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parser.go
170 lines (135 loc) · 3.09 KB
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parser.go
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package mjpeg
import (
"io"
"log"
"bufio"
"fmt"
)
type FormatError string
func (e FormatError) Error() string { return string(e) }
const DEF_BUF_SZ = 4096
const DEF_BLK_SZ = 256
var SOI = []byte { 0xff, 0xd8 }
var EOI = []byte { 0xff, 0xd9 }
type Reader interface {
io.Reader
ReadByte() (c byte, err error)
}
type Parser struct {
r Reader
buf []byte
read int
cnt int64
}
func NewParser(r io.Reader) (*Parser, error) {
p := new(Parser)
if rr, ok := r.(Reader); ok {
p.r = rr
} else {
p.r = bufio.NewReader(r)
}
p.buf = make([]byte, DEF_BUF_SZ)
p.read = 0
p.cnt = 0
return p, nil
}
// func (this *Parser) parse()(c chan interface{}){
// c := make(chan interface{})
// var err error
// for {
// log.Printf("start parsing")
// frame, err := this.parseFrame()
// if err == io.EOF {
// c <- err
// }
// if frame != nil {
// c <- frame
// }
// select t := c.(type) {
// case errc := <- this.closing:
// errc <- err
// return
// }
// if err == io.EOF {
// c <- err
// }
// // if err != nil {
// // log.Print(err)
// // }
// if data != nil {
// c <- data
// }
// //time.Sleep(100 * time.Millisecond)
// }
// }
func (this *Parser) parse(handle func([]byte)){
for {
frame, err := this.parseFrame()
if err == io.EOF {
break
}
// if err != nil {
// t.Logf("can not parse frame %s", err)
// }
if frame != nil {
this.cnt++
handle(frame)
}
}
}
func (this *Parser) parseFrame() ([]byte, error){
bound := this.read + DEF_BLK_SZ
if bound > cap(this.buf) {
// allocate double what's needed, for future growth.
dubSize := (cap(this.buf))*2
newBuf := make([]byte, len(this.buf), dubSize)
copy(newBuf, this.buf)
this.buf = newBuf
}
//fmt.Printf("buf len %d, cap %d\n", len(this.buf), cap(this.buf))
chunk, err := io.ReadFull(this.r, this.buf[this.read:bound])
if err != nil {
log.Printf("goes here %s\n", err)
return nil, err
}
this.read += chunk
//grow the slice by read bytes
this.buf = this.buf[:this.read]
//fmt.Printf("buf len %d, cap %d\n", len(this.buf), cap(this.buf))
imgStart := IndexOfBytes(this.buf, SOI)
imgEnd := IndexOfBytes(this.buf, EOI)
if imgStart < 0 {
return nil, FormatError("SOI not located")
}
if imgEnd < 0 {
return nil, FormatError("EOI not located")
}
imgEnd = imgEnd + 2 //add last two bytes of EOI
fmt.Printf("start %d, end %d\n", imgStart, imgEnd)
imgBuf := append([]byte{}, this.buf[imgStart:imgEnd]...)
rest := len(this.buf) - imgEnd
copy(this.buf[0:], this.buf[imgEnd:])
this.buf = this.buf[:rest]
this.read = rest
return imgBuf, nil
}
func IndexOfBytes(buf []byte, search []byte) (int){
start := 0
m := len(search)
n := len(buf) - m
matched := 0
for ; start < n; start++ {
matched = 0
for next := 0; next < m ; next++ {
if buf[start+next] == search[next] {
matched++
} else {
break
}
}
if matched == m {
return start
}
}
return -1
}