How to Publish a KMP Library to Maven Central Without a Mac

• Prerequisites
• Step 1: Configure the vanniktech-maven-publish Plugin
• Step 2: Configure Maven Publishing
• Step 3: Export and Configure the GPG Key
• Step 4: Create the GitHub Actions Workflow
• Step 5: Publish Your Library

Publishing a Kotlin Multiplatform (KMP) library that supports iOS and macOS to Maven Central can be done efficiently, even without access to a Mac. This tutorial outlines the process using the vanniktech-maven-publish plugin on a Linux machine. The steps are adaptable to Windows as well.

Prerequisites

Before proceeding, ensure you have the following:

1. Sonatype Account: A valid account on Sonatype Central Repository.
2. Validated Namespace: A namespace approved by Sonatype.
3. GPG Key: A GPG key for signing your artifacts.
4. Maven Central Credentials: Your username and password (or token) for Maven Central.
5. GPG Key Password: The passphrase for your GPG key.

Step 1: Configure the vanniktech-maven-publish Plugin

Add the plugin to your libs.versions.toml file:

[versions]
vanniktech = "0.30.0"

[plugins]
vanniktech-maven-publish = { id = "com.vanniktech.maven.publish", version.ref = "vanniktech" }

Update your root build.gradle.kts:

alias(libs.plugins.vanniktech.maven.publish).apply(false)

In the build.gradle.kts file of your library, apply the plugin:

plugins {
    alias(libs.plugins.vanniktech.maven.publish)
}

Step 2: Configure Maven Publishing

Set up your library configuration in the build.gradle.kts file:

mavenPublishing {
    coordinates(
        groupId = "io.github.kdroidfilter",
        artifactId = "kmplog",
        version = appVersion
    )

    pom {
        name.set("Kmp RealTime Logger")
        description.set("KMP RealTime Logger is a Kotlin Multiplatform logging library that replicates the Android Log API for use across all major platforms. It supports configurable log levels, throwable logging, and real-time log broadcasting to devices on the same local network, making debugging easier and more efficient.")
        inceptionYear.set("2024")
        url.set("https://github.com/kdroidFilter/KmpRealTimeLogger")

        licenses {
            license {
                name.set("MIT")
                url.set("https://opensource.org/licenses/MIT")
            }
        }

        developers {
            developer {
                id.set("kdroidfilter")
                name.set("Elyahou Hadass")
                email.set("elyahou.hadass@gmail.com")
            }
        }

        scm {
            url.set("https://github.com/kdroidFilter/KmpRealTimeLogger")
        }
    }

    publishToMavenCentral(SonatypeHost.CENTRAL_PORTAL)

    signAllPublications()
}

Step 3: Export and Configure the GPG Key

Convert your GPG key to Base64 format:

gpg --export-secret-keys --armor <key-id> | grep -v '\-\-' | grep -v '^=\.' | tr -d '\n' > base64key.txt

Create a secret in your GitHub repository for the Base64 key:

1. Go to Settings > Secrets and Variables > New repository secret.
2. Add a secret named SIGNINGINMEMORYKEY and paste the Base64 key.

Add these additional secrets:

• SIGNINGKEYID: The ID of your GPG key.
• SIGNINGPASSWORD: The password for your GPG key.
• MAVENCENTRALUSERNAME: The username of your Sonatype token.
• MAVENCENTRALPASSWORD: The password of your Sonatype token.

Step 4: Create the GitHub Actions Workflow

Create a file at .github/workflows/publish-on-maven-central.yml with the following content:

name: Publish to Maven Central

on:
  push:
    tags:
      - 'v*'

jobs:
  publish:
    runs-on: macos-latest

    steps:
      - name: Checkout code
        uses: actions/checkout@v3

      - name: Set up JDK
        uses: actions/setup-java@v3
        with:
          java-version: '17'
          distribution: 'temurin'

      - name: Set up Publish to Maven Central
        run: ./gradlew publishAndReleaseToMavenCentral --no-configuration-cache
        env:
          ORG_GRADLE_PROJECT_mavenCentralUsername: ${{ secrets.MAVENCENTRALUSERNAME }}
          ORG_GRADLE_PROJECT_mavenCentralPassword: ${{ secrets.MAVENCENTRALPASSWORD }}
          ORG_GRADLE_PROJECT_signingInMemoryKey: ${{ secrets.SIGNINGINMEMORYKEY }}
          ORG_GRADLE_PROJECT_signingInMemoryKeyId: ${{ secrets.SIGNINGKEYID }}
          ORG_GRADLE_PROJECT_signingInMemoryKeyPassword: ${{ secrets.SIGNINGPASSWORD }}

Step 5: Publish Your Library

To publish the library:

1. Create a Git tag starting with v (e.g., v1.0.0).
2. Push the tag to GitHub.

GitHub Actions will automatically upload your library to Maven Central using a macOS runner.

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With these steps, you can publish your KMP library seamlessly to Maven Central without owning a Mac. The workflow ensures compatibility with iOS and macOS and leverages GitHub Actions to streamline the process.