Issue #19012 has been updated by byroot (Jean Boussier).

I am not sure if there is a portable way to determine if the file descriptor behind an IO object is stream or datagram.

Yeah, me neither. I'll try to dig more. ---------------------------------------- Bug #19012: BasicSocket#recv* methods return an empty packet instead of nil on closed connections https://bugs.ruby-lang.org/issues/19012#change-100436 * Author: byroot (Jean Boussier) * Status: Open * Priority: Normal * Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN ---------------------------------------- `man recvmsg(2)` states:

Return Value These calls return the number of bytes received, or -1 if an error occurred. The return value will be 0 when the peer has performed an orderly shutdown.

But somehow the entire `receiv` family of methods in Ruby seem to interpret `0` as empty string instead of "EOF". ```ruby require 'socket' puts "=== pipes ===" r, w = IO.pipe r.read_nonblock(1, exception: false) # => :wait_readable w.close r.read_nonblock(1, exception: false) # => nil (EOF) puts "=== sockets ====" r, w = UNIXSocket.socketpair r.read_nonblock(1, exception: false) # => :wait_readable r.recvmsg_nonblock(1, exception: false) # => :wait_readable r.recv_nonblock(1, exception: false) # => :wait_readable w.close r.read_nonblock(1, exception: false) # => nil (EOF) r.recvmsg_nonblock(1, exception: false) # => ["", #<Addrinfo: empty-sockaddr SOCK_STREAM>, 128]] r.recvmsg # => ["", #<Addrinfo: empty-sockaddr SOCK_STREAM>, 0]] r.recv_nonblock(1, exception: false) # => "" ``` ### Expected behavior I would expect `recvmsg_nonblock`, `recvmsg`, `recv_nonblock` and `recv` to return `nil` when the connection is closed. -- https://bugs.ruby-lang.org/