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Protocol Buffers are a language-neutral, platform-neutral, extensible way of serializing structured data for use in communications protocols, data storage, and more, originally designed at Google (see).

protobuf.js is a pure JavaScript implementation with TypeScript support for node.js and the browser. It's easy to use, blazingly fast and works out of the box with .proto files!

Contents

• Installation
  How to include protobuf.js in your project.

• Usage
  A brief introduction to using the toolset.

  • Valid Message
  • Toolset
    

• Examples
  A few examples to get you started.

  • Using .proto files
  • Using JSON descriptors
  • Using reflection only
  • Using custom classes
  • Using services
  • Usage with TypeScript
    

• Additional documentation
  A list of available documentation resources.

• Performance
  A few internals and a benchmark on performance.

• Compatibility
  Notes on compatibility regarding browsers and optional libraries.

• Building
  How to build the library and its components yourself.

Installation

node.js

$> npm install protobufjs [--save --save-prefix=~]

var protobuf = require("protobufjs");

The command line utility lives in the protobufjs-cli package and must be installed separately:

$> npm install protobufjs-cli [--save --save-prefix=~]

Note that this library's versioning scheme is not semver-compatible for historical reasons. For guaranteed backward compatibility, always depend on ~6.A.B instead of ^6.A.B (hence the --save-prefix above).

Browsers

Development:

<script src="//cdn.rawgit.com/dcodeIO/protobuf.js/6.X.X/dist/protobuf.js"></script>

Production:

<script src="//cdn.rawgit.com/dcodeIO/protobuf.js/6.X.X/dist/protobuf.min.js"></script>

Remember to replace the version tag with the exact release your project depends upon.

The library supports CommonJS and AMD loaders and also exports globally as protobuf.

Distributions

Where bundle size is a factor, there are additional stripped-down versions of the full library (~19kb gzipped) available that exclude certain functionality:

• When working with JSON descriptors (i.e. generated by pbjs) and/or reflection only, see the light library (~16kb gzipped) that excludes the parser. CommonJS entry point is:

  var protobuf = require("protobufjs/light");

• When working with statically generated code only, see the minimal library (~6.5kb gzipped) that also excludes reflection. CommonJS entry point is:

  var protobuf = require("protobufjs/minimal");

Usage

Because JavaScript is a dynamically typed language, protobuf.js introduces the concept of a valid message in order to provide the best possible performance (and, as a side product, proper typings):

Valid message

A valid message is an object (1) not missing any required fields and (2) exclusively composed of JS types understood by the wire format writer.

There are two possible types of valid messages and the encoder is able to work with both of these for convenience:

• Message instances (explicit instances of message classes with default values on their prototype) always (have to) satisfy the requirements of a valid message by design and
• Plain JavaScript objects that just so happen to be composed in a way satisfying the requirements of a valid message as well.

In a nutshell, the wire format writer understands the following types:

• Explicit undefined and null are considered as not set if the field is optional.
• Repeated fields are Array.<T>.
• Map fields are Object.<string,T> with the key being the string representation of the respective value or an 8 characters long binary hash string for Long-likes.
• Types marked as optimal provide the best performance because no conversion step (i.e. number to low and high bits or base64 string to buffer) is required.

Toolset

With that in mind and again for performance reasons, each message class provides a distinct set of methods with each method doing just one thing. This avoids unnecessary assertions / redundant operations where performance is a concern but also forces a user to perform verification (of plain JavaScript objects that might just so happen to be a valid message) explicitly where necessary - for example when dealing with user input.

Note that Message below refers to any message class.

• Message.verify(message: Object): null|string
  verifies that a plain JavaScript object satisfies the requirements of a valid message and thus can be encoded without issues. Instead of throwing, it returns the error message as a string, if any.

  var payload = "invalid (not an object)";
  var err = AwesomeMessage.verify(payload);
  if (err)
    throw Error(err);

• Message.encode(message: Message|Object [, writer: Writer]): Writer
  encodes a message instance or valid plain JavaScript object. This method does not implicitly verify the message and it's up to the user to make sure that the payload is a valid message.

  var buffer = AwesomeMessage.encode(message).finish();

• Message.encodeDelimited(message: Message|Object [, writer: Writer]): Writer
  works like Message.encode but additionally prepends the length of the message as a varint.

