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Replace sparsefile.Copy with sparsefile.Overwrite
Copy will not be correct in rare cases when we need to override parts of already existing file with whole buffer of zeros.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,58 @@ | ||
| package sparsefile | ||
|
|
||
| import ( | ||
| "bytes" | ||
| "fmt" | ||
| "io" | ||
| ) | ||
|
|
||
| const maxBufSize = 64 * 1024 | ||
|
|
||
| func Overwrite(dst io.ReadWriteSeeker, src io.Reader) (written int64, skipped int64, err error) { | ||
| srcBuf := make([]byte, maxBufSize) | ||
| dstBuf := make([]byte, maxBufSize) | ||
| return overwriteBuffer(dst, src, srcBuf, dstBuf) | ||
| } | ||
|
|
||
| func overwriteBuffer(dst io.ReadWriteSeeker, src io.Reader, srcBuf, dstBuf []byte) (written int64, skipped int64, err error) { | ||
| var shiftedSrc []byte | ||
| dstPos, err := dst.Seek(0, io.SeekCurrent) | ||
| if err != nil { | ||
| return 0, 0, fmt.Errorf("unable to seek current: %w", err) | ||
| } | ||
| for { | ||
| nrSrc, er1 := src.Read(srcBuf) | ||
| if nrSrc == 0 && er1 == io.EOF { | ||
| break | ||
| } | ||
| nrDst, er2 := dst.Read(dstBuf[:nrSrc]) | ||
| nrMin := min(nrSrc, nrDst) | ||
| if bytes.Equal(dstBuf[:nrMin], srcBuf[:nrMin]) { | ||
| dstPos += int64(nrMin) | ||
| skipped += int64(nrMin) | ||
| shiftedSrc = srcBuf[nrMin:nrSrc] | ||
| } else { | ||
| shiftedSrc = srcBuf[0:nrSrc] | ||
| } | ||
| // rewind dstPost | ||
| dstPos, er2 = dst.Seek(dstPos, io.SeekStart) | ||
| if er2 != nil { | ||
| err = er2 | ||
| break | ||
| } | ||
| nw, ew := dst.Write(shiftedSrc) | ||
| if ew != nil { | ||
| err = ew | ||
| break | ||
| } | ||
| dstPos += int64(nw) | ||
| written += int64(nw) | ||
| if er1 != nil { | ||
| if er1 != io.EOF { | ||
| err = er1 | ||
| } | ||
| break | ||
| } | ||
| } | ||
| return | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,173 @@ | ||
| package sparsefile | ||
|
|
||
| import ( | ||
| "github.com/stretchr/testify/require" | ||
| "io" | ||
| "os" | ||
| "path" | ||
| "testing" | ||
| ) | ||
|
|
||
| func TestOverwrite(t *testing.T) { | ||
| tests := []struct { | ||
| name string | ||
| dstInitial string // Initial content of dst | ||
| src string // Content to overwrite dst with | ||
| srcBufSize int | ||
| dstBufSize int | ||
| wantWritten int64 // Expected number of bytes actually written | ||
| wantSkipped int64 // Expected number of bytes skipped because they are the same | ||
| wantFinal string // Expected final content of dst | ||
| wantErr bool // Whether an error is expected | ||
| }{ | ||
| { | ||
| name: "overwrite first chunk", | ||
| dstInitial: "Hello, World!", | ||
| src: "Greetings!", | ||
| srcBufSize: 8, | ||
| dstBufSize: 8, | ||
| wantFinal: "Greetings!ld!", | ||
| wantWritten: 10, | ||
| wantSkipped: 0, | ||
|
|
||
| wantErr: false, | ||
| }, | ||
| { | ||
| name: "Partial overwrite, some content same", | ||
| dstInitial: "Hello, World!", | ||
| src: "Hello, Go!", | ||
| wantFinal: "Hello, Go!ld!", | ||
| srcBufSize: 8, | ||
| dstBufSize: 8, | ||
| wantWritten: 3, | ||
| wantSkipped: 8, // "Hello, " is the same | ||
|
|
||
| wantErr: false, | ||
| }, | ||
| { | ||
| name: "Complete match, all skipped", | ||
| dstInitial: "Hello, World!", | ||
| src: "Hello, World!", | ||
| srcBufSize: 8, | ||
| dstBufSize: 8, | ||
| wantWritten: 0, | ||
| wantSkipped: 13, | ||
| wantFinal: "Hello, World!", | ||
| wantErr: false, | ||
| }, | ||
| { | ||
