Added GH build action

.github/workflows/build.yml

@@ -0,0 +1,33 @@
+name: Build on pull request against master
+
+on:
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out repository code
+        uses: actions/checkout@v2
+
+      - name: Set Java 8 up
+        uses: actions/setup-java@v2
+        with:
+          distribution: 'temurin'
+          java-version: '8'
+
+      - name: Build docker container
+        run: docker build -t native-libs .
+
+      - name: Build native library
+        run: docker run --rm -v $(pwd)/build:/native/build native-libs
+
+      - name: Print checksums
+        run: sha256sum ./build/libs/*
+
+      - name: Archive artifacts
+        uses: actions/upload-artifact@v2
+        with:
+          path: ./build/libs/*

build.gradle

@@ -149,6 +149,7 @@ task buildAltbn128(group: 'altbn128', description: 'builds altbn128 library with
 
 task buildSecp256k1CurrentOS(group: 'secp256k1', description: 'builds secp256k1 library for current OS (helpful for development)') {
     dependsOn 'cleanSecp256k1'
+    dependsOn 'replaceJniHeaders'
     doLast {
         exec {
             workingDir 'secp256k1'
@@ -193,6 +194,7 @@ task buildSecp256k1CurrentOS(group: 'secp256k1', description: 'builds secp256k1
 
 task buildSecp256k1Cross(group: 'secp256k1', description: 'builds secp256k1 for Linux, Mac and Windows (only linux library supports reproducibility)') {
     dependsOn 'cleanSecp256k1'
+    dependsOn 'replaceJniHeaders'
     doLast {
         exec {
             workingDir 'secp256k1'
@@ -255,13 +257,16 @@ task generateJniHeaders(group: 'JNI', type: JavaCompile, description: 'generates
 }
 
 task replaceJniHeaders(group: 'JNI', description: 'Replaces JNI old headers with generated headers (for each library)') {
-    copy {
-        from 'build/generated/jni/org_bitcoin_NativeSecp256k1.h'
-        into 'secp256k1/jni/'
-    }
-    copy {
-        from 'build/generated/jni/org_bitcoin_Secp256k1Context.h'
-        into 'secp256k1/jni/'
+    dependsOn 'generateJniHeaders'
+    doLast {
+        copy {
+            from "${buildDir}/generated/jni/org_bitcoin_NativeSecp256k1.h"
+            into "${rootDir}/secp256k1/jni/"
+        }
+        copy {
+            from "${buildDir}/generated/jni/org_bitcoin_Secp256k1Context.h"
+            into "${rootDir}/secp256k1/jni/"
+        }
     }
 }