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PHP Protobuf - Google's Protocol Buffers for PHP

Overview

Protocol Buffers are a way of encoding structured data in an efficient yet extensible format. It might be used in file formats and RPC protocols.

PHP Protobuf is Google's Protocol Buffers implementation for PHP with a goal to provide high performance, including a protoc plugin to generate PHP classes from .proto files. The heavy-lifting (a parsing and a serialization) is done by a PHP extension.

Requirements

  • PHP 5.3 or above
  • Pear's Console_CommandLine (for the protoc plugin)
  • Google's protoc compiler version 2.6 or above

Getting started

Installation

  1. Clone the source code

    git clone https://github.com/allegro/php-protobuf

  2. Go to the source code directory

    cd php-protobuf

  3. Build and install the PHP extension (follow instructions at php.net)

  4. Install protoc plugin dependencies

    composer install

Usage

  1. Assume you have a file foo.proto

    message Foo
{
    required int32 bar = 1;
    optional string baz = 2;
    repeated float spam = 3;
}

  2. Compile foo.proto

    php protoc-gen-php.php foo.proto

  3. Create Foo message and populate it with some data

    require_once 'Foo.php';

$foo = new Foo();
$foo->setBar(1);
$foo->setBaz('two');
$foo->appendSpam(3.0);
$foo->appendSpam(4.0);

  4. Serialize a message to a string

    $packed = $foo->serializeToString();

  5. Parse a message from a string

    $parsedFoo = new Foo();
try {
    $parsedFoo->parseFromString($packed);
} catch (Exception $ex) {
    die('Oops.. there is a bug in this example, ' . $ex->getMessage());
}

  6. Let's see what we parsed out

    $parsedFoo->dump();

    It should produce output similar to the following:

    Foo {
  1: bar => 1
  2: baz => 'two'
  3: spam(2) =>
    [0] => 3
    [1] => 4
}

  7. If you would like you can reset an object to its initial state

    $parsedFoo->reset();

Guide

Compilation

PHP Protobuf comes with Google's protoc compiler plugin. You can run in directly:

php protoc-gen-php.php -o output_dir foo.proto

or pass it to the protoc:

protoc --plugin=protoc-gen-php.php --php_out=output_dir foo.proto

Put protoc-php-gen.php on the PATH or pass absolute path to protoc.

On Windows use protoc-gen-php.bat instead.

Command line options

  • -o out, --out=out - the destination directory for generated files (defaults to the current directory).
  • -I proto_path, --proto_path=proto_path - the directory in which to search for imports.
  • --protoc=protoc - the protoc compiler executable path.
  • -D define, --define=define - define a generator option (i.e. -Dnamespace='Foo\Bar\Baz').

Generator options

  • namespace - the namespace to be used by the generated PHP classes.

Message class

The classes generated during the compilation are PSR-0 compliant (each class is put into it's own file). If namespace generator option is not defined then a package name (if present) is used to create a namespace. If the package name is not set then a class is put into global space.

PHP Protobuf module implements ProtobufMessage class which encapsulates the protocol logic. A message compiled from a proto file extends this class providing message field descriptors. Based on these descriptors ProtobufMessage knows how to parse and serialize a message of a given type.

For each field a set of accessors is generated. The set of methods is different for single value fields (required / optional) and multi-value fields (repeated).

  • required / optional

      get{FIELD}()        // return field value
  set{FIELD}($value)  // set field value to $value

  • repeated

      append{FIELD}($value)       // append $value value to field
  clear{FIELD}()              // empty field
  get{FIELD}()                // return array of field values
  getAt{FIELD}($index)        // return field value at $index index
  getCount{FIELD}()           // return number of field values
  getIterator{FIELD}($index)  // return ArrayIterator for field values

{FIELD} is a camel cased field name.

Enum

PHP does not natively support enum type. Hence enum is represented by the PHP integer type. For convenience enum is compiled to a class with set of constants corresponding to its possible values.

Type mapping

The range of available build-in PHP types poses some limitations. PHP does not support 64-bit positive integer type. Note that parsing big integer values might result in getting unexpected results.

Protocol Buffers types map to PHP types as follows:

| Protocol Buffers | PHP    |
| ---------------- | ------ |
| double           | float  |
| float            |        |
| ---------------- | ------ |
| int32            | int    |
| int64            |        |
| uint32           |        |
| uint64           |        |
| sint32           |        |
| sint64           |        |
| fixed32          |        |
| fixed64          |        |
| sfixed32         |        |
| sfixed64         |        |
| ---------------- | ------ |
| bool             | bool   |
| ---------------- | ------ |
| string           | string |
| bytes            |        |

Not set value is represented by null type. To unset value just set its value to null.

Parsing

To parse message create a message class instance and call its parseFromString method passing it a serialized message. The errors encountered are signaled by throwing Exception. Exception message provides detailed explanation. Required fields not set are silently ignored.

$packed = /* serialized FooMessage */;
$foo = new FooMessage();

try {
    $foo->parseFromString($packed);
} catch (Exception $ex) {
    die('Parse error: ' . $e->getMessage());
}

$foo->dump(); // see what you got

Serialization

To serialize a message call serializeToString method. It returns a string containing protobuf-encoded message. The errors encountered are signaled by throwing Exception. Exception message provides detailed explanation. A required field not set triggers an error.

$foo = new FooMessage()
$foo->setBar(1);

try {
    $packed = $foo->serializeToString();
} catch (Exception $ex) {
    die 'Serialize error: ' . $e->getMessage();
}

/* do some cool stuff with protobuf-encoded $packed */

Debugging

There might be situations you need to investigate what an actual content of a given message is. What var_dump gives on a message instance is somewhat obscure.

The ProtobufMessage class comes with dump method which prints out a message content to the standard output. It takes one optional argument specifying whether you want to dump only set fields (by default it dumps only set fields). Pass false as an argument to dump all fields. Format it produces is similar to var_dump.

Alternatively you can use printDebugString() method which produces output in protocol buffers text format.

IDE Helper and Auto-Complete Support

To integrate this extension with your IDE (PhpStorm, Eclipse etc.) and get auto-complete support, simply include stubs\ProtobufMessage.php anywhere under your project root.

References