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README.md
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README.md
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# Go file permissions test
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by Brandon Dyck <brandon@dyck.us>
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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`.
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## Usage
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### `go-perm-test`
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Prints the results as a CSV in the format
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```<expected permissions>,<actual permissions>```
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where each set of permissions is an octal integer.
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### `go-perm-test <filename>`
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Inserts the results into an SQLite database called `filename`.
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There are two objects in the DB schema: a table `result_raw(expected INT, actual INT)` and a view `result`.
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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.
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## Findings
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Permissions as observed through `os.Stat` depend entirely upon the owner's write bit set through `os.Chmod`:
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```
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sqlite> select distinct actual, expected_uw from result;
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actual|expected_uw
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292|0
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438|1
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```
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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)
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17
go.mod
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17
go.mod
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module git.codemonkeysoftware.net/b/go-perm-test
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go 1.22.1
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require (
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github.com/dustin/go-humanize v1.0.1 // indirect
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github.com/google/uuid v1.3.0 // indirect
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github.com/mattn/go-isatty v0.0.16 // indirect
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github.com/ncruces/go-strftime v0.1.9 // indirect
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github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
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golang.org/x/sys v0.16.0 // indirect
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modernc.org/libc v1.41.0 // indirect
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modernc.org/mathutil v1.6.0 // indirect
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modernc.org/memory v1.7.2 // indirect
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modernc.org/sqlite v1.29.1 // indirect
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zombiezen.com/go/sqlite v1.3.0 // indirect
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)
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23
go.sum
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go.sum
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github.com/dustin/go-humanize v1.0.1 h1:GzkhY7T5VNhEkwH0PVJgjz+fX1rhBrR7pRT3mDkpeCY=
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github.com/dustin/go-humanize v1.0.1/go.mod h1:Mu1zIs6XwVuF/gI1OepvI0qD18qycQx+mFykh5fBlto=
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github.com/google/uuid v1.3.0 h1:t6JiXgmwXMjEs8VusXIJk2BXHsn+wx8BZdTaoZ5fu7I=
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github.com/google/uuid v1.3.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
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github.com/mattn/go-isatty v0.0.16 h1:bq3VjFmv/sOjHtdEhmkEV4x1AJtvUvOJ2PFAZ5+peKQ=
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github.com/mattn/go-isatty v0.0.16/go.mod h1:kYGgaQfpe5nmfYZH+SKPsOc2e4SrIfOl2e/yFXSvRLM=
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github.com/ncruces/go-strftime v0.1.9 h1:bY0MQC28UADQmHmaF5dgpLmImcShSi2kHU9XLdhx/f4=
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github.com/ncruces/go-strftime v0.1.9/go.mod h1:Fwc5htZGVVkseilnfgOVb9mKy6w1naJmn9CehxcKcls=
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github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec h1:W09IVJc94icq4NjY3clb7Lk8O1qJ8BdBEF8z0ibU0rE=
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github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec/go.mod h1:qqbHyh8v60DhA7CoWK5oRCqLrMHRGoxYCSS9EjAz6Eo=
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golang.org/x/sys v0.0.0-20220811171246-fbc7d0a398ab/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
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golang.org/x/sys v0.16.0 h1:xWw16ngr6ZMtmxDyKyIgsE93KNKz5HKmMa3b8ALHidU=
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golang.org/x/sys v0.16.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
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modernc.org/libc v1.41.0 h1:g9YAc6BkKlgORsUWj+JwqoB1wU3o4DE3bM3yvA3k+Gk=
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modernc.org/libc v1.41.0/go.mod h1:w0eszPsiXoOnoMJgrXjglgLuDy/bt5RR4y3QzUUeodY=
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modernc.org/mathutil v1.6.0 h1:fRe9+AmYlaej+64JsEEhoWuAYBkOtQiMEU7n/XgfYi4=
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modernc.org/mathutil v1.6.0/go.mod h1:Ui5Q9q1TR2gFm0AQRqQUaBWFLAhQpCwNcuhBOSedWPo=
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modernc.org/memory v1.7.2 h1:Klh90S215mmH8c9gO98QxQFsY+W451E8AnzjoE2ee1E=
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modernc.org/memory v1.7.2/go.mod h1:NO4NVCQy0N7ln+T9ngWqOQfi7ley4vpwvARR+Hjw95E=
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modernc.org/sqlite v1.29.1 h1:19GY2qvWB4VPw0HppFlZCPAbmxFU41r+qjKZQdQ1ryA=
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modernc.org/sqlite v1.29.1/go.mod h1:hG41jCYxOAOoO6BRK66AdRlmOcDzXf7qnwlwjUIOqa0=
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zombiezen.com/go/sqlite v1.3.0 h1:98g1gnCm+CNz6AuQHu0gqyw7gR2WU3O3PJufDOStpUs=
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zombiezen.com/go/sqlite v1.3.0/go.mod h1:yRl27//s/9aXU3RWs8uFQwjkTG9gYNGEls6+6SvrclY=
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133
main_windows.go
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133
main_windows.go
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package main
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import (
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"fmt"
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"io/fs"
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"os"
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"strings"
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"zombiezen.com/go/sqlite"
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"zombiezen.com/go/sqlite/sqlitex"
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)
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type Result struct{ Expected, Actual fs.FileMode }
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type SQLiteEmitter struct {
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conn *sqlite.Conn
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}
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func (s *SQLiteEmitter) Close() error {
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return s.conn.Close()
