gst-plugins-rs/net/webrtc/src/webrtcsrc/imp.rs

// SPDX-License-Identifier: MPL-2.0

use gst::prelude::*;

use crate::signaller::{prelude::*, Signallable, Signaller};
use crate::utils::{Codec, Codecs, NavigationEvent, AUDIO_CAPS, RTP_CAPS, VIDEO_CAPS};
use crate::webrtcsrc::WebRTCSrcPad;
use anyhow::{Context, Error};
use gst::glib;
use gst::glib::once_cell::sync::Lazy;
use gst::subclass::prelude::*;
use gst_webrtc::WebRTCDataChannel;
use std::borrow::BorrowMut;
use std::collections::HashSet;
use std::str::FromStr;
use std::sync::atomic::AtomicU16;
use std::sync::atomic::Ordering;
use std::sync::Mutex;
use url::Url;

const DEFAULT_STUN_SERVER: Option<&str> = Some("stun://stun.l.google.com:19302");
const DEFAULT_ENABLE_DATA_CHANNEL_NAVIGATION: bool = false;

static CAT: Lazy<gst::DebugCategory> = Lazy::new(|| {
    gst::DebugCategory::new(
        "webrtcsrc",
        gst::DebugColorFlags::empty(),
        Some("WebRTC src"),
    )
});

const RTP_TWCC_URI: &str =
    "http://www.ietf.org/id/draft-holmer-rmcat-transport-wide-cc-extensions-01";

struct Settings {
    stun_server: Option<String>,
    signaller: Signallable,
    meta: Option<gst::Structure>,
    video_codecs: Vec<Codec>,
    audio_codecs: Vec<Codec>,
    enable_data_channel_navigation: bool,
}

#[derive(Default)]
pub struct WebRTCSrc {
    settings: Mutex<Settings>,
    n_video_pads: AtomicU16,
    n_audio_pads: AtomicU16,
    state: Mutex<State>,
}

#[glib::object_subclass]
impl ObjectSubclass for WebRTCSrc {
    const NAME: &'static str = "GstWebRTCSrc";
    type Type = super::WebRTCSrc;
    type ParentType = gst::Bin;
    type Interfaces = (gst::URIHandler, gst::ChildProxy);
}

impl ObjectImpl for WebRTCSrc {
    fn properties() -> &'static [glib::ParamSpec] {
        static PROPS: Lazy<Vec<glib::ParamSpec>> = Lazy::new(|| {
            vec![
                glib::ParamSpecString::builder("stun-server")
                    .flags(glib::ParamFlags::READWRITE)
                    .default_value(DEFAULT_STUN_SERVER)
                    .build(),
                glib::ParamSpecObject::builder::<Signallable>("signaller")
                    .flags(glib::ParamFlags::READWRITE | glib::ParamFlags::CONSTRUCT_ONLY)
                    .blurb("The Signallable object to use to handle WebRTC Signalling")
                    .build(),
                glib::ParamSpecBoxed::builder::<gst::Structure>("meta")
                    .flags(glib::ParamFlags::READWRITE | gst::PARAM_FLAG_MUTABLE_READY)
                    .blurb("Free form metadata about the consumer")
                    .build(),
                gst::ParamSpecArray::builder("video-codecs")
                    .flags(glib::ParamFlags::READWRITE | gst::PARAM_FLAG_MUTABLE_READY)
                    .blurb(&format!("Names of video codecs to be be used during the SDP negotiation. Valid values: [{}]",
                        Codecs::video_codec_names().into_iter().collect::<Vec<String>>().join(", ")
                    ))
                    .element_spec(&glib::ParamSpecString::builder("video-codec-name").build())
                    .build(),
                gst::ParamSpecArray::builder("audio-codecs")
                    .flags(glib::ParamFlags::READWRITE | gst::PARAM_FLAG_MUTABLE_READY)
                    .blurb(&format!("Names of audio codecs to be be used during the SDP negotiation. Valid values: [{}]",
                        Codecs::audio_codec_names().into_iter().collect::<Vec<String>>().join(", ")
                    ))
                    .element_spec(&glib::ParamSpecString::builder("audio-codec-name").build())
                    .build(),
                glib::ParamSpecBoolean::builder("enable-data-channel-navigation")
                    .nick("Enable data channel navigation")
                    .blurb("Enable navigation events through a dedicated WebRTCDataChannel")
                    .default_value(DEFAULT_ENABLE_DATA_CHANNEL_NAVIGATION)
                    .mutable_ready()
                    .build(),
            ]
        });

