From 0c501e250725fa5a0cb60a0a5326d25a25a0fdb0 Mon Sep 17 00:00:00 2001
From: Alessandro Ros <aler9.dev@gmail.com>
Date: Mon, 21 Apr 2025 15:01:46 +0200
Subject: [PATCH] webrtc: improve JavaScript classes (#4455)

* add close() method

* move support functions into classes as static methods

* convert arrow functions into standard functions

* make most methods private

* add JSDocs
---
 internal/servers/webrtc/publisher.js | 427 ++++++++++++----------
 internal/servers/webrtc/reader.js    | 520 +++++++++++++++------------
 2 files changed, 513 insertions(+), 434 deletions(-)

diff --git a/internal/servers/webrtc/publisher.js b/internal/servers/webrtc/publisher.js
index 03b2c3d6..62ae52b3 100644
--- a/internal/servers/webrtc/publisher.js
+++ b/internal/servers/webrtc/publisher.js
@@ -1,29 +1,83 @@
 'use strict';
 
-(() => {
+/**
+ * @callback OnError
+ * @param {string} err - error.
+ */
 
-  const unquoteCredential = (v) => (
-    JSON.parse(`"${v}"`)
-  );
+/**
+ * @callback OnConnected
+ */
 
-  const linkToIceServers = (links) => (
-    (links !== null) ? links.split(', ').map((link) => {
+/**
+ * @typedef Conf
+ * @type {object}
+ * @property {string} url - absolute URL of the WHIP endpoint.
+ * @property {MediaStream} stream - stream that contains outgoing tracks.
+ * @property {string} videoCodec - outgoing video codec.
+ * @property {number} videoBitrate - outgoing video bitrate.
+ * @property {string} audioCodec - outgoing audio bitrate.
+ * @property {number} audioBitrate - outgoing audio bitrate.
+ * @property {boolean} audioVoice - whether audio is voice.
+ * @property {OnError} onError - called when there's an error.
+ * @property {OnConnected} onConnected - called when connected.
+ */
+
+/** WebRTC/WHIP publisher. */
+class MediaMTXWebRTCPublisher {
+  /**
+   * Create a MediaMTXWebRTCPublisher.
+   * @param {Conf} conf - configuration.
+   */
+  constructor(conf) {
+    this.retryPause = 2000;
+    this.conf = conf;
+    this.state = 'running';
+    this.restartTimeout = null;
+    this.pc = null;
+    this.offerData = null;
+    this.sessionUrl = null;
+    this.queuedCandidates = [];
+    this.#start();
+  }
+
+  /**
+   * Close the publisher and all its resources.
+   */
+  close = () => {
+    this.state = 'closed';
+
+    if (this.pc !== null) {
+      this.pc.close();
+    }
+
+    if (this.restartTimeout !== null) {
+      clearTimeout(this.restartTimeout);
+    }
+  };
+
+  static #unquoteCredential(v) {
+    return JSON.parse(`"${v}"`);
+  }
+
+  static #linkToIceServers(links) {
+    return (links !== null) ? links.split(', ').map((link) => {
       const m = link.match(/^<(.+?)>; rel="ice-server"(; username="(.*?)"; credential="(.*?)"; credential-type="password")?/i);
       const ret = {
         urls: [m[1]],
       };
 
       if (m[3] !== undefined) {
-        ret.username = unquoteCredential(m[3]);
-        ret.credential = unquoteCredential(m[4]);
+        ret.username = this.#unquoteCredential(m[3]);
+        ret.credential = this.#unquoteCredential(m[4]);
         ret.credentialType = 'password';
       }
 
       return ret;
-    }) : []
-  );
+    }) : [];
+  }
 
-  const parseOffer = (offer) => {
+  static #parseOffer(offer) {
     const ret = {
       iceUfrag: '',
       icePwd: '',
@@ -41,9 +95,9 @@
     }
 
     return ret;
-  };
+  }
 
-  const generateSdpFragment = (od, candidates) => {
+  static #generateSdpFragment(od, candidates) {
     const candidatesByMedia = {};
     for (const candidate of candidates) {
       const mid = candidate.sdpMLineIndex;
@@ -71,9 +125,9 @@
     }
 
     return frag;
-  };
+  }
 
-  const setCodec = (section, codec) => {
+  static #setCodec(section, codec) {
     const lines = section.split('\r\n');
     const lines2 = [];
     const payloadFormats = [];
@@ -110,9 +164,9 @@
     }
 
     return lines3.join('\r\n');
-  };
+  }
 
-  const setVideoBitrate = (section, bitrate) => {
+  static #setVideoBitrate(section, bitrate) {
     let lines = section.split('\r\n');
 
     for (let i = 0; i < lines.length; i++) {
@@ -123,9 +177,9 @@
     }
 
     return lines.join('\r\n');
-  };
+  }
 
-  const setAudioBitrate = (section, bitrate, voice) => {
+  static #setAudioBitrate(section, bitrate, voice) {
     let opusPayloadFormat = '';
     let lines = section.split('\r\n');
 
