jsonm

jsonm

"Listen very carefully, I shall say 'zis only once!"

jsonm is a performant, safe way to compress JSON messages, in similar vein to jsonc and jsonh. jsonm makes messages up to several orders of magnitude smaller by getting rid of repeated names and values.

jsonm is best friends with libraries like socket.io that maintain a persistent connection between a client and a server. Modern browsers can gzip messages sent over websockets, and jsonm can make them even smaller for maximum responsiveness of web applications.

Examples

jsonm packs

[
    { "firstName": "Francis", "lastName": "Doe" },
    { "firstName": "Anna", "lastName": "Smith" },
    { "firstName": "Agent", "lastName": "Smith", "isAlias": true },
    { "firstName": "Anna", "lastName": "Francis" }
]

into

[ 0,
    ["firstName", "lastName", "Francis", "Doe"],
    [3, 4, "Anna", "Smith"],
    [3, 4, "isAlias", "Agent", 8, true],
    [3, 4, 7, 5]
]

Note how common substrings like "firstName", "lastName", and "John" are not repeated but replaced by a dictionary index. jsonm also represents objects using arrays to avoid quotation signs in pure JSON (e.g., {"3":"Anna"})

The dictionary is built up on the fly and re-used for future messages sent. When sending the same message again it'll be even smaller:

[0,[3,4,5,6],[3,4,7,8],[3,4,9,10,8,11],[3,4,7,5],1]

Messages coming later also benefit from the dictionary:

[
    { "firstName": "Bryan", "lastName": "Fuller" },
    { "firstName": "Anna", "lastName": "Adams" },
    { "firstName": "Tim", "lastName": "Peterson" },
    { "firstName": "Francis", "lastName": "Peterson" }
]

becomes

[0,[3,4,"Bryan","Fuller"],[3,4,7,"Adams"],[3,4,"Tim","Peterson"],[3,4,5,16]]

By avoiding repetition, jsonm can for example help decrease the size of messages sent from a web server to the client. It effectively leaves out all information the client already knows about.

Installation

$ npm install --save jsonm

Usage

jsonm is designed for sending messages between a sender and a receiver. The sender packs messages and the receiver unpacks them.

Sender, packing a message:

var packer = new jsonm.Packer();
var packed = packer.pack(message);

Receiver, unpacking a message:

var unpacker = new jsonm.Unpacker();
unpacker.unpack(packed); // returns message

Note that both the packer and unpacker maintain a stateful dictionary. Don't lose them! But when the connection ends just start over with a new packer and unpacker.

Working with Strings

jsonm provides packString() for dealing with messages in string form.

packString() can be used to efficiently pack multi-line strings. For example, a string "foo\nbar" is packed as if ["foo", "bar"] was packed:

var packed = packer.packString("foo\nbar");
unpacker.unpack(packed); // returns "foo\nbar"

packString() can also efficiently pack JSON objects in string format, internally parsing and stringifying them:

var packed = packer.packString('{"foo":"bar"}');
unpacker.unpack(packed); // returns '{"foo":"bar"}'

Related Projects

• JSONC: https://github.com/tcorral/JSONC
• JSONH: https://github.com/WebReflection/JSONH
• JSONR: http://www.cliws.com/e/06pogA9VwXylo_GknPEeFA/

These projects pack uniform JavaScript objects, eliminating the need for repeating the keys of each object. As an example, JSONH can pack

[
    { "firstName": "John", "lastName": "Doe", "isAlias": false },
    { "firstName": "Anna", "lastName": "Smith", "isAlias": false },
    { "firstName": "Agent", "lastName": "Smith", "isAlias": true }
]

into

[3,"firstName","lastName","isAlias","John","Doe",false,"Anna","Smith",false,"Agent","Smith",true]

JSONH, JSONM, and JSONR don't apply memoization and only help with uniform data or data with a recurring scheme. Unlike jsom, however, they are stateless, which can make it easier to use them in some cases.