        PROPS.as_ref()
    }

    fn set_property(&self, _id: usize, value: &glib::Value, pspec: &glib::ParamSpec) {
        match pspec.name() {
            "signaller" => {
                let signaller = value
                    .get::<Option<Signallable>>()
                    .expect("type checked upstream");
                if let Some(signaller) = signaller {
                    self.settings.lock().unwrap().signaller = signaller;
                }
                // else: signaller not set as a construct property
                //       => use default Signaller
            }
            "video-codecs" => {
                self.settings.lock().unwrap().video_codecs = value
                    .get::<gst::ArrayRef>()
                    .expect("Type checked upstream")
                    .as_slice()
                    .iter()
                    .filter_map(|codec_name| {
                        Codecs::find(codec_name.get::<&str>().expect("Type checked upstream"))
                    })
                    .collect::<Vec<Codec>>()
            }
            "audio-codecs" => {
                self.settings.lock().unwrap().audio_codecs = value
                    .get::<gst::ArrayRef>()
                    .expect("Type checked upstream")
                    .as_slice()
                    .iter()
                    .filter_map(|codec_name| {
                        Codecs::find(codec_name.get::<&str>().expect("Type checked upstream"))
                    })
                    .collect::<Vec<Codec>>()
            }
            "stun-server" => {
                self.settings.lock().unwrap().stun_server = value
                    .get::<Option<String>>()
                    .expect("type checked upstream")
            }
            "meta" => {
                self.settings.lock().unwrap().meta = value
                    .get::<Option<gst::Structure>>()
                    .expect("type checked upstream")
            }
            "enable-data-channel-navigation" => {
                let mut settings = self.settings.lock().unwrap();
                settings.enable_data_channel_navigation = value.get::<bool>().unwrap();
            }
            _ => unimplemented!(),
        }
    }

    fn property(&self, _id: usize, pspec: &glib::ParamSpec) -> glib::Value {
        match pspec.name() {
            "signaller" => self.settings.lock().unwrap().signaller.to_value(),
            "video-codecs" => gst::Array::new(
                self.settings
                    .lock()
                    .unwrap()
                    .video_codecs
                    .iter()
                    .map(|v| &v.name),
            )
            .to_value(),
            "audio-codecs" => gst::Array::new(
                self.settings
                    .lock()
                    .unwrap()
                    .audio_codecs
                    .iter()
                    .map(|v| &v.name),
            )
            .to_value(),
            "stun-server" => self.settings.lock().unwrap().stun_server.to_value(),
            "meta" => self.settings.lock().unwrap().meta.to_value(),
            "enable-data-channel-navigation" => {
                let settings = self.settings.lock().unwrap();
                settings.enable_data_channel_navigation.to_value()
            }
            name => panic!("{} getter not implemented", name),
        }
    }

    fn signals() -> &'static [glib::subclass::Signal] {
        static SIGNALS: Lazy<Vec<glib::subclass::Signal>> = Lazy::new(|| {
            vec![
                /**
                 * WebRTCSrc::request-encoded-filter:
                 * @producer_id: Identifier of the producer
                 * @pad_name: The name of the output pad
                 * @allowed_caps: the allowed caps for the output pad
                 *
                 * This signal can be used to insert a filter
                 * element between:
                 *
                 * - the depayloader and the decoder.
                 * - the depayloader and downstream element if
                 *   no decoders are used.
                 *
                 * Returns: the element to insert.
                 */
                glib::subclass::Signal::builder("request-encoded-filter")
                    .param_types([
                        String::static_type(),
                        String::static_type(),
                        Option::<gst::Caps>::static_type(),
                    ])
                    .return_type::<gst::Element>()
                    .build(),
            ]
        });

        SIGNALS.as_ref()
    }

    fn constructed(&self) {
        self.parent_constructed();
        let signaller = self.settings.lock().unwrap().signaller.clone();

        self.connect_signaller(&signaller);

        let obj = &*self.obj();

        obj.set_suppressed_flags(gst::ElementFlags::SINK | gst::ElementFlags::SOURCE);
        obj.set_element_flags(gst::ElementFlags::SOURCE);
    }
}

impl Default for Settings {
    fn default() -> Self {
        let signaller = Signaller::default();

        Self {
            stun_server: DEFAULT_STUN_SERVER.map(|v| v.to_string()),
            signaller: signaller.upcast(),
            meta: Default::default(),
            audio_codecs: Codecs::audio_codecs()
                .into_iter()
                .filter(|codec| codec.has_decoder())
                .collect(),
            video_codecs: Codecs::video_codecs()
                .into_iter()
                .filter(|codec| codec.has_decoder())
                .collect(),
            enable_data_channel_navigation: DEFAULT_ENABLE_DATA_CHANNEL_NAVIGATION,
        }
    }
}

#[allow(dead_code)]
struct SignallerSignals {
    error: glib::SignalHandlerId,
    session_started: glib::SignalHandlerId,
    session_ended: glib::SignalHandlerId,
    request_meta: glib::SignalHandlerId,
    session_description: glib::SignalHandlerId,
    handle_ice: glib::SignalHandlerId,
}

impl WebRTCSrc {
    fn webrtcbin(&self) -> gst::Bin {
        let state = self.state.lock().unwrap();
        let webrtcbin = state
            .webrtcbin
            .as_ref()
            .expect("We should never call `.webrtcbin()` when state not > Ready")
            .clone()
            .downcast::<gst::Bin>()
            .unwrap();

        webrtcbin
    }

    fn signaller(&self) -> Signallable {
        self.settings.lock().unwrap().signaller.clone()
    }