@@ -153,66 +207,46 @@
     }
 
     return lines.join('\r\n');
-  };
+  }
 
-  const editOffer = (sdp, videoCodec, audioCodec, audioBitrate, audioVoice) => {
+  static #editOffer(sdp, videoCodec, audioCodec, audioBitrate, audioVoice) {
     const sections = sdp.split('m=');
 
     for (let i = 0; i < sections.length; i++) {
       if (sections[i].startsWith('video')) {
-        sections[i] = setCodec(sections[i], videoCodec);
+        sections[i] = this.#setCodec(sections[i], videoCodec);
       } else if (sections[i].startsWith('audio')) {
-        sections[i] = setAudioBitrate(setCodec(sections[i], audioCodec), audioBitrate, audioVoice);
+        sections[i] = this.#setAudioBitrate(this.#setCodec(sections[i], audioCodec), audioBitrate, audioVoice);
       }
     }
 
     return sections.join('m=');
-  };
+  }
 
-  const editAnswer = (sdp, videoBitrate) => {
+  static #editAnswer(sdp, videoBitrate) {
     const sections = sdp.split('m=');
 
     for (let i = 0; i < sections.length; i++) {
       if (sections[i].startsWith('video')) {
-        sections[i] = setVideoBitrate(sections[i], videoBitrate);
+        sections[i] = this.#setVideoBitrate(sections[i], videoBitrate);
       }
     }
 
     return sections.join('m=');
-  };
+  }
 
-  const retryPause = 2000;
-
-  class MediaMTXWebRTCPublisher {
-    constructor(conf) {
-      this.conf = conf;
-      this.state = 'initializing';
-      this.restartTimeout = null;
-      this.pc = null;
-      this.offerData = null;
-      this.sessionUrl = null;
-      this.queuedCandidates = [];
-
-      this.start();
-    }
-
-    start = () => {
-      this.state = 'running';
-
-      this.requestICEServers()
-        .then((iceServers) => this.setupPeerConnection(iceServers))
-        .then((offer) => this.sendOffer(offer))
-        .then((answer) => this.setAnswer(answer))
-        .catch((err) => {
-          this.handleError(err.toString());
-        });
-    };
-
-    handleError = (err) => {
-      if (this.state === 'restarting' || this.state === 'error') {
-        return;
-      }
+  #start() {
+    this.#requestICEServers()
+      .then((iceServers) => this.#setupPeerConnection(iceServers))
+      .then((offer) => this.#sendOffer(offer))
+      .then((answer) => this.#setAnswer(answer))
+      .catch((err) => {
+        this.#handleError(err.toString());
+      });
+  }
 
+  #handleError(err) {
+    if (this.state === 'running') {
       if (this.pc !== null) {
         this.pc.close();
         this.pc = null;
@@ -228,167 +262,170 @@
       }
 
       this.queuedCandidates = [];
+      this.state = 'restarting';
 
-      if (this.state === 'running') {
-        this.state = 'restarting';
+      this.restartTimeout = window.setTimeout(() => {
+        this.restartTimeout = null;
+        this.state = 'running';
+        this.#start();
+      }, this.retryPause);
 
-        this.restartTimeout = window.setTimeout(() => {
-          this.restartTimeout = null;
-          this.start();
-        }, retryPause);
-
-        if (this.conf.onError !== undefined) {
-          this.conf.onError(err + ', retrying in some seconds');
-        }
-      } else {
-        this.state = 'error';
-
-        if (this.conf.onError !== undefined) {
-          this.conf.onError(err);
-        }
+      if (this.conf.onError !== undefined) {
+        this.conf.onError(`${err}, retrying in some seconds`);
       }
-    };
+    }
+  }
 
-    requestICEServers = () => {
-      return fetch(this.conf.url, {
-        method: 'OPTIONS',
-      })
-        .then((res) => linkToIceServers(res.headers.get('Link')));
-    };
+  #requestICEServers() {
+    return fetch(this.conf.url, {
+      method: 'OPTIONS',
+    })
+      .then((res) => MediaMTXWebRTCPublisher.#linkToIceServers(res.headers.get('Link')));
+  }
 
-    setupPeerConnection = (iceServers) => {
-      this.pc = new RTCPeerConnection({
-        iceServers,
-        // https://webrtc.org/getting-started/unified-plan-transition-guide
-        sdpSemantics: 'unified-plan',
+  #setupPeerConnection(iceServers) {
+    if (this.state !== 'running') {
+      throw new Error('closed');
+    }
+
+    this.pc = new RTCPeerConnection({
+      iceServers,
+      // https://webrtc.org/getting-started/unified-plan-transition-guide
+      sdpSemantics: 'unified-plan',
+    });
+
+    this.pc.onicecandidate = (evt) => this.#onLocalCandidate(evt);
+    this.pc.onconnectionstatechange = () => this.#onConnectionState();
+
+    this.conf.stream.getTracks().forEach((track) => {
+      this.pc.addTrack(track, this.conf.stream);
+    });
+
+    return this.pc.createOffer()
+      .then((offer) => {
+        this.offerData = MediaMTXWebRTCPublisher.#parseOffer(offer.sdp);
+
+        return this.pc.setLocalDescription(offer)
+          .then(() => offer.sdp);
       });
+  }
 
-      this.pc.onicecandidate = (evt) => this.onLocalCandidate(evt);
-      this.pc.onconnectionstatechange = () => this.onConnectionState();
+  #sendOffer(offer) {
+    if (this.state !== 'running') {
+      throw new Error('closed');
+    }
 
