How to encode and decode websocket permessage-deflate using zlib library in C?

Question

All I'm trying to code for a WebSocket payload using per-message-deflate. I am trying to use some test code, but my encoding is not suitable, can you help me.

Here is my code:

char a[180] = "{\"type\":\"message\",\"channel\":\"C04U0F9CW\",\"text\":\"TestingMessage\",\"id\":757}";
char b[180];
char c[180];
int i;
// deflate
// zlib struct
z_stream defstream;
defstream.zalloc = Z_NULL;
defstream.zfree = Z_NULL;
defstream.opaque = Z_NULL;
defstream.avail_in = (uInt)strlen(a)+1; // size of input, string + terminator
defstream.next_in = (Bytef *)a; // input char array
defstream.avail_out = (uInt)sizeof(b); // size of output
defstream.next_out = (Bytef *)b; // output char array

//deflateInit(&defstream, Z_SYNC_FLUSH);
deflateInit2(&defstream, Z_DEFAULT_COMPRESSION, Z_DEFLATED, 15, 8, Z_DEFAULT_STRATEGY);
deflate(&defstream, Z_SYNC_FLUSH);
deflateEnd(&defstream);
for(i=0;i<=(char*)defstream.next_out - b;i++)
{
        printf("%X",(Bytef)b[i]);
}
printf("\n%s\n",(Bytef *)b);
// This is one way of getting the size of the output
printf("Deflated size is: %lu\n", (char*)defstream.next_out - b);

my conclusion

kml@kml-VirtualBox:~/zlib-1.2.11/test$ gcc test.c -lz && ./a.out 
789CAA562AA92C4855B252CA4D2D2E4E4C4F55D2514ACE48CCCB4BCD18A391B98841AB8593A873454B522B4A804221A9C5259979E9BE70D599294A56E6A6E6B5C0000FFFF2E
x  V* ,HU R M-.NLOU QJ H  K  9   Y: EKR+J B!  % y  pՙ)JV    

Deflated size is: 72
Inflate:
73
{"type":"message","channel":"C04U0F9CW","text":"TestingMessage","id":757}

So, I expect that I will like the payload

AA562AA92C4855B252CA4D2D2E4E4C4F55D2514ACE48CCCB4BCD018A391B98841AB8593A8703454B522B4A804221A9C5259979E9BE70D599294A56E6A6E6B50000

This is the Fiddler Webmasters traffic capture for this particular message.

Please help me get the correct encoding for each message.

Here is some more upgrade information
GET https://127.0.0.1/websoc.html HTTP/1.1
Host: mpmulti-yklu.slack-msgs.com
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:53.0) Gecko/20100101 Firefox/53.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate, br
Sec-WebSocket-Version: 13
Sec-WebSocket-Extensions: permessage-deflate
Sec-WebSocket-Key: FriWg0AWhiLhLXXnfJK8kA==
Connection: keep-alive, Upgrade
Pragma: no-cache
Cache-Control: no-cache
Upgrade: websocket

Answer

HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: S2Q+O/tRM0/mIG//Er2hDdqD0eY=
Sec-Websocket-Extensions: permessage-deflate; server_no_context_takeover; client_no_context_takeover
X-Via: haproxy-ext90

Answer 1

, defstream.avail_in , . , .

int l = (uInt)strlen(a);
defstream.avail_in = l; // size of input, string + terminator

, z_stream , , .

, , -deflate.

" 789CAA562AA92C4855B252CA4D2D2E4E4C4F55D2514ACE48CCCB4BCD18A391B98841AB8593A873454B522B4A804221A9C5259979E9BE70D599294A56E6A6E6B5C0000FFFF2E"

789C - 0000FFFF (00FFFF) - . 0 00, '0' '00'. 5C - . Thye '2E' ,

int d = memcmp(msgend, &b[defstream.total_out - 4], 4) ? 0 : 4;
for(i=0;i<defstream.total_out - d;i++)
{
        printf("%2X",(Bytef)b[i]);
}

,

" AA562AA92C4855B252CA4D2D2E4E4C4F55D2514ACE48CCCB4BCD018A391B98841AB8593A8703454B522B4A804221A9C5259979E9BE70D599294A56E6A6E6B50000"

, 2 0, "00", ( ).

, , , .