Filtering streams.
streamfilter
is a function based filter for streams inspired per gulp-filter
but no limited to Gulp nor to objectMode streams.
First, install streamfilter
in your project:
npm install --save streamfilter
There are 3 common usages:
import FilterStream from 'streamfilter';
const filter = new FilterStream((chunk, encoding, cb) => {
const mustBeFiltered = chunk.length() > 128;
if(mustBeFiltered) {
cb(true);
return;
}
cb(false);
});
// Print to stdout a filtered stdin
process.stdin
.pipe(filter)
.pipe(process.stdout);
import FilterStream from 'streamfilter';
const filter = new FilterStream((chunk, encoding, cb) => {
const mustBeFiltered = chunk.length() > 128;
if(mustBeFiltered) {
cb(true);
return;
}
cb(false);
}, {
restore: true
});
// Print accepted chunks in stdout
filter.pipe(process.stdout);
// Print filtered one to stderr
filter.restore.pipe(process.stderr);
Let's reach total hype!
import FilterStream from 'streamfilter';
import { Transform } from 'stream';
// Filter values
const filter = new FilterStream((chunk, encoding, cb) => {
const mustBeFiltered = chunk.length() > 128;
if(mustBeFiltered) {
cb(true);
return;
}
cb(false);
}, {
restore: true,
passthrough: true
});
// Uppercase strings
const mySuperTransformStream = new Transform({
transform: (chunk, encoding, cb) => cb(
null,
Buffer.from(
chunk.toString(encoding).toUpperCase(),
encoding,
),
),
});
// Pipe stdin
process.stdin.pipe(filter)
// Edit kept chunks
.pipe(mySuperTransformStream)
// Restore filtered chunks
.pipe(filter.restore)
// and output!
.pipe(process.stdout)
Note that in this case, this is your responsibility to end the restore stream by piping in another stream or ending him manually.
Filter piped in streams according to the given filterCallback
that takes the
following arguments: chunk
the actual chunk, encoding
the chunk encoding,
filterResultCallbackthe function to call as the result of the filtering process with
truein argument to filter her or
false` otherwise.
Options are passed in as is in the various stream instances spawned by this
module. So, to use the objectMode, simply pass in the options.objectMode
value set to true
.
Kind: global function
Returns: Stream
- The filtering stream
Param | Type | Description |
---|---|---|
filterCallback | function |
Callback applying the filters |
options | Object |
Filtering options |
options.passthrough | boolean |
Set to true , this option change the restore stream nature from a readable stream to a passthrough one, allowing you to reuse the filtered chunks in an existing pipeline. |
options.restore | boolean |
Set to true , this option create a readable stream allowing you to use the filtered chunks elsewhere. The restore stream is exposed in the FilterStream instance as a restore named property. |