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}
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func sqlViewColSpec() string {
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var cols []string
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var whos = []rune{'o', 'g', 'u'}
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var whats = []rune{'x', 'w', 'r'}
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for _, fieldName := range []string{"expected", "actual"} {
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cols = append(cols, fmt.Sprintf("%s", fieldName))
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for iwho, who := range whos {
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cols = append(cols, fmt.Sprintf("%[1]s & (7 << %[3]d * 3) >> (%[3]d * 3) AS %[1]s_%[2]c", fieldName, who, iwho))
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for iwhat, what := range whats {
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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))
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}
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}
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}
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return strings.Join(cols, ",\n")
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}
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const createTable = `CREATE TABLE result_raw (
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expected INT NOT NULL,
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actual INT NOT NULL
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);`
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var createView string = `CREATE VIEW result AS
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SELECT
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` + sqlViewColSpec() + `
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FROM result_raw;`
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func NewSQLite(path string) (*SQLiteEmitter, error) {
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conn, err := sqlite.OpenConn(path, sqlite.OpenCreate|sqlite.OpenReadWrite|sqlite.OpenWAL)
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if err != nil {
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return nil, err
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}
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fmt.Println(createView)
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err = sqlitex.Execute(conn, createTable, &sqlitex.ExecOptions{})
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if err != nil {
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return nil, fmt.Errorf("NewSQLite: cannot create table: %w", err)
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}
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err = sqlitex.Execute(conn, createView, &sqlitex.ExecOptions{})
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if err != nil {
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return nil, fmt.Errorf("NewSQLite: cannot create view: %w", err)
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}
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return &SQLiteEmitter{
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conn: conn,
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}, nil
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}
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func (s *SQLiteEmitter) Emit(r Result) error {
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return sqlitex.Execute(s.conn, "INSERT INTO result_raw(expected, actual) VALUES (?, ?)", &sqlitex.ExecOptions{
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Args: []any{r.Expected, r.Actual},
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})
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}
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func emitCSV(r Result) error {
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_, err := fmt.Printf("%03o,%03o\n", r.Expected, r.Actual)
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if err != nil {
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return fmt.Errorf("emitCSV: %w", err)
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}
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return nil
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}
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func getData(emit func(Result) error) (err error) {
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f, err := os.CreateTemp("", "go-perm-test-*")
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if err != nil {
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return err
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}
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path := f.Name()
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f.Close()
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for mode := fs.FileMode(0); mode <= os.ModePerm; mode++ {
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err := os.Chmod(path, mode)
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if err != nil {
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return fmt.Errorf("cannot set mode 0%03o on %s: %w", mode, path, err)
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}
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info, err := os.Stat(path)
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if err != nil {
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return fmt.Errorf("cannot stat %s: %w", path, err)
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}
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result := Result{
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Expected: mode,
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Actual: info.Mode(),
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}
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err = emit(result)
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if err != nil {
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return err
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}
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}
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return nil
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}
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func run() error {
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var emit func(Result) error
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if len(os.Args) < 2 {
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emit = emitCSV
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} else {
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dbPath := os.Args[1]
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db, err := NewSQLite(dbPath)
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if err != nil {
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return err
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}
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defer db.Close()
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emit = db.Emit
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}
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return getData(emit)
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}
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func main() {
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err := run()
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if err != nil {
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fmt.Fprintf(os.Stderr, "%s: %s\n", os.Args[0], err)
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os.Exit(1)
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}
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}
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