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 jsonh and jsonc. jsonm makes messages up to several orders of magnitude smaller by getting rid of repeated names and values.

Examples

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

becomes

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

Note how common substrings "firstName", "lastName", and "John" are not repeated but replaced by a dictionary index.

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:

[1,[3,4,5,6],[3,4,7,8],[3,4,9,8]]

Other messages that come after that also benefit from the dictionary:

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

becomes

[2,[3,4,"Bryan","Fuller"],[3,4,5,"Adams"],[3,4,"Tim","Peterson"]]

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(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.

Related Projects

• JSONH: https://github.com/WebReflection/JSONH
• JSONC: https://github.com/tcorral/JSONC

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