-      this.conf.stream.getTracks().forEach((track) => {
-        this.pc.addTrack(track, this.conf.stream);
-      });
+    offer = MediaMTXWebRTCPublisher.#editOffer(
+      offer,
+      this.conf.videoCodec,
+      this.conf.audioCodec,
+      this.conf.audioBitrate,
+      this.conf.audioVoice);
 
-      return this.pc.createOffer()
-        .then((offer) => {
-          this.offerData = parseOffer(offer.sdp);
-
-          return this.pc.setLocalDescription(offer)
-            .then(() => offer.sdp);
-        });
-    };
-
-    sendOffer = (offer) => {
-      offer = editOffer(
-        offer,
-        this.conf.videoCodec,
-        this.conf.audioCodec,
-        this.conf.audioBitrate,
-        this.conf.audioVoice);
-
-      return fetch(this.conf.url, {
-        method: 'POST',
-        headers: {
-          'Content-Type': 'application/sdp',
-        },
-        body: offer,
-      })
-        .then((res) => {
-          switch (res.status) {
+    return fetch(this.conf.url, {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/sdp',
+      },
+      body: offer,
+    })
+      .then((res) => {
+        switch (res.status) {
           case 201:
             break;
           case 400:
             return res.json().then((e) => { throw new Error(e.error); });
           default:
             throw new Error(`bad status code ${res.status}`);
-          }
-
-          this.sessionUrl = new URL(res.headers.get('location'), this.conf.url).toString();
-
-          return res.text();
-        });
-    };
-
-    setAnswer = (answer) => {
-      if (this.state !== 'running') {
-        return;
-      }
-
-      answer = editAnswer(answer, this.conf.videoBitrate);
-
-      return this.pc.setRemoteDescription(new RTCSessionDescription({
-        type: 'answer',
-        sdp: answer,
-      }))
-        .then(() => {
-          if (this.queuedCandidates.length !== 0) {
-            this.sendLocalCandidates(this.queuedCandidates);
-            this.queuedCandidates = [];
-          }
-        });
-    };
-
-    onLocalCandidate = (evt) => {
-      if (this.state !== 'running') {
-        return;
-      }
-
-      if (evt.candidate !== null) {
-        if (this.sessionUrl === null) {
-          this.queuedCandidates.push(evt.candidate);
-        } else {
-          this.sendLocalCandidates([evt.candidate]);
         }
-      }
-    };
 
-    sendLocalCandidates = (candidates) => {
-      fetch(this.sessionUrl, {
-        method: 'PATCH',
-        headers: {
-          'Content-Type': 'application/trickle-ice-sdpfrag',
-          'If-Match': '*',
-        },
-        body: generateSdpFragment(this.offerData, candidates),
-      })
-        .then((res) => {
-          switch (res.status) {
+        this.sessionUrl = new URL(res.headers.get('location'), this.conf.url).toString();
+
+        return res.text();
+      });
+  }
+
+  #setAnswer(answer) {
+    if (this.state !== 'running') {
+      throw new Error('closed');
+    }
+
+    answer = MediaMTXWebRTCPublisher.#editAnswer(answer, this.conf.videoBitrate);
+
+    return this.pc.setRemoteDescription(new RTCSessionDescription({
+      type: 'answer',
+      sdp: answer,
+    }))
+      .then(() => {
+        if (this.state !== 'running') {
+          return;
+        }
+
+        if (this.queuedCandidates.length !== 0) {
+          this.#sendLocalCandidates(this.queuedCandidates);
+          this.queuedCandidates = [];
+        }
+      });
+  }
+
+  #onLocalCandidate(evt) {
+    if (this.state !== 'running') {
+      return;
+    }
+
+    if (evt.candidate !== null) {
+      if (this.sessionUrl === null) {
+        this.queuedCandidates.push(evt.candidate);
+      } else {
+        this.#sendLocalCandidates([evt.candidate]);
+      }
+    }
+  }
+
+  #sendLocalCandidates(candidates) {
+    fetch(this.sessionUrl, {
+      method: 'PATCH',
+      headers: {
+        'Content-Type': 'application/trickle-ice-sdpfrag',
+        'If-Match': '*',
+      },
+      body: MediaMTXWebRTCPublisher.#generateSdpFragment(this.offerData, candidates),
+    })
+      .then((res) => {
+        switch (res.status) {
           case 204:
             break;
           case 404:
             throw new Error('stream not found');
           default:
             throw new Error(`bad status code ${res.status}`);
-          }
-        })
-        .catch((err) => {
-          this.handleError(err.toString());
-        });
-    };
-
-    onConnectionState = () => {
-      if (this.state !== 'running') {
-        return;
-      }
-
-      // "closed" can arrive before "failed" and without
-      // the close() method being called at all.
-      // It happens when the other peer sends a termination
-      // message like a DTLS CloseNotify.
-      if (this.pc.connectionState === 'failed'
-        || this.pc.connectionState === 'closed'
-      ) {
-        this.handleError('peer connection closed');
-      } else if (this.pc.connectionState === 'connected') {
-        if (this.conf.onConnected !== undefined) {
-          this.conf.onConnected();
         }
-      }
-    };
-
+      })
+      .catch((err) => {
+        this.#handleError(err.toString());
+      });
   }
 
