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package btree | ||
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import "io" | ||
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// seekableBuffer is a buffer that can be seeked into. | ||
// this replicates the behavior of a file on disk without having to write to disk | ||
// which is useful for testing. | ||
type seekableBuffer struct { | ||
buf []byte | ||
pos int | ||
} | ||
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func newSeekableBuffer() *seekableBuffer { | ||
return &seekableBuffer{} | ||
} | ||
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func (b *seekableBuffer) Write(p []byte) (int, error) { | ||
n := copy(b.buf[b.pos:], p) | ||
if n < len(p) { | ||
b.buf = append(b.buf, p[n:]...) | ||
} | ||
b.pos += len(p) | ||
return len(p), nil | ||
} | ||
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func (b *seekableBuffer) Seek(offset int64, whence int) (int64, error) { | ||
switch whence { | ||
case io.SeekStart: | ||
b.pos = int(offset) | ||
case io.SeekCurrent: | ||
b.pos += int(offset) | ||
case io.SeekEnd: | ||
b.pos = len(b.buf) + int(offset) | ||
} | ||
if b.pos < 0 { | ||
b.pos = 0 | ||
} | ||
if b.pos > len(b.buf) { | ||
b.pos = len(b.buf) | ||
} | ||
return int64(b.pos), nil | ||
} | ||
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func (b *seekableBuffer) Read(p []byte) (int, error) { | ||
if b.pos >= len(b.buf) { | ||
return 0, io.EOF | ||
} | ||
n := copy(p, b.buf[b.pos:]) | ||
b.pos += n | ||
return n, nil | ||
} | ||
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var _ io.ReadWriteSeeker = &seekableBuffer{} |
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package btree | ||
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import ( | ||
"io" | ||
"testing" | ||
) | ||
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func TestSeekableBuffer(t *testing.T) { | ||
t.Run("Write", func(t *testing.T) { | ||
b := newSeekableBuffer() | ||
n, err := b.Write([]byte("hello")) | ||
if err != nil { | ||
t.Fatal(err) | ||
} | ||
if n != 5 { | ||
t.Fatalf("expected to write 5 bytes, wrote %d", n) | ||
} | ||
if string(b.buf) != "hello" { | ||
t.Fatalf("expected to write 'hello', wrote %s", string(b.buf)) | ||
} | ||
}) | ||
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t.Run("write to end", func(t *testing.T) { | ||
b := newSeekableBuffer() | ||
if _, err := b.Write([]byte("hello")); err != nil { | ||
t.Fatal(err) | ||
} | ||
if _, err := b.Seek(-2, io.SeekEnd); err != nil { | ||
t.Fatal(err) | ||
} | ||
if _, err := b.Write([]byte("world")); err != nil { | ||
t.Fatal(err) | ||
} | ||
if string(b.buf) != "helworld" { | ||
t.Fatalf("expected to write 'helworld', wrote %s", string(b.buf)) | ||
} | ||
}) | ||
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t.Run("Seek", func(t *testing.T) { | ||
b := newSeekableBuffer() | ||
if _, err := b.Write([]byte("helloo")); err != nil { | ||
t.Fatal(err) | ||
} | ||
if _, err := b.Seek(0, io.SeekStart); err != nil { | ||
t.Fatal(err) | ||
} | ||
if _, err := b.Write([]byte("world")); err != nil { | ||
t.Fatal(err) | ||
} | ||
if string(b.buf) != "worldo" { | ||
t.Fatalf("expected to write 'worldo', wrote %s", string(b.buf)) | ||
} | ||
}) | ||
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t.Run("Read", func(t *testing.T) { | ||
b := newSeekableBuffer() | ||
if _, err := b.Write([]byte("hello")); err != nil { | ||
t.Fatal(err) | ||
} | ||
if _, err := b.Seek(0, io.SeekStart); err != nil { | ||
t.Fatal(err) | ||
} | ||
buf := make([]byte, 5) | ||
n, err := b.Read(buf) | ||
if err != nil { | ||
t.Fatal(err) | ||
} | ||
if n != 5 { | ||
t.Fatalf("expected to read 5 bytes, read %d", n) | ||
} | ||
if string(buf) != "hello" { | ||
t.Fatalf("expected to read 'hello', read %s", string(buf)) | ||
} | ||
}) | ||
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t.Run("read from middle", func(t *testing.T) { | ||
b := newSeekableBuffer() | ||
if _, err := b.Write([]byte("hello")); err != nil { | ||
t.Fatal(err) | ||
} | ||
if _, err := b.Seek(2, io.SeekStart); err != nil { | ||
t.Fatal(err) | ||
} | ||
buf := make([]byte, 3) | ||
n, err := b.Read(buf) | ||
if err != nil { | ||
t.Fatal(err) | ||
} | ||
if n != 3 { | ||
t.Fatalf("expected to read 3 bytes, read %d", n) | ||
} | ||
if string(buf) != "llo" { | ||
t.Fatalf("expected to read 'llo', read %s", string(buf)) | ||
} | ||
}) | ||
} |