Using javac to generate header

jni/android/build.gradle.kts

@@ -0,0 +1,48 @@
+plugins {
+    id("com.android.library")
+    kotlin("android")
+}
+
+kotlin {
+    explicitApi()
+}
+
+dependencies {
+    api(project(":jni"))
+    implementation(kotlin("stdlib-jdk8"))
+}
+
+android {
+    defaultConfig {
+        compileSdkVersion(30)
+        minSdkVersion(21)
+        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
+        externalNativeBuild {
+            cmake {}
+        }
+    }
+
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_1_8
+        targetCompatibility = JavaVersion.VERSION_1_8
+    }
+
+    externalNativeBuild {
+        cmake {
+            setPath("src/main/CMakeLists.txt")
+        }
+    }
+    ndkVersion = "21.3.6528147"
+
+    afterEvaluate {
+        tasks.withType<com.android.build.gradle.tasks.factory.AndroidUnitTest>().all {
+            enabled = false
+        }
+    }
+}
+
+afterEvaluate {
+    configure(listOf("Debug", "Release").map { tasks["externalNativeBuild$it"] }) {
+        dependsOn(":native:buildSecp256k1Android")
+    }
+}

jni/android/src/main/AndroidManifest.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<manifest package="fr.acinq.secp256k1.jni">
+</manifest>

jni/android/src/main/CMakeLists.txt

@@ -0,0 +1,14 @@
+cmake_minimum_required(VERSION 3.10.0)
+
+add_library( secp256k1-jni SHARED
+    ${CMAKE_CURRENT_LIST_DIR}/../../../../native/jni/src/org_bitcoin_Secp256k1CFunctions.c
+)
+
+target_include_directories( secp256k1-jni
+    PUBLIC ${CMAKE_CURRENT_LIST_DIR}/../../../../native/secp256k1
+    PUBLIC ${CMAKE_CURRENT_LIST_DIR}/../../../../native/jni/headers/java
+)
+
+target_link_libraries( secp256k1-jni
+    ${CMAKE_CURRENT_LIST_DIR}/../../../../native/build/android/${ANDROID_ABI}/libsecp256k1.a
+)

jni/android/src/main/kotlin/fr/acinq/secp256k1/jni/NativeSecp256k1Loader.kt

@@ -0,0 +1,16 @@
+package fr.acinq.secp256k1.jni
+
+import fr.acinq.secp256k1.Secp256k1
+import org.bitcoin.NativeSecp256k1
+
+public object NativeSecp256k1Loader {
+
+    @JvmStatic
+    @Synchronized
+    @Throws(Exception::class)
+    fun load(): Secp256k1 {
+        System.loadLibrary("secp256k1-jni")
+        return NativeSecp256k1
+    }
+
+}