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