    // Maps the `webrtcbin` pad to our exposed source pad using the pad stream ID.
    fn get_src_pad_from_webrtcbin_pad(&self, webrtcbin_src: &gst::Pad) -> Option<WebRTCSrcPad> {
        self.get_stream_id(
            Some(webrtcbin_src.property::<gst_webrtc::WebRTCRTPTransceiver>("transceiver")),
            None,
        )
        .and_then(|stream_id| {
            self.obj().iterate_src_pads().into_iter().find_map(|s| {
                let pad = s.ok()?.downcast::<WebRTCSrcPad>().unwrap();
                if pad.imp().stream_id() == stream_id {
                    Some(pad)
                } else {
                    None
                }
            })
        })
    }

    fn send_navigation_event(&self, evt: gst_video::NavigationEvent) {
        if let Some(data_channel) = &self.state.lock().unwrap().data_channel.borrow_mut() {
            let nav_event = NavigationEvent {
                mid: None,
                event: evt,
            };
            match serde_json::to_string(&nav_event).ok() {
                Some(str) => {
                    gst::trace!(CAT, imp: self, "Sending navigation event to peer");
                    data_channel.send_string(Some(str.as_str()));
                }
                None => {
                    gst::error!(CAT, imp: self, "Could not serialize navigation event");
                }
            }
        }
    }

    fn handle_webrtc_src_pad(&self, bin: &gst::Bin, pad: &gst::Pad) {
        let srcpad = self.get_src_pad_from_webrtcbin_pad(pad);
        if let Some(ref srcpad) = srcpad {
            let stream_id = srcpad.imp().stream_id();
            let mut builder = gst::event::StreamStart::builder(&stream_id);
            if let Some(stream_start) = pad.sticky_event::<gst::event::StreamStart>(0) {
                builder = builder
                    .seqnum(stream_start.seqnum())
                    .group_id(stream_start.group_id().unwrap_or_else(gst::GroupId::next));
            }

            gst::debug!(CAT, imp: self, "Storing id {stream_id} on {pad:?}");
            pad.store_sticky_event(&builder.build()).ok();
        }

        let ghostpad = gst::GhostPad::builder(gst::PadDirection::Src)
            .with_target(pad)
            .unwrap()
            .proxy_pad_chain_function(glib::clone!(@weak self as this => @default-panic, move
                |pad, parent, buffer| {
                    let padret = gst::ProxyPad::chain_default(pad, parent, buffer);
                    let ret = this.state.lock().unwrap().flow_combiner.update_flow(padret);

                    ret
                }
            ))
            .proxy_pad_event_function(glib::clone!(@weak self as this => @default-panic, move |pad, parent, event| {
                let event = if let gst::EventView::StreamStart(stream_start) = event.view() {
                    let webrtcpad = pad.peer().unwrap();

                    this.get_src_pad_from_webrtcbin_pad(&webrtcpad)
                        .map(|srcpad| {
                            gst::event::StreamStart::builder(&srcpad.imp().stream_id())
                                .seqnum(stream_start.seqnum())
                                .group_id(stream_start.group_id().unwrap_or_else(gst::GroupId::next))
                                .build()
                        }).unwrap_or(event)
                } else {
                    event
                };

                gst::Pad::event_default(pad, parent, event)
            }))
            .build();

        if self.settings.lock().unwrap().enable_data_channel_navigation {
            pad.add_probe(
                gst::PadProbeType::EVENT_UPSTREAM,
                glib::clone!(@weak self as this => @default-panic, move |_pad, info| {
                    let Some(ev) = info.event() else {
                        return gst::PadProbeReturn::Ok;
                    };
                    if ev.type_() != gst::EventType::Navigation {
                        return gst::PadProbeReturn::Ok;
                    };

                    this.send_navigation_event (gst_video::NavigationEvent::parse(ev).unwrap());

                    gst::PadProbeReturn::Ok
                }),
            );
        }

        bin.add_pad(&ghostpad)
            .expect("Adding ghostpad to the bin should always work");

        if let Some(srcpad) = srcpad {
            let producer_id = self.signaller().property::<String>("producer-peer-id");
            let encoded_filter = self.obj().emit_by_name::<Option<gst::Element>>(
                "request-encoded-filter",
                &[&producer_id, &srcpad.name(), &srcpad.allowed_caps()],
            );

            if srcpad.imp().needs_decoding() {
                let decodebin = gst::ElementFactory::make("decodebin3")
                    .build()
                    .expect("decodebin3 needs to be present!");
                self.obj().add(&decodebin).unwrap();
                decodebin.sync_state_with_parent().unwrap();
                decodebin.connect_pad_added(
                    glib::clone!(@weak self as this, @weak srcpad => move |_webrtcbin, pad| {
                        if pad.direction() == gst::PadDirection::Sink {
                            return;
                        }

