get the default broadcast network address.

2026-08-03 15:44:21 +02:00
parent cffedd6dbf
commit 1f9208560f
6 changed files with 71 additions and 11 deletions
@@ -0,0 +1,33 @@
+#lang racket/base
+
+;; Network helpers used by UPnP and SSDP.
+
+(require racket/udp
+         simple-log)
+
+(provide upnp-default-ipv4-address)
+
+(sl-def-log upnp-network)
+
+(define ssdp-multicast-address "239.255.255.250")
+(define ssdp-multicast-port 1900)
+
+;; Return the local IPv4 address selected by the operating system for traffic
+;; to the SSDP multicast destination. No datagram is transmitted.
+(define (upnp-default-ipv4-address)
+  (let ([socket (udp-open-socket ssdp-multicast-address
+                                 ssdp-multicast-port)])
+    (dynamic-wind
+      void
+      (lambda ()
+        (udp-connect! socket ssdp-multicast-address ssdp-multicast-port)
+        (define-values (local-address local-port remote-address remote-port)
+          (udp-addresses socket #t))
+        (dbg-upnp-network
+         "Selected UPnP IPv4 address ~a for SSDP destination ~a:~a"
+         local-address
+         ssdp-multicast-address
+         ssdp-multicast-port)
+        local-address)
+      (lambda ()
+        (udp-close socket)))))