HTTP/1.1 - Transfer-Encoding: chunked - delay in the middle of response

Question

I am using WINC1500 WiFi (with Arduino) to connect to a server (https) and to send some API requests. In the header I send:

POST /api/myapi.php HTTP/1.1
Host: myserver.com
Accept: application/json, text/javascript, */*; q=0.01
Content-Type: application/x-www-form-urlencoded; charset=iso-8859-1
Connection: keep-alive
Content-Length: 10

my_content

The server response is ok, something like this:

HTTP/1.1 200 OK
Date: Tue, 03 Sep 2019 16:31:14 GMT
Server: Apache
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate
Pragma: no-cache
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Transfer-Encoding: chunked
Content-Type: application/json

18f
BlaBlaBla.... (399 chars = 18f in hexa)
0

The problem is that, after the first chunk, there is a delay in waiting for the terminating chunk. THe last chunk is an empty one. This is an example to understand it:

HTTP/1.1 200 OK 
Content-Type: text/plain 
Transfer-Encoding: chunked

7\r\n
Mozilla\r\n 
9\r\n
Developer\r\n
7\r\n
Network\r\n
0\r\n 
\r\n

Ok... Let's look at the time line:

19:31:13.685 -> connecting...
19:31:14.325 -> posting...
19:31:15.745 -> end posting...
19:31:15.864 ->     HTTP/1.1 200 OK
19:31:15.864 ->     Date: Tue, 03 Sep 2019 16:31:14 GMT
19:31:15.864 ->     Server: Apache
19:31:15.864 ->     Expires: Thu, 19 Nov 1981 08:52:00 GMT
19:31:15.864 ->     Cache-Control: no-store, no-cache, must-revalidate
19:31:15.864 ->     Pragma: no-cache
19:31:15.904 ->     Keep-Alive: timeout=5, max=100
19:31:15.904 ->     Connection: Keep-Alive
19:31:15.904 ->     Transfer-Encoding: chunked
19:31:15.904 ->     Content-Type: application/json
19:31:15.904 ->     
19:31:15.904 -> waitingChunkLength: 18f
19:31:15.904 -> 399
19:31:15.945 -> waitingChunk: BlaBlaBla.... (399 chars)
19:31:20.875 -> waitingChunkLength: 0
19:31:20.875 -> 0
19:31:20.875 -> waitingChunkTrailer: 
19:31:20.875 -> Done...
Connection closed

After receiving the first and only chunk, there is a huge delay before receiving the last (terminating) chunk. Actually, the last chunk is send just before the connection to be closed by server. I believe that is happening because of the idle time. There are 5 seconds of inactivity, so the server must close the connection.

I try to send a message ("OK") to server just after receiving the first chunk. In this case, the server is responding immediately, but is closing the connection (I believe because of inadequate message):

19:45:43.818 -> connecting...
19:45:44.688 -> posting...
19:45:46.207 -> end posting...
19:45:46.322 ->     HTTP/1.1 200 OK
19:45:46.322 ->     Date: Tue, 03 Sep 2019 16:45:44 GMT
19:45:46.322 ->     Server: Apache
19:45:46.322 ->     Expires: Thu, 19 Nov 1981 08:52:00 GMT
19:45:46.322 ->     Cache-Control: no-store, no-cache, must-revalidate
19:45:46.322 ->     Pragma: no-cache
19:45:46.322 ->     Keep-Alive: timeout=5, max=100
19:45:46.358 ->     Connection: Keep-Alive
19:45:46.358 ->     Transfer-Encoding: chunked
19:45:46.358 ->     Content-Type: application/json
19:45:46.358 ->     
19:45:46.358 -> 
19:45:46.358 -> waitingChunkLength: 18f
19:45:46.358 -> 399
19:45:46.398 -> waitingChunk: BlaBlaBla.... (399 chars)
19:45:46.517 -> waitingChunkLength: 0
19:45:46.517 -> 0
19:45:46.517 -> waitingChunkTrailer: 
19:45:46.517 -> Done...
Connection closed

I need to know where is the problem. Should I send a special message to server after each chunk? Because of this behaviour I cannot take advantage of "Keep-alive" session.

Junior · Accepted Answer · 2019-09-03 23:08:08Z

0

After changing firmware a couple of times without success, I go back to the code and try different things. The problem seems to be last line in POST action:

client.print("Content-Length: ");
client.println(10);
client.println();
client.println("my_content");

This last line should be:

client.print("my_content");

... println appends a carriage return character (ASCII 13, or '\r') and a newline character (ASCII 10, or '\n') after text. So, this extra (unexpected) characters give me so much troubles those days. Hope this solve your problems too.

answered Sep 3, 2019 at 23:08

Junior

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