                        srcpad.set_target(Some(pad)).unwrap();
                    }),
                );

                gst::debug!(CAT, imp: self, "Decoding for {}", srcpad.imp().stream_id());

                if let Some(encoded_filter) = encoded_filter {
                    let filter_sink_pad = encoded_filter
                        .static_pad("sink")
                        .expect("encoded filter must expose a static sink pad");

                    let parsebin = gst::ElementFactory::make("parsebin")
                        .build()
                        .expect("parsebin needs to be present!");
                    self.obj().add_many([&parsebin, &encoded_filter]).unwrap();

                    parsebin.connect_pad_added(move |_, pad| {
                        pad.link(&filter_sink_pad)
                            .expect("parsebin ! encoded_filter linking failed");
                        encoded_filter
                            .link(&decodebin)
                            .expect("encoded_filter ! decodebin3 linking failed");

                        encoded_filter.sync_state_with_parent().unwrap();
                    });

                    ghostpad
                        .link(&parsebin.static_pad("sink").unwrap())
                        .expect("webrtcbin ! parsebin linking failed");

                    parsebin.sync_state_with_parent().unwrap();
                } else {
                    let sinkpad = decodebin
                        .static_pad("sink")
                        .expect("decodebin has a sink pad");
                    ghostpad
                        .link(&sinkpad)
                        .expect("webrtcbin ! decodebin3 linking failed");
                }
            } else {
                gst::debug!(
                    CAT,
                    imp: self,
                    "NO decoding for {}",
                    srcpad.imp().stream_id()
                );

                if let Some(encoded_filter) = encoded_filter {
                    let filter_sink_pad = encoded_filter
                        .static_pad("sink")
                        .expect("encoded filter must expose a static sink pad");
                    let filter_src_pad = encoded_filter
                        .static_pad("src")
                        .expect("encoded filter must expose a static src pad");

                    self.obj().add(&encoded_filter).unwrap();

                    ghostpad
                        .link(&filter_sink_pad)
                        .expect("webrtcbin ! encoded_filter linking failed");
                    srcpad.set_target(Some(&filter_src_pad)).unwrap();

                    encoded_filter.sync_state_with_parent().unwrap();
                } else {
                    srcpad.set_target(Some(&ghostpad)).unwrap();
                }
            }
        } else {
            gst::debug!(CAT, imp: self, "Unused webrtcbin pad {pad:?}");
        }
    }

    fn prepare(&self) -> Result<(), Error> {
        let webrtcbin = gst::ElementFactory::make("webrtcbin")
            .property("bundle-policy", gst_webrtc::WebRTCBundlePolicy::MaxBundle)
            .build()
            .with_context(|| "Failed to make element webrtcbin".to_string())?;

        if let Some(stun_server) = self.settings.lock().unwrap().stun_server.as_ref() {
            webrtcbin.set_property("stun-server", stun_server);
        }

        let bin = gst::Bin::new();
        bin.connect_pad_removed(glib::clone!(@weak self as this => move |_, pad|
            this.state.lock().unwrap().flow_combiner.remove_pad(pad);
        ));
        bin.connect_pad_added(glib::clone!(@weak self as this => move |_, pad|
            this.state.lock().unwrap().flow_combiner.add_pad(pad);
        ));
        webrtcbin.connect_pad_added(
            glib::clone!(@weak self as this, @weak bin, => move |_webrtcbin, pad| {
                if pad.direction() == gst::PadDirection::Sink {
                    return;
                }

                this.handle_webrtc_src_pad(&bin, pad);
            }),
        );

        webrtcbin.connect_closure(
            "on-ice-candidate",
            false,
            glib::closure!(@weak-allow-none self as this => move |
                    _webrtcbin: gst::Bin,
                    sdp_m_line_index: u32,
                    candidate: String| {
                this.unwrap().on_ice_candidate(sdp_m_line_index, candidate);
            }),
        );

        webrtcbin.connect_closure(
            "on-data-channel",
            false,
            glib::closure!(@weak-allow-none self as this => move |
                    _webrtcbin: gst::Bin,
                    data_channel: glib::Object| {
                this.unwrap().on_data_channel(data_channel);
            }),
        );

        bin.add(&webrtcbin).unwrap();
        self.obj().add(&bin).context("Could not add `webrtcbin`")?;

        let mut state = self.state.lock().unwrap();
        state.webrtcbin.replace(webrtcbin);

        Ok(())
    }

    fn get_stream_id(
        &self,
        transceiver: Option<gst_webrtc::WebRTCRTPTransceiver>,
        mline: Option<u32>,
    ) -> Option<String> {
        let mline = transceiver.map_or(mline, |t| Some(t.mlineindex()));