• Message.decode(reader: Reader|Uint8Array): Message
  decodes a buffer to a message instance. If required fields are missing, it throws a util.ProtocolError with an instance property set to the so far decoded message. If the wire format is invalid, it throws an Error.

  try {
    var decodedMessage = AwesomeMessage.decode(buffer);
  } catch (e) {
      if (e instanceof protobuf.util.ProtocolError) {
        // e.instance holds the so far decoded message with missing required fields
      } else {
        // wire format is invalid
      }
  }

• Message.decodeDelimited(reader: Reader|Uint8Array): Message
  works like Message.decode but additionally reads the length of the message prepended as a varint.

• Message.create(properties: Object): Message
  creates a new message instance from a set of properties that satisfy the requirements of a valid message. Where applicable, it is recommended to prefer Message.create over Message.fromObject because it doesn't perform possibly redundant conversion.

  var message = AwesomeMessage.create({ awesomeField: "AwesomeString" });

• Message.fromObject(object: Object): Message
  converts any non-valid plain JavaScript object to a message instance using the conversion steps outlined within the table above.

  var message = AwesomeMessage.fromObject({ awesomeField: 42 });
  // converts awesomeField to a string

• Message.toObject(message: Message [, options: ConversionOptions]): Object
  converts a message instance to an arbitrary plain JavaScript object for interoperability with other libraries or storage. The resulting plain JavaScript object might still satisfy the requirements of a valid message depending on the actual conversion options specified, but most of the time it does not.

  var object = AwesomeMessage.toObject(message, {
    enums: String,  // enums as string names
    longs: String,  // longs as strings (requires long.js)
    bytes: String,  // bytes as base64 encoded strings
    defaults: true, // includes default values
    arrays: true,   // populates empty arrays (repeated fields) even if defaults=false
    objects: true,  // populates empty objects (map fields) even if defaults=false
    oneofs: true    // includes virtual oneof fields set to the present field's name
  });

For reference, the following diagram aims to display relationships between the different methods and the concept of a valid message:

In other words: verify indicates that calling create or encode directly on the plain object will [result in a valid message respectively] succeed. fromObject, on the other hand, does conversion from a broader range of plain objects to create valid messages. (ref)

Examples

Using .proto files

It is possible to load existing .proto files using the full library, which parses and compiles the definitions to ready to use (reflection-based) message classes:

// awesome.proto
package awesomepackage;
syntax = "proto3";

message AwesomeMessage {
    string awesome_field = 1; // becomes awesomeField
}

protobuf.load("awesome.proto", function(err, root) {
    if (err)
        throw err;

    // Obtain a message type
    var AwesomeMessage = root.lookupType("awesomepackage.AwesomeMessage");

    // Exemplary payload
    var payload = { awesomeField: "AwesomeString" };

    // Verify the payload if necessary (i.e. when possibly incomplete or invalid)
    var errMsg = AwesomeMessage.verify(payload);
    if (errMsg)
        throw Error(errMsg);

    // Create a new message
    var message = AwesomeMessage.create(payload); // or use .fromObject if conversion is necessary

    // Encode a message to an Uint8Array (browser) or Buffer (node)
    var buffer = AwesomeMessage.encode(message).finish();
    // ... do something with buffer

    // Decode an Uint8Array (browser) or Buffer (node) to a message
    var message = AwesomeMessage.decode(buffer);
    // ... do something with message

    // If the application uses length-delimited buffers, there is also encodeDelimited and decodeDelimited.

    // Maybe convert the message back to a plain object
    var object = AwesomeMessage.toObject(message, {
        longs: String,
        enums: String,
        bytes: String,
        // see ConversionOptions
    });
});

Additionally, promise syntax can be used by omitting the callback, if preferred:

protobuf.load("awesome.proto")
    .then(function(root) {
       ...
    });

Using JSON descriptors

The library utilizes JSON descriptors that are equivalent to a .proto definition. For example, the following is identical to the .proto definition seen above:

// awesome.json
{
  "nested": {
    "awesomepackage": {
      "nested": {
        "AwesomeMessage": {
          "fields": {
            "awesomeField": {
              "type": "string",
              "id": 1
            }
          }
        }
      }
    }
  }
}

JSON descriptors closely resemble the internal reflection structure:

• Bold properties are required. Italic types are abstract.
• T.fromJSON(name, json) creates the respective reflection object from a JSON descriptor
• T#toJSON() creates a JSON descriptor from the respective reflection object (its name is used as the key within the parent)

Exclusively using JSON descriptors instead of .proto files enables the use of just the light library (the parser isn't required in this case).

