net/webrtc/whep: add WHEP client signaller

Rewrite the whepsrc element with WHEP Client as a signaller
on top of webrtcsrc

Cargo.lock

@@ -2956,6 +2956,7 @@ dependencies = [
  "aws-smithy-http",
  "aws-smithy-types",
  "aws-types",
+ "bytes",
  "chrono",
  "clap",
  "ctrlc",

net/webrtc/Cargo.toml

@@ -61,6 +61,8 @@ warp = {version = "0.3", optional = true }
 ctrlc = {version = "3.4.0", optional = true }
 
 
+bytes = "1"
+
 [dev-dependencies]
 gst-plugin-rtp = { path = "../rtp" }
 tokio = { version = "1", features = ["signal"] }
@@ -79,7 +81,7 @@ path = "src/lib.rs"
 gst-plugin-version-helper.workspace = true
 
 [features]
-default = ["v1_22", "aws", "janus", "livekit", "whip"]
+default = ["v1_22", "aws", "janus", "livekit", "whip", "whep"]
 static = []
 capi = []
 v1_22 = ["gst/v1_22", "gst-app/v1_22", "gst-video/v1_22", "gst-webrtc/v1_22", "gst-sdp/v1_22", "gst-rtp/v1_22"]
@@ -91,6 +93,7 @@ aws = ["dep:aws-config", "dep:aws-types", "dep:aws-credential-types", "dep:aws-s
 janus = ["dep:http"]
 livekit = ["dep:livekit-protocol", "dep:livekit-api"]
 whip = ["dep:async-recursion", "dep:reqwest", "dep:warp", "dep:ctrlc"]
+whep = ["dep:async-recursion", "dep:reqwest", "dep:warp"]
 
 [package.metadata.capi]
 min_version = "0.9.21"

net/webrtc/src/lib.rs

@@ -24,6 +24,8 @@ pub mod signaller;
 pub mod utils;
 pub mod webrtcsink;
 pub mod webrtcsrc;
+#[cfg(feature = "whep")]
+mod whep_signaller;
 #[cfg(feature = "whip")]
 mod whip_signaller;
 

net/webrtc/src/utils.rs

@@ -104,9 +104,9 @@ use crate::RUNTIME;
 use futures::future;
 use futures::prelude::*;
 use gst::ErrorMessage;
-#[cfg(feature = "whip")]
+#[cfg(any(feature = "whip", feature = "whep"))]
 use reqwest::header::HeaderMap;
-#[cfg(feature = "whip")]
+#[cfg(any(feature = "whip", feature = "whep"))]
 use reqwest::redirect::Policy;
 use std::sync::Mutex;
 use std::time::Duration;
@@ -239,7 +239,7 @@ where
     res
 }
 
-#[cfg(feature = "whip")]
+#[cfg(any(feature = "whip", feature = "whep"))]
 pub fn parse_redirect_location(
     headermap: &HeaderMap,
     old_url: &reqwest::Url,
@@ -280,13 +280,13 @@ pub fn parse_redirect_location(
     }
 }
 
-#[cfg(feature = "whip")]
+#[cfg(any(feature = "whip", feature = "whep"))]
 pub fn build_reqwest_client(pol: Policy) -> reqwest::Client {
     let client_builder = reqwest::Client::builder();
     client_builder.redirect(pol).build().unwrap()
 }
 
-#[cfg(feature = "whip")]
+#[cfg(any(feature = "whip", feature = "whep"))]
 pub fn set_ice_servers(
     webrtcbin: &gst::Element,
     headermap: &HeaderMap,

net/webrtc/src/webrtcsrc/imp.rs

@@ -586,7 +586,7 @@ impl Session {
             .map(|codec| {
                 let name = &codec.name;
 
-                let (media, clock_rate, pt) =  if codec.stream_type == gst::StreamType::AUDIO {
+                let (media, clock_rate, pt) = if codec.stream_type == gst::StreamType::AUDIO {
                     ("audio", 48000, 96)
                 } else {
                     //video stream type
@@ -740,7 +740,7 @@ impl Session {
 
