Kotlin Profiles

The kotlin profile generates a Maven project from your .proto files. Buffy uses protoc-gen-java to generate the message classes and packages them together with the Kotlin standard library so the artifact can be consumed naturally from Kotlin code. Kotlin can call Java protobuf classes directly, so no separate Kotlin code generation is required.

Available variants:

• maven_central — Publish to Maven Central.
• git — Push the generated Maven project to a Git remote.

Required tools

• protoc — Protocol Buffers compiler.
• java — A JDK (11 or newer recommended).
• mvn — Apache Maven; the Kotlin compiler is downloaded automatically as a Maven plugin, no separate kotlin binary is required.
• gpg — GnuPG, for the maven_central variant.
• git — For the git variant.

The maven_central variant

Generates a Maven project that compiles both Java (from protoc) and Kotlin sources, then publishes the resulting JAR (with sources and Javadoc) to Maven Central via the Sonatype Central Portal.

Example

# .buffy/kotlin-example.toml
[kotlin.maven_central]
group_id = "io.github.example"
artifact_id = "tomato-kotlin"
url = "https://github.com/example/tomato"
auto_publish = false
wait_until = "uploaded"

[kotlin.maven_central.scm]
connection = "scm:git:git://github.com/example/tomato.git"
url = "https://github.com/example/tomato"

Fields

• group_id — Maven group ID.
• artifact_id — Maven artifact ID.
• url — Project URL embedded in the POM.
• scm — Source-control coordinates.
• protobuf_version — Pin protobuf-java runtime.
• kotlin_version — Pin Kotlin compiler version.
• auto_publish — Auto-release after upload validates.
• wait_until — How far to wait in the pipeline.

The group_id field

The Maven groupId. Must match a namespace verified for your Sonatype account.

group_id = "io.github.example"

The artifact_id field

The Maven artifactId.

artifact_id = "tomato-kotlin"

The url field

The project URL embedded in the POM <url> tag.

url = "https://github.com/example/tomato"

The scm section

[kotlin.maven_central.scm]
connection = "scm:git:git://github.com/example/tomato.git"
url = "https://github.com/example/tomato"

The protobuf_version field

Optional. Pin a specific version of the com.google.protobuf:protobuf-java runtime dependency. If omitted, Buffy queries Maven Central for the latest release.

protobuf_version = "4.29.3"

The kotlin_version field

Optional. Pin a specific version of the Kotlin compiler and standard library. If omitted, Buffy queries Maven Central for the latest release of org.jetbrains.kotlin:kotlin-stdlib.

kotlin_version = "2.0.21"

The auto_publish field

See auto_publish in Java profiles.

The wait_until field

See wait_until in Java profiles.

Required environment variables

Same as Java.

Example consumer usage

<dependency>
  <groupId>io.github.example</groupId>
  <artifactId>tomato-kotlin</artifactId>
  <version>0.1.0</version>
</dependency>

import io.github.example.tomato.GreeterOuterClass.HelloRequest

val req = HelloRequest.newBuilder().setName("World").build()
println(req.name)

The git variant

Like the Java git variant, but with Kotlin tooling configured in the POM.

Example

# .buffy/kotlin.toml
[kotlin.git]
group_id = "com.example"
artifact_id = "tomato-kotlin"
url = "https://github.com/example/tomato-kotlin"
remote = "git@github.com:example/tomato-kotlin.git"
branch = "main"
keep = ["README.md"]

[kotlin.git.scm]
connection = "scm:git:git://github.com/example/tomato-kotlin.git"
url = "https://github.com/example/tomato-kotlin"

Fields

The same fields as maven_central, plus:

• remote — Git URL the artifact is pushed to.
• branch — Branch to push to.
• keep — Files to preserve from the remote.

These behave identically to the same-named fields in Java profiles.