What is a typical life cycle of a Unix Datagram Socket?

Question

This is strictly in the context of Unix Datagram Sockets: family = AF_UNIX/AF_LOCAL type = SOCK_DGRAM

Does the following look correct for a scenario where a client sends message to server ? Server send to client not required as of now.

1. Listening/Server socket:

   1.1. Create socket using socket()

   1.2. bind() to a file path

   1.3. recv() or recvfrom() or recvmsg() or read() which'll be blocking by default unless specified via fcntl().

2. Client socket:

   2.1. Create socket using socket()

   2.2. bind() to the file path in 1.2. This throws EADDRINUSE that address already in use. If connect() is used instead then it results in EPERM operation not permitted.

   2.3. sendto() or sendmsg() or write()

Answer 1

Your listening/server socket logic looks correct but for the client socket:

bind() to the file path in 1.2. This throws EADDRINUSE that address already in use.

...naturally, because the listening socket has already claimed that address.

The client socket would normally want to connect() to the path on which the listening socket is listening.

If connect() is used instead then it results in EPERM operation not permitted.

I'm not sure why you would get that error. I was thinking a permission problem, but permission problems seem to result in EACCES, not EPERM. Try without using connect()? If you omit connect() for datagram sockets this means you have to use sendto() to specify the destination address for every packet. You cannot use send() or write() which expect the destination address to have been preselected using connect().