                         filtered_s.extend(s.iter().filter_map(|(key, value)| {
                             if key.starts_with("extmap-") {
-                                        return Some((key, value.to_owned()));
+                                return Some((key, value.to_owned()));
                             }
 
                             None
@@ -774,7 +774,6 @@ impl Session {
         }
 
         webrtcbin.emit_by_name::<()>("set-remote-description", &[&answer, &None::<gst::Promise>]);
-
     }
 
     fn handle_offer(
@@ -1707,3 +1706,57 @@ pub(super) mod livekit {
         type ParentType = crate::webrtcsrc::BaseWebRTCSrc;
     }
 }
+
+#[cfg(feature = "whep")]
+pub(super) mod whep {
+    use super::*;
+    use crate::whep_signaller::WhepClientSignaller;
+
+    #[derive(Default)]
+    pub struct WhepClientSrc {}
+
+    impl ObjectImpl for WhepClientSrc {
+        fn constructed(&self) {
+            self.parent_constructed();
+            let element = self.obj();
+            let ws = element
+                .upcast_ref::<crate::webrtcsrc::BaseWebRTCSrc>()
+                .imp();
+
+            let _ = ws.set_signaller(WhepClientSignaller::default().upcast());
+
+            let obj = &*self.obj();
+
+            obj.set_suppressed_flags(gst::ElementFlags::SINK | gst::ElementFlags::SOURCE);
+            obj.set_element_flags(gst::ElementFlags::SOURCE);
+        }
+    }
+
+    impl GstObjectImpl for WhepClientSrc {}
+
+    impl BinImpl for WhepClientSrc {}
+
+    impl ElementImpl for WhepClientSrc {
+        fn metadata() -> Option<&'static gst::subclass::ElementMetadata> {
+            static ELEMENT_METADATA: Lazy<gst::subclass::ElementMetadata> = Lazy::new(|| {
+                gst::subclass::ElementMetadata::new(
+                    "WhepClientSrc",
+                    "Source/Network/WebRTC",
+                    "WebRTC source element using WHEP Client as the signaller",
+                    "Sanchayan Maity <sanchayan@asymptotic.io>",
+                )
+            });
+
+            Some(&*ELEMENT_METADATA)
+        }
+    }
+
+    impl BaseWebRTCSrcImpl for WhepClientSrc {}
+
+    #[glib::object_subclass]
+    impl ObjectSubclass for WhepClientSrc {
+        const NAME: &'static str = "GstWhepClientSrc";
+        type Type = crate::webrtcsrc::WhepClientSrc;
+        type ParentType = crate::webrtcsrc::BaseWebRTCSrc;
+    }
+}

net/webrtc/src/webrtcsrc/mod.rs

@@ -59,6 +59,11 @@ glib::wrapper! {
     pub struct LiveKitWebRTCSrc(ObjectSubclass<imp::livekit::LiveKitWebRTCSrc>) @extends BaseWebRTCSrc, gst::Bin, gst::Element, gst::Object, gst::ChildProxy;
 }
 
+#[cfg(feature = "whep")]
+glib::wrapper! {
+    pub struct WhepClientSrc(ObjectSubclass<imp::whep::WhepClientSrc>) @extends BaseWebRTCSrc, gst::Bin, gst::Element, gst::Object, @implements gst::URIHandler, gst::ChildProxy;
+}
+
 glib::wrapper! {
     pub struct WebRTCSrcPad(ObjectSubclass<pad::WebRTCSrcPad>) @extends gst::GhostPad, gst::ProxyPad, gst::Pad, gst::Object;
 }
@@ -139,5 +144,13 @@ pub fn register(plugin: Option<&gst::Plugin>) -> Result<(), glib::BoolError> {
         LiveKitWebRTCSrc::static_type(),
     )?;
 
