binary with `dataxl -version`.
+
 ## Release Notes
 
 Create a release by pushing a version tag:
@@ -96,3 +110,6 @@ go install git.rumginger.org/agent/dataxl/cmd/dataxl@v0.1.0
 - Preserve headers as the contract between spreadsheet data and structured data.
 - Prefer explicit errors over silent best-effort conversion when a format is unsupported.
 - Keep dependencies small unless a format needs a mature parser/writer.
+- Keep CLI/file I/O in `main.go`; conversion behavior should remain testable through `convert`.
+- Keep format-specific behavior in its structured or table adapter.
+- Document round-trip limitations when a representation cannot preserve a value exactly.

go.mod

@@ -1,20 +1,20 @@
 module git.rumginger.org/agent/dataxl
 
-go 1.24.0
+go 1.25.0
 
 require (
 	github.com/BurntSushi/toml v1.6.0
-	github.com/xuri/excelize/v2 v2.10.1
+	github.com/xuri/excelize/v2 v2.11.0
 	gopkg.in/yaml.v3 v3.0.1
 )
 
 require (
-	github.com/richardlehane/mscfb v1.0.6 // indirect
+	github.com/richardlehane/mscfb v1.0.7 // indirect
 	github.com/richardlehane/msoleps v1.0.6 // indirect
 	github.com/tiendc/go-deepcopy v1.7.2 // indirect
 	github.com/xuri/efp v0.0.1 // indirect
 	github.com/xuri/nfp v0.0.2-0.20250530014748-2ddeb826f9a9 // indirect
-	golang.org/x/crypto v0.48.0 // indirect
+	golang.org/x/crypto v0.53.0 // indirect
-	golang.org/x/net v0.50.0 // indirect
+	golang.org/x/net v0.56.0 // indirect
-	golang.org/x/text v0.34.0 // indirect
+	golang.org/x/text v0.39.0 // indirect
 )

