SocketReadMessage¶

Reads whatever has arrived on a socket, as a ByteArray. It waits for the first byte, so an echo server's answer can be read straight back:

$ wo 'srv = SocketOpen[0]; SocketListen[srv, WriteString[#["SourceSocket"], "Hello, " <> #["Data"] <> "!"] &]; c = SocketConnect[srv["DestinationPort"]]; WriteString[c, "sockets"]; ByteArrayToString[SocketReadMessage[c]]'
Hello, sockets!

$ wo 'srv = SocketOpen[0]; SocketListen[srv, WriteString[#["SourceSocket"], "abcd"] &]; c = SocketConnect[srv["DestinationPort"]]; WriteString[c, "go"]; Head[SocketReadMessage[c]]'
ByteArray

Reading a socket that has been closed says so, and gives $Failed:

c = SocketConnect["127.0.0.1:1"]; SocketReadMessage[c]
(* The socket object SocketObject[…] is invalid or not open. *)
(* $Failed *)

That one is deliberately not a testcase. Wolfram reports an unusable socket as a Failure[…] object rather than as a printed line plus $Failed, and it connects lazily, so SocketReadMessage on this very input waits for a first byte that never comes and never returns at all — see "Sockets" in the conformance gaps. The behaviour above is covered by the unit tests in tests/interpreter_tests/sockets.rs instead.