JSONStream

streaming JSON.parse and stringify

example

 
var request = require('request')
  , JSONStream = require('JSONStream')
  , es = require('event-stream')
 
request({url: 'http://isaacs.couchone.com/registry/_all_docs'})
  .pipe(JSONStream.parse('rows.*'))
  .pipe(es.mapSync(function (data) {
    console.error(data)
    return data
  }))

JSONStream.parse(path)

parse stream of values that match a path

  JSONStream.parse('rows.*.doc')

The .. operator is the recursive descent operator from JSONPath, which will match a child at any depth (see examples below).

If your keys have keys that include . or * etc, use an array instead. ['row', true, /^doc/].

If you use an array, RegExps, booleans, and/or functions. The .. operator is also available in array representation, using {recurse: true}. any object that matches the path will be emitted as 'data' (and piped down stream)

If path is empty or null, no 'data' events are emitted.

Examples

query a couchdb view:

curl -sS localhost:5984/tests/_all_docs&include_docs=true

you will get something like this:

{"total_rows":129,"offset":0,"rows":[
  { "id":"change1_0.6995461115147918"
  , "key":"change1_0.6995461115147918"
  , "value":{"rev":"1-e240bae28c7bb3667f02760f6398d508"}
  , "doc":{
      "_id":  "change1_0.6995461115147918"
    , "_rev": "1-e240bae28c7bb3667f02760f6398d508","hello":1}
  },
  { "id":"change2_0.6995461115147918"
  , "key":"change2_0.6995461115147918"
  , "value":{"rev":"1-13677d36b98c0c075145bb8975105153"}
  , "doc":{
      "_id":"change2_0.6995461115147918"
    , "_rev":"1-13677d36b98c0c075145bb8975105153"
    , "hello":2
    }
  },
]}
 

we are probably most interested in the rows.*.doc

create a Stream that parses the documents from the feed like this:

var stream = JSONStream.parse(['rows', true, 'doc']) //rows, ANYTHING, doc 
 
stream.on('data', function(data) {
  console.log('received:', data);
});

awesome!

recursive patterns (..)

JSONStream.parse('docs..value') (or JSONStream.parse(['docs', {recurse: true}, 'value']) using an array) will emit every value object that is a child, grand-child, etc. of the docs object. In this example, it will match exactly 5 times at various depth levels, emitting 0, 1, 2, 3 and 4 as results.

{
  "total": 5,
  "docs": [
    {
      "key": {
        "value": 0,
        "some": "property"
      }
    },
    {"value": 1},
    {"value": 2},
    {"blbl": [{}, {"a":0, "b":1, "value":3}, 10]},
    {"value": 4}
  ]
}

JSONStream.parse(pattern, map)

provide a function that can be used to map or filter the json output. map is passed the value at that node of the pattern, if map return non-nullish (anything but null or undefined) that value will be emitted in the stream. If it returns a nullish value, nothing will be emitted.

JSONStream.stringify(open, sep, close)

Create a writable stream.

you may pass in custom open, close, and seperator strings. But, by default, JSONStream.stringify() will create an array, (with default options open='[\n', sep='\n,\n', close='\n]\n')

If you call JSONStream.stringify(false) the elements will only be seperated by a newline.

If you only write one item this will be valid JSON.

If you write many items, you can use a RegExp to split it into valid chunks.

JSONStream.stringifyObject(open, sep, close)

Very much like JSONStream.stringify, but creates a writable stream for objects instead of arrays.

Accordingly, open='{\n', sep='\n,\n', close='\n}\n'.

When you .write() to the stream you must supply an array with [ key, data ] as the first argument.

unix tool

query npm to see all the modules that browserify has ever depended on.

curl https://registry.npmjs.org/browserify | JSONStream 'versions.*.dependencies'

numbers

There are occasional problems parsing and unparsing very precise numbers.

I have opened an issue here:

https://github.com/creationix/jsonparse/issues/2

+1

Acknowlegements

this module depends on https://github.com/creationix/jsonparse by Tim Caswell and also thanks to Florent Jaby for teaching me about parsing with: https://github.com/Floby/node-json-streams

license

Dual-licensed under the MIT License or the Apache License, version 2.0