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