        // Same logic as gst_pad_create_stream_id and friends, making a hash of
        // the URI and adding `:<some-id>`, here the ID is the mline of the
        // stream in the SDP.
        mline.map(|mline| {
            let mut cs = glib::Checksum::new(glib::ChecksumType::Sha256).unwrap();
            cs.update(
                self.uri()
                    .expect("get_stream_id should never be called if no URI has been set")
                    .as_bytes(),
            );

            format!("{}:{mline}", cs.string().unwrap())
        })
    }

    fn unprepare(&self) -> Result<(), Error> {
        gst::info!(CAT, imp: self, "unpreparing");

        let obj = self.obj();
        self.maybe_stop_signaller();
        self.state.lock().unwrap().session_id = None;
        for pad in obj.src_pads() {
            obj.remove_pad(&pad)
                .map_err(|err| anyhow::anyhow!("Couldn't remove pad? {err:?}"))?;
        }

        self.n_video_pads.store(0, Ordering::SeqCst);
        self.n_audio_pads.store(0, Ordering::SeqCst);

        Ok(())
    }

    fn connect_signaller(&self, signaller: &Signallable) {
        let instance = &*self.obj();

        let _ = self
            .state
            .lock()
            .unwrap()
            .signaller_signals
            .insert(SignallerSignals {
            error: signaller.connect_closure(
                "error",
                false,
                glib::closure!(@watch instance => move |
                _signaller: glib::Object, error: String| {
                    gst::element_error!(
                        instance,
                        gst::StreamError::Failed,
                        ["Signalling error: {}", error]
                    );
                }),
            ),

            session_started: signaller.connect_closure(
                "session-started",
                false,
                glib::closure!(@watch instance => move |
                        _signaller: glib::Object,
                        session_id: &str,
                        _peer_id: &str| {
                    let imp = instance.imp();
                    gst::info!(CAT, imp: imp, "Session started: {session_id}");
                    imp.state.lock().unwrap().session_id =
                        Some(session_id.to_string());
                }),
            ),

            session_ended: signaller.connect_closure(
                "session-ended",
                false,
                glib::closure!(@watch instance => move |_signaler: glib::Object, _session_id: &str|{
                    instance.imp().state.lock().unwrap().session_id = None;
                    instance.iterate_src_pads().into_iter().for_each(|pad|
                        { if let Err(e) = pad.map(|pad| pad.push_event(gst::event::Eos::new())) {
                            gst::error!(CAT, "Could not send EOS: {e:?}");
                        }}
                    );

                    false
                }),
            ),

            request_meta: signaller.connect_closure(
                "request-meta",
                false,
                glib::closure!(@watch instance => move |
                    _signaller: glib::Object| -> Option<gst::Structure> {
                    instance.imp().settings.lock().unwrap().meta.clone()
                }),
            ),

            session_description: signaller.connect_closure(
                "session-description",
                false,
                glib::closure!(@watch instance => move |
                        _signaller: glib::Object,
                        _peer_id: &str,
                        desc: &gst_webrtc::WebRTCSessionDescription| {
                    assert_eq!(desc.type_(), gst_webrtc::WebRTCSDPType::Offer);

                    instance.imp().handle_offer(desc);
                }),
            ),

            // sdp_mid is exposed for future proofing, see
            // https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/issues/1174,
            // at the moment sdp_m_line_index must be Some
            handle_ice: signaller.connect_closure(
                "handle-ice",
                false,
                glib::closure!(@watch instance => move |
                        _signaller: glib::Object,
                        peer_id: &str,
                        sdp_m_line_index: u32,
                        _sdp_mid: Option<String>,
                        candidate: &str| {
                    instance.imp().handle_ice(peer_id, Some(sdp_m_line_index), None, candidate);
                }),
            ),
        });

        // previous signals are disconnected when dropping the old structure
    }

    // Creates and adds our `WebRTCSrcPad` source pad, returning caps accepted
    // downstream
    fn create_and_probe_src_pad(&self, caps: &gst::Caps, stream_id: &str) -> bool {
        gst::log!(CAT, "Creating pad for {caps:?}, stream: {stream_id}");

        let obj = self.obj();
        let media_type = caps
            .structure(0)
            .expect("Passing empty caps is invalid")
            .get::<&str>("media")
            .expect("Only caps with a `media` field are expected when creating the pad");

        let (template, name, raw_caps) = if media_type == "video" {
            (
                obj.pad_template("video_%u").unwrap(),
                format!("video_{}", self.n_video_pads.fetch_add(1, Ordering::SeqCst)),
                VIDEO_CAPS.to_owned(),
            )
        } else if media_type == "audio" {
            (
                obj.pad_template("audio_%u").unwrap(),
                format!("audio_{}", self.n_audio_pads.fetch_add(1, Ordering::SeqCst)),
                AUDIO_CAPS.to_owned(),
            )
        } else {
            gst::info!(CAT, imp: self, "Not an audio or video media {media_type:?}");

