1 // Copyright 2013 Matt T. Proud
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
7 // http://www.apache.org/licenses/LICENSE-2.0
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
22 "github.com/golang/protobuf/proto"
25 var errInvalidVarint = errors.New("invalid varint32 encountered")
27 // ReadDelimited decodes a message from the provided length-delimited stream,
28 // where the length is encoded as 32-bit varint prefix to the message body.
29 // It returns the total number of bytes read and any applicable error. This is
30 // roughly equivalent to the companion Java API's
31 // MessageLite#parseDelimitedFrom. As per the reader contract, this function
32 // calls r.Read repeatedly as required until exactly one message including its
33 // prefix is read and decoded (or an error has occurred). The function never
34 // reads more bytes from the stream than required. The function never returns
35 // an error if a message has been read and decoded correctly, even if the end
36 // of the stream has been reached in doing so. In that case, any subsequent
37 // calls return (0, io.EOF).
38 func ReadDelimited(r io.Reader, m proto.Message) (n int, err error) {
39 // Per AbstractParser#parsePartialDelimitedFrom with
40 // CodedInputStream#readRawVarint32.
41 var headerBuf [binary.MaxVarintLen32]byte
42 var bytesRead, varIntBytes int
43 var messageLength uint64
44 for varIntBytes == 0 { // i.e. no varint has been decoded yet.
45 if bytesRead >= len(headerBuf) {
46 return bytesRead, errInvalidVarint
48 // We have to read byte by byte here to avoid reading more bytes
49 // than required. Each read byte is appended to what we have
51 newBytesRead, err := r.Read(headerBuf[bytesRead : bytesRead+1])
52 if newBytesRead == 0 {
56 // A Reader should not return (0, nil), but if it does,
57 // it should be treated as no-op (according to the
58 // Reader contract). So let's go on...
61 bytesRead += newBytesRead
62 // Now present everything read so far to the varint decoder and
63 // see if a varint can be decoded already.
64 messageLength, varIntBytes = proto.DecodeVarint(headerBuf[:bytesRead])
67 messageBuf := make([]byte, messageLength)
68 newBytesRead, err := io.ReadFull(r, messageBuf)
69 bytesRead += newBytesRead
74 return bytesRead, proto.Unmarshal(messageBuf, m)