sse-transform

A transform stream for converting JavaScript objects or JSON streams into Server-Sent Events. Only known fields (including comments) are processed and all other fields are ignored.

Default Mode

In default mode JSON objects are delimited using CrLf (\r\n). Each encountered JSON object is parsed and transformed into SSE format. If a JSON object isn't able to be parsed an error event is emitted on the stream and no transform is performed.

Basic Usage

'use strict';
 
var sse = require('sse-transform');
var through = require('through2');
 
 
var xform = sse();
 
xform.pipe(through(function (chunk, encoding, done) {
    console.log(chunk.toString('utf8'));
    done();
}));
 
xform.write('{"data":"foo"}\r\n');
xform.write('{"id":123,"data":"abc"}\r\n');
xform.write('{"event":"myevent","data":"foo\\nbar"}\r\n');
xform.write('{"event":"myevent2","data":"moo\\nmar"}\r\n');
xform.end();

Output

data:foo
 
 
id:123
data:abc
 
 
event:myevent
data:foo
data:bar
 
 
event:myevent2
data:moo
data:mar
 
 

Object Mode

In object mode each field processed such that if it is a string, newline delimiting rules are applied and each newline results in a new field entry (see data fields below). If a non-string-literal is encountered, the value is JSON.stringified during transform.

Basic Usage

'use strict';
 
var sse = require('sse-transform');
var through = require('through2');
 
 
var xform = sse({ objectMode: true });
 
xform.pipe(through(function (chunk, encoding, done) {
    console.log(chunk.toString('utf8'));
    done();
}));
 
xform.write({ data: 'foo'});
xform.write({ id:123, data: 'abc' });
xform.write({ event: 'myevent', data: 'foo\nbar' });
xform.write({ event: 'myevent2', data: 'moo\nmar' });
xform.write({ event: 'myevent', data: { foo: true, bar: 123, baz: 'foo\nbar' }});
xform.end();

Output

data:foo
 
 
id:123
data:abc
 
 
event:myevent
data:foo
data:bar
 
 
event:myevent2
data:moo
data:mar
 
 
event:myevent
data:{"foo":true,"bar":123,"baz":"foo\nbar"}
 
 

Fields

The JSON or JavaScript object written to the stream can contain any properties, but only the following will be consumed by sse-transform, any other being ignored.

• event - An event can contain any character besides carriage return or line feed. If the value contains a carriage return or line feed, the value is split on that character and the first segment used as the value.

• data - The data field can include any string, including strings with carriage returns and/or line feeds. If the string contains newline characters, the string is split and multiple data fields are written per the SSE specification.

• id - An id can contain any character besides carriage return or line feed. If the value contains a carriage return or line feed, the value is split on that character and the first segment used as the value.

• retry - Per the Mozilla docs: "The reconnection time to use when attempting to send the event. This must be an integer, specifying the reconnection time in milliseconds. If a non-integer value is specified, the field is ignored."

• $comment - Setting this property to include a comment in the event (any line starting with :). Comments can be used for keep-alives, etc.