ios - Detect HTML encoding when NSURLResponse returns nil for textEncodingName -

i'm loading website html using call -

    nsmutableurlrequest *request = [nsmutableurlrequest requestwithurl:url];     [request setvalue:@"utf-8" forhttpheaderfield:@"accept-encoding"];     [request setvalue:@"text/html" forhttpheaderfield:@"accept"];     [nsurlconnection sendasynchronousrequest:request                                        queue:[nsoperationqueue currentqueue]                            completionhandler:^(nsurlresponse *response, nsdata *data, nserror *error) { ... } 

and then, convert nsdata nsstring, need know encoding, call -

nsstring *textencoding = [response textencodingname]; 

from code block, returns nil on websites won't specify "content-encoding" header field.

if don't know encoding, [[nsstring alloc] initwithdata:data encoding:responseencoding] won't give me readable html.

how can detect right encoding websites don't send "content-encoding" header field?

it possible try different encodings , see 1 results readable text -

static int encodingpriority[] = {     nsutf8stringencoding,     nsasciistringencoding,     nsisolatin1stringencoding,     nsisolatin2stringencoding,     nsunicodestringencoding,     nswindowscp1251stringencoding,     nswindowscp1252stringencoding,     nswindowscp1253stringencoding,     nswindowscp1254stringencoding,     nswindowscp1250stringencoding,     nsnextstepstringencoding,     nsjapaneseeucstringencoding,     nsnonlossyasciistringencoding,     nsshiftjisstringencoding,          /* kcfstringencodingdosjapanese */     nsiso2022jpstringencoding,        /* iso 2022 japanese encoding e-mail */     nsmacosromanstringencoding,     nsutf16bigendianstringencoding,     nsutf16littleendianstringencoding,     nsutf32stringencoding,     nsutf32bigendianstringencoding,     nsutf32littleendianstringencoding };  #define required_html_string    @"<html"  - (nsstring *)htmlstringforunknownencodingdata:(nsdata *)data detectedencoding:(nsstringencoding *)detectedencoding {     nsstringencoding encoding;     nsstring *html;      (int = 0; < sizeof(encodingpriority); i++) {         encoding = encodingpriority[i];          // try encoding         html = [[nsstring alloc] initwithdata:data encoding:encoding];          // need find text, because bad encoding return unreadable text         if (html && [html rangeofstring:required_html_string options:nscaseinsensitivesearch].location != nsnotfound) {             *detectedencoding = encoding;             return html;         }     }     return nil; } 

then, detect encoding html in nsdata using, call -

nsstringencoding encoding; html = [self htmlstringforunknownencodingdata:data detectedencoding:&encoding];  if (html)     nslog("encoding detected!"); else     nslog("no encoding detected");