fix(webrtc): fix GStreamer WHEP interop (#4720)

## Summary

This PR fixes GStreamer interoperability issues during WebRTC/WHEP
negotiation with ZLMediaServer.

GStreamer could fail to establish the connection for two separate
reasons:

1. ZLMediaServer generated a non-compliant ICE `ufrag`. The generated
value contained `_`, which is not a valid ICE character, so GStreamer
rejected the SDP.
2. ZLMediaServer did not correctly handle `bundle-only` offers and could
answer an accepted bundled m-line with `port=0`, which caused the later
WHEP negotiation to fail.

## Changes

- Generate ICE `ufrag` values using ICE-compliant characters only.
- Preserve and handle `a=bundle-only` correctly during SDP parsing and
answer generation.
- Return `port=9` instead of `port=0` for accepted bundled m-lines.
- Add regression coverage for `bundle-only` SDP handling.
- URL-encode `delete_webrtc` query parameters in the returned `Location`
header so ICE-safe identifiers remain round-trippable over HTTP.

## Validation

- Built with WebRTC and SCTP enabled.
- Added regression test: `test_webrtc_regression`
- Verified:
  - ICE-safe identifier round-trip through `delete_webrtc`
  - `bundle-only` SDP answer generation

webrtc/Sdp.cpp

@@ -799,6 +799,7 @@ void RtcSession::loadFrom(const string &str) {
             rtc_media.fingerprint = sdp.getItemClass<SdpAttrFingerprint>('a', "fingerprint");
         }
         rtc_media.ice_lite = media.getItem('a', "ice-lite").operator bool();
+        rtc_media.bundle_only = media.getItem('a', "bundle-only").operator bool();
         auto ice_options = media.getItemClass<SdpAttrIceOption>('a', "ice-options");
         rtc_media.ice_trickle = ice_options.trickle;
         rtc_media.ice_renomination = ice_options.renomination;
@@ -1650,14 +1651,23 @@ static RtpDirection matchDirection(RtpDirection offer_direction, RtpDirection su
     }
 }
 
-static DtlsRole mathDtlsRole(DtlsRole role) {
-    switch (role) {
-        case DtlsRole::actpass:
-        case DtlsRole::active: return DtlsRole::passive;
-        case DtlsRole::passive: return DtlsRole::active;
-        default: CHECK(0, "invalid role:", getDtlsRoleString(role)); return DtlsRole::passive;
-    }
-}
+static DtlsRole mathDtlsRole(DtlsRole role) {
+    switch (role) {
+        case DtlsRole::actpass:
+        case DtlsRole::active: return DtlsRole::passive;
+        case DtlsRole::passive: return DtlsRole::active;
+        default: CHECK(0, "invalid role:", getDtlsRoleString(role)); return DtlsRole::passive;
+    }
+}
+
+static uint16_t getAnswerMediaPort(const RtcMedia &offer_media) {
+    // RFC 8843: bundle-only m-lines may use port=0 in the offer but still need a
+    // real port placeholder in the accepted answer.
+    if (!offer_media.port && offer_media.bundle_only) {
+        return 9;
+    }
+    return offer_media.port;
+}
 
 void RtcConfigure::createMediaOffer(const std::shared_ptr<RtcSession> &ret) const {
     int index = 0;
@@ -1824,13 +1834,14 @@ void RtcConfigure::matchMedia(const std::shared_ptr<RtcSession> &ret, const RtcM
 
 RETRY:
 
-    if (offer_media.type == TrackApplication) {
-        RtcMedia answer_media = offer_media;
-        answer_media.role = mathDtlsRole(offer_media.role);
-        answer_media.ice_ufrag = configure.ice_ufrag;
-        answer_media.ice_pwd = configure.ice_pwd;
-        answer_media.fingerprint = configure.fingerprint;
-        answer_media.ice_lite = configure.ice_lite;
+    if (offer_media.type == TrackApplication) {
+        RtcMedia answer_media = offer_media;
+        answer_media.port = getAnswerMediaPort(offer_media);
+        answer_media.role = mathDtlsRole(offer_media.role);
+        answer_media.ice_ufrag = configure.ice_ufrag;
+        answer_media.ice_pwd = configure.ice_pwd;
+        answer_media.fingerprint = configure.fingerprint;
+        answer_media.ice_lite = configure.ice_lite;
 #ifdef ENABLE_SCTP
         answer_media.candidate = configure.candidate;
 #else
@@ -1867,14 +1878,14 @@ RETRY:
             // All codecs for this media in the offer are not supported
             continue;
         }
-        RtcMedia answer_media;
-        answer_media.type = offer_media.type;
-        answer_media.mid = offer_media.mid;
-        answer_media.proto = offer_media.proto;
-        answer_media.port = offer_media.port;
-        answer_media.addr = offer_media.addr;
-        answer_media.bandwidth = offer_media.bandwidth;
-        answer_media.rtcp_addr = offer_media.rtcp_addr;
+        RtcMedia answer_media;
+        answer_media.type = offer_media.type;
+        answer_media.mid = offer_media.mid;
+        answer_media.proto = offer_media.proto;
+        answer_media.port = getAnswerMediaPort(offer_media);
+        answer_media.addr = offer_media.addr;
+        answer_media.bandwidth = offer_media.bandwidth;
+        answer_media.rtcp_addr = offer_media.rtcp_addr;
         answer_media.rtcp_mux = offer_media.rtcp_mux && configure.rtcp_mux;
         answer_media.rtcp_rsize = offer_media.rtcp_rsize && configure.rtcp_rsize;
         answer_media.ice_trickle = offer_media.ice_trickle && configure.ice_trickle;

webrtc/Sdp.h

@@ -652,6 +652,9 @@ public:
     bool rtcp_rsize { false };
     SdpAttrRtcp rtcp_addr;
 
+    //////// bundle ////////
+    bool bundle_only { false };
+
     //////// ice ////////
     bool ice_trickle { false };
     bool ice_lite { false };

webrtc/WebRtcTransport.cpp

@@ -137,7 +137,12 @@ static std::string getServerPrefix() {
     // 拷贝tcp端口  [AUTO-TRANSLATED:23191878]
     // Copy tcp port
     memcpy(buf + 6, &(reinterpret_cast<sockaddr_in *>(&addr)->sin_port), 2);
-    auto ret = encodeBase64(string(buf, 8)) + '_';
+    // RFC 5245 §15.4: ice-char = ALPHA / DIGIT / "+" / "/"
+    auto ret = encodeBase64(string(buf, 8));
+    // Remove base64 '=' padding (not a valid ice-char)
+    ret.erase(std::remove(ret.begin(), ret.end(), '='), ret.end());
+    // Use '/' separator instead of '_' (not a valid ice-char)
+    ret += '/';
     InfoL << "MediaServer(" << host << ":" << udp_port << ":" << tcp_port << ") prefix: " << ret;
     return ret;
 }