Question

所有我试图使用per-message-deflate编码WebSocket有效负载。我试图使用一些测试代码，但我的编码不正确，请你帮我。

这是我的代码：

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);

我的输出是

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}

所以我希望有效载荷会像我这样

AA562AA92C4855B252CA4D2D2E4E4C4F55D2514ACE48CCCB4BCD018A391B98841AB8593A8703454B522B4A804221A9C5259979E9BE70D599294A56E6A6E6B50000

This is the fiddler WebSocket traffic capture for that particular message

请帮助我获取正确的per-message-deflate编码。

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

响应

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

代码是正确的，但 defstream.avail_in 期望精确的长度，而不是额外的空字符。如果您将提供确切的输入长度，它将正常工作。试试这个

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

请尝试了解z_stream如何分配值检查代码，然后您将更好地了解这一点。

我认为很多人都在尝试解码，而且他们没有为每条消息放弃获得适当的价值。

检查输出

“的 789CAA562AA92C4855B252CA4D2D2E4E4C4F55D2514ACE48CCCB4BCD18A391B98841AB8593A873454B522B4A804221A9C5259979E9BE70D599294A56E6A6E6B5C0000FFFF2E ”

此处 789C 是标头， 0000FFFF或根据您的代码（00FFFF）是deflate消息的预告片。这里0代表00，因为你的输出是打印一个'0'而不是'00'。因为额外的一个尺码，你得到额外的5C。当您尝试以下代码
时，Thye'2E'也将被移除
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]); }

所以你的预期答案是

“的 AA562AA92C4855B252CA4D2D2E4E4C4F55D2514ACE48CCCB4BCD018A391B98841AB8593A8703454B522B4A804221A9C5259979E9BE70D599294A56E6A6E6B50000 ”

根据您的输出，2个字节为0，因此根据您的代码，它将为“00”并且您的输出跟随打印每个半字节（半字节）。

请尝试这对我有用，我现在能够正确解码。

如何在C中使用zlib库对websocket permessage-deflate进行编码和解码？

1 个答案: