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jpeg_decode.js
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jpeg_decode.js
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function processJPEG(data){
console.log(data);
console.log(typeof data);
var info={
valid:true,
filesize:data.length,
nextp:-1,
headers:[],
hasextraneous:false,
extraneous:""
};
for(var p=0;p<data.length;p++){
var header=processHeader(data,p)
console.log(header)
if(p>0){
var prevheader=info.headers.last();
if(prevheader.haslen || (hexdec(prevheader.type)>=0xd0 && hexdec(prevheader.type)<=0xd7)){//allow content for RST market sections
console.log("prevtype: "+prevheader.type)
console.log("prevoffset: "+prevheader.p)
console.log("nextoffset: "+p)
prevheader.actuallen=(p-prevheader.p)-2;//subtract marker bytes from previous header len - this is differencing the start position of two headers, so it includes marker bytes
prevheader.contentlen=prevheader.actuallen;
if(prevheader.haslenbytes){
prevheader.contentlen-=2;//if we scanned in the data and the header has no length bytes, don't subtract them!
}
prevheader.content=data.substr(prevheader.contentp,prevheader.contentlen);
if(prevheader.actuallen==0) prevheader.contentlen=0
if(prevheader.type=="da"){//postprocess scan header
prevheader.extendeddata = postprocessSOS(prevheader);
}
}
//console.log(p+" "+prevheader.p+" "+prevheader.actuallen)
}
info.headers.push(header);
if((p==0 && (header.type!="d8" && header.type!="4f")) || !header.valid){
//console.log((p==0 && header.type!="d8"))
console.log("invalid header at position 0")
info.valid=false;
break;
}
var nextp=header.nextp
if(header.type=="93") nextp=scanJPEGEnd(data,nextp);
if(header.type=="da") nextp=scanJPEG(data,nextp)
if(hexdec(header.type)>=0xd0 && hexdec(header.type)<=0xd7) nextp=scanJPEG(data,nextp)//fixed: support restart markers
if(info.nextp<nextp) info.nextp=nextp
if(header.type=="d9"){
info.nextp=nextp
break;
}
console.log("advancing position "+p+" -> "+(nextp-1))
if((nextp-1) < p){
console.error("error: parsing loop detected")
break;
}
p=nextp-1
}
if(info.filesize>info.nextp){
info.hasextraneous=true
info.extraneous=data.substring(info.nextp)
}
console.log(info)
return info;
}
function scanJPEGEnd(data,ps){
for(p=ps;p<data.length;p++){
var hb=pad(data.charCodeAt(p).toString(16),2)
var lb=pad(data.charCodeAt(p+1).toString(16),2)
var dlb=data.charCodeAt(p+1)
if(hb=="ff" && lb=="d9" ) return p;//OPTIONAL: && (dlb<0xd0 || dlb>0xd7) d0-d7 are restart markers, we could ignore during scan
}
return p
}
function scanJPEG(data,ps){
for(p=ps;p<data.length;p++){
var hb=pad(data.charCodeAt(p).toString(16),2)
var lb=pad(data.charCodeAt(p+1).toString(16),2)
var dlb=data.charCodeAt(p+1)
if(hb=="ff" && lb!="00" ) return p;//OPTIONAL: && (dlb<0xd0 || dlb>0xd7) d0-d7 are restart markers, we could ignore during scan
}
return p
}
function processHeader(data,p){
var header={valid:true,magic:"00",type:"00",haslen:true,haslenbytes:true,p:p,len:0,actuallen:0,contentp:(p+2),content:"",nextp:(p+2),contentlen:0,desc:{},hasextendeddata:false,extendedtype:"",extendeddata:{}}
var hb=pad(data.charCodeAt(p).toString(16),2)
var lb=pad(data.charCodeAt(p+1).toString(16),2)
var dlb=data.charCodeAt(p+1)
header.magic=hb
header.valid=(hb=="ff");
header.type=lb;
//console.log(hb+lb)
if(!header.valid) return header;
header.desc=jpeg_headerdump_name(header.type)
header.haslenbytes = header.haslen=(header.type!="4f" && header.type!="d8" && header.type!="d9");//fixed: support restart markers
if(header.type=="93" || (dlb>=0xd0 && dlb<=0xd7)) header.haslenbytes=false;
if(!header.haslen){
header.len='None (No content)'
return header
}
if(!header.haslenbytes){//J2K-SOD scan's from end of marker with no length bytes (fixed 16-bit)
header.len='None (Scanned)'
return header;
}
header.contentp+=2
hb=pad(data.charCodeAt(p+2).toString(16),2)
lb=pad(data.charCodeAt(p+3).toString(16),2)
header.len=parseInt(hb+lb,16)
header.nextp+=header.len
if(header.haslenbytes) header.contentlen=header.len-2
header.content=data.substr(header.contentp,header.contentlen);//will be revised by processing above
//console.log(header.type+header.content+isJFIF(header.content))
//if(header.type=="c0"){
if(dlb>=0xc0 && dlb<=0xc3){
header.hasextendeddata=true;
header.extendedtype="SOF";
header.extendeddata=processSOF0(header.content);
}
if(header.type=='ee'){
var app14=processAPP14(header.content);
if(app14.valid){
header.hasextendeddata=true;
header.extendedtype=app14.type;
header.extendeddata=app14.info;
}
}
if(header.type=="e0" && isJFIF(header.content)){
header.hasextendeddata=true;
header.extendedtype="JFIF";
header.extendeddata=processJFIF(header.content);
}
if(header.type=="e1" && isEXIF(header.content)){
header.hasextendeddata=true;
header.extendedtype="EXIF";
header.extendeddata=processEXIF(header.content);
}
if(header.type=="da"){//technically by spec. SOS has a header length, but we include the scan data as its content because of jpdump limitations
header.len+=" (Scanned)";
header.hasextendeddata=true;
header.extendedtype="Scan";
header.extendeddata=processSOS(header.content);
}
return header
}