+    #[cfg(feature = "whep")]
+    gst::Element::register(
+        plugin,
+        "whepclientsrc",
+        gst::Rank::PRIMARY,
+        WhepClientSrc::static_type(),
+    )?;
+
     Ok(())
 }

net/webrtc/src/whep_signaller/client.rs

@@ -0,0 +1,600 @@
+// Copyright (C) 2022, Asymptotic Inc.
+//      Author: Sanchayan Maity <sanchayan@asymptotic.io>
+//
+// This Source Code Form is subject to the terms of the Mozilla Public License, v2.0.
+// If a copy of the MPL was not distributed with this file, You can obtain one at
+// <https://mozilla.org/MPL/2.0/>.
+//
+// SPDX-License-Identifier: MPL-2.0
+
+use crate::signaller::{Signallable, SignallableImpl};
+use crate::utils::{
+    build_reqwest_client, parse_redirect_location, set_ice_servers, wait, wait_async, WaitError,
+};
+use crate::RUNTIME;
+use async_recursion::async_recursion;
+use bytes::Bytes;
+use futures::future;
+use gst::glib::RustClosure;
+use gst::{glib, prelude::*, subclass::prelude::*};
+use gst_sdp::*;
+use gst_webrtc::*;
+use once_cell::sync::Lazy;
+use reqwest::header::{HeaderMap, HeaderValue};
+use reqwest::StatusCode;
+use std::sync::Mutex;
+
+static CAT: Lazy<gst::DebugCategory> = Lazy::new(|| {
+    gst::DebugCategory::new(
+        "whep-client-signaller",
+        gst::DebugColorFlags::empty(),
+        Some("WHEP Client Signaller"),
+    )
+});
+
+const MAX_REDIRECTS: u8 = 10;
+const DEFAULT_TIMEOUT: u32 = 15;
+const SESSION_ID: &str = "whep-client";
+
+#[derive(Debug, Clone)]
+struct Settings {
+    whep_endpoint: Option<String>,
+    auth_token: Option<String>,
+    use_link_headers: bool,
+    timeout: u32,
+}
+
+#[allow(clippy::derivable_impls)]
+impl Default for Settings {
+    fn default() -> Self {
+        Self {
+            whep_endpoint: None,
+            auth_token: None,
+            use_link_headers: false,
+            timeout: DEFAULT_TIMEOUT,
+        }
+    }
+}
+
+#[derive(Debug)]
+enum State {
+    Stopped,
+    Post { redirects: u8 },
+    Running { whep_resource: String },
+}
+
+impl Default for State {
+    fn default() -> Self {
+        Self::Stopped
+    }
+}
+
+pub struct WhepClient {
+    settings: Mutex<Settings>,
+    state: Mutex<State>,
+    canceller: Mutex<Option<future::AbortHandle>>,
+    client: reqwest::Client,
+}
+
+impl Default for WhepClient {
+    fn default() -> Self {
+        // We'll handle redirects manually since the default redirect handler does not
+        // reuse the authentication token on the redirected server
+        let pol = reqwest::redirect::Policy::none();
+        let client = build_reqwest_client(pol);
+
+        Self {
+            settings: Mutex::new(Settings::default()),
+            state: Mutex::new(State::default()),
+            canceller: Mutex::new(None),
+            client,
+        }
+    }
+}
+
+impl ObjectImpl for WhepClient {
+    fn properties() -> &'static [glib::ParamSpec] {
+        static PROPERTIES: Lazy<Vec<glib::ParamSpec>> = Lazy::new(|| {
+            vec![
+                glib::ParamSpecString::builder("whep-endpoint")
+                    .nick("WHEP Endpoint")
+                    .blurb("The WHEP server endpoint to POST SDP offer to.")
+                    .build(),
+                glib::ParamSpecBoolean::builder("use-link-headers")
+                    .nick("Use Link Headers")
+                    .blurb("Use link headers to configure STUN/TURN servers if present in WHEP endpoint response.")
+                    .build(),
+                glib::ParamSpecString::builder("auth-token")
+                    .nick("Authorization Token")
+                    .blurb("Authentication token to use, will be sent in the HTTP Header as 'Bearer <auth-token>'")
+                    .build(),
+                glib::ParamSpecUInt::builder("timeout")
+                    .nick("Timeout")
+                    .blurb("Value in seconds to timeout WHEP endpoint requests (0 = No timeout).")
+                    .maximum(3600)
+                    .default_value(DEFAULT_TIMEOUT)
+                    .readwrite()
+                    .build(),
+            ]
+        });
+        PROPERTIES.as_ref()
+    }
+
+    fn set_property(&self, _id: usize, value: &glib::Value, pspec: &glib::ParamSpec) {
+        match pspec.name() {
+            "whep-endpoint" => {
+                let mut settings = self.settings.lock().unwrap();
