WebRTC client & server

Cargo.toml

@@ -17,6 +17,7 @@ members = [
     "bin/full-node",
     "bin/light-base",
     "bin/wasm-node/rust",
+    "bin/webrtc-server",
 ]
 
 [features]

bin/wasm-node/javascript/src/index.ts

@@ -17,3 +17,7 @@
 
 export { HealthChecker, SmoldotHealth, healthChecker } from './health.js';
 export * from './client.js'; // TODO: precise exports
+
+// TODO: remove this, just for prototyping
+import connect from './webrtc/index.js';
+connect('127.0.0.1', 'udp', 41000);

bin/wasm-node/javascript/src/webrtc/index.ts

@@ -0,0 +1,249 @@
+// Smoldot
+// Copyright (C) 2019-2022  Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: GPL-3.0-or-later WITH Classpath-exception-2.0
+
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+// # Overview
+//
+// ## ICE
+//
+// RFCs: 8839, 8445
+// See also: https://tools.ietf.org/id/draft-ietf-rtcweb-sdp-08.html#rfc.section.5.2.3
+//
+// The WebRTC protocol uses ICE in order to establish a connection.
+//
+// In a typical ICE setup, there are two endpoints, called agents, that want to communicate. One
+// of these two agents is the local browser, while the other agent is the target of the
+// connection.
+//
+// Even though in this specific context all we want is a simple client-server communication, it
+// is helpful to keep in mind that ICE was designed to solve the problem of NAT traversal.
+//
+// The ICE workflow works as follows:
+//
+// - An "offerer" (the local browser) determines ways in which it could be accessible (either an
+//   IP address or through a relay using a TURN server), which are called "candidates". It then
+//   generates a small text payload in a format called SDP, that describes the request for a
+//   connection.
+// - The offerer sends this SDP-encoded message to the answerer. The medium through which this
+//   exchange is done is out of scope of the ICE protocol.
+// - The answerer then finds its own candidates, and generates an answer, again in the SDP format.
+//   This answer is sent back to the offerer.
+// - Each agent then tries to connect to the remote's candidates.
+//
+// The code below only runs on one of the two agents, and simulates steps 2 and 3.
+// We pretend to send the offer to the remote agent (the target of the connection), then pretend
+// that it has found a valid IP address for itself (i.e. a candidate), then pretend that the SDP
+// answer containing this candidate has been sent back.
+// This will cause the browser to execute step 4: try to connect to the remote's candidate.
+//
+// This process involves parsing the offer generated by the browser in order for the answer to
+// match the browser's demands.
+//
+// ## TCP or UDP
+//
+// The SDP message generated by the offerer contains the list of so-called "media streams" that it
+// wants to open. In our specific use-case, we configure the browser to always request one data
+// stream.
+//
+// WebRTC by itself doesn't hardcode any specific protocol for these media streams. Instead, it is
+// the SDP message of the offerer that specifies which protocol to use. In our use case, one data
+// stream, we know that the browser will always request either TCP+DTLS+SCTP, or UDP+DTLS+SCTP.
+//
+// After the browser generates an SDP offer (by calling `createOffer`), we are allowed to tweak
+// the actual SDP payload that we pass to `setLocalDescription` and that the browser will actually
+// end up using for its local description. Thanks to this, we can force the browser to use TCP
+// or to use UDP, no matter which one of the two it has requested in its offer.
+//
+// ## DTLS+SCTP
+//
+// RFCs: 8841, 8832
+//
+// In both cases (TCP or UDP), the next layer is DTLS. DTLS is similar to the well-known TLS
+// protocol, except that it doesn't guarantee ordering of delivery (as this is instead provided
+// by the SCTP layer on top of DTLS). In other words, once the TCP or UDP connection is
+// established, the browser will try to perform a DTLS handshake.
+//
+// During the ICE negotiation, each agent must include in its SDP packet a hash of the self-signed
+// certificate that it will use during the DTLS handshake.
+// In our use-case, where we try to hand-crate the SDP answer generated by the remote, this is
+// problematic as at this stage we have no way to know the certificate that the remote is going
+// to use.
+//
+// To solve that problem, instead of each node generating their own random certificate, like you
+// normally would, every libp2p node uses the same hardcoded publicly-known certificate.
+// As such, the TLS layer won't offer any protection and another encryption layer will need to be
+// negotiated on top of the DTLS+SCTP stream, like is the case for plain TCP connections.
+//
+// TODO: this is only one potential solution; see ongoing discussion in https://github.com/libp2p/specs/issues/220
+// # About main thread vs worker
+//
+// You might wonder why this code is not executed within the WebWorker.
+// The reason is that at the time of writing it is not allowed to create WebRTC connections within
+// a WebWorker.
+//
+// See also https://github.com/w3c/webrtc-extensions/issues/64
+//
+
+export default function(targetIp: string, protocol: 'tcp' | 'udp', targetPort: number) {
+    // Create a new peer connection.
+    const pc = new RTCPeerConnection();
+
+    // Create a new data channel. This will trigger a new negotiation (see
+    // `negotiationneeded` handler below).
+    const dataChannel = pc.createDataChannel("data");
+
+    // Log any connection state changes.
+    pc.onconnectionstatechange = (_event) => {
+        console.log("conn state: " + pc.connectionState);
+    };
+
+    // Log any ICE connection state changes.
+    pc.oniceconnectionstatechange = (_event) => {
+        console.log("ICE conn state: " + pc.iceConnectionState);
+    };
+
+    // When a new negotion is triggered, set both local and remote descriptions.
+    pc.onnegotiationneeded = async (_event) => {
+        // Create a new offer and set it as local description.
+        var sdpOffer = (await pc.createOffer()).sdp!;
+        // Replace ICE user and password with ones expected by the server.
+        sdpOffer = sdpOffer.replace(/^a=ice-ufrag.*$/m, 'a=ice-ufrag:V6j+')
+        sdpOffer = sdpOffer.replace(/^a=ice-pwd.*$/m, 'a=ice-pwd:OEKutPgoHVk/99FfqPOf444w');
+        // Replace trickle option with ice2 since we won't be sending any
+        // additional candidates.
+        sdpOffer = sdpOffer.replace(/^a=ice-options:.*$/m, 'a=ice-options:ice2');
+        await pc.setLocalDescription({ type: 'offer', sdp: sdpOffer });
+
+        console.log(pc.localDescription!.sdp);
+
