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/*
** Copyright (C) 2021 Gabriele De Blasi
**
** This software is provided 'as-is', without any express or implied
** warranty. In no event will the authors be held liable for any damages
** arising from the use of this software.
**
** Permission is granted to anyone to use this software for any purpose,
** including commercial applications, and to alter it and redistribute it
** freely, subject to the following restrictions:
**
** 1. The origin of this software must not be misrepresented; you must not
** claim that you wrote the original software. If you use this software
** in a product, an acknowledgment in the product documentation would be
** appreciated but is not required.
** 2. Altered source versions must be plainly marked as such, and must not be
** misrepresented as being the original software.
** 3. This notice may not be removed or altered from any source distribution.
**
** Created on: 2021-11-30T09:30:00+01:00
** Author: Gabriele De Blasi <gabriele.de.blasi@cern.ch>
**
*/
import { EventEmitter } from "node:events";
import http from "node:http";
import { parse } from "content-type";
import VarBuffer from "./VarBuffer.js";
/**
* @typedef {import('http').ClientRequest} Request
* @typedef {import('http').IncomingMessage} Response
*
* @typedef {{ user: string, password: string }} Authentication
* @typedef {{ src: string, auth?: Authentication, contentLength?: boolean, jpegMagicBytes: boolean,
* headerDelimiter: string, boundary?: string, throttle?: number }} MJPEGConsumerOptions
*/
const SearchStates = { HEADER_END: 1, CONTENT_END: 2, NEXT_BOUNDARY: 3 };
const CRLFx2 = "\r\n\r\n";
const JPEG_MAGIC_BYTES = Buffer.from("ffd8ff", "hex");
/**
* @param {function} fun
*/
function frameSkip(fun) {
const DELTA = 10; // ms
let deadline = 0;
return function(/** @type {any[]} */ ...args) {
const now = Date.now();
if (now + DELTA < deadline) { return; }
deadline = now + this.throttle;
fun(...args);
};
}
/**
* @implements {CamExpress.Consumer}
* @extends {EventEmitter}
* @emits :
* - 'frame' when a new jpeg frame is received from source
* - 'ended' once the stream is stopped at the source
* - 'error' when an error occurs
* - 'close' once the connection with source is closed
*/
class MJPEGConsumer extends EventEmitter {
/**
* @param {MJPEGConsumerOptions} options
*/
constructor(options) {
super();
this.src = options?.src ?? "";
this.user = options?.auth?.user;
this.pass = options?.auth?.password;
this.contentLength = options?.contentLength ?? true;
this.boundary = options?.boundary;
this.headerDelimiter = options?.headerDelimiter;
this.jpegMagicBytes = options?.jpegMagicBytes ?? false;
this._connected = false;
this._buffer = new VarBuffer();
this._initialThrottle = options?.throttle;
this.updateThrottle(options?.throttle);
/** @type {Request|null} */
this._req = null;
this._state = SearchStates.HEADER_END;
this._offset = 0; // search start byte in buffer
this._contentStart = 0;
this._frameEnd = 0;
/** @type {Buffer|null} */
this._delimiter = null;
this.emitError = (err) => {
if (this._connected) {
this.emit("error", err);
}
};
this.emitFrame = this.throttle ?
frameSkip(this.emit.bind(this, "frame")) : // limit the frame rate
this.emit.bind(this, "frame"); // no throttle => direct emit to reduce frame loss
}
updateThrottle(throttle) {
if (throttle && throttle < MJPEGConsumer.MIN_THROTTLE_VALUE) {
throttle = MJPEGConsumer.MIN_THROTTLE_VALUE; // Assert throttle min value
console.warn(
`The throttle ${throttle} is too low and` +
` was replaced with ${MJPEGConsumer.MIN_THROTTLE_VALUE} ms`
);
}
this.throttle = Number(throttle);
}
connect() {
if (this._connected) { return; }
this._connected = true;
this._buffer.reset();
this._delimiter = this.jpegMagicBytes ? JPEG_MAGIC_BYTES :
Buffer.from(this.headerDelimiter || CRLFx2);
const opts = {
auth: (this.user && this.pass) ? `${this.user}:${this.pass}` : undefined
};
const req = this._req = http.get(this.src, opts);
req
.on("error", this.emitError)
.once("close", () => {
req.removeAllListeners();
// disconnect if the current connection has been terminated by the source
if (req === this._req) {
this.disconnect();
}
})
.on("response", (res) => {
res
.on("error", this.emitError)
.once("close", () => res.removeAllListeners());
if ((res.headers["content-type"] ?? "").includes("multipart/x-mixed-replace")) {
try {
this.parse(res);
}
catch (err) {
this.emitError(err);
}
}
else {
this.emitError(new Error("No MJPEG stream detected"));
this.disconnect();
}
})
.end();
}
disconnect() {
if (!this._connected) { return; }
this._connected = false;
this._req?.destroy();
this.emit("close");
this._req = null;
}
/**
* @param {Response} res
*/
parse(res) {
/** @type {Buffer} */ let boundary;
try {
boundary = Buffer.from(this.boundary ??