+                settings.whep_endpoint = value.get().expect("WHEP endpoint should be a string");
+            }
+            "use-link-headers" => {
+                let mut settings = self.settings.lock().unwrap();
+                settings.use_link_headers = value
+                    .get()
+                    .expect("use-link-headers should be a boolean value");
+            }
+            "auth-token" => {
+                let mut settings = self.settings.lock().unwrap();
+                settings.auth_token = value.get().expect("Auth token should be a string");
+            }
+            "timeout" => {
+                let mut settings = self.settings.lock().unwrap();
+                settings.timeout = value.get().expect("type checked upstream");
+            }
+            _ => unimplemented!(),
+        }
+    }
+
+    fn property(&self, _id: usize, pspec: &glib::ParamSpec) -> glib::Value {
+        match pspec.name() {
+            "whep-endpoint" => {
+                let settings = self.settings.lock().unwrap();
+                settings.whep_endpoint.to_value()
+            }
+            "use-link-headers" => {
+                let settings = self.settings.lock().unwrap();
+                settings.use_link_headers.to_value()
+            }
+            "auth-token" => {
+                let settings = self.settings.lock().unwrap();
+                settings.auth_token.to_value()
+            }
+            "timeout" => {
+                let settings = self.settings.lock().unwrap();
+                settings.timeout.to_value()
+            }
+            _ => unimplemented!(),
+        }
+    }
+}
+
+#[glib::object_subclass]
+impl ObjectSubclass for WhepClient {
+    const NAME: &'static str = "GstWhepClientSignaller";
+    type Type = super::WhepClientSignaller;
+    type ParentType = glib::Object;
+    type Interfaces = (Signallable,);
+}
+
+impl WhepClient {
+    fn raise_error(&self, msg: String) {
+        self.obj()
+            .emit_by_name::<()>("error", &[&format!("Error: {msg}")]);
+    }
+
+    fn handle_future_error(&self, err: WaitError) {
+        match err {
+            WaitError::FutureAborted => {
+                gst::warning!(CAT, imp: self, "Future aborted")
+            }
+            WaitError::FutureError(err) => self.raise_error(err.to_string()),
+        };
+    }
+
+    fn sdp_message_parse(&self, sdp_bytes: Bytes, _webrtcbin: &gst::Element) {
+        let sdp = match sdp_message::SDPMessage::parse_buffer(&sdp_bytes) {
+            Ok(sdp) => sdp,
+            Err(_) => {
+                self.raise_error("Could not parse answer SDP".to_string());
+                return;
+            }
+        };
+
+        let remote_sdp = WebRTCSessionDescription::new(WebRTCSDPType::Answer, sdp);
+
+        self.obj()
+            .emit_by_name::<()>("session-description", &[&SESSION_ID, &remote_sdp]);
+    }
+
+    async fn parse_endpoint_response(
+        &self,
+        sess_desc: WebRTCSessionDescription,
+        resp: reqwest::Response,
+        redirects: u8,
+        webrtcbin: gst::Element,
+    ) {
+        let endpoint;
+        let use_link_headers;
+
+        {
+            let settings = self.settings.lock().unwrap();
+            endpoint =
+                reqwest::Url::parse(settings.whep_endpoint.as_ref().unwrap().as_str()).unwrap();
+            use_link_headers = settings.use_link_headers;
+            drop(settings);
+        }
+
+        match resp.status() {
+            StatusCode::OK | StatusCode::NO_CONTENT => {
+                gst::info!(CAT, imp: self, "SDP offer successfully send");
+            }
+
+            StatusCode::CREATED => {
+                gst::debug!(CAT, imp: self, "Response headers: {:?}", resp.headers());
+
+                if use_link_headers {
+                    if let Err(e) = set_ice_servers(&webrtcbin, resp.headers()) {
+                        self.raise_error(e.to_string());
+                        return;
+                    };
+                }
+
+                /* See section 4.2 of the WHEP specification */
+                let location = match resp.headers().get(reqwest::header::LOCATION) {
+                    Some(location) => location,
+                    None => {
+                        self.raise_error(
+                            "Location header field should be present for WHEP resource URL"
+                                .to_string(),
+                        );