-  window.MediaMTXWebRTCPublisher = MediaMTXWebRTCPublisher;
+  #onConnectionState() {
+    if (this.state !== 'running') {
+      return;
+    }
 
-})();
+    // "closed" can arrive before "failed" and without
+    // the close() method being called at all.
+    // It happens when the other peer sends a termination
+    // message like a DTLS CloseNotify.
+    if (this.pc.connectionState === 'failed'
+      || this.pc.connectionState === 'closed'
+    ) {
+      this.#handleError('peer connection closed');
+    } else if (this.pc.connectionState === 'connected') {
+      if (this.conf.onConnected !== undefined) {
+        this.conf.onConnected();
+      }
+    }
+  }
+
+}
+
+window.MediaMTXWebRTCPublisher = MediaMTXWebRTCPublisher;
diff --git a/internal/servers/webrtc/reader.js b/internal/servers/webrtc/reader.js
index 7fa1c04a..b71c65d3 100644
--- a/internal/servers/webrtc/reader.js
+++ b/internal/servers/webrtc/reader.js
@@ -1,16 +1,65 @@
 'use strict';
 
-(() => {
+/**
+ * @callback OnError
+ * @param {string} err - error.
+ */
 
-  const supportsNonAdvertisedCodec = (codec, fmtp) => (
-    new Promise((resolve) => {
+/**
+ * @callback OnTrack
+ * @param {RTCTrackEvent} evt - track event.
+ */
+
+/**
+ * @typedef Conf
+ * @type {object}
+ * @property {string} url - absolute URL of the WHEP endpoint.
+ * @property {OnError} onError - called when there's an error.
+ * @property {OnTrack} onTrack - called when there's a track available.
+ */
+
+/** WebRTC/WHEP reader. */
+class MediaMTXWebRTCReader {
+  /**
+   * Create a MediaMTXWebRTCReader.
+   * @param {Conf} conf - configuration.
+   */
+  constructor(conf) {
+    this.retryPause = 2000;
+    this.conf = conf;
+    this.state = 'getting_codecs';
+    this.restartTimeout = null;
+    this.pc = null;
+    this.offerData = null;
+    this.sessionUrl = null;
+    this.queuedCandidates = [];
+    this.#getNonAdvertisedCodecs();
+  }
+
+  /**
+   * Close the reader and all its resources.
+   */
+  close() {
+    this.state = 'closed';
+
+    if (this.pc !== null) {
+      this.pc.close();
+    }
+
+    if (this.restartTimeout !== null) {
+      clearTimeout(this.restartTimeout);
+    }
+  }
+
+  static #supportsNonAdvertisedCodec(codec, fmtp) {
+    return new Promise((resolve) => {
       const payloadType = 118; // TODO: dynamic
       const pc = new RTCPeerConnection({ iceServers: [] });
       const mediaType = 'audio';
       pc.addTransceiver(mediaType, { direction: 'recvonly' });
       pc.createOffer()
         .then((offer) => {
-          if (offer.sdp.includes(' ' + codec)) { // codec is advertised, there's no need to add it manually
+          if (offer.sdp.includes(` ${codec}`)) { // codec is advertised, there's no need to add it manually
             throw new Error('already present');
           }
           const sections = offer.sdp.split(`m=${mediaType}`);
@@ -24,24 +73,24 @@
           offer.sdp = sections.join(`m=${mediaType}`);
           return pc.setLocalDescription(offer);
         })
-        .then(() => {
-          return pc.setRemoteDescription(new RTCSessionDescription({
+        .then(() => (
+          pc.setRemoteDescription(new RTCSessionDescription({
             type: 'answer',
             sdp: 'v=0\r\n'
             + 'o=- 6539324223450680508 0 IN IP4 0.0.0.0\r\n'
             + 's=-\r\n'
             + 't=0 0\r\n'
             + 'a=fingerprint:sha-256 0D:9F:78:15:42:B5:4B:E6:E2:94:3E:5B:37:78:E1:4B:54:59:A3:36:3A:E5:05:EB:27:EE:8F:D2:2D:41:29:25\r\n'
-            + `m=${mediaType} 9 UDP/TLS/RTP/SAVPF ${payloadType}` + '\r\n'
+            + `m=${mediaType} 9 UDP/TLS/RTP/SAVPF ${payloadType}\r\n`
             + 'c=IN IP4 0.0.0.0\r\n'
             + 'a=ice-pwd:7c3bf4770007e7432ee4ea4d697db675\r\n'
             + 'a=ice-ufrag:29e036dc\r\n'
             + 'a=sendonly\r\n'
             + 'a=rtcp-mux\r\n'
-            + `a=rtpmap:${payloadType} ${codec}` + '\r\n'
-            + ((fmtp !== undefined) ? `a=fmtp:${payloadType} ${fmtp}` + '\r\n' : ''),
-          }));
-        })
+            + `a=rtpmap:${payloadType} ${codec}\r\n`
+            + ((fmtp !== undefined) ? `a=fmtp:${payloadType} ${fmtp}\r\n` : ''),
+          }))
+        ))
         .then(() => {
           resolve(true);
         })
@@ -51,31 +100,31 @@
         .finally(() => {
           pc.close();
         });
-    })
-  );
+    });
+  }
 
-  const unquoteCredential = (v) => (
-    JSON.parse(`"${v}"`)
-  );
+  static #unquoteCredential(v) {
+    return JSON.parse(`"${v}"`);
+  }
 
