Exposed helper methods for reading index bytes.

index/encoding_helpers.go

@@ -18,6 +18,8 @@ import (
  "hash"
  "hash/crc32"
  "unsafe"
+
+ "github.com/pkg/errors"
 )
 
 // enbuf is a helper type to populate a byte slice with various types.
@@ -86,6 +88,60 @@ type decbuf struct {
  e error
 }
 
+// newDecbufAt returns a new decoding buffer. It expects the first 4 bytes
+// after offset to hold the big endian encoded content length, followed by the contents and the expected
+// checksum.
+func newDecbufAt(bs ByteSlice, off int) decbuf {
+ if bs.Len() < off+4 {
+ return decbuf{e: errInvalidSize}
+ }
+ b := bs.Range(off, off+4)
+ l := int(binary.BigEndian.Uint32(b))
+
+ if bs.Len() < off+4+l+4 {
+ return decbuf{e: errInvalidSize}
+ }
+
+ // Load bytes holding the contents plus a CRC32 checksum.
+ b = bs.Range(off+4, off+4+l+4)
+ dec := decbuf{b: b[:len(b)-4]}
+
+ if exp := binary.BigEndian.Uint32(b[len(b)-4:]); dec.crc32() != exp {
+ return decbuf{e: errInvalidChecksum}
+ }
+ return dec
+}
+
+// decbufUvarintAt returns a new decoding buffer. It expects the first bytes
+// after offset to hold the uvarint-encoded buffers length, followed by the contents and the expected
+// checksum.
+func newDecbufUvarintAt(bs ByteSlice, off int) decbuf {
+ // We never have to access this method at the far end of the byte slice. Thus just checking
+ // against the MaxVarintLen32 is sufficient.
+ if bs.Len() < off+binary.MaxVarintLen32 {
+ return decbuf{e: errInvalidSize}
+ }
+ b := bs.Range(off, off+binary.MaxVarintLen32)
+
+ l, n := binary.Uvarint(b)
+ if n <= 0 || n > binary.MaxVarintLen32 {
+ return decbuf{e: errors.Errorf("invalid uvarint %d", n)}
+ }
+
+ if bs.Len() < off+n+int(l)+4 {
+ return decbuf{e: errInvalidSize}
+ }
+
+ // Load bytes holding the contents plus a CRC32 checksum.
+ b = bs.Range(off+n, off+n+int(l)+4)
+ dec := decbuf{b: b[:len(b)-4]}
+
+ if dec.crc32() != binary.BigEndian.Uint32(b[len(b)-4:]) {
+ return decbuf{e: errInvalidChecksum}
+ }
+ return dec
+}
+
 func (d *decbuf) uvarint() int { return int(d.uvarint64()) }
 func (d *decbuf) uvarint32() uint32 { return uint32(d.uvarint64()) }
 func (d *decbuf) be32int() int { return int(d.be32()) }