Read from socket

Question

I need to read from an AF_UNIX socket to a buffer using the function read from C, but I don't know the buffer size.

I think the best way is to read N bytes until the read returns 0 (no more writers in the socket). Is this correct? Is there a way to guess the size of the buffer being written on the socket?

I was thinking that a socket is a special file. Opening the file in binary mode and getting the size would help me in knowing the correct size to give to the buffer?

I'm a very new to C, so please keep that in mind.

Answer 1

On common way is to use ioctl(..) to query FIONREAD of the socket which will return how much data is available.

int len = 0;
ioctl(sock, FIONREAD, &len);
if (len > 0) {
  len = read(sock, buffer, len);
}