JSONStream
streaming JSON.parse and stringify
install
npm install JSONStream
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.
If you want to have keys emitted, you can prefix your * operator with $: obj.$* - in this case the data passed to the stream is an object with a key holding the key and a value property holding the data.
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);
});
//emits anything from _before_ the first match
stream.on('header', function (data) {
console.log('header:', data) // => {"total_rows":129,"offset":0}
})
awesome!
In case you wanted the contents the doc emitted:
var stream = JSONStream.parse(['rows', true, 'doc', {emitKey: true}]) //rows, ANYTHING, doc, items in docs with keys
stream.on('data', function(data) {
console.log('key:', data.key);
console.log('value:', data.value);
});
You can also emit the path:
var stream = JSONStream.parse(['rows', true, 'doc', {emitPath: true}]) //rows, ANYTHING, doc, items in docs with keys
stream.on('data', function(data) {
console.log('path:', data.path);
console.log('value:', data.value);
});
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 also emits 'header' and 'footer' events,
the 'header' event contains anything in the output that was before
the first match, and the 'footer', is anything after the last match.
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
numbers will be emitted as numbers.
huge numbers that cannot be represented in memory as javascript numbers will be emitted as strings.
cf https://github.com/creationix/jsonparse/commit/044b268f01c4b8f97fb936fc85d3bcfba179e5bb for details.
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