+                        return;
+                    }
+                };
+
+                let location = match location.to_str() {
+                    Ok(loc) => loc,
+                    Err(e) => {
+                        self.raise_error(format!("Failed to convert location to string: {e}"));
+                        return;
+                    }
+                };
+
+                let url = reqwest::Url::parse(endpoint.as_str()).unwrap();
+
+                gst::debug!(CAT, imp: self, "WHEP resource: {:?}", location);
+
+                let url = match url.join(location) {
+                    Ok(joined_url) => joined_url,
+                    Err(err) => {
+                        self.raise_error(format!("URL join operation failed: {err:?}"));
+                        return;
+                    }
+                };
+
+                match resp.bytes().await {
+                    Ok(ans_bytes) => {
+                        let mut state = self.state.lock().unwrap();
+                        *state = match *state {
+                            State::Post { redirects: _r } => State::Running {
+                                whep_resource: url.to_string(),
+                            },
+                            _ => {
+                                self.raise_error("Expected to be in POST state".to_string());
+                                return;
+                            }
+                        };
+                        drop(state);
+
+                        self.sdp_message_parse(ans_bytes, &webrtcbin)
+                    }
+                    Err(err) => self.raise_error(err.to_string()),
+                }
+            }
+
+            status if status.is_redirection() => {
+                if redirects < MAX_REDIRECTS {
+                    match parse_redirect_location(resp.headers(), &endpoint) {
+                        Ok(redirect_url) => {
+                            {
+                                let mut state = self.state.lock().unwrap();
+                                *state = match *state {
+                                    State::Post { redirects: _r } => State::Post {
+                                        redirects: redirects + 1,
+                                    },
+                                    /*
+                                     * As per section 4.6 of the specification, redirection is
+                                     * not required to be supported for the PATCH and DELETE
+                                     * requests to the final WHEP resource URL. Only the initial
+                                     * POST request may support redirection.
+                                     */
+                                    State::Running { .. } => {
+                                        self.raise_error(
+                                            "Unexpected redirection in RUNNING state".to_string(),
+                                        );
+                                        return;
+                                    }
+                                    State::Stopped => unreachable!(),
+                                };
+                                drop(state);
+                            }
+
+                            gst::warning!(
+                                CAT,
+                                imp: self,
+                                "Redirecting endpoint to {}",
+                                redirect_url.as_str()
+                            );
+
+                            self.do_post(sess_desc, webrtcbin, redirect_url).await
+                        }
+                        Err(e) => self.raise_error(e.to_string()),
+                    }
+                } else {
+                    self.raise_error("Too many redirects. Unable to connect.".to_string());
+                }
+            }
+
+            s => {
+                match resp.bytes().await {
+                    Ok(r) => {
+                        let res = r.escape_ascii().to_string();
+
+                        // FIXME: Check and handle 'Retry-After' header in case of server error
+                        self.raise_error(format!("Unexpected response: {} - {}", s.as_str(), res));
+                    }
+                    Err(err) => self.raise_error(err.to_string()),
+                }
+            }
