JSON Machine

This README.md is in sync with this branch, not the lastest version. For specific version see its commited README.md.

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TL;DR;

JSON Machine is efficient drop-in replacement for inefficient iteration of big JSONs files or streams for PHP 5.6+:

<?php

// this often causes Allowed Memory Size Exhausted
- $users = json_decode(file_get_contents('500MB-users.json'));
// this takes few kB of memory no matter the file size
+ $users = \JsonMachine\JsonMachine::fromFile('500MB-users.json');

foreach ($users as $id => $user) {
    // just process $user as usual
}

Random access like $users[42] or counting results like count($users) is not possible by design. Use above-mentioned foreach and find the item or count the collection there.

Requires ext-json if used out of the box. See custom decoder.

Introduction

JSON Machine is an efficient, easy-to-use and fast JSON stream parser based on generators developed for unpredictably long JSON streams or documents. Main features are:

• Constant memory footprint for unpredictably large JSON documents.
• Ease of use. Just iterate JSON of any size with foreach. No events and callbacks.
• Efficient iteration on any subtree of the document, specified by Json Pointer
• Speed. Performace critical code contains no unnecessary function calls, no regular expressions and uses native json_decode to decode JSON document chunks by default. See custom decoder.

Parsing JSON documents

Simple document

Let's say that big.json contains this really big JSON document:

// big.json
{
    "apple": {
        "color": "red"
    },
    "pear": {
        "color": "yellow"
    }
}

It can be parsed this way:

<?php

$jsonStream = \JsonMachine\JsonMachine::fromFile('big.json');

foreach ($jsonStream as $name => $data) {
    // 1st iteration: $name === "apple" and $data === ["color" => "red"]
    // 2nd iteration: $name === "pear" and $data === ["color" => "yellow"]
}

Parsing a json array instead of a json object follows the same logic. The key in a foreach will be a numeric index of an item.

If you prefered JSON Machine to return objects instead of arrays, wrap JsonMachine call into JsonMachine\objects() helper function. This works with any from* function with any json pointer.

foreach (objects(JsonMachine::fromFile('some.json')) as $object) {
    echo $object->example;
}

Parsing a subtree

If you want to iterate only fruits-key subtree in this fruits.json:

// fruits.json
{
    "fruits-key": {
        "apple": {
            "color": "red"
        },
        "pear": {
            "color": "yellow"
        }
    }
}

do it like this:

<?php

$jsonStream = \JsonMachine\JsonMachine::fromFile("fruits.json", "/fruits-key" /* <- Json Pointer */);
foreach ($jsonStream as $name => $data) {
    // The same as above, which means:
    // 1st iteration: $name === "apple" and $data === ["color" => "red"]
    // 2nd iteration: $name === "pear" and $data === ["color" => "yellow"]
}

Note:

Value of fruits-key is not loaded into memory at once, but only one item in fruits-key at a time. It is always one item in memory at a time at the level/subtree you are currently iterating. Thus the memory consumption is constant.

Few words about Json Pointer

It's a way of addressing one item in JSON document. See the Json Pointer RFC 6901. It's very handy, because sometimes the JSON structure goes deeper, and you want to iterate a subtree, not the main level. So you just specify the pointer to the JSON array or object you want to iterate and off you go. When the parser hits the collection you specified, iteration begins. It is always a second parameter in all JsonMachine::from* functions. If you specify pointer to scalar value (which logically cannot be iterated) or non existent position in the document, an exception is thrown.

Some examples:

Json Pointer value	Will iterate through
"" (empty string - default)	["this", "array"] or {"a": "this", "b": "object"} will be iterated (main level)
"/result/items"	{"result":{"items":["this","array","will","be","iterated"]}}
"/0/items"	[{"items":["this","array","will","be","iterated"]}] (supports array indexes)
"/" (gotcha! - a slash followed by an empty string, see the spec)	{"":["this","array","will","be","iterated"]}

Using custom decoder

As a third parameter of all JsonMachine::from* functions is optional instance of JsonMachine\JsonDecoder\Decoder. If none specified, ExtJsonDecoder is used by default. It requires ext-json PHP extension to be present, because it uses json_decode. When json_decode doesn't do what you want, you can make or use your own decoder which must implement JsonMachine\JsonDecoder\Decoder.

Available decoders

• ExtJsonDecoder - Default. Uses json_decode to decode keys and values.
• PassThruDecoder - uses json_decode to decode keys but returns values as pure JSON strings.

Parsing stream API responses

Stream API response or any other JSON stream is parsed exactly the same way as file is. The only difference is, you use JsonMachine::fromStream($streamResource) for it, where $streamResource is the stream resource with the JSON document. The rest is the same as with parsing files. Here are some examples of popular http clients which support streaming responses:

GuzzleHttp

Guzzle uses its own streams, but they can be converted back to PHP streams by calling \GuzzleHttp\Psr7\StreamWrapper::getResource(). Pass the result of this function to JsonMachine::fromStream function and you're set up. See working GuzzleHttp example.

Symfony HttpClient

A stream response of Symfony HttpClient works as iterator. And because JSON Machine is based on iterators, the integration with Symfony HttpClient is very simple. See HttpClient example.

Efficiency of parsing streams/files

JSON Machine reads the stream or file 1 JSON item at a time and generates corresponding 1 PHP array at a time. This is the most efficient way, because if you had say 10,000 users in JSON file and wanted to parse it using json_decode(file_get_contents('big.json')), you'd have the whole string in memory as well as all the 10,000 PHP structures. Following table demonstrates a concept of the difference:

	String items in memory at a time	Decoded PHP items in memory at a time	Total
json_decode()	10000	10000	20000
JsonMachine::fromStream(), ::fromFile(), ::fromIterable()	1	1	2

This means, that JsonMachine::fromStream is constantly efficient for any size of processed JSON. 100 GB no problem.

Efficiency of parsing in-memory JSON strings

There is also a method JsonMachine::fromString(). You may wonder, why is it there. Why just not use json_decode? True, when parsing short strings, JSON Machine may be overhead. But if you are forced to parse a big string and the stream is not available, JSON Machine may be better than json_decode. The reason is that unlike json_decode it still traverses the JSON string one item at a time and doesn't load the whole resulting PHP structure into memory at once.

Let's continue with the example with 10,000 users. This time they are all in string in memory. When decoding that string with json_decode, 10,000 arrays (objects) is created in memory and then the result is returned. JSON Machine on the other hand creates single array for found item in the string and yields it back to you. When you process this item and iterate to the next one, another single array is created. This is the same behaviour as with streams/files. Following table puts the concept into perspective:

	String items in memory at a time	Decoded PHP items in memory at a time	Total
json_decode()	10000	10000	20000
JsonMachine::fromString()	10000	1	10001

The reality is even brighter. JsonMachine::fromString consumes about 5 times less memory than json_decode.

Error handling

When any part of the JSON stream is malformed, SyntaxError exception is thrown. Better solution is on the way.

Running tests

tests/run.sh

This uses php and composer installation already present in your machine.

Running tests on all supported PHP platforms

Install docker to your machine and run

tests/docker-run-all-platforms.sh

This needs no php nor composer installation on your machine. Only Docker.

Installation

composer require halaxa/json-machine

or clone or download this repository (not recommended).

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License

Apache 2.0

Cogwheel element: Icons made by TutsPlus from www.flaticon.com is licensed by CC 3.0 BY