@eyevinn/srt is a Node.js Native Addon that provides bindings to Secure Reliable Transport SDK.
npm install --save @eyevinn/srt
Installing from NPM downloads and builds SRT SDK and NodeJS addon for your operating system × architecture.
Please refer to build instructions for your OS of the SRT project.
This is providing a NodeJS binding layer that at its build-time assumes that plain libSRT already can be built on your system.
We will merely pull in an SRT codebase from a GIT repo here (that may be local or remote), and attempt to compile it (using the specific toolchain and commands invoked for each OS). See scripts/build-srt-sdk.js. Then linking the result of it into the compiled NodeJS add-on we provide here via the Gyp tool.
Everything we need on the NodeJS side of things (N-API, Gyp) gets installed via NPM, as you install this package.
However, it is not provided with this any dependencies of building libSRT itself (we only try to invoke the toolchain correctly, whichever it is, on your OS).
As you install all of the prerequisites, or even build the library already in your environment, this package should work also likewise.
For Windows it is a little different: We invoke vcpkg to fetch and build all of the dependencies (and therefore assume this to be already installed).
We therefore refer to build instructions of SRT for all steps prior to invoking vcpkg that need to be performed here likewise: https://github.com/Haivision/srt/blob/master/docs/build-win.md#2-preparing-dependencies
const { SRT } = require('@eyevinn/srt');
const srt = new SRT();
const socket = srt.createSocket();
srt.bind(socket, "0.0.0.0", 1234);
srt.listen(socket, 2);
const fd = srt.accept(socket);
if (fd) {
const chunk = srt.read(fd, 1316);
}
class SRT {
createSocket(sender?:Boolean): socket:Number
bind(socket:Number, address:String, port:Number): result:Number
listen(socket:Number, backlog:Number): result:Number
connect(socket:Number, host:String, port:Number): result:Number
accept(socket:Number): fileDescriptor:Number
close(socket:Number): result:Number
read(socket:Number, chunkSize:Number): chunk:Buffer
write(socket:Number, chunk:Buffer): result:Number
setSockOpt(socket:Number, option:Number, value): result:Number
getSockOpt(socket:Number, option:Number): value
getSockState(socket:Number): value:Number
epollCreate(): epid:Number
epollAddUsock(epid:Number, socket:Number, events:Number): result:Number
epollUWait(epid:Number, msTimeOut:Number): events:Array
stats(socket:Number, clear:Boolean): stats:SRTStats
}
The N-API binding layer to the SRT SDK is such that every native call are blocking I/O and runs synchroneuosly with the wrapping JS function call. This means that these functions are called from the Node.js proc main-thread / event loop. This creates a throughput limit and in general having blocking operations can impact application performance in an unpredictable way. To address this issue we have an "async variant" of the API where the native blocking calls are put on a JS Worker thread instead (big thanks to @tchakabam for this contribution). The Async API is a candidate to replace the main API in the next major release. Example with async/await:
const { SRT, AsyncSRT } = require('@eyevinn/srt');
(async function() {
const asyncSrt = new AsyncSRT();
const socket = await asyncSrt.createSocket(false);
let result = await asyncSrt.bind(socket, "0.0.0.0", 1234);
result = await asyncSrt.listen(socket, 2);
})();
or with promises:
const { SRT, AsyncSRT } = require('@eyevinn/srt');
const asyncSrt = new AsyncSRT();
let mySocket;
asyncSrt.createSocket(false)
.catch((err) => console.error(err))
.then((result) => {
mySocket = result;
return result;
})
.then((socket) => asyncSrt.bind(socket, "0.0.0.0", 1234))
.then((result) => {
if (result !== 0) {
throw new Error('Failed bind');
}
return asyncSrt.listen(mySocket, 2);
})
.then((result) => {
if (!result) {
console.log("Listen success");
} else {
throw new Error('SRT listen error: ' + result);
}
});
In order to perform on certain use-cases where larger chunks of data split into packets
would need to be sent/received in bursts, we provide "modes" and a high-level class called AsyncReaderWriter, which can be initialized an existing AsyncSRT instance, i.e a worker thread, and a given SRT socket identifier. It therefore allows to plug-into any concept of a
connection on either side. A client connection instance can therefore just be a socket created
with a successful connection state via the SRT API, and then using the reader-writer for
any sort of transmission upon it.
Also, we provide a class to allow building a server that can accept multiple incoming connections(SRTServer and its friend SRTConnection). The latter server-side connection object has the method SRTConnection#getReaderWriter() to allow using the reader-writer
in order to communicate with the respective client.
The best example to see all this in action at once is taking a look at the respective integration test(s).
These components also all have JSdoc annotations that should help with their usage.
A custom readable stream API is also available, example (in listener mode):
const fs = require('fs');
const dest = fs.createWriteStream('./output');
const { SRTReadStream } = require('@eyevinn/srt');
const srt = new SRTReadStream('0.0.0.0', 1234);
srt.listen(readStream => {
readStream.pipe(dest);
});
of in caller mode:
const srt = new SRTReadStream('127.0.0.1', 1234);
srt.connect(readStream => {
readStream.pipe(dest);
});
Example of a writable stream
const fs = require('fs');
const source = fs.createReadStream('./input');
const { SRTWriteStream } = require('@eyevinn/srt');
const srt = new SRTWriteStream('127.0.0.1', 1234);
srt.connect(writeStream => {
source.pipe(writeStream);
});
On macOS 10.15 (but not on prior versions), if your OpenSSL system install points to the one from the XCode SDK (which is usually the case), you will encounter:
ld: cannot link directly with dylib/framework, your binary is not an allowed client of /usr/lib/libcrypto.dylib for architecture x86_64
Step 1) Install/Upgrade to latest OpenSSL: brew install openssl or brew upgrade openssl if already installed (or install any free-speech OpenSSL distro to your system somehow, using Homebrew here is an example).
Step 2) Set in your environment: export PKG_CONFIG_PATH="/usr/local/opt/openssl/lib/pkgconfig". Adapt the path should it differ on your setup where your free-speech OpenSSL is installed.
This is due to novel Apple policy for the usage of some of the developer libraries. You can therefore not use these libraries to link with this build.
It is likely you have already an actual free distribution of OpenSSL installed, for example via Homebrew. Still in this case you may encounter this issue with v1.1, while with v1.0 (until a certain patch) it seems that the linkage performed by brew install actually prevails the one of the Apple binaries here. However, with v1.1, this is not the case anymore.
Fixing this dependency by downgrading to an older implememtation is for obvious security concerns not recommendable.
Our recommended fix here will simply have the SRT build system be pointed to where your non-Apple OpenSSL install lives, and use that.
In addition to contributing code, you can help to triage issues. This can include reproducing bug reports, or asking for vital information such as version numbers or reproduction instructions.
Copyright 2020 Eyevinn Technology
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