First commit

README.md

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+# Go file permissions test
+by Brandon Dyck <brandon@dyck.us>
+
+This is an experiment to see how `os.Chmod` and `os.Stat` interact on Windows. The program creates a temporary file, then for each possible set of permissions (0–0777), sets those permissions on the file with `os.Chmod` and checks the resulting permissions with `os.Stat`.
+
+## Usage
+
+### `go-perm-test`
+
+Prints the results as a CSV in the format
+
+```<expected permissions>,<actual permissions>```
+
+where each set of permissions is an octal integer.
+
+### `go-perm-test <filename>`
+
+Inserts the results into an SQLite database called `filename`.
+There are two objects in the DB schema: a table `result_raw(expected INT, actual INT)` and a view `result`.
+
+The `result` view breaks down the permissions into separate fields: The raw data are in the `expected` and `actual` columns, 3-bit fields are in `{expected,actual}_{u,g,o}` columns, and 1-bit fields are in `{expected,actual}_{u,g,o}{r,w,x}` columns.
+
+## Findings
+
+Permissions as observed through `os.Stat` depend entirely upon the owner's write bit set through `os.Chmod`:
+
+```
+sqlite> select distinct actual, expected_uw from result;
+actual|expected_uw
+292|0
+438|1
+```
+
+This obviously isn't an exhaustive treatment of the subject, and I'm not really interested in doing one, but it corraborates [Michal Pristas’s findings.](https://archive.is/RZ8WP)

go.mod

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+module git.codemonkeysoftware.net/b/go-perm-test
+
+go 1.22.1
+
+require (
+	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/google/uuid v1.3.0 // indirect
+	github.com/mattn/go-isatty v0.0.16 // indirect
+	github.com/ncruces/go-strftime v0.1.9 // indirect
+	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
+	golang.org/x/sys v0.16.0 // indirect
+	modernc.org/libc v1.41.0 // indirect
+	modernc.org/mathutil v1.6.0 // indirect
+	modernc.org/memory v1.7.2 // indirect
+	modernc.org/sqlite v1.29.1 // indirect
+	zombiezen.com/go/sqlite v1.3.0 // indirect
+)

go.sum

@@ -0,0 +1,23 @@
+github.com/dustin/go-humanize v1.0.1 h1:GzkhY7T5VNhEkwH0PVJgjz+fX1rhBrR7pRT3mDkpeCY=
+github.com/dustin/go-humanize v1.0.1/go.mod h1:Mu1zIs6XwVuF/gI1OepvI0qD18qycQx+mFykh5fBlto=
+github.com/google/uuid v1.3.0 h1:t6JiXgmwXMjEs8VusXIJk2BXHsn+wx8BZdTaoZ5fu7I=
+github.com/google/uuid v1.3.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
+github.com/mattn/go-isatty v0.0.16 h1:bq3VjFmv/sOjHtdEhmkEV4x1AJtvUvOJ2PFAZ5+peKQ=
+github.com/mattn/go-isatty v0.0.16/go.mod h1:kYGgaQfpe5nmfYZH+SKPsOc2e4SrIfOl2e/yFXSvRLM=
+github.com/ncruces/go-strftime v0.1.9 h1:bY0MQC28UADQmHmaF5dgpLmImcShSi2kHU9XLdhx/f4=
+github.com/ncruces/go-strftime v0.1.9/go.mod h1:Fwc5htZGVVkseilnfgOVb9mKy6w1naJmn9CehxcKcls=
+github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec h1:W09IVJc94icq4NjY3clb7Lk8O1qJ8BdBEF8z0ibU0rE=
+github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec/go.mod h1:qqbHyh8v60DhA7CoWK5oRCqLrMHRGoxYCSS9EjAz6Eo=
+golang.org/x/sys v0.0.0-20220811171246-fbc7d0a398ab/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.16.0 h1:xWw16ngr6ZMtmxDyKyIgsE93KNKz5HKmMa3b8ALHidU=
+golang.org/x/sys v0.16.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+modernc.org/libc v1.41.0 h1:g9YAc6BkKlgORsUWj+JwqoB1wU3o4DE3bM3yvA3k+Gk=
+modernc.org/libc v1.41.0/go.mod h1:w0eszPsiXoOnoMJgrXjglgLuDy/bt5RR4y3QzUUeodY=
+modernc.org/mathutil v1.6.0 h1:fRe9+AmYlaej+64JsEEhoWuAYBkOtQiMEU7n/XgfYi4=
+modernc.org/mathutil v1.6.0/go.mod h1:Ui5Q9q1TR2gFm0AQRqQUaBWFLAhQpCwNcuhBOSedWPo=
+modernc.org/memory v1.7.2 h1:Klh90S215mmH8c9gO98QxQFsY+W451E8AnzjoE2ee1E=
+modernc.org/memory v1.7.2/go.mod h1:NO4NVCQy0N7ln+T9ngWqOQfi7ley4vpwvARR+Hjw95E=
+modernc.org/sqlite v1.29.1 h1:19GY2qvWB4VPw0HppFlZCPAbmxFU41r+qjKZQdQ1ryA=
+modernc.org/sqlite v1.29.1/go.mod h1:hG41jCYxOAOoO6BRK66AdRlmOcDzXf7qnwlwjUIOqa0=
+zombiezen.com/go/sqlite v1.3.0 h1:98g1gnCm+CNz6AuQHu0gqyw7gR2WU3O3PJufDOStpUs=
+zombiezen.com/go/sqlite v1.3.0/go.mod h1:yRl27//s/9aXU3RWs8uFQwjkTG9gYNGEls6+6SvrclY=

