[Bug]: Call serializeSessionDescriptionInit and return STATUS_BUFFER_TOO_SMALL about amazon-kinesis-video-streams-webrtc-sdk-c

[disa6302]

@liquanqing ,

Could you highlight what your application looks like? The API in our sample is invoked twice. Once to get the size:

CHK_STATUS(serializeSessionDescriptionInit(&offerSessionDescriptionInit, NULL, &buffLen));

buffLen is initialized to 0 in the viewer sample. In the function, the second parameter is NULL, which means nothing gets copied into sessionDescriptionJSON as part of SNPRINTF. The check CHK(sessionDescriptionJSON == NULL) evaluates to TRUE leading to the rest of the logic to happen. Once the size is retrieved, the next call is made:

SignalingMessage message;
CHK_STATUS(serializeSessionDescriptionInit(&offerSessionDescriptionInit, message.payload, &buffLen));

In this call, the SDK serializes the SDP.

Could you attach logs and how you are invoking the APIs in your application?

[liquanqing]

@disa6302
Hi, I have not modify the code in sample and just run kvsWebRTCClientViewer.exe, and it occur STATUS_BUFFER_TOO_SMALL
and go to CleanUp.

The point of the question is ：
“ the second parameter is NULL, which means nothing gets copied into sessionDescriptionJSON as part of SNPRINTF ”
This has worked in Linux or Other Platform, but in Windows with gcc version 8.1.0 (x86_64-posix-seh-rev0, Built by MinGW-W64 project), it is not work.

while ((next = STRNCHR(curr, (UINT32) (tail - curr), '\n')) != NULL) {
        lineLen = (UINT32) (next - curr);

        if (lineLen > 0 && curr[lineLen - 1] == '\r') {
            lineLen--;
        }

        amountWritten =
            SNPRINTF(sessionDescriptionJSON + *sessionDescriptionJSONLen, sessionDescriptionJSON == NULL ? 0 : inputSize - *sessionDescriptionJSONLen,
                     "%*.*s%s", lineLen, lineLen, curr, SESSION_DESCRIPTION_INIT_LINE_ENDING);
        CHK(sessionDescriptionJSON == NULL || ((inputSize - *sessionDescriptionJSONLen) >= amountWritten), STATUS_BUFFER_TOO_SMALL);

        *sessionDescriptionJSONLen += amountWritten;
        curr = next + 1;
    }

in the code， sessionDescriptionJSON is NULL, but *sessionDescriptionJSONLen will increase after "*sessionDescriptionJSONLen += amountWritten", and it will make the first parameter of SNPRINTF is "NOT NULL",
firstly , the memory address is invalided.
secondly, in windows, it will return -1 (UINT32_MAX),
these will make the problem.
the debug information as follow :

so , i do a little change as follow and it worked :

SNPRINTF(sessionDescriptionJSON == NULL ? NULL :
sessionDescriptionJSON + *sessionDescriptionJSONLen, sessionDescriptionJSON == NULL ? 0 : inputSize - *sessionDescriptionJSONLen,
                     "%*.*s%s", lineLen, lineLen, curr, SESSION_DESCRIPTION_INIT_LINE_ENDING);