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index.js
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/* Requires */
const http = require('http').Server;
const spawn = require('child_process').spawn;
const parseUrl = require('url').parse;
const messages = require('./rest_messages');
const defaultEncoder = {
/*
* encoder command or location
*/
command: 'avconv',
/*
* Function that returns the required flags, the video is expected to be
* written to stdout
*
* Note: for video size you have to use a string like
* `-f video4linux2 -video_size 1280x960 -i ${webcam} -f webm -deadline realtime pipe:1`
* The other option is to scan the available resolutions and choose one based
* on certain policy, the avlib/ffmpeg command for this is
* `-f video4linux2 -list_formats all -i ${webcam}`
*/
flags(webcam) {
return `-f video4linux2 -i ${webcam} -f webm -deadline realtime pipe:1`;
},
/*
* MIME type of the output stream
*/
mimeType: 'video/webm',
/*
* Function that detects the success of the encoder process,
* does cb(true) in case of succes, any other value for failure
*
* Calling cb more than one time has no effect
*
* encoderProcess is of type ChildProcess
*
* This default isn't perfect but covers most of the cases
*/
isSuccessful(encoderProcess, cb) {
let started = false;
encoderProcess.stderr.setEncoding('utf8');
encoderProcess.stderr.on('data', (data) => {
/* I trust that the output is line-buffered */
const startedText = /Press ctrl-c to stop encoding/;
if(startedText.test(data)) {
cb(true);
started = true;
}
});
/* If the process start was not detected and it exited it's surely a failure */
encoderProcess.on('exit', () => {
if(!started) cb(false);
});
}
};
/* Utility functions */
function fileExists(file) {
const access = require('fs').access;
return new Promise((accept, reject) => access(file, (err) => err ? reject(false) : accept(true)));
}
function isValidWebcamDefault(webcam) {
const webcamRegex = /\/dev\/video[0-9]+/;
return new Promise((accept, reject) => {
/* Si no tiene pinta de webcam es un error */
if(!webcamRegex.test(webcam)) {
reject(false);
} else {
/* Si no existe el fichero también */
fileExists(webcam).then(accept, reject);
}
});
}
/* Returns the isValidWebcam for a given whitelist */
function isValidWebcamWhitelist(whitelistArray) {
const whitelist = {};
/* We create the map*/
whitelistArray.forEach((webcam) => whitelist[webcam] = 'valid');
return (webcam) => new Promise((accept, reject) => webcam in whitelist? accept(true) : reject(false));
}
function defaultPage(req, res, req_url) {
res.writeHead(404);
res.end(`
<!DOCTYPE html>
<html>
<head><title>４０４ ｎｏｔ－ｆｏｕｎｄ</title></head>
<body><p>Ｓｏｒｒｙ， ｗｅ ｄｏｎ＇ｔ ｋｎｏｗ ｗｈａｔ ｔｏ ｄｏ</p></body>
</html>
`);
}
function fillDefaults(obj, defaults) {
for(var key in defaults) {
if(obj[key] === undefined)
obj[key] = defaults[key];
}
return obj;
}
function message(res, code, ...args) {
const response = messages[code].apply(message, args);
res.writeHead(response.http_code, { 'Content-Type': 'application/json' });
res.end(response.toString());
}
/*
* This is the internal streamWebcam function, the returned promise resolves to
* the spawned process
*/
function streamWebcam(webcam, {
command = defaultEncoder.command,
flags = defaultEncoder.flags,
isSuccessful = defaultEncoder.isSuccessful
} = {}) {
const encoderFlags = flags(webcam).split(' ');
const videoEncoder = spawn(command, encoderFlags);
return new Promise((accept, reject) => {
/* Called when is determined if the encoder has succeeded */
function resolveSucess(hasSucceeded) {
if(hasSucceeded === true) accept(videoEncoder);
else reject(hasSucceeded);
}
isSuccessful(videoEncoder, resolveSucess);
});
}
exports.streamWebcam = (encoder) =>
streamWebcam(encoder).then((encoderProcess) => encoderProcess.stdout);
const createHTTPStreamingServer = exports.createHTTPStreamingServer = ({
permittedWebcams,
isValidWebcam = isValidWebcamDefault,
webcamEndpoint = '/webcam',
additionalEndpoints = {},
encoder = defaultEncoder
} = {}) => {
additionalEndpoints[webcamEndpoint] = (req, res, reqUrl) => {
const webcam = reqUrl.query.webcam;
isValidWebcam(webcam).then(
() => streamWebcam(webcam, encoder).then(
(encoderProcess) => {
const video = encoderProcess.stdout;
res.writeHead(200, { 'Content-Type': encoder.mimeType });
video.pipe(res);
res.on('close', () => encoderProcess.kill('SIGTERM'));
/* Sometimes the client disconnects but the encoder keeps running :\ */
res.connection.on('close', () => encoderProcess.kill('SIGTERM'));
}, () => message(res, 'webcam_in_use', webcam)),
() => message(res, 'invalid_webcam', webcam));
};
additionalEndpoints.default = additionalEndpoints.default || defaultPage;
fillDefaults(encoder, defaultEncoder);
if(permittedWebcams) {
isValidWebcam = isValidWebcamWhitelist(permittedWebcams);
}
const server = http((req, res) => {
const reqUrl = parseUrl(req.url, true);
const processRequest = additionalEndpoints[reqUrl.pathname] || additionalEndpoints.default;
processRequest(req, res, reqUrl);
});
return server;
};