main_windows.go

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+package main
+
+import (
+	"fmt"
+	"io/fs"
+	"os"
+	"strings"
+
+	"zombiezen.com/go/sqlite"
+	"zombiezen.com/go/sqlite/sqlitex"
+)
+
+type Result struct{ Expected, Actual fs.FileMode }
+
+type SQLiteEmitter struct {
+	conn *sqlite.Conn
+}
+
+func (s *SQLiteEmitter) Close() error {
+	return s.conn.Close()
+}
+
+func sqlViewColSpec() string {
+	var cols []string
+	var whos = []rune{'o', 'g', 'u'}
+	var whats = []rune{'x', 'w', 'r'}
+	for _, fieldName := range []string{"expected", "actual"} {
+		cols = append(cols, fmt.Sprintf("%s", fieldName))
+		for iwho, who := range whos {
+			cols = append(cols, fmt.Sprintf("%[1]s & (7 << %[3]d * 3) >> (%[3]d * 3) AS %[1]s_%[2]c", fieldName, who, iwho))
+			for iwhat, what := range whats {
+				cols = append(cols, fmt.Sprintf("%[1]s & (1 << %[3]d * 3 + %[5]d) >> (%[3]d * 3 + %[5]d) AS %[1]s_%[2]c%[4]c", fieldName, who, iwho, what, iwhat))
+			}
+		}
+	}
+	return strings.Join(cols, ",\n")
+}
+
+const createTable = `CREATE TABLE result_raw (
+	expected INT NOT NULL,
+	actual INT NOT NULL
+);`
+
+var createView string = `CREATE VIEW result AS
+SELECT
+` + sqlViewColSpec() + `
+FROM result_raw;`
+
+func NewSQLite(path string) (*SQLiteEmitter, error) {
+	conn, err := sqlite.OpenConn(path, sqlite.OpenCreate|sqlite.OpenReadWrite|sqlite.OpenWAL)
+	if err != nil {
+		return nil, err
+	}
+	fmt.Println(createView)
+	err = sqlitex.Execute(conn, createTable, &sqlitex.ExecOptions{})
+	if err != nil {
+		return nil, fmt.Errorf("NewSQLite: cannot create table: %w", err)
+	}
+	err = sqlitex.Execute(conn, createView, &sqlitex.ExecOptions{})
+	if err != nil {
+		return nil, fmt.Errorf("NewSQLite: cannot create view: %w", err)
+	}
+	return &SQLiteEmitter{
+		conn: conn,
+	}, nil
+}
+
+func (s *SQLiteEmitter) Emit(r Result) error {
+	return sqlitex.Execute(s.conn, "INSERT INTO result_raw(expected, actual) VALUES (?, ?)", &sqlitex.ExecOptions{
+		Args: []any{r.Expected, r.Actual},
+	})
+}
+
+func emitCSV(r Result) error {
+	_, err := fmt.Printf("%03o,%03o\n", r.Expected, r.Actual)
+	if err != nil {
+		return fmt.Errorf("emitCSV: %w", err)
+	}
+	return nil
+}
+
+func getData(emit func(Result) error) (err error) {
+	f, err := os.CreateTemp("", "go-perm-test-*")
+	if err != nil {
+		return err
+	}
+	path := f.Name()
+	f.Close()
+
+	for mode := fs.FileMode(0); mode <= os.ModePerm; mode++ {
+		err := os.Chmod(path, mode)
+		if err != nil {
+			return fmt.Errorf("cannot set mode 0%03o on %s: %w", mode, path, err)
+		}
+		info, err := os.Stat(path)
+		if err != nil {
+			return fmt.Errorf("cannot stat %s: %w", path, err)
+		}
+		result := Result{
+			Expected: mode,
+			Actual:   info.Mode(),
+		}
+		err = emit(result)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func run() error {
+	var emit func(Result) error
+	if len(os.Args) < 2 {
+		emit = emitCSV
+	} else {
+		dbPath := os.Args[1]
+		db, err := NewSQLite(dbPath)
+		if err != nil {
+			return err
+		}
+		defer db.Close()
+		emit = db.Emit
+	}
+	return getData(emit)
+}
+
+func main() {
+	err := run()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "%s: %s\n", os.Args[0], err)
+		os.Exit(1)
+	}
+}