            return false;
        };

        let caps_with_raw = [caps.clone(), raw_caps.clone()]
            .into_iter()
            .collect::<gst::Caps>();
        let ghost = gst::GhostPad::builder_from_template(&template)
            .name(name)
            .build()
            .downcast::<WebRTCSrcPad>()
            .unwrap();
        ghost.imp().set_stream_id(stream_id);
        obj.add_pad(&ghost)
            .expect("Adding ghost pad should never fail");

        let downstream_caps = ghost.peer_query_caps(Some(&caps_with_raw));
        if let Some(first_struct) = downstream_caps.structure(0) {
            if first_struct.has_name(raw_caps.structure(0).unwrap().name()) {
                ghost.imp().set_needs_decoding(true)
            }
        }

        true
    }

    fn handle_offer(&self, offer: &gst_webrtc::WebRTCSessionDescription) {
        gst::log!(CAT, imp: self, "Got offer {}", offer.sdp().to_string());

        let sdp = offer.sdp();
        let direction = gst_webrtc::WebRTCRTPTransceiverDirection::Recvonly;
        let webrtcbin = self.webrtcbin();
        for (i, media) in sdp.medias().enumerate() {
            let codec_names = {
                let settings = self.settings.lock().unwrap();
                settings
                    .video_codecs
                    .iter()
                    .chain(settings.audio_codecs.iter())
                    .map(|codec| codec.name.clone())
                    .collect::<HashSet<String>>()
            };
            let caps = media
                .formats()
                .filter_map(|format| {
                    format.parse::<i32>().ok().and_then(|pt| {
                        let mut mediacaps = media.caps_from_media(pt)?;
                        let s = mediacaps.structure(0).unwrap();
                        if !codec_names.contains(s.get::<&str>("encoding-name").ok()?) {
                            return None;
                        }

                        let mut filtered_s = gst::Structure::new_empty("application/x-rtp");
                        filtered_s.extend(s.iter().filter_map(|(key, value)| {
                            if key.starts_with("rtcp-") {
                                None
                            } else {
                                Some((key, value.to_owned()))
                            }
                        }));

                        if media
                            .attributes_to_caps(mediacaps.get_mut().unwrap())
                            .is_err()
                        {
                            gst::warning!(
                                CAT,
                                imp: self,
                                "Failed to retrieve attributes from media!"
                            );
                            return None;
                        }

                        let s = mediacaps.structure(0).unwrap();

                        filtered_s.extend(s.iter().filter_map(|(key, value)| {
                            if key.starts_with("extmap-") {
                                if let Ok(s) = value.get::<String>() {
                                    if s == RTP_TWCC_URI {
                                        return Some((key, value.to_owned()));
                                    }
                                }
                            }

                            None
                        }));

                        Some(filtered_s)
                    })
                })
                .collect::<gst::Caps>();

            if !caps.is_empty() {
                let stream_id = self.get_stream_id(None, Some(i as u32)).unwrap();
                if self.create_and_probe_src_pad(&caps, &stream_id) {
                    gst::info!(
                        CAT,
                        imp: self,
                        "Adding transceiver for {stream_id} with caps: {caps:#?}"
                    );
                    let transceiver = webrtcbin.emit_by_name::<gst_webrtc::WebRTCRTPTransceiver>(
                        "add-transceiver",
                        &[&direction, &caps],
                    );

                    transceiver.set_property("do_nack", true);
                    transceiver.set_property("fec-type", gst_webrtc::WebRTCFECType::UlpRed);
                }
            } else {
                gst::info!(
                    CAT,
                    "Not using media: {media:#?} as it doesn't match our codec restrictions"
                );
            }
        }

        webrtcbin.emit_by_name::<()>("set-remote-description", &[&offer, &None::<gst::Promise>]);

        let obj = self.obj();
        obj.no_more_pads();

        let promise =
            gst::Promise::with_change_func(glib::clone!(@weak self as this => move |reply| {
                    this.on_answer_created(reply);
                }
            ));

        webrtcbin.emit_by_name::<()>("create-answer", &[&None::<gst::Structure>, &promise]);
    }

    fn on_answer_created(&self, reply: Result<Option<&gst::StructureRef>, gst::PromiseError>) {
        let reply = match reply {
            Ok(Some(reply)) => {
                if !reply.has_field_with_type(
                    "answer",
                    gst_webrtc::WebRTCSessionDescription::static_type(),
                ) {
                    gst::element_error!(
                        self.obj(),
                        gst::StreamError::Failed,
                        ["create-answer::Promise returned with no reply"]
                    );
                    return;
                } else if reply.has_field_with_type("error", glib::Error::static_type()) {
                    gst::element_error!(
                        self.obj(),
                        gst::LibraryError::Failed,
                        ["create-offer::Promise returned with error: {:?}", reply]
                    );
                    return;
                }