+        }
+    }
+
+    async fn whep_offer(&self, webrtcbin: gst::Element) {
+        let local_desc =
+            webrtcbin.property::<Option<WebRTCSessionDescription>>("local-description");
+
+        let sess_desc = match local_desc {
+            None => {
+                self.raise_error("Local description is not set".to_string());
+                return;
+            }
+            Some(mut local_desc) => {
+                local_desc.set_type(WebRTCSDPType::Offer);
+                local_desc
+            }
+        };
+
+        gst::debug!(
+            CAT,
+            imp: self,
+            "Sending offer SDP: {:?}",
+            sess_desc.sdp().as_text()
+        );
+
+        let timeout;
+        let endpoint;
+
+        {
+            let settings = self.settings.lock().unwrap();
+            timeout = settings.timeout;
+            endpoint =
+                reqwest::Url::parse(settings.whep_endpoint.as_ref().unwrap().as_str()).unwrap();
+            drop(settings);
+        }
+
+        if let Err(e) = wait_async(
+            &self.canceller,
+            self.do_post(sess_desc, webrtcbin, endpoint),
+            timeout,
+        )
+        .await
+        {
+            self.handle_future_error(e);
+        }
+    }
+
+    #[async_recursion]
+    async fn do_post(
+        &self,
+        offer: WebRTCSessionDescription,
+        webrtcbin: gst::Element,
+        endpoint: reqwest::Url,
+    ) {
+        let auth_token;
+
+        {
+            let settings = self.settings.lock().unwrap();
+            auth_token = settings.auth_token.clone();
+            drop(settings);
+        }
+
+        let sdp = offer.sdp();
+        let body = sdp.as_text().unwrap();
+
+        gst::info!(CAT, imp: self, "Using endpoint {}", endpoint.as_str());
+
+        let mut headermap = HeaderMap::new();
+        headermap.insert(
+            reqwest::header::CONTENT_TYPE,
+            HeaderValue::from_static("application/sdp"),
+        );
+
+        if let Some(token) = auth_token.as_ref() {
+            let bearer_token = "Bearer ".to_owned() + token.as_str();
+            headermap.insert(
+                reqwest::header::AUTHORIZATION,
+                HeaderValue::from_str(bearer_token.as_str())
+                    .expect("Failed to set auth token to header"),
+            );
+        }
+
+        gst::debug!(
+            CAT,
+            imp: self,
+            "Url for HTTP POST request: {}",
+            endpoint.as_str()
+        );
+
+        let resp = self
+            .client
+            .request(reqwest::Method::POST, endpoint.clone())
+            .headers(headermap)
+            .body(body)
+            .send()
+            .await;
+
+        match resp {
+            Ok(r) => {
+                #[allow(unused_mut)]
+                let mut redirects;
+
+                {
+                    let state = self.state.lock().unwrap();
+                    redirects = match *state {
+                        State::Post { redirects } => redirects,
+                        _ => {
+                            self.raise_error("Trying to do POST in unexpected state".to_string());
+                            return;
+                        }
+                    };
+                    drop(state);
+                }
+
+                self.parse_endpoint_response(offer, r, redirects, webrtcbin)
+                    .await
+            }
+            Err(err) => self.raise_error(err.to_string()),
+        }
+    }
+
+    fn terminate_session(&self) {
+        let settings = self.settings.lock().unwrap();
+        let state = self.state.lock().unwrap();
+        let timeout = settings.timeout;
+
+        let resource_url = match *state {
+            State::Running {
+                whep_resource: ref whep_resource_url,
+            } => whep_resource_url.clone(),
+            _ => {
+                self.raise_error("Terminated in unexpected state".to_string());
+                return;
+            }
+        };
+
+        drop(state);
+
+        let mut headermap = HeaderMap::new();
+        if let Some(token) = &settings.auth_token {
+            let bearer_token = "Bearer ".to_owned() + token.as_str();
+            headermap.insert(
+                reqwest::header::AUTHORIZATION,
+                HeaderValue::from_str(bearer_token.as_str())
+                    .expect("Failed to set auth token to header"),
