Add compute_kzg_proof to java bindings (#94)

bindings/java/c_kzg_4844_jni.c

@@ -125,6 +125,34 @@ JNIEXPORT void JNICALL Java_ethereum_ckzg4844_CKZG4844JNI_freeTrustedSetup(JNIEn
   reset_trusted_setup();
 }
 
+JNIEXPORT jbyteArray JNICALL Java_ethereum_ckzg4844_CKZG4844JNI_computeKzgProof(JNIEnv *env, jclass thisCls, jbyteArray blob, jbyteArray z_bytes)
+{
+  if (settings == NULL)
+  {
+    throw_exception(env, TRUSTED_SETUP_NOT_LOADED);
+    return NULL;
+  }
+
+  Blob *blob_native = (Blob *)(*env)->GetByteArrayElements(env, blob, NULL);
+  Bytes32 *z_native = (Bytes32 *)(*env)->GetByteArrayElements(env, z_bytes, NULL);
+
+  jbyteArray proof = (*env)->NewByteArray(env, BYTES_PER_PROOF);
+  KZGProof *proof_native = (KZGProof *)(uint8_t *)(*env)->GetByteArrayElements(env, proof, NULL);
+
+  C_KZG_RET ret = compute_kzg_proof(proof_native, blob_native, z_native, settings);
+
+  (*env)->ReleaseByteArrayElements(env, blob, (jbyte *)blob_native, JNI_ABORT);
+  (*env)->ReleaseByteArrayElements(env, proof, (jbyte *)proof_native, 0);
+
+  if (ret != C_KZG_OK)
+  {
+    throw_c_kzg_exception(env, ret, "There was an error while computing kzg proof.");
+    return NULL;
+  }
+
+  return proof;
+}
+
 JNIEXPORT jbyteArray JNICALL Java_ethereum_ckzg4844_CKZG4844JNI_computeAggregateKzgProof(JNIEnv *env, jclass thisCls, jbyteArray blobs, jlong count)
 {
   if (settings == NULL)

bindings/java/c_kzg_4844_jni.h

@@ -42,6 +42,13 @@ extern "C"
    */
   JNIEXPORT void JNICALL Java_ethereum_ckzg4844_CKZG4844JNI_freeTrustedSetup(JNIEnv *, jclass);
 
+  /*
+   * Class:     ethereum_ckzg4844_CKZG4844JNI
+   * Method:    computeKzgProof
+   * Signature: ([B[B)[B
+   */
+  JNIEXPORT jbyteArray JNICALL Java_ethereum_ckzg4844_CKZG4844JNI_computeKzgProof(JNIEnv *, jclass, jbyteArray, jbyteArray);
+
   /*
    * Class:     ethereum_ckzg4844_CKZG4844JNI
    * Method:    computeAggregateKzgProof

bindings/java/src/main/java/ethereum/ckzg4844/CKZG4844JNI.java

@@ -113,6 +113,16 @@ public class CKZG4844JNI {
    */
   public static native void freeTrustedSetup();
 
+  /**
+   * Compute proof at point z for the polynomial represented by blob.
+   *
+   * @param blob blob bytes
+   * @param z_bytes a point
+   * @return the proof
+   * @throws CKZGException if there is a crypto error
+   */
+  public static native byte[] computeKzgProof(byte[] blob, byte[] z_bytes);
+
   /**
    * Calculates aggregated proof for the given blobs
    *

bindings/java/src/test/java/ethereum/ckzg4844/CKZG4844JNITest.java

@@ -82,6 +82,15 @@ public class CKZG4844JNITest {
             parameters.getProof()));
   }
 
+  @Test
+  public void checkComputeKzgProof() {
+    loadTrustedSetup();
+    final byte[] blob = TestUtils.createRandomBlob();
+    final byte[] z_bytes = TestUtils.randomBLSFieldElementBytes();
+    CKZG4844JNI.computeKzgProof(blob, z_bytes);
+    CKZG4844JNI.freeTrustedSetup();
+  }
+
   @Test
   public void checkCustomExceptionIsThrownAsExpected() {
 

bindings/java/src/testFixtures/java/ethereum/ckzg4844/TestUtils.java

@@ -128,6 +128,10 @@ public class TestUtils {
     return randomBLSFieldElement();
   }
 
+  public static byte[] randomBLSFieldElementBytes() {
+    return randomBLSFieldElement().toArray(ByteOrder.LITTLE_ENDIAN);
+  }
+
   private static InputStream readResource(final String resource) {
     return Thread.currentThread().getContextClassLoader().getResourceAsStream(resource);
   }