+        // Use the fake SDP response, which normally the client would've
+        // received through the STUN server.
+        //
+        // Note that the trailing line feed is important, as otherwise Chrome
+        // fails to parse the payload.
+        const remoteSdp =
+            // Version of the SDP protocol. Always 0. (RFC8866)
+            "v=0" + "\n" +
+            // Identifies the creator of the SDP document. We are allowed to use dummy values
+            // (`-` and `0.0.0.0`) to remain anonymous, which we do. Note that "IN" means
+            // "Internet". (RFC8866)
+            // TODO: handle IPv6
+            "o=- " + (Date.now() / 1000).toFixed() + " 0 IN IP4 " + targetIp + "\n" +
+            // Name for the session. We are allowed to pass a dummy `-`. (RFC8866)
+            "s=-" + "\n" +
+            // Start and end of the validity of the session. `0 0` means that the session never
+            // expires. (RFC8866)
+            "t=0 0" + "\n" +
+            // TODO: remove eventually; this was added just for testing because things didn't seem to work
+            "a=group:BUNDLE 0" + "\n" +
+
+            // A lite implementation is only appropriate for devices that will
+            // *always* be connected to the public Internet and have a public
+            // IP address at which it can receive packets from any
+            // correspondent.  ICE will not function when a lite implementation
+            // is placed behind a NAT (RFC8445).
+            "a=ice-lite" + "\n" +
+
+            // A `m=` line describes a request to establish a certain protocol.
+            // The protocol in this line (i.e. `TCP/DTLS/SCTP` or `UDP/DTLS/SCTP`) must always be
+            // the same as the one in the offer. We know that this is true because we tweak the
+            // offer to match the protocol.
+            // The `<fmt>` component must always be `pc-datachannel` for WebRTC.
+            // The rest of the SDP payload adds attributes to this specific media stream.
+            // RFCs: 8839, 8866, 8841
+            "m=application " + targetPort + " " + (protocol == 'tcp' ? "TCP" : "UDP") + "/DTLS/SCTP webrtc-datachannel" + "\n" +
+            // Indicates the IP address of the remote.
+            // Note that "IN" means "Internet".
+            // TODO: handle IPv6
+            "c=IN IP4 " + targetIp + "\n" +
+            // TODO: remove eventually; goes together with `mid:0`
+            "a=mid:0" + "\n" +
+            // Indicates that we are complying with RFC8839 (as oppposed to the legacy RFC5245).
+            "a=ice-options:ice2" + "\n" +
+            // Randomly-generated username and password (the line after). Used only for
+            // connectivity checks, which is irrelevant for our situation, but it is mandatory
+            // anyway. (RFC8839)
+            // The username must have at least 24 bits of entropy, and the password at least 128
+            // bits of entropy. (RFC8845)
+            "a=ice-ufrag:" + genRandomPayload(24) + "\n" +
+            "a=ice-pwd:" + genRandomPayload(128) + "\n" +
+            // Fingerprint of the certificate that the server will use during the TLS
+            // handshake. (RFC8122)
+            // As explained at the top-level documentation, we use a hardcoded certificate.
+            // TODO: proper certificate and fingerprint
+            "a=fingerprint:sha-256 0B:0D:39:5C:85:07:8C:E3:A7:76:E9:CD:21:90:64:F0:88:FE:A4:9F:AA:6F:AD:A4:5A:50:0B:14:C7:03:8D:5D" + "\n" +
+
+            // "TLS ID" uniquely identifies a TLS association.
+            // The ICE protocol uses a "TLS ID" system to indicate whether a fresh DTLS connection
+            // must be reopened in case of ICE renegotiation. Considering that ICE renegotiations
+            // never happen in our use case, we can simply put a random value and not care about
+            // it. Note however that the TLS ID in the answer must be present if and only if the
+            // offer contains one. (RFC8842)
+            // TODO: is it true that renegotiations never happen? what about a connection closing?
+            // TODO: If the answerer receives an offer that does not contain an SDP "tls-id" attribute, the answerer MUST NOT insert a "tls-id" attribute in the answer.
+            // TODO: right now browsers don't send it "a=tls-id:" + genRandomPayload(120) + "\n" +
+            // "tls-id" attribute MUST be present in the initial offer and respective answer (RFC8839).
+            // "a=tls-id:abc3de65cddef001be82" + "\n" +
+
+            // Indicates that the remote DTLS server will only listen for incoming
+            // connections. (RFC5763)
+            // The answerer (server) must not be located behind a NAT (RFC6135).
+            "a=setup:passive" + "\n" +
+            // The SCTP port (RFC8841)
+            // Note it's different from the "m=" line port value, which
+            // indicates the port of the underlying transport-layer protocol
+            // (UDP or TCP)
+            "a=sctp-port:5000" + "\n" +
+            // The maximum SCTP user message size (in bytes) (RFC8841)
+            "a=max-message-size:100000" + "\n" +
+            // A transport address for a candidate that can be used for connectivity checks (RFC8839).
+            "a=candidate:1 1 " + (protocol == 'tcp' ? "TCP" : "UDP") + " 2113667327 " + targetIp + " " + targetPort + " typ host" + "\n" +
+            // Indicate that there will be no further candidates.
+            "a=end-of-candidates" + "\n";
+
+        await pc.setRemoteDescription({ type: "answer", sdp: remoteSdp });
+
+        console.log(pc.remoteDescription!.sdp);
+    };
+
+    dataChannel.onopen = () => {
+        console.log(`'${dataChannel.label}' opened`);
+    };
+
+    dataChannel.onerror = (error) => {
+        console.log(`'${dataChannel.label}' errored: ${error}`);
+    };
+
+    dataChannel.onclose = () => {
+        console.log(`'${dataChannel.label}' closed`);
+    };
+
+    dataChannel.onmessage = (m) => {
+        console.log(`new message on '${dataChannel.label}': '${m.data}'`);
+    }
+}
+
+/**
+ * Generates a random payload whose grammar is: ALPHA / DIGIT / "+" / "/"
+ */
+function genRandomPayload(entryopyBits: number): string {
+    // Note that the grammar is letter, digits, +, and /. In other words, this is base64 except
+    // without the potential trailing `=`. This trailing `=` is annoying to handle so we just use
+    // hexadecimal.
+    let data = new Uint8Array(Math.ceil(entryopyBits / 8));
+    window.crypto.getRandomValues(data);
+    return [...data].map(x => x.toString(16).padStart(2, '0')).join('');
+}

