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a91ee49705
This is inspired by https://github.com/kythe/kythe/blob/master/kythe/go/platform/delimited/delimited.go but bit improved and tailored to our needs. Signed-off-by: Bartek Plotka <bwplotka@gmail.com> Fixed typos in the comment. Signed-off-by: Bartek Plotka <bwplotka@gmail.com> Moved to chunked* naming, added flusher. Signed-off-by: Bartek Plotka <bwplotka@gmail.com>
104 lines
3 KiB
Go
104 lines
3 KiB
Go
// Copyright 2019 The Prometheus Authors
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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 remote
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import (
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"bufio"
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"encoding/binary"
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"github.com/gogo/protobuf/proto"
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"io"
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"net/http"
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)
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// ChunkedWriter is an io.Writer wrapper that allows streaming by adding uvarint delimiter before each write in a form
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// of length of the corresponded byte array.
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type ChunkedWriter struct {
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writer io.Writer
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flusher http.Flusher
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}
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// NewChunkedWriter constructs a ChunkedWriter.
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func NewChunkedWriter(w io.Writer, f http.Flusher) *ChunkedWriter {
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return &ChunkedWriter{writer: w, flusher: f}
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}
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// Write writes given bytes to the stream. It adds uvarint delimiter before each message.
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// Returned bytes number represents sent bytes for a given buffer. The number does not include delimiter bytes.
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// It does the flushing for you.
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func (w *ChunkedWriter) Write(b []byte) (int, error) {
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if len(b) == 0 {
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return 0, nil
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}
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var buf [binary.MaxVarintLen64]byte
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v := binary.PutUvarint(buf[:], uint64(len(b)))
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if _, err := w.writer.Write(buf[:v]); err != nil {
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return 0, err
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}
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n, err := w.writer.Write(b)
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if err != nil {
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return n, err
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}
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w.flusher.Flush()
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return n, nil
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}
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// ChunkedReader is a buffered reader that expects uvarint delimiter before each message.
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// It will allocate as much as the biggest frame defined by delimiter (on top of bufio.Reader allocations).
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type ChunkedReader struct {
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b *bufio.Reader
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data []byte
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}
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// NewChunkedReader constructs a ChunkedReader.
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func NewChunkedReader(r io.Reader) *ChunkedReader {
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return &ChunkedReader{b: bufio.NewReader(r)}
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}
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// Next returns the next length-delimited record from the input, or io.EOF if
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// there are no more records available. Returns io.ErrUnexpectedEOF if a short
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// record is found, with a length of n but fewer than n bytes of data.
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//
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// NOTE: The slice returned is valid only until a subsequent call to Next. It's a caller's responsibility to copy the
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// returned slice if needed.
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func (r *ChunkedReader) Next() ([]byte, error) {
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size, err := binary.ReadUvarint(r.b)
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if err != nil {
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return nil, err
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}
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if cap(r.data) < int(size) {
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r.data = make([]byte, size)
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} else {
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r.data = r.data[:size]
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}
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if _, err := io.ReadFull(r.b, r.data); err != nil {
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return nil, err
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}
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return r.data, nil
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}
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// NextProto consumes the next available record by calling r.Next, and decodes
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// it into the protobuf with proto.Unmarshal.
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func (r *ChunkedReader) NextProto(pb proto.Message) error {
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rec, err := r.Next()
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if err != nil {
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return err
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}
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return proto.Unmarshal(rec, pb)
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}
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