                reply
            }
            Ok(None) => {
                gst::element_error!(
                    self.obj(),
                    gst::StreamError::Failed,
                    ["create-answer::Promise returned with no reply"]
                );

                return;
            }
            Err(err) => {
                gst::element_error!(
                    self.obj(),
                    gst::LibraryError::Failed,
                    ["create-answer::Promise returned with error {:?}", err]
                );

                return;
            }
        };

        let answer = reply
            .value("answer")
            .unwrap()
            .get::<gst_webrtc::WebRTCSessionDescription>()
            .expect("Invalid argument");

        self.webrtcbin()
            .emit_by_name::<()>("set-local-description", &[&answer, &None::<gst::Promise>]);

        let session_id = {
            let state = self.state.lock().unwrap();
            match &state.session_id {
                Some(id) => id.to_owned(),
                _ => {
                    gst::element_error!(
                        self.obj(),
                        gst::StreamError::Failed,
                        ["Signalling error, no session started while requesting to send an SDP offer"]
                    );

                    return;
                }
            }
        };

        gst::log!(CAT, imp: self, "Sending SDP, {}", answer.sdp().to_string());
        let signaller = self.signaller();
        signaller.send_sdp(&session_id, &answer);
    }

    fn on_data_channel(&self, data_channel: glib::Object) {
        gst::info!(CAT, imp: self, "Received data channel {data_channel:?}");
        let mut state = self.state.lock().unwrap();
        state.data_channel = data_channel.dynamic_cast::<WebRTCDataChannel>().ok();
    }

    fn on_ice_candidate(&self, sdp_m_line_index: u32, candidate: String) {
        let signaller = self.signaller();
        let session_id = match self.state.lock().unwrap().session_id.as_ref() {
            Some(id) => id.to_string(),
            _ => {
                gst::element_error!(
                        self.obj(),
                        gst::StreamError::Failed,
                        ["Signalling error, no session started while requesting to propose ice candidates"]
                    );

                return;
            }
        };
        signaller.add_ice(&session_id, &candidate, sdp_m_line_index, None::<String>);
    }

    /// Called by the signaller with an ice candidate
    fn handle_ice(
        &self,
        peer_id: &str,
        sdp_m_line_index: Option<u32>,
        _sdp_mid: Option<String>,
        candidate: &str,
    ) {
        let sdp_m_line_index = match sdp_m_line_index {
            Some(m_line) => m_line,
            None => {
                gst::error!(CAT, imp: self, "No mandatory mline");
                return;
            }
        };
        gst::log!(CAT, imp: self, "Got ice from {peer_id}: {candidate}");

        self.webrtcbin()
            .emit_by_name::<()>("add-ice-candidate", &[&sdp_m_line_index, &candidate]);
    }

    fn maybe_start_signaller(&self) {
        let obj = self.obj();
        let mut state = self.state.lock().unwrap();
        if state.signaller_state == SignallerState::Stopped
            && obj.current_state() >= gst::State::Paused
        {
            self.signaller().start();

            gst::info!(CAT, imp: self, "Started signaller");
            state.signaller_state = SignallerState::Started;
        }
    }

    fn maybe_stop_signaller(&self) {
        let mut state = self.state.lock().unwrap();
        if state.signaller_state == SignallerState::Started {
            self.signaller().stop();
            state.signaller_state = SignallerState::Stopped;
            gst::info!(CAT, imp: self, "Stopped signaller");
        }
    }
}

impl ElementImpl for WebRTCSrc {
    fn metadata() -> Option<&'static gst::subclass::ElementMetadata> {
        static ELEMENT_METADATA: Lazy<gst::subclass::ElementMetadata> = Lazy::new(|| {
            gst::subclass::ElementMetadata::new(
                "WebRTCSrc",
                "Source/Network/WebRTC",
                "WebRTC src",
                "Thibault Saunier <tsaunier@igalia.com>",
            )
        });

        Some(&*ELEMENT_METADATA)
    }

    fn pad_templates() -> &'static [gst::PadTemplate] {
        static PAD_TEMPLATES: Lazy<Vec<gst::PadTemplate>> = Lazy::new(|| {
            let mut video_caps_builder = gst::Caps::builder_full()
                .structure_with_any_features(VIDEO_CAPS.structure(0).unwrap().to_owned())
                .structure(RTP_CAPS.structure(0).unwrap().to_owned());

            for codec in Codecs::video_codecs() {
                video_caps_builder =
                    video_caps_builder.structure(codec.caps.structure(0).unwrap().to_owned());
            }

            let mut audio_caps_builder = gst::Caps::builder_full()
                .structure_with_any_features(AUDIO_CAPS.structure(0).unwrap().to_owned())
                .structure(RTP_CAPS.structure(0).unwrap().to_owned());

