fix(udp): receive(0) tests and bad call to getnameinfo

2 files changed, 20 insertions, 0 deletions

diff --git a/src/udp.c b/src/udp.c
index 712ad50..a782699 100644
--- a/src/udp.c
+++ b/src/udp.c
@@ -277,6 +277,7 @@ static int meth_receivefrom(lua_State *L) {
         lua_pushliteral(L, "out of memory");
         return 2;
     }
+    memset(&addr, 0, sizeof(addr));
     err = socket_recvfrom(&udp->sock, dgram, wanted, &got, (SA *) &addr,
             &addr_len, tm);
     /* Unlike TCP, recv() of zero is not closed, but a zero-length packet. */
@@ -286,6 +287,17 @@ static int meth_receivefrom(lua_State *L) {
         if (wanted > sizeof(buf)) free(dgram);
         return 2;
     }
+    /* a zero-length request may be satisfied by some kernels (notably
+     * Darwin/BSD) without ever touching the sender's address -- only
+     * resolve it when the OS actually reported one, instead of feeding
+     * getnameinfo() a garbage/zeroed sockaddr. */
+    if (addr.ss_family != AF_INET && addr.ss_family != AF_INET6) {
+        lua_pushlstring(L, dgram, got);
+        lua_pushnil(L);
+        lua_pushnil(L);
+        if (wanted > sizeof(buf)) free(dgram);
+        return 3;
+    }
     err = getnameinfo((struct sockaddr *)&addr, addr_len, addrstr,
         INET6_ADDRSTRLEN, portstr, 6, NI_NUMERICHOST | NI_NUMERICSERV);
         if (err) {
diff --git a/src/wsocket.c b/src/wsocket.c
index 86c6994..b2b668c 100644
--- a/src/wsocket.c
+++ b/src/wsocket.c
@@ -286,6 +286,14 @@ int socket_recvfrom(p_socket ps, char *data, size_t count, size_t *got,
         }
         if (taken == 0) return IO_CLOSED;
         err = WSAGetLastError();
+        /* a zero-length request is trivially "too small" for any
+         * non-empty datagram; unlike POSIX, which truncates and succeeds
+         * silently, Windows reports this as WSAEMSGSIZE even though the
+         * datagram -- and its sender's address, already written to addr/
+         * len above -- was still consumed. Normalize it to match POSIX's
+         * silent-truncation instead of surfacing a platform-specific
+         * error for what is otherwise a successful, if empty, receive. */
+        if (count == 0 && err == WSAEMSGSIZE) return IO_DONE;
         /* On UDP, a connreset simply means the previous send failed.
          * So we try again.
          * On TCP, it means our socket is now useless, so the error passes.