Sockets: fix getipaddr() (#56528)

Author: barucden

stdlib/Sockets/src/addrinfo.jl

@@ -282,16 +282,14 @@ See also [`getipaddrs`](@ref).
 """
 function getipaddr(addr_type::Type{T}) where T<:IPAddr
     addrs = getipaddrs(addr_type)
+    isempty(addrs) && error("No networking interface available")
 
-    if length(addrs) == 0
-        error("No networking interface available")
-    end
-
-    # Prefer the first IPv4 address
+    # When `addr_type` is `IPAddr`, `addrs` contain IP addresses of all types
+    # In that case, we prefer to return the first IPv4
     i = something(findfirst(ip -> ip isa IPv4, addrs), 1)
     return addrs[i]
 end
-getipaddr() = getipaddr(IPv4)
+getipaddr() = getipaddr(IPAddr)
 
 
 """

stdlib/Sockets/test/runtests.jl

@@ -639,11 +639,26 @@ end
 
 @testset "getipaddrs" begin
     @test getipaddr() in getipaddrs()
-    try
-        getipaddr(IPv6) in getipaddrs(IPv6)
-    catch
-        if !isempty(getipaddrs(IPv6))
-            @test "getipaddr(IPv6) errored when it shouldn't have!"
+
+    has_ipv4 = !isempty(getipaddrs(IPv4))
+    if has_ipv4
+        @test getipaddr(IPv4) in getipaddrs(IPv4)
+    else
+        @test_throws "No networking interface available" getipaddr(IPv4)
+    end
+
+    has_ipv6 = !isempty(getipaddrs(IPv6))
+    if has_ipv6
+        @test getipaddr(IPv6) in getipaddrs(IPv6)
+    else
+        @test_throws "No networking interface available" getipaddr(IPv6)
+    end
+
+    @testset "getipaddr() prefers IPv4 over IPv6" begin
+        if has_ipv4
+            @test getipaddr() isa IPv4
+        else
+            @test getipaddr() isa IPv6
         end
     end