Protobuf in gRPC

Protocol Buffers, or Protobuf, is a language-agnostic data serialization format developed by Google. It enables efficient and extensible communication between systems by serializing structured data. Unlike traditional formats like JSON or XML, Protobuf produces binary output, resulting in smaller payloads and faster data transmission.

Protocol Buffers Definition Syntax

At its core, Protocol Buffers uses a concise and language-agnostic syntax to define data structures, enabling seamless communication between different programming languages. The syntax is defined in a .proto file, which acts as a blueprint for creating messages.

Let’s break down the key components of the Definition Syntax:

1-Message Types:

In Protobuf, messages are the fundamental units of data. They are defined using the message keyword, followed by the name of the message and a set of fields enclosed in curly braces. Each field has a unique name, a field type, and a unique numeric tag.

syntax = "proto3";

message Person {
  required string name = 1;
  required int32 id = 2;
  optional string email = 3;
}

we’ve defined a Person message with three fields: name, id, and an optional email.

2-Field Rules:

Each field in a message has a defined rule, indicating whether the field is required, optional, or repeated. The field rules are specified using keywords like required, optional, or repeated.

message AddressBook {
  repeated Person people = 1;
}

Here, the people field is marked as repeated, allowing multiple Person entries in the AddressBook.

4-Field Number:

In Protocol Buffers, the field number is a unique identifier assigned to each field within a message. This number serves as a way to distinguish and reference fields when serializing and deserializing data. Field numbers play a crucial role in maintaining backward compatibility and allowing for the evolution of message structures over time

• Each field within a message must have a unique field number.
• The field number is assigned by the developer and is used to identify the field in the binary-encoded data.
• Fields in a message are tagged with their field numbers in the order they appear in the .proto file.
• The order of field numbers is significant, and it determines the order in which fields are serialized.
• Certain field numbers are reserved for specific purposes. For example, field numbers 1 to 15 are more efficient to encode because they require fewer bytes in the binary representation.
• Field numbers 19,000 to 19,999 are reserved for the Protocol Buffers implementation

syntax = "proto3";

message Person {
  required string name = 1;
  required int32 id = 2;
  optional string email = 3;
}

Here the Person message has three fields: name with field number 1, id with field number 2, and email with field number 3.

5-Scalar Value Types:

Protobuf supports a variety of scalar value types, including integers, floating-point numbers, booleans, and strings. Additionally, enumerations can be defined for fields with a limited set of values.

enum PhoneType {
  MOBILE = 0;
  HOME = 1;
  WORK = 2;
}

message PhoneNumber {
  required string number = 1;
  optional PhoneType type = 2 [default = HOME];
}

we’ve defined an enumeration PhoneType and used it in the PhoneNumber message.

Defining Messages with Protobuf

Let’s dive deeper into the Protobuf message definition with a practical example for a messaging application:

syntax = "proto3";

message ChatMessage {
  string sender_username = 1;
  string content = 2;
  int64 timestamp = 3;
}

Here, we’ve created a ChatMessage message with fields for the sender’s username, message content, and a timestamp. This simplicity showcases the elegance of Protobuf for defining structured data.

gRPC Service Definition

Now, let’s integrate above created message into a gRPC service for a chat application:

service ChatService {
  rpc SendMessage (ChatMessage) returns (Confirmation);
}

message Confirmation {
  bool success = 1;
  string message = 2;
}

In this example, the ChatService provides a method SendMessage that takes a ChatMessage as input and returns a Confirmation message. This illustrates how seamlessly Protobuf integrates into gRPC service definitions for real-world applications.