transform-expected v0.1.1

Transform-Expected

Apply a stream transformation to objects or buffers that meet some expectation and pass objects that do not meet that expectation unchanged.

Note: I have only used this for streams with objectMode set to true and the expectation functions are currently geared for that particular use-case.

Installation

Node.js

For Node.js, use npm:

npm install transform-expected

..then require Transform-Expected:

var TransformExpected = require('transform-expected');

API

Transform-Expected is a simple extension of node's built in stream.Transform interface.

new TransformExpected(options)

• options Object passed along to the internal stream.Transform constructor.

• expectation Function Returns true if the current object or buffer is "expected".

Options can be omitted and the expected function can be passed in as the first argument. If both are omitted, then a general "expect everything" function is used so that this will act exactly like a regular stream.Transform object.

transformExpected._expected(chunk, encoding, callback)

• chunk Buffer | String The chunk to be transformed. Will always be a buffer unless the decodeStrings option was set to false.

• encoding String If the chunk is a string, then this is the encoding type. (Ignore if decodeStrings chunk is a buffer.)

• callback Function Call this function (optionally with an error argument) when you are done processing the supplied chunk.

Note: This function MUST NOT be called directly. It should be implemented by child classes, and called by the internal Transform-Expected class methods only.

transformExpected._unexpected(chunk, encoding, callback)

• chunk Buffer | String The chunk to be transformed. Will always be a buffer unless the decodeStrings option was set to false.

• encoding String If the chunk is a string, then this is the encoding type. (Ignore if decodeStrings chunk is a buffer.)

• callback Function Call this function (optionally with an error argument) when you are done processing the supplied chunk.

Note: This function MUST NOT be called directly. It should be implemented by child classes, and called by the internal Transform-Expected class methods only.

Transform.expectProperty(propertyName)

• propertyName String Returns an expectation function that returns true if propertyName was found inside of the current stream.

Transform.expectTypeOf(typeOf)

• typeOf String Returns an expectation function that returns true if the stream is of type typeOf.

Quick Example

var myTransform = new TransformExpected({ objectMode: true }, TransformExpected.expectTypeOf("string"));

myTransform._expected = function(str, encoding, done) {
    this.push(str.toUpperCase());
    done();
};

myTransform.write({val: "testing"});
myTransform.write("testing");
myTransform.write([1, 2, 3]);

Assuming you had myTransformpiped into another stream, that stream would receive:

{val:"testing"}
"TESTING"
[1, 2, 3]