| name: "Complete match, dst buffer larger", | ||
| dstInitial: "Hello, World!", | ||
| src: "Hello, World!", | ||
| srcBufSize: 8, | ||
| dstBufSize: 10, | ||
| wantWritten: 0, | ||
| wantSkipped: 13, | ||
| wantFinal: "Hello, World!", | ||
| wantErr: false, | ||
| }, | ||
| { | ||
| name: "Partial match in the middle", | ||
| dstInitial: "Hello, W12345678World!", | ||
| src: "123456781234567812345678", | ||
| srcBufSize: 8, | ||
| dstBufSize: 10, | ||
| wantWritten: 16, | ||
| wantSkipped: 8, | ||
| wantFinal: "123456781234567812345678", | ||
| wantErr: false, | ||
| }, | ||
| { | ||
| name: "Partial match at the end", | ||
| dstInitial: "Hello, W123456", | ||
| src: "12345678123456", | ||
| srcBufSize: 8, | ||
| dstBufSize: 30, | ||
| wantWritten: 8, | ||
| wantSkipped: 6, | ||
| wantFinal: "12345678123456", | ||
| wantErr: false, | ||
| }, | ||
| { | ||
| name: "dst initial is empty", | ||
| dstInitial: "", | ||
| src: "12345678123456", | ||
| wantFinal: "12345678123456", | ||
| srcBufSize: 8, | ||
| dstBufSize: 30, | ||
| wantWritten: 14, | ||
| wantSkipped: 0, | ||
|
|
||
| wantErr: false, | ||
| }, | ||
| { | ||
| name: "dst initial is larger than src", | ||
| dstInitial: "000000000000000000000000000", | ||
| src: "12345678123456", | ||
| wantFinal: "123456781234560000000000000", | ||
| srcBufSize: 8, | ||
| dstBufSize: 30, | ||
| wantWritten: 14, | ||
| wantSkipped: 0, | ||
|
|
||
| wantErr: false, | ||
| }, | ||
| { | ||
| name: "input is multiplier of src buffer", | ||
| dstInitial: "1234567812345678", | ||
| src: "1234567812345678", | ||
| wantFinal: "1234567812345678", | ||
| srcBufSize: 8, | ||
| dstBufSize: 8, | ||
| wantWritten: 0, | ||
| wantSkipped: 16, | ||
|
|
||
| wantErr: false, | ||
| }, | ||
| } | ||
|
|
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| createFileWithContent := func(t *testing.T, name string, content string) (f *os.File, closer func()) { | ||
| t.Helper() | ||
|
|
||
| f, err := os.Create(name) | ||
| require.NoError(t, err) | ||
| _, err = io.WriteString(f, content) | ||
| require.NoError(t, err) | ||
| _, err = f.Seek(0, io.SeekStart) | ||
| require.NoError(t, err) | ||
| return f, func() { | ||
| require.NoError(t, f.Close()) | ||
| } | ||
| } | ||
|
|
||
| for _, tt := range tests { | ||
| t.Run(tt.name, func(t *testing.T) { | ||
| tmp := t.TempDir() | ||
| src, closerSrc := createFileWithContent(t, path.Join(tmp, "src.tmp"), tt.src) | ||
| dst, closerDst := createFileWithContent(t, path.Join(tmp, "dst.tmp"), tt.dstInitial) | ||
| defer closerDst() | ||
| defer closerSrc() | ||
|
|
||
| written, skipped, err := overwriteBuffer(dst, src, make([]byte, tt.srcBufSize), make([]byte, tt.dstBufSize)) | ||
| if (err != nil) != tt.wantErr { | ||
| t.Errorf("Overwrite() error = %v, wantErr %v", err, tt.wantErr) | ||
| return | ||
| } | ||
|
|
||
| // Check the final content of dst | ||
| _, err = dst.Seek(0, io.SeekStart) | ||
| require.NoError(t, err) | ||
| finalDstContent, err := io.ReadAll(dst) | ||
| require.NoError(t, err) | ||
| if string(finalDstContent) != tt.wantFinal { | ||
| t.Errorf("Final dst content = %v, want %v", string(finalDstContent), tt.wantFinal) | ||
| } | ||
| if written != tt.wantWritten { | ||
| t.Errorf("Overwrite() written = %v, want %v", written, tt.wantWritten) | ||
| } | ||
| if skipped != tt.wantSkipped { | ||
| t.Errorf("Overwrite() skipped = %v, want %v", skipped, tt.wantSkipped) | ||
| } | ||
| }) | ||
| } | ||
| } |