// compressedChunkGreaterN like compressedChunk produces a single, compressed,
// snappy-framed block. The returned block will have decoded length at most n
// and encoded length greater than n.
func compressedChunkGreaterN(t *testing.T, n int) []byte {
decoded := make([]byte, n)
var numTries int
var encoded []byte
for len(encoded) <= n && numTries < 3 {
numTries++
nrd, err := io.ReadFull(rand.Reader, decoded)
if err != nil {
t.Errorf("crypto/rand: %v", err)
return nil
}
if nrd != n {
t.Errorf("crypto/rand: bad read (%d bytes)", nrd)
return nil
}
encoded, err = snappy.Encode(encoded[:cap(encoded)], decoded)
if err != nil {
t.Errorf("snappy: %v", err)
return nil
}
}
if len(encoded) <= n {
t.Error(errNotEnoughEntropy)
return nil
}
return compressedChunk(t, decoded)
}
// write attempts to encode p as a block and write it to the underlying writer.
// The returned int may not equal p's length if compression below
// MaxBlockSize-4 could not be achieved.
func (w *writer) write(p []byte) (int, error) {
var err error
if len(p) > MaxBlockSize {
return 0, errors.New(fmt.Sprintf("block too large %d > %d", len(p), MaxBlockSize))
}
w.dst = w.dst[:cap(w.dst)] // Encode does dumb resize w/o context. reslice avoids alloc.
w.dst, err = snappy.Encode(w.dst, p)
if err != nil {
return 0, err
}
block := w.dst
n := len(p)
compressed := true
// check for data which is better left uncompressed. this is determined if
// the encoded content is longer than the source.
if len(w.dst) >= len(p) {
compressed = false
block = p[:n]
}
if !w.sentStreamID {
_, err := w.writer.Write(streamID)
if err != nil {
return 0, err
}
w.sentStreamID = true
}
// set the block type
if compressed {
writeHeader(w.hdr, blockCompressed, block, p[:n])
} else {
writeHeader(w.hdr, blockUncompressed, block, p[:n])
}
_, err = w.writer.Write(w.hdr)
if err != nil {
return 0, err
}
_, err = w.writer.Write(block)
if err != nil {
return 0, err
}
return n, nil
}
// compressedChunk encodes b returning a single, compressed, snappy-framed
// block. compressedChunk can encode source data larger than allowed in the
// specification.
func compressedChunk(t *testing.T, src []byte) []byte {
encoded, err := snappy.Encode(nil, src)
if err != nil {
t.Errorf("snappy: %v", err)
return nil
}
if len(encoded) > (1<<24)-5 { // account for the 4-byte checksum
t.Errorf("block data too large %d", len(src))
return nil
}
chunk := make([]byte, len(encoded)+8)
writeHeader(chunk[:8], blockCompressed, encoded, src)
copy(chunk[8:], encoded)
return chunk
}