khenaidoo | 59ce9dd | 2019-11-11 13:05:32 -0500 | [diff] [blame] | 1 | // Copyright 2013 Matt T. Proud |
| 2 | // |
| 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 |
| 6 | // |
| 7 | // http://www.apache.org/licenses/LICENSE-2.0 |
| 8 | // |
| 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. |
| 14 | |
| 15 | package pbutil |
| 16 | |
| 17 | import ( |
| 18 | "encoding/binary" |
| 19 | "errors" |
| 20 | "io" |
| 21 | |
| 22 | "github.com/golang/protobuf/proto" |
| 23 | ) |
| 24 | |
| 25 | var errInvalidVarint = errors.New("invalid varint32 encountered") |
| 26 | |
| 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 |
| 47 | } |
| 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 |
| 50 | // read before. |
| 51 | newBytesRead, err := r.Read(headerBuf[bytesRead : bytesRead+1]) |
| 52 | if newBytesRead == 0 { |
| 53 | if err != nil { |
| 54 | return bytesRead, err |
| 55 | } |
| 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... |
| 59 | continue |
| 60 | } |
| 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]) |
| 65 | } |
| 66 | |
| 67 | messageBuf := make([]byte, messageLength) |
| 68 | newBytesRead, err := io.ReadFull(r, messageBuf) |
| 69 | bytesRead += newBytesRead |
| 70 | if err != nil { |
| 71 | return bytesRead, err |
| 72 | } |
| 73 | |
| 74 | return bytesRead, proto.Unmarshal(messageBuf, m) |
| 75 | } |