HTTP

• Each line of the HTTP header should end in \r\n (<CR><LF>)
  • Therefore, an empty line should be two characters long.
  • If the line starts with a space, it continues the previous line. Must remove the \r\n from the previous line.
• First line of HTTP Request → Request Line.
  • Has METHOD URI VERSION format.
• First line of HTTP Response → Status Line
  • Has VERSION STATUS REASON
• Other lines have KEY:VALUE
• Stateless. HTTP Server does not remember previous client requests
• Takes two round trips + File transmission time
  • One round trip to initiate TCP connection
  • One round trip for HTTP request and response

Status Codes

• 200 OK
• 301 Moved Permanently → Redirect
• 400 Bad Request
• 404 Not Found
• 451 Legal Problems
• 505 HTTP Version Not Supported

Conditional Get

• HTTP request
  • If-modified-since: date
• HTTP response
  • HTTP/1.0 304 Not Modified
  • HTTP/1.0 200 OK Last-Modified: date
• For updating caches