I solved myself the problem, which is non trivial.
Web server can use different scheme for separate header lines.
You can have
'\n' or '\r\n' or '\n\r'.
Believe me beacause I tested a lot of embedded web server (not the bigger ones).
The (most) important part of the header is the Content-Length.
If you (as me) are planning to change the body, you must carefull re-write the Content-Length value.
Follow the code.
The "line" variable is a line you want to analyze, for example (Content-Length). It is simple to extract it from the header
Qt Code: 
  1. int Util::getCR(const QByteArray &line)
  2. {
  3. int c = 0;
  4. char ch;
  5. QChar sc;
  6.     for(int i=0;i<line.size();i++)
  7. {
  8.         sc = line.at(i);
  9.         if (sc.isDigit())
  10.             ch = sc.unicode() - '0';
  11.         //qDebug()<<"UTIL getCR byte"<<line.at(i)<<sc.unicode()*1;;
  12.  
  13.  
  14.         if (c == 13)
  15.  
  16.         {
  17.            // We found CR ASCCI '0D'
  18.            // Check if there is a LF
  19.  
  20.            if (i == line.size()-1)
  21.            {
  22.                     sc = line.at(i+1);
  23.                     c = sc.unicode() * 1;
  24.                     if (c == 10)
  25.                         return i+1;
  26.            }
  27.            else
  28.             return i;
  29.  
  30.         }
  31.         else
  32.             // Do the same but first is '0A'
  33.             if ( c == 10)
  34.             {
  35.             // We found CR ASCCI '0D'
  36.             // Check if there is a LF
  37.  
  38.             if (i == line.size()-1)
  39.             {
  40.                      sc = line.at(i+1);
  41.                      c = sc.unicode() * 1;
  42.                      if (c == 13)
  43.                          return i+1;
  44.             }
  45.             else
  46.              return i;
  47.             }
  48. }
  49.  
  50.  
  51.  
  52. }
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