-  const linkToIceServers = (links) => (
-    (links !== null) ? links.split(', ').map((link) => {
+  static #linkToIceServers(links) {
+    return (links !== null) ? links.split(', ').map((link) => {
       const m = link.match(/^<(.+?)>; rel="ice-server"(; username="(.*?)"; credential="(.*?)"; credential-type="password")?/i);
       const ret = {
         urls: [m[1]],
       };
 
       if (m[3] !== undefined) {
-        ret.username = unquoteCredential(m[3]);
-        ret.credential = unquoteCredential(m[4]);
+        ret.username = this.#unquoteCredential(m[3]);
+        ret.credential = this.#unquoteCredential(m[4]);
         ret.credentialType = 'password';
       }
 
       return ret;
-    }) : []
-  );
+    }) : [];
+  }
 
-  const parseOffer = (sdp) => {
+  static #parseOffer(sdp) {
     const ret = {
       iceUfrag: '',
       icePwd: '',
@@ -93,9 +142,9 @@
     }
 
     return ret;
-  };
+  }
 
-  const reservePayloadType = (payloadTypes) => {
+  static #reservePayloadType(payloadTypes) {
     // everything is valid between 30 and 127, except for interval between 64 and 95
     // https://chromium.googlesource.com/external/webrtc/+/refs/heads/master/call/payload_type.h#29
     for (let i = 30; i <= 127; i++) {
@@ -106,90 +155,90 @@
       }
     }
     throw Error('unable to find a free payload type');
-  };
+  }
 
-  const enableStereoPcmau = (payloadTypes, section) => {
-    let lines = section.split('\r\n');
+  static #enableStereoPcmau(payloadTypes, section) {
+    const lines = section.split('\r\n');
 
-    let payloadType = reservePayloadType(payloadTypes);
+    let payloadType = this.#reservePayloadType(payloadTypes);
     lines[0] += ` ${payloadType}`;
     lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} PCMU/8000/2`);
     lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);
 
-    payloadType = reservePayloadType(payloadTypes);
+    payloadType = this.#reservePayloadType(payloadTypes);
     lines[0] += ` ${payloadType}`;
     lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} PCMA/8000/2`);
     lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);
 
     return lines.join('\r\n');
-  };
+  }
 
-  const enableMultichannelOpus = (payloadTypes, section) => {
-    let lines = section.split('\r\n');
+  static #enableMultichannelOpus(payloadTypes, section) {
+    const lines = section.split('\r\n');
 
-    let payloadType = reservePayloadType(payloadTypes);
+    let payloadType = this.#reservePayloadType(payloadTypes);
     lines[0] += ` ${payloadType}`;
     lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} multiopus/48000/3`);
     lines.splice(lines.length - 1, 0, `a=fmtp:${payloadType} channel_mapping=0,2,1;num_streams=2;coupled_streams=1`);
     lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);
 
-    payloadType = reservePayloadType(payloadTypes);
+    payloadType = this.#reservePayloadType(payloadTypes);
     lines[0] += ` ${payloadType}`;
     lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} multiopus/48000/4`);
     lines.splice(lines.length - 1, 0, `a=fmtp:${payloadType} channel_mapping=0,1,2,3;num_streams=2;coupled_streams=2`);
     lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);
 
-    payloadType = reservePayloadType(payloadTypes);
+    payloadType = this.#reservePayloadType(payloadTypes);
     lines[0] += ` ${payloadType}`;
     lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} multiopus/48000/5`);
     lines.splice(lines.length - 1, 0, `a=fmtp:${payloadType} channel_mapping=0,4,1,2,3;num_streams=3;coupled_streams=2`);
     lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);
 
-    payloadType = reservePayloadType(payloadTypes);
+    payloadType = this.#reservePayloadType(payloadTypes);
     lines[0] += ` ${payloadType}`;
     lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} multiopus/48000/6`);
     lines.splice(lines.length - 1, 0, `a=fmtp:${payloadType} channel_mapping=0,4,1,2,3,5;num_streams=4;coupled_streams=2`);
     lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);
 
-    payloadType = reservePayloadType(payloadTypes);
+    payloadType = this.#reservePayloadType(payloadTypes);
     lines[0] += ` ${payloadType}`;
     lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} multiopus/48000/7`);
     lines.splice(lines.length - 1, 0, `a=fmtp:${payloadType} channel_mapping=0,4,1,2,3,5,6;num_streams=4;coupled_streams=4`);
     lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);
 
-    payloadType = reservePayloadType(payloadTypes);
+    payloadType = this.#reservePayloadType(payloadTypes);
     lines[0] += ` ${payloadType}`;
     lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} multiopus/48000/8`);
     lines.splice(lines.length - 1, 0, `a=fmtp:${payloadType} channel_mapping=0,6,1,4,5,2,3,7;num_streams=5;coupled_streams=4`);
     lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);
 
     return lines.join('\r\n');
-  };
+  }
 
-  const enableL16 = (payloadTypes, section) => {
-    let lines = section.split('\r\n');
+  static #enableL16(payloadTypes, section) {
+    const lines = section.split('\r\n');
 
-    let payloadType = reservePayloadType(payloadTypes);
+    let payloadType = this.#reservePayloadType(payloadTypes);
     lines[0] += ` ${payloadType}`;
     lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} L16/8000/2`);
     lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);
 
