tn3270 is a pure TypeScript implementation of the Telnet protocol necessary to negotiate a connection from a software 3270 emulator and a host that accepts 3270 connections.
I use tn3270 as the basis for my own 3270 emulator EL-3270. I factored out the connection code to better expose it for others to use in their own emulators. I hope that it also exposes the protocol in an easy to understand way.
These two documents explain the protocol exhaustively.
I also found this summary of Telnet commands by Dave Marshall very helpful.
npm install --save tn3270
tn3270 negotiates a session with the host and if successful returns an Observable stream of data from the host to the emulator. A write API supports data transfer from the emulator back to the host.
All the other complex details of the 3270 data stream are delegated to the emulator, of which EL-3270 is a good example.
Because the API surface is so small, I've reproduced it here in full.
import { Observable } from 'rxjs/Observable';
export declare class Tn3270 {
host: string;
port: number;
model: string;
stream$: Observable<Buffer>;
constructor(host: string, port: number, model: string);
write(bytes: any): void;
}
writeaccepts either an array of bytes or a Node.jsBuffer.
Here's how I use tn3270 in my Electron 3270 emulator.
import { Tn3270 } from 'tn3270';
ipcMain.on('connect', (event: any,
host: string,
port: number,
model: string) => {
theTn3270 = new Tn3270(host, port, model);
theConnection = theTn3270.stream$.subscribe({
next: (data: Buffer) => {
const view = new Uint8Array(data.length);
for (let i = 0; i < data.length; i++)
view[i] = data[i];
theWindow.webContents.send('data', view);
},
error: (error: Error) => theWindow.webContents.send('error', error.message),
complete: () => theWindow.webContents.send('disconnected')
});
});Many thanks to Ricardo Bánffy for his 3270 Font, republished here for convenience. I actually grabbed the TTF versions from the S3 bucket https://s3.amazonaws.com/3270font/3270_fonts_4cfe95c.zip that Ricardo references.
The 3270 font can be included in your app simply via the fonts/3270.css file. Here's how I use it in my Angular CLI projects, just like any other font in angular.json.
"styles": [
"node_modules/roboto-fontface/css/roboto/roboto-fontface.css",
"node_modules/tn3270/fonts/3270.css"
],