parse(res.headers["content-type"] ?? "")?.parameters?.boundary);
}
catch (err) {
// retrieve boundary param by regex
// (see https://datatracker.ietf.org/doc/html/rfc2046#section-5.1.1)
const match = (res.headers["content-type"] ?? "")
.match(/boundary="?([\w\s'()+,\-./:=?]{1,70})"?;?/);
if (!match) { throw err; } // boundary missing or invalid
boundary = Buffer.from(match[1].trimEnd());
}
// minimum parsable header length
const minHeaderLen = boundary.length + this._delimiter.length;
res
.on("data", (chunk) => { // eslint-disable-line complexity, max-statements
this._buffer.add(chunk);
let index = 0;
while (this._buffer.length > minHeaderLen) {
switch (this._state) {
case SearchStates.HEADER_END:
index = this._buffer.buffer().indexOf(this._delimiter, this._offset);
if (index >= 0) {
this._contentStart = this._offset =
index + (this.jpegMagicBytes ? 0 : this._delimiter.length);
}
else if (this._buffer.length > MJPEGConsumer.MAX_HEADER_LENGTH) {
if (!this.jpegMagicBytes) {
// fallback solution: search for JPEG magic numbers
index = this._buffer.buffer().indexOf(JPEG_MAGIC_BYTES);
}
if (index >= 0) {
this._contentStart = this._offset = index;
}
else { // drop data
this._buffer.shift(MJPEGConsumer.MAX_HEADER_LENGTH);
this._offset = 0;
console.warn(
`Discarded the first ${MJPEGConsumer.MAX_HEADER_LENGTH} ` +
"bytes as the maximum header length has been reached.");
return;
}
}
else {
// set starting byte for next search considering the worst case:
// e.g. last 3 bytes equal to '\r\n\r' (with CRLFx2 as delimiter)
this._offset =
this._buffer.length - Math.abs(this._delimiter.length - 1);
if (this._offset < 0) { this._offset = 0; }
return;
}
// choice between content-Length and boundary
{
const match = this.contentLength ?
this._buffer.slice(0, index).toString("ascii")
.match(/Content-Length:\s*(\d+)/i) : null;
if (!match) {
this._state = SearchStates.NEXT_BOUNDARY;
break;
}
this._frameEnd = this._contentStart + Number(match[1]);
this._state = SearchStates.CONTENT_END;
}
/* falls through */
case SearchStates.CONTENT_END:
if (this._buffer.length < this._frameEnd) { return; }
this.emitFrame(
this._buffer.slice(this._contentStart, this._frameEnd));
this._buffer.shift(this._frameEnd);
this._offset = 0;
this._state = SearchStates.HEADER_END;
break;
case SearchStates.NEXT_BOUNDARY:
index = this._buffer.buffer().indexOf(boundary, this._offset);
if (index === -1) {
// same as above
this._offset = this._buffer.length - (boundary.length - 1);
if (this._offset < 0) {
this._offset = 0;
}
else if (this._buffer.length > MJPEGConsumer.MAX_CONTENT_LENGTH) {
this._buffer.shift(this._offset);
this._offset = 0;
}
return;
}
this.emitFrame(this._buffer.slice(this._contentStart, index));
this._buffer.shift(index);
this._offset = boundary.length; // re-start from after the boundary
/* falls through */
default:
this._state = SearchStates.HEADER_END;
break;
}
}
})
.on("end", this.emit.bind(this, "ended"));
}
}
MJPEGConsumer.MAX_HEADER_LENGTH = 2048; // bytes
MJPEGConsumer.MAX_CONTENT_LENGTH = 20971520; // bytes (= 20 MiB)
MJPEGConsumer.MIN_THROTTLE_VALUE = 17; // ms (~ 60 fps)
export default MJPEGConsumer;
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