-    payloadType = reservePayloadType(payloadTypes);
+    payloadType = this.#reservePayloadType(payloadTypes);
     lines[0] += ` ${payloadType}`;
     lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} L16/16000/2`);
     lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);
 
-    payloadType = reservePayloadType(payloadTypes);
+    payloadType = this.#reservePayloadType(payloadTypes);
     lines[0] += ` ${payloadType}`;
     lines.splice(lines.length - 1, 0, `a=rtpmap:${payloadType} L16/48000/2`);
     lines.splice(lines.length - 1, 0, `a=rtcp-fb:${payloadType} transport-cc`);
 
     return lines.join('\r\n');
-  };
+  }
 
-  const enableStereoOpus = (section) => {
+  static #enableStereoOpus(section) {
     let opusPayloadFormat = '';
-    let lines = section.split('\r\n');
+    const lines = section.split('\r\n');
 
     for (let i = 0; i < lines.length; i++) {
       if (lines[i].startsWith('a=rtpmap:') && lines[i].toLowerCase().includes('opus/')) {
@@ -203,7 +252,7 @@
     }
 
     for (let i = 0; i < lines.length; i++) {
-      if (lines[i].startsWith('a=fmtp:' + opusPayloadFormat + ' ')) {
+      if (lines[i].startsWith(`a=fmtp:${opusPayloadFormat} `)) {
         if (!lines[i].includes('stereo')) {
           lines[i] += ';stereo=1';
         }
@@ -214,9 +263,9 @@
     }
 
     return lines.join('\r\n');
-  };
+  }
 
-  const editOffer = (sdp, nonAdvertisedCodecs) => {
+  static #editOffer(sdp, nonAdvertisedCodecs) {
     const sections = sdp.split('m=');
 
     const payloadTypes = sections.slice(1)
@@ -225,16 +274,16 @@
 
     for (let i = 1; i < sections.length; i++) {
       if (sections[i].startsWith('audio')) {
-        sections[i] = enableStereoOpus(sections[i]);
+        sections[i] = this.#enableStereoOpus(sections[i]);
 
         if (nonAdvertisedCodecs.includes('pcma/8000/2')) {
-          sections[i] = enableStereoPcmau(payloadTypes, sections[i]);
+          sections[i] = this.#enableStereoPcmau(payloadTypes, sections[i]);
         }
         if (nonAdvertisedCodecs.includes('multiopus/48000/6')) {
-          sections[i] = enableMultichannelOpus(payloadTypes, sections[i]);
+          sections[i] = this.#enableMultichannelOpus(payloadTypes, sections[i]);
         }
         if (nonAdvertisedCodecs.includes('L16/48000/2')) {
-          sections[i] = enableL16(payloadTypes, sections[i]);
+          sections[i] = this.#enableL16(payloadTypes, sections[i]);
         }
 
         break;
@@ -242,9 +291,9 @@
     }
 
     return sections.join('m=');
-  };
+  }
 
-  const generateSdpFragment = (od, candidates) => {
+  static #generateSdpFragment(od, candidates) {
     const candidatesByMedia = {};
     for (const candidate of candidates) {
       const mid = candidate.sdpMLineIndex;
@@ -254,50 +303,28 @@
       candidatesByMedia[mid].push(candidate);
     }
 
-    let frag = 'a=ice-ufrag:' + od.iceUfrag + '\r\n'
-      + 'a=ice-pwd:' + od.icePwd + '\r\n';
+    let frag = `a=ice-ufrag:${od.iceUfrag}\r\n`
+      + `a=ice-pwd:${od.icePwd}\r\n`;
 
     let mid = 0;
 
     for (const media of od.medias) {
       if (candidatesByMedia[mid] !== undefined) {
-        frag += 'm=' + media + '\r\n'
-          + 'a=mid:' + mid + '\r\n';
+        frag += `m=${media}\r\n`
+          + `a=mid:${mid}\r\n`;
 
         for (const candidate of candidatesByMedia[mid]) {
-          frag += 'a=' + candidate.candidate + '\r\n';
+          frag += `a=${candidate.candidate}\r\n`;
         }
       }
       mid++;
     }
 
     return frag;
-  };
-
-  const retryPause = 2000;
-
-  class MediaMTXWebRTCReader {
-    constructor(conf) {
-      this.conf = conf;
-      this.state = 'initializing';
-      this.restartTimeout = null;
-      this.pc = null;
-      this.offerData = null;
-      this.sessionUrl = null;
-      this.queuedCandidates = [];
-
-      this.getNonAdvertisedCodecs()
-        .then(() => this.start())
-        .catch((err) => {
-          this.handleError(err);
-        });
-    }
-
-    handleError = (err) => {
-      if (this.state === 'restarting' || this.state === 'error') {
-        return;
-      }
+  }
 
+  #handleError(err) {
+    if (this.state === 'running') {
       if (this.pc !== null) {
         this.pc.close();
         this.pc = null;
@@ -313,92 +340,106 @@
       }
 
       this.queuedCandidates = [];
+      this.state = 'restarting';
 
-      if (this.state === 'running') {
-        this.state = 'restarting';
+      this.restartTimeout = window.setTimeout(() => {
+        this.restartTimeout = null;
+        this.state = 'running';
+        this.#start();
+      }, this.retryPause);
 
