mirror of https://bitbucket.org/ausocean/av.git
113 lines
2.2 KiB
Go
113 lines
2.2 KiB
Go
/*
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NAME
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lex.go
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DESCRIPTION
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lex.go provides a lexer to extract separate JPEG images from a JPEG stream.
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This could either be a series of descrete JPEG images, or an MJPEG stream.
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AUTHOR
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Dan Kortschak <dan@ausocean.org>
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Saxon Nelson-Milton <saxon@ausocean.org>
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LICENSE
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lex.go is Copyright (C) 2017 the Australian Ocean Lab (AusOcean)
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It is free software: you can redistribute it and/or modify them
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under the terms of the GNU General Public License as published by the
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Free Software Foundation, either version 3 of the License, or (at your
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option) any later version.
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It is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with revid in gpl.txt. If not, see http://www.gnu.org/licenses.
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*/
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package jpeg
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import (
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"bufio"
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"bytes"
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"fmt"
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"io"
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"time"
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"bitbucket.org/ausocean/utils/logger"
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)
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var Log logger.LoggerIF
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var noDelay = make(chan time.Time)
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func init() {
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close(noDelay)
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}
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// Lex parses JPEG frames read from src into separate writes to dst with
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// successive writes being performed not earlier than the specified delay.
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func Lex(dst io.Writer, src io.Reader, delay time.Duration) error {
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var tick <-chan time.Time
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if delay == 0 {
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tick = noDelay
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} else {
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ticker := time.NewTicker(delay)
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defer ticker.Stop()
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tick = ticker.C
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}
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r := bufio.NewReader(src)
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for {
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buf := make([]byte, 2, 4<<10)
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n, err := r.Read(buf)
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if n < 2 {
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return io.ErrUnexpectedEOF
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}
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if err != nil {
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return err
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}
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if !bytes.Equal(buf, []byte{0xff, 0xd8}) {
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return fmt.Errorf("parser: not JPEG frame start: %#v", buf)
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}
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nImg := 1
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var last byte
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for {
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b, err := r.ReadByte()
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if err != nil {
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if err == io.EOF {
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return io.ErrUnexpectedEOF
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}
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return err
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}
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buf = append(buf, b)
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if last == 0xff && b == 0xd8 {
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nImg++
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}
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if last == 0xff && b == 0xd9 {
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nImg--
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}
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if nImg == 0 {
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<-tick
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Log.Debug("writing buf", "len(buf)", len(buf))
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_, err = dst.Write(buf)
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if err != nil {
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return err
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}
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break
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}
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last = b
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}
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}
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}
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