85 lines
1.9 KiB
Go
85 lines
1.9 KiB
Go
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package toolkit
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import (
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"bytes"
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"context"
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"crypto/sha256"
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"errors"
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"fmt"
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"io"
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"io/fs"
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"os"
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"dev.mediocregopher.com/mediocre-go-lib.git/mctx"
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"dev.mediocregopher.com/mediocre-go-lib.git/mlog"
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"github.com/sergi/go-diff/diffmatchpatch"
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)
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var differ = diffmatchpatch.New()
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// WriteFileCheckChanged uses the given callback to collect data to be written
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// to the given filepath with the given permission bits set. If the file's
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// contents have been modified (or if the file didn't previously exist) then
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// true is returned.
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func WriteFileCheckChanged(
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ctx context.Context,
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logger *mlog.Logger,
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path string,
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mode os.FileMode,
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fn func(io.Writer) error,
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) (
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bool, error,
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) {
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var (
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buf = new(bytes.Buffer)
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h = sha256.New()
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w = io.MultiWriter(buf, h)
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changed bool
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)
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if err := fn(w); err != nil {
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return false, fmt.Errorf("callback returned: %w", err)
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}
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f, err := os.Open(path)
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if errors.Is(err, fs.ErrNotExist) {
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changed = true
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// fine, we'll just write the file
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} else if err != nil {
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return false, fmt.Errorf("reading contents of existing file: %w", err)
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} else {
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var (
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existingBuf = new(bytes.Buffer)
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existingH = sha256.New()
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existingW = io.MultiWriter(existingBuf, existingH)
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_, copyErr = io.Copy(existingW, f)
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closeErr = f.Close()
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)
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if err := errors.Join(closeErr, copyErr); err != nil {
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return false, fmt.Errorf("hashing existing file: %w", err)
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}
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changed = !bytes.Equal(h.Sum(nil), existingH.Sum(nil))
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if changed && logger.MaxLevel() >= mlog.LevelDebug.Int() {
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var (
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ctx = mctx.Annotate(ctx, "path", path)
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diff = differ.DiffPrettyText(
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differ.DiffMain(existingBuf.String(), buf.String(), false),
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)
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)
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logger.Debug(ctx, "WriteFileCheckChanged diff:\n"+diff)
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}
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}
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if changed {
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if err := os.WriteFile(path, buf.Bytes(), mode); err != nil {
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return false, fmt.Errorf("writing file: %w", err)
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}
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}
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return changed, nil
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}
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