1.3.0 • Public • Published

    XDR, for Javascript

    Read/write XDR encoded data structures (RFC 4506)

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    XDR is an open data format, specified in RFC 4506. This library provides a way to read and write XDR data from javascript. It can read/write all of the primitive XDR types and also provides facilities to define readers for the compound XDR types (enums, structs and unions)


    via npm:

    npm install --save js-xdr


    You can find some examples here.

    First, let's import the library:

    var xdr = require('js-xdr');

    Now, let's look at how to decode some primitive types:

    // booleans
    xdr.Bool.fromXDR([0, 0, 0, 0]); // returns false
    xdr.Bool.fromXDR([0, 0, 0, 1]); // returns true
    // the inverse of `fromXDR` is `toXDR`, which returns a Buffer
    xdr.Bool.toXDR(true); // returns Buffer.from([0,0,0,1])
    // XDR ints and unsigned ints can be safely represented as
    // a javascript number
    xdr.Int.fromXDR([0xff, 0xff, 0xff, 0xff]); // returns -1
    xdr.UnsignedInt.fromXDR([0xff, 0xff, 0xff, 0xff]); // returns 4294967295
    // XDR Hypers, however, cannot be safely represented in the 53-bits
    // of precision we get with javascript numbers, and so we have a custom class
    // for those numbers.  Hyper and UnsignedHyper both use
    //https://www.npmjs.com/package/long to represent the 64-bit numbers
    var result = xdr.Hyper.fromXDR([0, 0, 0, 0, 0, 0, 0, 0]); // returns an instance of xdr.Hyper
    // convert the hyper to a string
    result.toString(); // return '0'
    // math!
    var ten = result.add(10);
    var minusone = result.subtract(1);
    // construct a number from a string
    var big = xdr.Hyper.fromString('1099511627776');
    // encode the hyper back into xdr
    big.toXDR(); // <Buffer 00 00 01 00 00 00 00 00>


    There are a couple of caveats to be aware of with this library:

    1. We do not support quadruple precision floating point values. Attempting to read or write these values will throw errors.
    2. NaN is not handled perfectly for floats and doubles. There are several forms of NaN as defined by IEEE754 and the browser polyfill for node's Buffer class seems to handle them poorly.

    Code generation

    js-xdr by itself does not have any ability to parse XDR IDL files and produce a parser for your custom data types. Instead, that is the responsibility of xdrgen. xdrgen will take your .x files and produce a javascript file that target this library to allow for your own custom types.

    See js-stellar-base for an example (check out the src/generated directory)


    Please see CONTRIBUTING.md for details.

    To develop and test js-xdr itself

    1. Clone the repo
    git clone https://github.com/stellar/js-xdr.git
    1. Install dependencies inside js-xdr folder
    cd js-xdr
    npm install
    1. Install Node 6.14.0

    Because we support earlier versions of Node, please install and develop on Node 6.14.0 so you don't get surprised when your code works locally but breaks in CI.

    Here's out to install nvm if you haven't: https://github.com/creationix/nvm

    nvm install
    # if you've never installed 6.14.0 before you'll want to re-install yarn
    npm install -g yarn

    If you work on several projects that use different Node versions, you might it helpful to install this automatic version manager: https://github.com/wbyoung/avn

    4. Observe the project's code style
    While you're making changes, make sure to run the linter-watcher to catch any
       linting errors (in addition to making sure your text editor supports ESLint)
    node_modules/.bin/gulp watch

    If you're working on a file not in src, limit your code to Node 6.16 ES! See what's supported here: https://node.green/ (The reason is that our npm library must support earlier versions of Node, so the tests need to run on those versions.)




    npm i js-xdr

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