42 lines
1.4 KiB
Markdown
42 lines
1.4 KiB
Markdown
# src.lwithers.me.uk/go/writefile
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[](https://godoc.org/src.lwithers.me.uk/go/writefile)
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This package implements the common Unix technique of writing a new file by first
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writing a temporary file, then ensuring it is fsync()ed, before calling rename()
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to atomically move into its final resting place.
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What problem does this solve? It prevents writing a partial output file, or
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corrupting an existing file with a partially-written new version, if there is a
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crash or other unexpected exit of the program.
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Example:
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```
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finalFname, out, err := writefile.New("my-file")
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if err != nil {
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return err
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}
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defer writefile.Abort(out)
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// … write to ‘out’ …
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return writefile.Commit(finalFname, out)
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```
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The `New()` method returns a final filename string which is later passed to
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`Commit()`. This will typically match the filename argument passed to `New()`,
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except if the file is a symlink, in which case the symlink is dereferenced
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and its target is overwritten. If this behaviour is undesired, the following
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pattern may be used instead:
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```
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out, err := writefile.NewNoDeref("my-file")
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// …
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return writefile.Commit("my-file", out)
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```
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The temporary file being written will have 0600 permissions. If an existing
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file is overwritten by `Commit()`, the call will attempt to inherit the existing
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permissions. Otherwise, the final file is left with 0600.
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