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tessl/maven-com-google-protobuf--protobuf-kotlin

Kotlin language bindings and extensions for Google Protocol Buffers providing idiomatic Kotlin APIs with DSL builders and type safety.

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protobuf-kotlin

The protobuf-kotlin library provides idiomatic Kotlin language bindings and extensions for Google Protocol Buffers. It offers type-safe extension functions, DSL builders, enhanced collection types, and seamless interoperability with Java protobuf code while providing Kotlin-specific features like nullable types and enhanced type safety.

Package Information

  • Package Name: com.google.protobuf:protobuf-kotlin
  • Package Type: maven
  • Language: Kotlin
  • Installation: Add to your Maven dependencies or Gradle build file:
<dependency>
    <groupId>com.google.protobuf</groupId>
    <artifactId>protobuf-kotlin</artifactId>
    <version>4.31.1</version>
</dependency>
implementation("com.google.protobuf:protobuf-kotlin:4.31.1")

Core Imports

import com.google.protobuf.kotlin.*

For specific functionality:

// ByteString extensions
import com.google.protobuf.kotlin.toByteStringUtf8
import com.google.protobuf.kotlin.plus
import com.google.protobuf.kotlin.isNotEmpty

// Any message operations
import com.google.protobuf.kotlin.isA
import com.google.protobuf.kotlin.unpack

// Extension field operations
import com.google.protobuf.kotlin.get
import com.google.protobuf.kotlin.set
import com.google.protobuf.kotlin.contains

Basic Usage

import com.google.protobuf.kotlin.*
import com.google.protobuf.ByteString
import com.google.protobuf.Any as ProtoAny

// ByteString operations
val message = "Hello, Protocol Buffers!"
val byteString = message.toByteStringUtf8()
val combined = byteString + " From Kotlin!".toByteStringUtf8()
val isEmpty = byteString.isNotEmpty() // true

// Any message type checking and unpacking
val packedMessage: ProtoAny = // ... some packed message
if (packedMessage.isA<MyMessageType>()) {
    val unpacked = packedMessage.unpack<MyMessageType>()
    // Use unpacked message
}

// Extension field access (with generated message builders)
val builder = MyExtendableMessage.newBuilder()
builder[myExtensionField] = "extension value"
val hasExtension = builder.contains(myExtensionField)
val extensionValue = builder[myExtensionField]

Architecture

The protobuf-kotlin library is built around several key design patterns:

  • Extension Functions: Kotlin extension functions add idiomatic APIs to existing Java protobuf types
  • Type Safety: Heavy use of generics and reified types for compile-time type checking
  • Immutable Collections: All collection wrappers provide unmodifiable views for safety
  • Java Interoperability: Designed to work seamlessly across Kotlin/Java boundaries
  • Generated Code Support: Many APIs are optimized for use by protoc-generated Kotlin code
  • DSL Infrastructure: Provides foundation for type-safe DSL builders in generated code

Capabilities

ByteString Extensions

Kotlin idiomatic extensions for ByteString operations including conversion from strings and byte arrays, concatenation, indexing, and utility functions.

fun String.toByteStringUtf8(): ByteString
operator fun ByteString.plus(other: ByteString): ByteString
operator fun ByteString.get(index: Int): Byte
fun ByteString.isNotEmpty(): Boolean
fun ByteArray.toByteString(): ByteString
fun ByteBuffer.toByteString(): ByteString

ByteString Extensions

Any Message Operations

Type-safe operations for protocol buffer Any messages, allowing runtime type checking and unpacking with compile-time type safety through reified generics.

inline fun <reified T : Message> ProtoAny.isA(): Boolean
inline fun <reified T : Message> ProtoAny.unpack(): T

Any Message Operations

Extension Field Access

Operator overloads for intuitive extension field access on extendable messages and builders, providing get, set, and contains operations with full type safety.

operator fun <M : GeneratedMessage.ExtendableMessage<M>, B : GeneratedMessage.ExtendableBuilder<M, B>, T : Any> 
    B.set(extension: ExtensionLite<M, T>, value: T)
    
operator fun <M : GeneratedMessage.ExtendableMessage<M>, MorBT : GeneratedMessage.ExtendableMessageOrBuilder<M>, T : Any> 
    MorBT.get(extension: ExtensionLite<M, T>): T
    
operator fun <M : GeneratedMessage.ExtendableMessage<M>, MorBT : GeneratedMessage.ExtendableMessageOrBuilder<M>> 
    MorBT.contains(extension: ExtensionLite<M, *>): Boolean

Extension Field Access

DSL Infrastructure

Core infrastructure for generated protobuf DSL including collection wrappers, proxy types, and annotations for type-safe message building.

@ProtoDslMarker
@OnlyForUseByGeneratedProtoCode
annotation class ProtoDslMarker

class DslList<E, P : DslProxy>
class DslMap<K, V, P : DslProxy>
abstract class DslProxy

class ExtensionList<E, M : MessageLite>

DSL Infrastructure

Types

Core Annotations

@ProtoDslMarker
annotation class ProtoDslMarker

@RequiresOptIn(
    message = "This API is only intended for use by generated protobuf code",
    level = RequiresOptIn.Level.ERROR
)
annotation class OnlyForUseByGeneratedProtoCode

Extension Types

// From Java protobuf library (imported)
import com.google.protobuf.ExtensionLite
import com.google.protobuf.GeneratedMessage
import com.google.protobuf.Message
import com.google.protobuf.MessageLite
import com.google.protobuf.ByteString
import com.google.protobuf.Any as ProtoAny
import java.nio.ByteBuffer
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mavenpkg:maven/com.google.protobuf/protobuf-kotlin@4.31.x
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