stream-log-playback

A simple library that reproduces a data stream for development purposes, while respecting order and time separation between events

The library providers both recorder and playback functions

The recorder StreamLogRecorder is an implementation of pass-throught Writablestream can be wired either in a pipeline e.g.

const {StreamLogRecorder} = require('stream-log-playback');

const streamRecorder = StreamLogRecorder.createInterface({
	fileName : 'stream.log'
	});

someOtherStream.pipe(streamRecorder).pipe(process.stdout);

or data can be pushed using write function.

const {StreamLogRecorder} = require('stream-log-playback');

const streamRecorder = StreamLogRecorder.createInterface({
	fileName : 'stream.log'
	});
  
streamRecorder.write(JSON.strigify({data:1}));
streamRecorder.write(JSON.strigify({data:2}));

streamRecorder.end();

StreamLogRecorder.createInterface(options)

Create a recorder

options object properties

property | Description ---------------|------------ fileName | name of file containing the log to read flags | usual createFileStream flags. Default value is 'w' create, but if set 'a' it will ammend on existing file new entries autoclose. | usual createFileStream option. Default is true.

In either case the recorder will persist the data to a file called stream.log, and the pass the original data to next stage of the pipeline.

The generated format is as following

{	"dt": 151.321274,	"rawJson": "{\"key\":2500178}"}
{	"dt": 20.483183,	"rawJson": "{\"key\":2500356}"}

Each line represents an event with the properties

property name | description -------------- | ------------ dt | the time in msec the event was generated from the previous event rawJson | event details

So in the above example the first line says , wait for 151 msec before creating the first event.The second line for says wait for 20 msec.

The reader is an implementation of a Tranform and can be used either as

const {StreamLogReader} = require('stream-log-playback');

const reader = StreamLogReader.createInterface({
  fileName:'stream.log'
  });

reader.on('data',(lineEntry)=>{
  console.log(line.toString());
});

or wired in a pipeline

const {StreamLogReader} = require('stream-log-playback');

const reader =  StreamLogReader.createInterface({
  fileName:'stream.log'
  });

reader.pipe(someOtherStream);

StreamLogReader.createInterface(options)

Create a reader

• StreamLogReader

options object proerties

property | Description ---------------|------------ fileName | name of file containing the log to read timeResolution | don't wait if dt < timeResolution e.g. if timeResolution is 10 then the second event in the previous exmple will fire immediately. maxWait | if dt>maxWait then wait for maxWait e.g. is maxWait is 100 then in the above example the first event will fire after 100 msec.