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https://github.com/lennartcl/jsonm

json compressor for packing messages with memoization
https://github.com/lennartcl/jsonm

compression javascript json jsonm memoization nodejs websocket

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json compressor for packing messages with memoization

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README 

        
jsonm

=====



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



jsonm is a fast and safe way to compress JSON messages using memoization.

jsonm makes messages up to several orders of magnitude smaller by getting rid

of repeated names and values.



jsonm is best friends with **websocket** libraries like [socket.io](http://socket.io/).

Modern browsers can **gzip** messages sent over websockets, and jsonm can make them

even smaller for maximum responsiveness of web applications.



## Installation



```

$ npm install --save jsonm

```



In the client, jsonm works well with webpack or browserify.

Our npm distribution also includes a prepackaged client-side version in build/jsonm.js.



## Compression Examples



jsonm packs



```

[

    { "firstName": "Francis", "lastName": "Doe", "address": "Callison Lane 2775, Wilmington" },

    { "firstName": "Anna", "lastName": "Smith", "address": "Callison Lane 2775, Wilmington" },

    { "firstName": "Agent", "lastName": "Smith", "address": "Callison Lane 2775, Wilmington", "isAlias": true },

    { "firstName": "Anna", "lastName": "Francis", "address": "Callison Lane 2776, Wilmington" }

]

```



into 



```

[0,

    ["firstName", "lastName", "address", "Francis", "Doe", "Callison Lane 2775, Wilmington"],

    [3, 4, 5, "Anna", "Smith", 8],

    [3, 4, 5, "isAlias", "Agent", 10, 8, true],

    [3, 4, 5, 9, 6, "Callison Lane 2776, Wilmington"]

]

```



Notice how it eliminates all common substrings like `"firstName"` using memoization!

jsonm keeps a dictionary to compress future messages even further. 

Send the original message above a second time, and it becomes:



```

[0,[3,4,5,6,7,8],[3,4,5,9,10,8],[3,4,5,11,12,10,8,13],[3,4,5,9,6,14]]

```



Now let's consider a different message:



```

[

    { "firstName": "Bryan", "lastName": "Fuller" },

    { "firstName": "Anna", "lastName": "Adams" },

    { "firstName": "Tim", "lastName": "Peterson" },

    { "firstName": "Francis", "lastName": "Peterson" }

]

```



this becomes



```

[0,[3,4,"Bryan","Fuller"],[3,4,9,"Adams"],[3,4,"Tim","Peterson"],[3,4,6,23]]

```



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.



## 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:_



```

const packer = new jsonm.Packer();

let packedMessage = packer.pack(message);

```



_Receiver, unpacking a message:_



```

const unpacker = new jsonm.Unpacker();

let message = unpacker.unpack(packedMessage);

```



Both the packer and unpacker maintain a stateful dictionary. Don't lose them!

Create a new packer for each new connection, or use `packer.reset()` to

reset the dictionary of an existing packer.



### 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:



```

let 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:



```

let 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: https://github.com/dogada/RJSON



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]

```



JSONC, JSONH, 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.



# License



MIT