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MXS-2420 Add debug function for decoding response packet

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When debugging you occasionally want to find out what a packet
contains (e.g. delivered to clientReply). Manually looking into
the packet works, but is tedious. With this function you when
the execution has been stopped in GDB examine a protocol packet.

E.g.

Thread 3 "maxscale" hit Breakpoint 6, RWSplitSession::clientReply (this=0x7fffe401ed20, writebuf=0x7fffe401e910, backend_dcb=0x7fffe401dbe0) at /home/wikman/MariaDB/MaxScale/server/modules/routing/readwritesplit/rwsplitsession.cc:567
567	    DCB* client_dcb = backend_dcb->session->client_dcb;
(gdb) p dbg_decode_response(writebuf)
$30 = 0x7ffff0d40d54 "Packet no: 1, Payload len: 44, Command : ERR, Code: 1146, Message : Table 'test.blahasdf' doesn't exist"
This commit is contained in:
Johan Wikman 2019-04-03 14:55:07 +03:00
parent 2aa3515fc8
commit d2f31aab0a
1 changed files with 103 additions and 1 deletions
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104
server/core/mysql_utils.cc
View File

@ -380,4 +380,106 @@ std::unique_ptr<mxq::QueryResult> execute_query(MYSQL* conn, const std::string&
return rval;
}
}
}
#if defined(SS_DEBUG)
/**
* Return decoded MySQL response packet.
*
* Intended to be used when debugging with a GDB-based debugger.
* For instance, if GDB has been stopped by a breakpoint in
* clientReply() you can use this function for investigating
* what the response packet contains:
*
* (gdb) p dbg_decode_response(writebuf)
* $30 = 0x7ffff0d40d54 "Packet no: 1, Payload len: 44, Command : ERR,
* Code: 1146, Message : Table 'test.blahasdf' doesn't exist"
*
* @param pPacket A MySQL response packet.
*
* @return The packet decoded into a descriptive string.
*/
char *dbg_decode_response(GWBUF* pPacket)
{
uint8_t header[MYSQL_HEADER_LEN + 1];
gwbuf_copy_data(pPacket, 0, sizeof(header), header);
uint32_t payload_len = MYSQL_GET_PAYLOAD_LEN(header);
uint32_t packet_no = MYSQL_GET_PACKET_NO(header);
uint32_t command = std::numeric_limits<uint32_t>::max();
if (gwbuf_length(pPacket) > MYSQL_HEADER_LEN)
{
command = MYSQL_GET_COMMAND(header);
}
const int buflen = 1024; // Should be enough.
thread_local char buffer[buflen];
int len = buflen;
char* z = buffer;
int l = snprintf(z, len, "Packet no: %u, Payload len: %u", packet_no, payload_len);
z += l;
len -= l;
switch (command)
{
case 0x00:
snprintf(z, len, ", Command : OK");
break;
case 0xff:
{
l = snprintf(z, len, ", Command : ERR");
z += l;
len -= l;
uint8_t error[payload_len];
gwbuf_copy_data(pPacket, MYSQL_HEADER_LEN, payload_len, error);
uint32_t error_code = gw_mysql_get_byte2(&error[1]);
l = snprintf(z, len, ", Code: %u", error_code);
z += l;
len -= l;
const int message_index = 1 + 2 + 1 + 5;
uint8_t* pMessage = &error[message_index];
l = snprintf(z, len, ", Message : ");
z += l;
len -= l;
int message_len = payload_len - message_index;
if (message_len + 1 > len)
{
message_len = len - 1;
}
strncpy(z, (char*)pMessage, message_len);
z[message_len] = 0;
}
break;
case 0xfb:
snprintf(z, len, ", Command : GET_MORE_CLIENT_DATA");
break;
case std::numeric_limits<uint32_t>::max():
break;
default:
snprintf(z, len, ", Command : Result Set");
}
return buffer;
}
#endif