Step 4.1: /stream.sdp from the live config and PTP GM

- aes67_sdp_sap: aes67_sdp_build() builds the AES67 SDP (RFC 4566 +
  RFC 7273) with the same lines and order as the web UI preview;
  GET /stream.sdp serves it as application/sdp.
- aes67_ptp: public aes67_ptp_gm_id(), aes67_ptp_locked(),
  aes67_ptp_now_ns(). Clock IDs are now uppercase (RFC 7273 style), also
  in status.ptp, which the UI copies into ts-refclk.
- aes67_net: aes67_net_netif() returns the AES67 interface.
- Verified on board: /stream.sdp byte-identical to the UI's sdp() for
  the same config/status; mono, L16, ptime 0.333, ttl 8, clk_offset
  4294967295 and session_ver all follow the config.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

components/aes67_sdp_sap/CMakeLists.txt

@@ -1,2 +1,3 @@
 idf_component_register(SRCS "aes67_sdp_sap.c"
-                       INCLUDE_DIRS "include")
+                       INCLUDE_DIRS "include"
+                       PRIV_REQUIRES aes67_net aes67_ptp aes67_web esp_netif)

components/aes67_sdp_sap/aes67_sdp_sap.c

@@ -1,7 +1,89 @@
 #include "aes67_sdp_sap.h"
 
-// Stub (build step 0).
+#include <stdio.h>
+#include <string.h>
+
+#include "aes67_cfg.h"
+#include "aes67_net.h"
+#include "aes67_ptp.h"
+#include "aes67_web.h"
+#include "esp_netif.h"
+
+#define SDP_MAX 1024
+
+// Same lines, in the same order, as the SDP preview in web/index.html.
+size_t aes67_sdp_build(char *buf, size_t size)
+{
+    cJSON *a = cfg_get("aes67");
+    cJSON *p = cfg_get("ptp");
+    if (!a || !p) {
+        cJSON_Delete(a);
+        cJSON_Delete(p);
+        return 0;
+    }
+#define NUM(o, k) cJSON_GetObjectItemCaseSensitive(o, k)->valuedouble
+#define STR(o, k) cJSON_GetObjectItemCaseSensitive(o, k)->valuestring
+    char ip[16] = "0.0.0.0";
+    esp_netif_ip_info_t info;
+    esp_netif_t *netif = aes67_net_netif();
+    if (netif && esp_netif_get_ip_info(netif, &info) == ESP_OK && info.ip.addr) {
+        snprintf(ip, sizeof(ip), IPSTR, IP2STR(&info.ip));
+    }
+    char gm[24];
+    if (!aes67_ptp_gm_id(gm)) {
+        strcpy(gm, "00-00-00-00-00-00-00-00");
+    }
+    int ch = (int)NUM(a, "channels");
+    char info_ch[16];
+    snprintf(info_ch, sizeof(info_ch), ch == 1 ? "mono" : ch == 2 ? "stereo" : "%d ch", ch);
+    int dom = (int)NUM(p, "domain");
+    int pt = (int)NUM(a, "pt");
+
+    int n = snprintf(buf, size,
+                     "v=0\r\n"
+                     "o=- %.0f %.0f IN IP4 %s\r\n"
+                     "s=%s\r\n"
+                     "c=IN IP4 %s/%d\r\n"
+                     "t=0 0\r\n"
+                     "a=clock-domain:PTPv2 %d\r\n"
+                     "m=audio %d RTP/AVP %d\r\n"
+                     "i=%s\r\n"
+                     "a=rtpmap:%d %s/%d/%d\r\n"
+                     "a=recvonly\r\n"
+                     "a=ptime:%g\r\n"
+                     "a=ts-refclk:ptp=IEEE1588-2008:%s:%d\r\n"
+                     "a=mediaclk:direct=%.0f\r\n",
+                     NUM(a, "session_id"), NUM(a, "session_ver"), ip,
+                     STR(a, "name"),
+                     STR(a, "mcast"), (int)NUM(a, "ttl"),
+                     dom,
+                     (int)NUM(a, "port"), pt,
+                     info_ch,
+                     pt, STR(a, "encoding"), (int)NUM(a, "rate"), ch,
+                     NUM(a, "ptime"),
+                     gm, dom,
+                     NUM(a, "clk_offset"));
+#undef NUM
+#undef STR
+    cJSON_Delete(a);
+    cJSON_Delete(p);
+    return n > 0 && (size_t)n < size ? (size_t)n : 0;
+}
+
+static esp_err_t sdp_get(httpd_req_t *req)
+{
+    char buf[SDP_MAX];
+    size_t len = aes67_sdp_build(buf, sizeof(buf));
+    if (!len) {
+        return httpd_resp_send_err(req, HTTPD_500_INTERNAL_SERVER_ERROR, "SDP build failed");
+    }
+    httpd_resp_set_type(req, "application/sdp");
+    httpd_resp_set_hdr(req, "Cache-Control", "no-store");
+    return httpd_resp_send(req, buf, len);
+}
+
 esp_err_t aes67_sdp_sap_init(void)
 {
-    return ESP_OK;
+    static const httpd_uri_t uri = { .uri = "/stream.sdp", .method = HTTP_GET, .handler = sdp_get };
+    return web_register_uri(&uri);
 }

components/aes67_sdp_sap/include/aes67_sdp_sap.h

@@ -2,6 +2,11 @@
 // Core component: must not depend on main/ (project code).
 #pragma once
 
+#include <stddef.h>
+
 #include "esp_err.h"
 
+// Registers GET /stream.sdp. (SAP: step 5.)
 esp_err_t aes67_sdp_sap_init(void);
+// Build the current SDP (RFC 4566 + RFC 7273, AES67). Returns the length, or 0 if it didn't fit.
+size_t aes67_sdp_build(char *buf, size_t size);