-        this.restartTimeout = window.setTimeout(() => {
-          this.restartTimeout = null;
-          this.start();
-        }, retryPause);
-
-        if (this.conf.onError !== undefined) {
-          this.conf.onError(err + ', retrying in some seconds');
-        }
-      } else {
-        this.state = 'error';
-
-        if (this.conf.onError !== undefined) {
-          this.conf.onError(err);
-        }
+      if (this.conf.onError !== undefined) {
+        this.conf.onError(`${err}, retrying in some seconds`);
       }
-    };
+    } else if (this.state === 'getting_codecs') {
+      this.state = 'failed';
 
-    getNonAdvertisedCodecs = () => {
-      return Promise.all([
-        ['pcma/8000/2'],
-        ['multiopus/48000/6', 'channel_mapping=0,4,1,2,3,5;num_streams=4;coupled_streams=2'],
-        ['L16/48000/2'],
-      ]
-        .map((c) => supportsNonAdvertisedCodec(c[0], c[1]).then((r) => (r) ? c[0] : false)))
-        .then((c) => c.filter((e) => e !== false))
-        .then((codecs) => {
-          this.nonAdvertisedCodecs = codecs;
-        });
-    };
+      if (this.conf.onError !== undefined) {
+        this.conf.onError(err);
+      }
+    }
+  }
 
-    start = () => {
-      this.state = 'running';
+  #getNonAdvertisedCodecs() {
+    Promise.all([
+      ['pcma/8000/2'],
+      ['multiopus/48000/6', 'channel_mapping=0,4,1,2,3,5;num_streams=4;coupled_streams=2'],
+      ['L16/48000/2'],
+    ]
+      .map((c) => MediaMTXWebRTCReader.#supportsNonAdvertisedCodec(c[0], c[1]).then((r) => ((r) ? c[0] : false))))
+      .then((c) => c.filter((e) => e !== false))
+      .then((codecs) => {
+        if (this.state !== 'getting_codecs') {
+          throw new Error('closed');
+        }
 
-      this.requestICEServers()
-        .then((iceServers) => this.setupPeerConnection(iceServers))
-        .then((offer) => this.sendOffer(offer))
-        .then((answer) => this.setAnswer(answer))
-        .catch((err) => {
-          this.handleError(err.toString());
-        });
-    };
-
-    requestICEServers = () => {
-      return fetch(this.conf.url, {
-        method: 'OPTIONS',
+        this.nonAdvertisedCodecs = codecs;
+        this.state = 'running';
+        this.#start();
       })
-        .then((res) => linkToIceServers(res.headers.get('Link')))
-    };
-
-    setupPeerConnection = (iceServers) => {
-      this.pc = new RTCPeerConnection({
-        iceServers,
-        // https://webrtc.org/getting-started/unified-plan-transition-guide
-        sdpSemantics: 'unified-plan',
+      .catch((err) => {
+        this.#handleError(err);
       });
+  }
 
-      const direction = 'recvonly';
-      this.pc.addTransceiver('video', { direction });
-      this.pc.addTransceiver('audio', { direction });
+  #start() {
+    this.#requestICEServers()
+      .then((iceServers) => this.#setupPeerConnection(iceServers))
+      .then((offer) => this.#sendOffer(offer))
+      .then((answer) => this.#setAnswer(answer))
+      .catch((err) => {
+        this.#handleError(err.toString());
+      });
+  }
 
-      this.pc.onicecandidate = (evt) => this.onLocalCandidate(evt);
-      this.pc.onconnectionstatechange = () => this.onConnectionState();
-      this.pc.ontrack = (evt) => this.onTrack(evt);
+  #requestICEServers() {
+    return fetch(this.conf.url, {
+      method: 'OPTIONS',
+    })
+      .then((res) => MediaMTXWebRTCReader.#linkToIceServers(res.headers.get('Link')));
+  }
 
-      return this.pc.createOffer()
-        .then((offer) => {
-          offer.sdp = editOffer(offer.sdp, this.nonAdvertisedCodecs);
-          this.offerData = parseOffer(offer.sdp);
+  #setupPeerConnection(iceServers) {
+    if (this.state !== 'running') {
+      throw new Error('closed');
+    }
 
-          return this.pc.setLocalDescription(offer)
-            .then(() => offer.sdp);
-        });
-    };
+    this.pc = new RTCPeerConnection({
+      iceServers,
+      // https://webrtc.org/getting-started/unified-plan-transition-guide
+      sdpSemantics: 'unified-plan',
+    });
 