bin/webrtc-server/Cargo.toml

@@ -0,0 +1,26 @@
+[package]
+name = "webrtc-server"
+version = "0.1.0"
+authors = ["Parity Technologies <[email protected]>", "Pierre Krieger <[email protected]>"]
+description = "webRTC server"
+repository = "https://github.com/paritytech/smoldot"
+license = "GPL-3.0-or-later WITH Classpath-exception-2.0"
+edition = "2021"
+publish = false
+
+[dependencies]
+anyhow = "1.0.56"
+async-std = { version = "1.10.0", features = ["attributes", "tokio1"] }
+clap = { version = "3.1.6", features = ["derive"] }
+futures = "0.3.17"
+rcgen = "0.8.14"
+webrtc = { version = "0.4.0", git = "https://github.com/melekes/webrtc", branch = "anton/168-allow-persistent-certificates" }
+webrtc-ice = "0.6.6"
+webrtc-dtls = "0.5.2"
+ctrlc = "3.2.1"
+tokio = { version = "1.17.0", default-features = false, features = ["net"] }
+rustls = "0.19.0"
+rustls-pemfile = "0.3.0"
+env_logger = "0.9.0"
+log = "0.4.14"
+chrono = "0.4.19"

bin/webrtc-server/README.md

@@ -0,0 +1,19 @@
+# WebRTC server
+
+## Certificate
+
+The certificate in `./static` was generated using the following commands:
+
+```
+$ openssl ecparam -name prime256v1 -genkey -noout -out server.pem
+$ openssl req -key server.pem -new -subj '/O=Parity/OU=Smoldot' -out server.csr
+$ openssl x509 -req -in server.csr -days 3650 -extfile extfile.conf -CA "$(mkcert -CAROOT)/rootCA.pem" -CAkey "$(mkcert -CAROOT)/rootCA-key.pem"  -CAcreateserial -out server.pub.pem
+$ openssl pkcs8 -topk8 -nocrypt -in server.pem -out server.private.pem
+$ mv server.private.pem server.pem
+
+# Cleanup.
+$ rm server.csr
+
+# Calculate sha256 fingerprint of the certificate
+$ openssl x509 -noout -fingerprint -sha256 -inform pem -in server.pub.pem
+```