go.sum

@@ -4,8 +4,8 @@ github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
-github.com/richardlehane/mscfb v1.0.6 h1:eN3bvvZCp00bs7Zf52bxNwAx5lJDBK1tCuH19qq5aC8=
+github.com/richardlehane/mscfb v1.0.7 h1:oeoiM0WE79vHwE8RpIYYvIAc8ajTH2mb6UZm55/+EB0=
-github.com/richardlehane/mscfb v1.0.6/go.mod h1:pe0+IUIc0AHh0+teNzBlJCtSyZdFOGgV4ZK9bsoV+Jo=
+github.com/richardlehane/mscfb v1.0.7/go.mod h1:pe0+IUIc0AHh0+teNzBlJCtSyZdFOGgV4ZK9bsoV+Jo=
 github.com/richardlehane/msoleps v1.0.6 h1:9BvkpjvD+iUBalUY4esMwv6uBkfOip/Lzvd93jvR9gg=
 github.com/richardlehane/msoleps v1.0.6/go.mod h1:BWev5JBpU9Ko2WAgmZEuiz4/u3ZYTKbjLycmwiWUfWg=
 github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
@@ -14,18 +14,18 @@ github.com/tiendc/go-deepcopy v1.7.2 h1:Ut2yYR7W9tWjTQitganoIue4UGxZwCcJy3orjrrI
 github.com/tiendc/go-deepcopy v1.7.2/go.mod h1:4bKjNC2r7boYOkD2IOuZpYjmlDdzjbpTRyCx+goBCJQ=
 github.com/xuri/efp v0.0.1 h1:fws5Rv3myXyYni8uwj2qKjVaRP30PdjeYe2Y6FDsCL8=
 github.com/xuri/efp v0.0.1/go.mod h1:ybY/Jr0T0GTCnYjKqmdwxyxn2BQf2RcQIIvex5QldPI=
-github.com/xuri/excelize/v2 v2.10.1 h1:V62UlqopMqha3kOpnlHy2CcRVw1V8E63jFoWUmMzxN0=
+github.com/xuri/excelize/v2 v2.11.0 h1:HxaEFl6sRN2+8J5a8HaKq+0M4FsjBGMnWWtjOCPSG88=
-github.com/xuri/excelize/v2 v2.10.1/go.mod h1:iG5tARpgaEeIhTqt3/fgXCGoBRt4hNXgCp3tfXKoOIc=
+github.com/xuri/excelize/v2 v2.11.0/go.mod h1:jxFLbzaIwGQ5ufFNvYfUOHqXhfPaNmP14KWfmNz2Uak=
 github.com/xuri/nfp v0.0.2-0.20250530014748-2ddeb826f9a9 h1:+C0TIdyyYmzadGaL/HBLbf3WdLgC29pgyhTjAT/0nuE=
 github.com/xuri/nfp v0.0.2-0.20250530014748-2ddeb826f9a9/go.mod h1:WwHg+CVyzlv/TX9xqBFXEZAuxOPxn2k1GNHwG41IIUQ=
-golang.org/x/crypto v0.48.0 h1:/VRzVqiRSggnhY7gNRxPauEQ5Drw9haKdM0jqfcCFts=
+golang.org/x/crypto v0.53.0 h1:QZ4Muo8THX6CizN2vPPd5fBGHyogrdK9fG4wLPFUsto=
-golang.org/x/crypto v0.48.0/go.mod h1:r0kV5h3qnFPlQnBSrULhlsRfryS2pmewsg+XfMgkVos=
+golang.org/x/crypto v0.53.0/go.mod h1:DNLU434OwVakk9PzuwV8w62mAJpRJL3vsgcfp4Qnsio=
-golang.org/x/image v0.25.0 h1:Y6uW6rH1y5y/LK1J8BPWZtr6yZ7hrsy6hFrXjgsc2fQ=
+golang.org/x/image v0.38.0 h1:5l+q+Y9JDC7mBOMjo4/aPhMDcxEptsX+Tt3GgRQRPuE=
-golang.org/x/image v0.25.0/go.mod h1:tCAmOEGthTtkalusGp1g3xa2gke8J6c2N565dTyl9Rs=
+golang.org/x/image v0.38.0/go.mod h1:/3f6vaXC+6CEanU4KJxbcUZyEePbyKbaLoDOe4ehFYY=
-golang.org/x/net v0.50.0 h1:ucWh9eiCGyDR3vtzso0WMQinm2Dnt8cFMuQa9K33J60=
+golang.org/x/net v0.56.0 h1:Rw8j/hFzGvJUZwNBXnAtf5sVDVt+65SK2C7IxCxZt5o=
-golang.org/x/net v0.50.0/go.mod h1:UgoSli3F/pBgdJBHCTc+tp3gmrU4XswgGRgtnwWTfyM=
+golang.org/x/net v0.56.0/go.mod h1:D3Ku6r+V6JROoZK144D2XfMHFcMq/0zSfLelVTCFKec=
-golang.org/x/text v0.34.0 h1:oL/Qq0Kdaqxa1KbNeMKwQq0reLCCaFtqu2eNuSeNHbk=
+golang.org/x/text v0.39.0 h1:UbZz4pLOvn600D6Oh6GGEI6VAmndrEBLv8/6BEXzyus=
-golang.org/x/text v0.34.0/go.mod h1:homfLqTYRFyVYemLBFl5GgL/DWEiH5wcsQ5gSh1yziA=
+golang.org/x/text v0.39.0/go.mod h1:3UwRclnC2g0TU9x8PZiyfOajCd1zaUNHF9cvqcQZ+ZM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=

scripts/build-release.sh

@@ -14,6 +14,10 @@ fi
 if [ -z "$version" ]; then
   version="dev"
 fi
+if [[ "$version" != "dev" && ! "$version" =~ ^v[0-9]+\.[0-9]+\.[0-9]+([.-][0-9A-Za-z.-]+)?$ ]]; then
+  echo "invalid release version: $version" >&2
+  exit 1
+fi
 
 rm -rf dist
 mkdir -p dist
@@ -40,7 +44,7 @@ for target in "${targets[@]}"; do
 
   CGO_ENABLED=0 GOOS="$goos" GOARCH="$goarch" go build \
     -trimpath \
-    -ldflags="-s -w" \
+    -ldflags="-s -w -X main.buildVersion=$version" \
     -o "$workdir/$binary" \
     ./cmd/dataxl
 
@@ -56,3 +60,4 @@ for target in "${targets[@]}"; do
 done
 
 (cd dist && sha256sum dataxl_* > checksums.txt)
+(cd dist && sha256sum -c checksums.txt)