Sockets: Add UDP multicast group support

Adds two functions `join_multicast_group()` and `leave_multicast_group` for usage with UDP multicast groups.

Author: staticfloat

stdlib/Sockets/src/Sockets.jl

@@ -22,6 +22,8 @@ export
     recv,
     recvfrom,
     send,
+    join_multicast_group,
+    leave_multicast_group,
     TCPSocket,
     UDPSocket,
     @ip_str,
@@ -727,6 +729,56 @@ end
 
 listenany(default_port) = listenany(localhost, default_port)
 
+function udp_set_membership(sock::UDPSocket, group_addr::String,
+                            interface_addr::Union{Nothing, String}, operation)
+    if interface_addr === nothing
+        interface_addr = C_NULL
+    end
+    r = ccall(:uv_udp_set_membership, Cint,
+              (Ptr{Cvoid}, Cstring, Cstring, Cint),
+              sock.handle, group_addr, interface_addr, operation)
+    uv_error("uv_udp_set_membership", r)
+    return
+end
+
+"""
+    join_multicast_group(sock::UDPSocket, group_addr, interface_addr = nothing)
+
+Join a socket to a particular multicast group defined by `group_addr`.
+If `interface_addr` is given, specifies a particular interface for multi-homed
+systems.  Use `leave_multicast_group()` to disable reception of a group.
+"""
+function join_multicast_group(sock::UDPSocket, group_addr::String,
+                              interface_addr::Union{Nothing, String} = nothing)
+    return udp_set_membership(sock, group_addr, interface_addr, 1)
+end
+function join_multicast_group(sock::UDPSocket, group_addr::IPAddr,
+                              interface_addr::Union{Nothing, IPAddr} = nothing)
+    if interface_addr !== nothing
+        interface_addr = string(interface_addr)
+    end
+    return join_multicast_group(sock, string(group_addr), interface_addr)
+end
+
+"""
+    leave_multicast_group(sock::UDPSocket, group_addr, interface_addr = nothing)
+
+Remove a socket from  a particular multicast group defined by `group_addr`.
+If `interface_addr` is given, specifies a particular interface for multi-homed
+systems.  Use `join_multicast_group()` to enable reception of a group.
+"""
+function leave_multicast_group(sock::UDPSocket, group_addr::String,
+                               interface_addr::Union{Nothing, String} = nothing)
+    return udp_set_membership(sock, group_addr, interface_addr, 0)
+end
+function leave_multicast_group(sock::UDPSocket, group_addr::IPAddr,
+                               interface_addr::Union{Nothing, IPAddr} = nothing)
+    if interface_addr !== nothing
+        interface_addr = string(interface_addr)
+    end
+    return leave_multicast_group(sock, string(group_addr), interface_addr)
+end
+
 """
     getsockname(sock::Union{TCPServer, TCPSocket}) -> (IPAddr, UInt16)
 

stdlib/Sockets/test/runtests.jl

@@ -391,17 +391,17 @@ end
 
 @testset "Local-machine broadcast" begin
     let a, b, c
-        # (Mac OS X's loopback interface doesn't support broadcasts)
+        # Apple does not support broadcasting on 127.255.255.255
         bcastdst = Sys.isapple() ? ip"255.255.255.255" : ip"127.255.255.255"
 
-        function create_socket()
+        function create_socket(addr::IPAddr, port)
             s = UDPSocket()
-            bind(s, ip"0.0.0.0", 2000, reuseaddr = true, enable_broadcast = true)
-            s
+            bind(s, addr, port, reuseaddr = true, enable_broadcast = true)
+            return s
         end
 
-        function wait_with_timeout(recvs)
-            TIMEOUT_VAL = 3*1e9 # nanoseconds
+        # Wait for futures to finish with a given timeout
+        function wait_with_timeout(recvs, TIMEOUT_VAL = 3*1e9)
             t0 = time_ns()
             recvs_check = copy(recvs)
             while ((length(filter!(t->!istaskdone(t), recvs_check)) > 0)
@@ -412,23 +412,55 @@ end
             map(wait, recvs)
         end
 
-        a, b, c = [create_socket() for i = 1:3]
+        # First, test IPv4 broadcast
+        port = 2000
+        a, b, c = [create_socket(ip"0.0.0.0", port) for i in 1:3]
         try
-            # bsd family do not allow broadcasting to ip"255.255.255.255"
-            # or ip"127.255.255.255"
+            # bsd family do not allow broadcasting on loopbacks
             @static if !Sys.isbsd() || Sys.isapple()
-                send(c, bcastdst, 2000, "hello")
+                send(c, bcastdst, port, "hello")
                 recvs = [@async @test String(recv(s)) == "hello" for s in (a, b)]
                 wait_with_timeout(recvs)
             end
         catch e
             if isa(e, Base.IOError) && Base.uverrorname(e.code) == "EPERM"
-                @warn "UDP broadcast test skipped (permission denied upon send, restrictive firewall?)"
+                @warn "UDP IPv4 broadcast test skipped (permission denied upon send, restrictive firewall?)"
             else
                 rethrow()
             end
         end
         [close(s) for s in [a, b, c]]
+
+        # Test ipv6 broadcast groups
+        a, b, c = [create_socket(ip"::", port) for i in 1:3]
+        try
+            # Exemplary Interface-local ipv6 multicast group, if we wanted this to actually be routed
+            # to other computers, we should use a link-local or larger address scope group
+            # bsd family and darwin do not allow broadcasting on loopbacks
+            @static if !Sys.isbsd() && !Sys.isapple()
+                group = ip"ff11::6a75:6c69:61"
+                join_multicast_group(a, group)
+                join_multicast_group(b, group)
+
+                send(c, group, port, "hello")
+                recvs = [@async @test String(recv(s)) == "hello" for s in (a, b)]
+                wait_with_timeout(recvs)
+
+                leave_multicast_group(a, group)
+                leave_multicast_group(b, group)
+
+                send(c, group, port, "hello")
+                recvs = [@async @test String(recv(s)) == "hello" for s in (a, b)]
+                # We only wait 200ms since we're pretty sure this is going to time out
+                @test_throws ErrorException wait_with_timeout(recvs, 2e8)
+            end
+        catch e
+            if isa(e, Base.IOError) && Base.uverrorname(e.code) == "EPERM"
+                @warn "UDP IPv6 broadcast test skipped (permission denied upon send, restrictive firewall?)"
+            else
+                rethrow()
+            end
+        end
     end
 end