+            );
+        }
+
+        drop(settings);
+
+        gst::debug!(CAT, imp: self, "DELETE request on {}", resource_url);
+
+        /* DELETE request goes to the WHEP resource URL. See section 3 of the specification. */
+        let client = build_reqwest_client(reqwest::redirect::Policy::default());
+        let future = async {
+            client
+                .delete(resource_url.clone())
+                .headers(headermap)
+                .send()
+                .await
+                .map_err(|err| {
+                    gst::error_msg!(
+                        gst::ResourceError::Failed,
+                        ["DELETE request failed {}: {:?}", resource_url, err]
+                    )
+                })
+        };
+
+        let res = wait(&self.canceller, future, timeout);
+        match res {
+            Ok(r) => {
+                gst::debug!(CAT, imp: self, "Response to DELETE : {}", r.status());
+            }
+            Err(e) => match e {
+                WaitError::FutureAborted => {
+                    gst::warning!(CAT, imp: self, "DELETE request aborted")
+                }
+                WaitError::FutureError(e) => {
+                    gst::error!(CAT, imp: self, "Error on DELETE request : {}", e)
+                }
+            },
+        };
+    }
+
+    pub fn on_webrtcbin_ready(&self) -> RustClosure {
+        glib::closure!(|signaller: &super::WhepClientSignaller,
+                        _consumer_identifier: &str,
+                        webrtcbin: &gst::Element| {
+            let obj_weak = signaller.downgrade();
+
+            webrtcbin.connect_notify(Some("ice-gathering-state"), move |webrtcbin, _pspec| {
+                let Some(obj) = obj_weak.upgrade() else {
+                    return;
+                };
+
+                let state = webrtcbin.property::<WebRTCICEGatheringState>("ice-gathering-state");
+
+                match state {
+                    WebRTCICEGatheringState::Gathering => {
+                        gst::info!(CAT, obj: obj, "ICE gathering started");
+                    }
+                    WebRTCICEGatheringState::Complete => {
+                        gst::info!(CAT, obj: obj, "ICE gathering complete");
+
+                        let webrtcbin = webrtcbin.clone();
+
+                        RUNTIME.spawn(async move { obj.imp().whep_offer(webrtcbin).await });
+                    }
+                    _ => (),
+                }
+            });
+        })
+    }
+}
+
+impl SignallableImpl for WhepClient {
+    fn start(&self) {
+        if self.settings.lock().unwrap().whep_endpoint.is_none() {
+            self.raise_error("WHEP endpoint URL must be set".to_string());
+            return;
+        }
+
+        let mut state = self.state.lock().unwrap();
+        *state = State::Post { redirects: 0 };
+        drop(state);
+
+        self.obj()
+            .emit_by_name::<()>("session-started", &[&SESSION_ID, &SESSION_ID]);
+        self.obj().emit_by_name::<()>(
+            "session-requested",
+            &[
+                &SESSION_ID,
+                &SESSION_ID,
+                &None::<gst_webrtc::WebRTCSessionDescription>,
+            ],
+        );
+    }
+
+    fn stop(&self) {}
+
+    fn end_session(&self, _session_id: &str) {
+        // Interrupt requests in progress, if any
+        if let Some(canceller) = &*self.canceller.lock().unwrap() {
+            canceller.abort();
+        }
+
+        let state = self.state.lock().unwrap();
+        if let State::Running { .. } = *state {
+            // Release server-side resources
+            drop(state);
+            self.terminate_session();
+        }
+    }
+}

net/webrtc/src/whep_signaller/mod.rs

@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: MPL-2.0
+
+use crate::signaller::Signallable;
+use gst::{glib, prelude::ObjectExt, subclass::prelude::ObjectSubclassIsExt};
+
+mod client;
+
+glib::wrapper! {
+    pub struct WhepClientSignaller(ObjectSubclass<client::WhepClient>) @implements Signallable;
+}
+
+unsafe impl Send for WhepClientSignaller {}
+unsafe impl Sync for WhepClientSignaller {}
+
+impl Default for WhepClientSignaller {
+    fn default() -> Self {
+        let sig: WhepClientSignaller = glib::Object::new();
+        sig.connect_closure("webrtcbin-ready", false, sig.imp().on_webrtcbin_ready());
+        sig
+    }
+}