Sending data over unix domain socket for UV4L data-channel - c++

Question

I have a question related to sending binary data from a Raspberry Pi to web client over WebRTC data channel. I have actually found a solution, but I believe it may be inefficient, and I'm not sure exactly why it works.
Basically, I have a UV4L server with WebRTC data channels enabled. My goal is to send data gathered over I2C to a web client over WebRTC. The UV4L documentation explains that a Unix domain socket must be created and data is passed through the socket from the UV4L server and the application running on the Raspberry. I used C code in my C++ project, since I am more familiar with the language.
This is how I'm creating the socket in my application code. The UV4L server is configured to create a connection with the appropriate socket.
struct thread_info *info = (struct thread_info *)args;
int fd = 0, connfd = 0, returned_len = 0;
fd = socket(AF_UNIX, SOCK_SEQPACKET, 0);
if (fd < 0) {
fprintf(stderr, "Failed to create socket file descriptor\n");
exit(1);
}
struct sockaddr_un addr;
addr.sun_family = AF_UNIX;
strncpy(addr.sun_path, "/tmp/uv4l.socket", sizeof(addr.sun_path)-1);
bind(fd, (struct sockaddr *) &addr, sizeof(addr));
if (listen(fd, 10)) {
fprintf(stderr, "Failed to listen on UNIX socket %d\n", errno);
exit(1);
}
socklen_t socket_length = sizeof(addr);
connfd = accept(fd,(struct sockaddr *)&addr, &socket_length);
if (connfd < 0) {
fprintf(stderr, "Failed to accept socket connection\n");
exit(1);
}
info->socketfd = connfd;
This connection is successful. I then use the file descriptor in another thread to send the data. The I2C library I'm using (pigpio) allows to copy data into as char * buffer, which I define char buffer[nb_reads];
I try to send this data using send directly, but I observe no messages on the other side of my data channel (browser). It's only when I encode the data as a base64 string that I actually get the expected result.
if (total_read > 0) {
size_t encoded_length;
unsigned char *encoded = base64_encode((const unsigned char*)buffer, total_read, &encoded_length);
ssize_t sent = send(info->socketfd, encoded, encoded_length, MSG_EOR);
if (sent < 0) {
fprintf(stderr, "Failed to send all necessary MPU6050 data");
}
free(encoded);
}
Why is it that I cannot just send the byte array directly?

Answer 1

WebRTC data channels can handle messages in two different binaryTypes: either Blob or ArrayBuffer. The latter is the only type of messages that UV4L supports (at the moment) and that expects to send or receive to/from the other peer (e.g. the browser). In other words, make sure the browser is interpreting the data as an ArrayBuffer.