First successful screenshot achieved.

src/packet/hello.c

@@ -32,24 +32,30 @@ msThreadCallbackSetFrame(struct mCoreThread *threadContext) {
     unsigned int stride = data->coreController->stride;
     color_t *outputBuffer = data->coreController->outputBuffer;
     unsigned width, height;
-    unsigned char *raw_data;
+    unsigned char *raw_data = NULL;
     size_t raw_data_len = 0;
-    struct msPacketSendFrame *send_frame;
+    struct msPacketSendFrame *send_frame = NULL;
-    struct msPacket *packet;
+    struct msPacket *packet = NULL;
-
-
 
     data->coreController->threadContext.core->desiredVideoDimensions(data->coreController->threadContext.core, &width, &height);
 
     send_frame = msPacketSendFrameNew(stride, width * height, outputBuffer);
     raw_data = msPacketSendFrameSerialize(send_frame, &raw_data_len);
+    if (!raw_data) {
+        goto return_ms_thread_callback_set_frame;
+    }
 
     packet = msPacketNew(PACKET_SEND_FRAME, raw_data_len, raw_data);
     msPacketSend(packet, data);
 
+return_ms_thread_callback_set_frame:
+    if (send_frame) {
         msPacketSendFrameDestroy(&send_frame);
+    }
+    if (packet) {
         msPacketDestroy(&packet);
     }
+}
 
 bool
 msPacketHelloHandle(const struct msPacket *packet, struct msPacketHello *hello,

src/packet/send_frame.c

@@ -27,14 +27,14 @@ unsigned char *
 msPacketSendFrameSerialize(struct msPacketSendFrame *const self, size_t *len) {
     unsigned char *bytes;
     unsigned int stride = self->stride;
-    size_t outputBufferSizeBytes = self->outputBufferSize * sizeof *self->outputBuffer;
+    size_t outputBufferSizeBytes = self->outputBufferSize * sizeof (uint32_t);
     stride = htobe32(stride);
     *len = (sizeof self->stride) + (sizeof self->outputBufferSize) + (outputBufferSizeBytes);
     outputBufferSizeBytes = htobe64(outputBufferSizeBytes);
     bytes = malloc(*len);
 #define GOTO_END_SERIALIZE_FAIL() \
     free(bytes); \
-    bytes = NULL;
+    bytes = NULL; \
     goto return_ms_packet_send_frame_serialize;
     FILE *fp = fmemopen(bytes, sizeof *bytes * *len, "w");
     if (fwrite(&self->stride, sizeof self->stride, 1, fp) == -1) {
@@ -43,10 +43,13 @@ msPacketSendFrameSerialize(struct msPacketSendFrame *const self, size_t *len) {
     if (fwrite(&outputBufferSizeBytes, sizeof outputBufferSizeBytes, 1, fp) == -1) {
         GOTO_END_SERIALIZE_FAIL();
     }
-    if (fwrite(self->outputBuffer, sizeof *self->outputBuffer, self->outputBufferSize, fp) == -1) {
+    for (size_t i = 0; i < self->outputBufferSize; i++) {
+        color_t pixel = self->outputBuffer[i];
+        if (fwrite(&pixel, sizeof pixel, 1, fp) == -1) {
             GOTO_END_SERIALIZE_FAIL();
         }
-    fclose(fp);
+    }
 return_ms_packet_send_frame_serialize:
+    fclose(fp);
     return bytes;
 }

tester.pl

@@ -40,11 +40,31 @@ sub retrieve_packet {
     (read $fh, my $size, 8) or return 0;
     $size = unpack('Q>', $size);
     (read $fh, my $raw_data, $size) or return 0;
-    say $id;
+    state $i = 0;
-    say $size;
+    if ($i == 500) {
+        read_send_frame($raw_data);
+    }
+    $i++;
     return 1;
 }
 
+sub read_send_frame {
+    my $raw_data = shift;
+    open my $fh, '<', \$raw_data;
+    (read $fh, my $stride, 4) or return 0;
+    $stride = unpack('N', $stride);
+    (read $fh, my $size, 8) or return 0;
+    $size = unpack('Q>', $size);
+    (read $fh, my $rgbx, $size) or return 0;
+    my @rgbx = split '', $rgbx;
+    for (my $i = 3; $i < length $rgbx; $i+=4) {
+        $rgbx[$i] = chr 255;
+    }
+    $rgbx = join '', @rgbx;
+    path('screenshot.rgbx')->spew($rgbx);
+    close $fh;
+}
+
 sub write_packet {
     my $fh = shift;
     my $id = shift;