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varint.go
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varint.go
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package encoder
import (
"io"
"github.com/gogo/protobuf/proto"
"github.com/pkg/errors"
)
const maxVarintLength = 10
var errExcessMaxLength = errors.Errorf("provided header exceeds the max varint length of %d bytes", maxVarintLength)
// readVarint at the beginning of a byte slice. This varint may be used to indicate
// the length of the remaining bytes in the reader.
func readVarint(r io.Reader) (uint64, error) {
b := make([]byte, 0, maxVarintLength)
for i := 0; i < maxVarintLength; i++ {
b1 := make([]byte, 1)
n, err := r.Read(b1)
if err != nil {
return 0, err
}
if n != 1 {
return 0, errors.New("did not read a byte from stream")
}
b = append(b, b1[0])
// If most significant bit is not set, we have reached the end of the Varint.
if b1[0]&0x80 == 0 {
break
}
// If the varint is larger than 10 bytes, it is invalid as it would
// exceed the size of MaxUint64.
if i+1 >= maxVarintLength {
return 0, errExcessMaxLength
}
}
vi, n := proto.DecodeVarint(b)
if n != len(b) {
return 0, errors.New("varint did not decode entire byte slice")
}
return vi, nil
}