A JSON descriptor can either be loaded the usual way:

protobuf.load("awesome.json", function(err, root) {
    if (err) throw err;

    // Continue at "Obtain a message type" above
});

Or it can be loaded inline:

var jsonDescriptor = require("./awesome.json"); // exemplary for node

var root = protobuf.Root.fromJSON(jsonDescriptor);

// Continue at "Obtain a message type" above

Using reflection only

Both the full and the light library include full reflection support. One could, for example, define the .proto definitions seen in the examples above using just reflection:

...
var Root  = protobuf.Root,
    Type  = protobuf.Type,
    Field = protobuf.Field;

var AwesomeMessage = new Type("AwesomeMessage").add(new Field("awesomeField", 1, "string"));

var root = new Root().define("awesomepackage").add(AwesomeMessage);

// Continue at "Create a new message" above
...

Detailed information on the reflection structure is available within the API documentation.

Using custom classes

Message classes can also be extended with custom functionality and it is also possible to register a custom constructor with a reflected message type:

...

// Define a custom constructor
function AwesomeMessage(properties) {
    // custom initialization code
    ...
}

// Register the custom constructor with its reflected type (*)
root.lookupType("awesomepackage.AwesomeMessage").ctor = AwesomeMessage;

// Define custom functionality
AwesomeMessage.customStaticMethod = function() { ... };
AwesomeMessage.prototype.customInstanceMethod = function() { ... };

// Continue at "Create a new message" above

(*) Besides referencing its reflected type through AwesomeMessage.$type and AwesomeMesage#$type, the respective custom class is automatically populated with:

• AwesomeMessage.create
• AwesomeMessage.encode and AwesomeMessage.encodeDelimited
• AwesomeMessage.decode and AwesomeMessage.decodeDelimited
• AwesomeMessage.verify
• AwesomeMessage.fromObject, AwesomeMessage.toObject and AwesomeMessage#toJSON

Afterwards, decoded messages of this type are instanceof AwesomeMessage.

Alternatively, it is also possible to reuse and extend the internal constructor if custom initialization code is not required:

...

// Reuse the internal constructor
var AwesomeMessage = root.lookupType("awesomepackage.AwesomeMessage").ctor;

// Define custom functionality
AwesomeMessage.customStaticMethod = function() { ... };
AwesomeMessage.prototype.customInstanceMethod = function() { ... };

// Continue at "Create a new message" above

Using services

The library also supports consuming services but it doesn't make any assumptions about the actual transport channel. Instead, a user must provide a suitable RPC implementation, which is an asynchronous function that takes the reflected service method, the binary request and a node-style callback as its parameters:

function rpcImpl(method, requestData, callback) {
    // perform the request using an HTTP request or a WebSocket for example
    var responseData = ...;
    // and call the callback with the binary response afterwards:
    callback(null, responseData);
}

Below is a working example with a typescript implementation using grpc npm package.

const grpc = require('grpc')

const Client = grpc.makeGenericClientConstructor({})
const client = new Client(
  grpcServerUrl,
  grpc.credentials.createInsecure()
)

const rpcImpl = function(method, requestData, callback) {
  client.makeUnaryRequest(
    method.name,
    arg => arg,
    arg => arg,
    requestData,
    callback
  )
}

Example:

// greeter.proto
syntax = "proto3";

service Greeter {
    rpc SayHello (HelloRequest) returns (HelloReply) {}
}

message HelloRequest {
    string name = 1;
}

message HelloReply {
    string message = 1;
}

...
var Greeter = root.lookup("Greeter");
var greeter = Greeter.create(/* see above */ rpcImpl, /* request delimited? */ false, /* response delimited? */ false);

greeter.sayHello({ name: 'you' }, function(err, response) {
    console.log('Greeting:', response.message);
});

Services also support promises:

greeter.sayHello({ name: 'you' })
    .then(function(response) {
        console.log('Greeting:', response.message);
    });

There is also an example for streaming RPC.

Note that the service API is meant for clients. Implementing a server-side endpoint pretty much always requires transport channel (i.e. http, websocket, etc.) specific code with the only common denominator being that it decodes and encodes messages.

Usage with TypeScript

The library ships with its own type definitions and modern editors like Visual Studio Code will automatically detect and use them for code completion.

The npm package depends on @types/node because of Buffer and @types/long because of Long. If you are not building for node and/or not using long.js, it should be safe to exclude them manually.