            for codec in Codecs::audio_codecs() {
                audio_caps_builder =
                    audio_caps_builder.structure(codec.caps.structure(0).unwrap().to_owned());
            }

            vec![
                gst::PadTemplate::with_gtype(
                    "video_%u",
                    gst::PadDirection::Src,
                    gst::PadPresence::Sometimes,
                    &video_caps_builder.build(),
                    WebRTCSrcPad::static_type(),
                )
                .unwrap(),
                gst::PadTemplate::with_gtype(
                    "audio_%u",
                    gst::PadDirection::Src,
                    gst::PadPresence::Sometimes,
                    &audio_caps_builder.build(),
                    WebRTCSrcPad::static_type(),
                )
                .unwrap(),
            ]
        });

        PAD_TEMPLATES.as_ref()
    }

    fn change_state(
        &self,
        transition: gst::StateChange,
    ) -> Result<gst::StateChangeSuccess, gst::StateChangeError> {
        let obj = &*self.obj();
        if let gst::StateChange::NullToReady = transition {
            if let Err(err) = self.prepare() {
                gst::element_error!(
                    obj,
                    gst::StreamError::Failed,
                    ["Failed to prepare: {}", err]
                );
                return Err(gst::StateChangeError);
            }
        }

        let mut ret = self.parent_change_state(transition);

        match transition {
            gst::StateChange::PausedToReady => {
                if let Err(err) = self.unprepare() {
                    gst::element_error!(
                        obj,
                        gst::StreamError::Failed,
                        ["Failed to unprepare: {}", err]
                    );
                    return Err(gst::StateChangeError);
                }
            }
            gst::StateChange::ReadyToPaused => {
                ret = Ok(gst::StateChangeSuccess::NoPreroll);
            }
            gst::StateChange::PlayingToPaused => {
                ret = Ok(gst::StateChangeSuccess::NoPreroll);
            }
            gst::StateChange::PausedToPlaying => {
                self.maybe_start_signaller();
            }
            _ => (),
        }

        ret
    }

    fn send_event(&self, event: gst::Event) -> bool {
        match event.view() {
            gst::EventView::Navigation(ev) => {
                self.send_navigation_event(gst_video::NavigationEvent::parse(ev).unwrap());
                true
            }
            _ => true,
        }
    }
}

impl GstObjectImpl for WebRTCSrc {}

impl BinImpl for WebRTCSrc {}

impl ChildProxyImpl for WebRTCSrc {
    fn child_by_index(&self, index: u32) -> Option<glib::Object> {
        if index == 0 {
            Some(self.signaller().upcast())
        } else {
            None
        }
    }

    fn children_count(&self) -> u32 {
        1
    }

    fn child_by_name(&self, name: &str) -> Option<glib::Object> {
        match name {
            "signaller" => {
                gst::info!(CAT, imp: self, "Getting signaller");
                Some(self.signaller().upcast())
            }
            _ => None,
        }
    }
}

impl URIHandlerImpl for WebRTCSrc {
    const URI_TYPE: gst::URIType = gst::URIType::Src;

    fn protocols() -> &'static [&'static str] {
        &["gstwebrtc", "gstwebrtcs"]
    }

    fn uri(&self) -> Option<String> {
        self.signaller().property::<Option<String>>("uri")
    }

    fn set_uri(&self, uri: &str) -> Result<(), glib::Error> {
        let uri = Url::from_str(uri)
            .map_err(|err| glib::Error::new(gst::URIError::BadUri, &format!("{:?}", err)))?;

        let socket_scheme = match uri.scheme() {
            "gstwebrtc" => Ok("ws"),
            "gstwebrtcs" => Ok("wss"),
            _ => Err(glib::Error::new(
                gst::URIError::BadUri,
                &format!("Invalid protocol: {}", uri.scheme()),
            )),
        }?;

        let mut url_str = uri.to_string();

        // Not using `set_scheme()` because it doesn't work with `http`
        // See https://github.com/servo/rust-url/pull/768 for a PR implementing that
        url_str.replace_range(0..uri.scheme().len(), socket_scheme);

        self.signaller().set_property("uri", &url_str);

        Ok(())
    }
}

#[derive(PartialEq)]
enum SignallerState {
    Started,
    Stopped,
}

struct State {
    session_id: Option<String>,
    signaller_state: SignallerState,
    webrtcbin: Option<gst::Element>,
    flow_combiner: gst_base::UniqueFlowCombiner,
    signaller_signals: Option<SignallerSignals>,
    data_channel: Option<WebRTCDataChannel>,
}

impl Default for State {
    fn default() -> Self {
        Self {
            signaller_state: SignallerState::Stopped,
            session_id: None,
            webrtcbin: None,
            flow_combiner: Default::default(),
            signaller_signals: Default::default(),
            data_channel: None,
        }
    }
}