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// 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)
}
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