-    sendOffer = (offer) => {
-      return fetch(this.conf.url, {
-        method: 'POST',
-        headers: {'Content-Type': 'application/sdp'},
-        body: offer,
-      })
-        .then((res) => {
-          switch (res.status) {
+    const direction = 'recvonly';
+    this.pc.addTransceiver('video', { direction });
+    this.pc.addTransceiver('audio', { direction });
+
+    this.pc.onicecandidate = (evt) => this.#onLocalCandidate(evt);
+    this.pc.onconnectionstatechange = () => this.#onConnectionState();
+    this.pc.ontrack = (evt) => this.#onTrack(evt);
+
+    return this.pc.createOffer()
+      .then((offer) => {
+        offer.sdp = MediaMTXWebRTCReader.#editOffer(offer.sdp, this.nonAdvertisedCodecs);
+        this.offerData = MediaMTXWebRTCReader.#parseOffer(offer.sdp);
+
+        return this.pc.setLocalDescription(offer)
+          .then(() => offer.sdp);
+      });
+  }
+
+  #sendOffer(offer) {
+    if (this.state !== 'running') {
+      throw new Error('closed');
+    }
+
+    return fetch(this.conf.url, {
+      method: 'POST',
+      headers: {'Content-Type': 'application/sdp'},
+      body: offer,
+    })
+      .then((res) => {
+        switch (res.status) {
           case 201:
             break;
           case 404:
@@ -407,93 +448,94 @@
             return res.json().then((e) => { throw new Error(e.error); });
           default:
             throw new Error(`bad status code ${res.status}`);
-          }
-
-          this.sessionUrl = new URL(res.headers.get('location'), this.conf.url).toString();
-
-          return res.text();
-        });
-    };
-
-    setAnswer = (answer) => {
-      if (this.state !== 'running') {
-        return;
-      }
-
-      return this.pc.setRemoteDescription(new RTCSessionDescription({
-        type: 'answer',
-        sdp: answer,
-      }))
-        .then(() => {
-          if (this.queuedCandidates.length !== 0) {
-            this.sendLocalCandidates(this.queuedCandidates);
-            this.queuedCandidates = [];
-          }
-        });
-    };
-
-    onLocalCandidate = (evt) => {
-      if (this.state !== 'running') {
-        return;
-      }
-
-      if (evt.candidate !== null) {
-        if (this.sessionUrl === null) {
-          this.queuedCandidates.push(evt.candidate);
-        } else {
-          this.sendLocalCandidates([evt.candidate]);
         }
-      }
-    };
 
-    sendLocalCandidates = (candidates) => {
-      fetch(this.sessionUrl, {
-        method: 'PATCH',
-        headers: {
-          'Content-Type': 'application/trickle-ice-sdpfrag',
-          'If-Match': '*',
-        },
-        body: generateSdpFragment(this.offerData, candidates),
-      })
-        .then((res) => {
-          switch (res.status) {
+        this.sessionUrl = new URL(res.headers.get('location'), this.conf.url).toString();
+
+        return res.text();
+      });
+  }
+
+  #setAnswer(answer) {
+    if (this.state !== 'running') {
+      throw new Error('closed');
+    }
+
+    return this.pc.setRemoteDescription(new RTCSessionDescription({
+      type: 'answer',
+      sdp: answer,
+    }))
+      .then(() => {
+        if (this.state !== 'running') {
+          return;
+        }
+
+        if (this.queuedCandidates.length !== 0) {
+          this.#sendLocalCandidates(this.queuedCandidates);
+          this.queuedCandidates = [];
+        }
+      });
+  }
+
+  #onLocalCandidate(evt) {
+    if (this.state !== 'running') {
+      return;
+    }
+
+    if (evt.candidate !== null) {
+      if (this.sessionUrl === null) {
+        this.queuedCandidates.push(evt.candidate);
+      } else {
+        this.#sendLocalCandidates([evt.candidate]);
+      }
+    }
+  }
+
+  #sendLocalCandidates(candidates) {
+    fetch(this.sessionUrl, {
+      method: 'PATCH',
+      headers: {
+        'Content-Type': 'application/trickle-ice-sdpfrag',
+        'If-Match': '*',
+      },
+      body: MediaMTXWebRTCReader.#generateSdpFragment(this.offerData, candidates),
+    })
+      .then((res) => {
+        switch (res.status) {
           case 204:
             break;
           case 404:
             throw new Error('stream not found');
           default:
             throw new Error(`bad status code ${res.status}`);
-          }
-        })
-        .catch((err) => {
-          this.handleError(err.toString());
-        });
-    };
-
-    onConnectionState = () => {
-      if (this.state !== 'running') {
-        return;
-      }
-
-      // "closed" can arrive before "failed" and without
-      // the close() method being called at all.
-      // It happens when the other peer sends a termination
-      // message like a DTLS CloseNotify.
-      if (this.pc.connectionState === 'failed'
-        || this.pc.connectionState === 'closed'
-      ) {
-        this.handleError('peer connection closed');
-      }
-    };
-
-    onTrack = (evt) => {
-      if (this.conf.onTrack !== undefined) {
-        this.conf.onTrack(evt);
-      }
-    };
-
+        }
+      })
+      .catch((err) => {
+        this.#handleError(err.toString());
+      });
   }
 
-  window.MediaMTXWebRTCReader = MediaMTXWebRTCReader;
+  #onConnectionState() {
+    if (this.state !== 'running') {
+      return;
+    }
 
-})();
+    // "closed" can arrive before "failed" and without
+    // the close() method being called at all.
+    // It happens when the other peer sends a termination
+    // message like a DTLS CloseNotify.
+    if (this.pc.connectionState === 'failed'
+      || this.pc.connectionState === 'closed'
+    ) {
+      this.#handleError('peer connection closed');
+    }
+  }
+
+  #onTrack(evt) {
+    if (this.conf.onTrack !== undefined) {
+      this.conf.onTrack(evt);
+    }
+  }
+}
+
+window.MediaMTXWebRTCReader = MediaMTXWebRTCReader;