[WIP] Initial Java binding through JNI.

WORKSPACE

@@ -120,3 +120,41 @@ python_configure(name = "local_config_python")
 register_toolchains("@local_config_python//:toolchain")
 
 tf_configure(name = "local_config_tf")
+
+# Java binding support.
+http_archive(
+    name = "fmeum_rules_jni",
+    sha256 = "8d685e381cb625e11fac330085de2ebc13ad497d30c4e9b09beb212f7c27e8e7",
+    url = "https://github.com/fmeum/rules_jni/releases/download/v0.3.0/rules_jni-v0.3.0.tar.gz",
+)
+
+load("@fmeum_rules_jni//jni:repositories.bzl", "rules_jni_dependencies")
+
+rules_jni_dependencies()
+
+load("@bazel_tools//tools/build_defs/repo:java.bzl", "java_import_external")
+
+java_import_external(
+    name = "junit_long",
+    jar_sha256 = "59721f0805e223d84b90677887d9ff567dc534d7c502ca903c0c2b17f05c116a",
+    jar_urls = [
+        "https://storage.googleapis.com/mirror.tensorflow.org/repo1.maven.org/maven2/junit/junit/4.12/junit-4.12.jar",
+        "https://repo1.maven.org/maven2/junit/junit/4.12/junit-4.12.jar",
+        "https://maven.ibiblio.org/maven2/junit/junit/4.12/junit-4.12.jar",
+    ],
+    licenses = ["reciprocal"],  # Common Public License Version 1.0
+    testonly_ = True,
+    deps = ["@org_hamcrest_core"],
+)
+
+java_import_external(
+    name = "org_hamcrest_core",
+    jar_sha256 = "66fdef91e9739348df7a096aa384a5685f4e875584cce89386a7a47251c4d8e9",
+    jar_urls = [
+        "https://storage.googleapis.com/mirror.tensorflow.org/repo1.maven.org/maven2/org/hamcrest/hamcrest-core/1.3/hamcrest-core-1.3.jar",
+        "https://repo1.maven.org/maven2/org/hamcrest/hamcrest-core/1.3/hamcrest-core-1.3.jar",
+        "https://maven.ibiblio.org/maven2/org/hamcrest/hamcrest-core/1.3/hamcrest-core-1.3.jar",
+    ],
+    licenses = ["notice"],  # New BSD License
+    testonly_ = True,
+)

java/com/google/riegeli/BUILD

@@ -0,0 +1,69 @@
+load("@fmeum_rules_jni//jni:defs.bzl", "cc_jni_library", "java_jni_library", "jni_headers")
+
+# Java interface for that will be implemented using JNI later.
+java_library(
+    name = "wrapper",
+    srcs = [
+        "RecordReader.java",
+        "RecordWriter.java",
+    ],
+)
+
+# Generate the native header.
+jni_headers(
+    name = "header",
+    lib = ":wrapper",
+)
+
+cc_jni_library(
+    name = "riegeli_jni",
+    srcs = [
+        "jni_record_reader.cc",
+        "jni_record_writer.cc",
+    ],
+    visibility = [
+    ],
+    deps = [
+        ":header",
+        "//riegeli/bytes:fd_reader",
+        "//riegeli/bytes:fd_writer",
+        "//riegeli/records:record_reader",
+        "//riegeli/records:record_writer",
+    ],
+)
+
+java_jni_library(
+    name = "loader",
+    srcs = [
+        "Loader.java",
+    ],
+    native_libs = [
+        ":riegeli_jni",
+    ],
+    visibility = [
+    ],
+    deps = [
+        ":wrapper",
+    ],
+)
+
+java_library(
+    name = "tests",
+    testonly = 1,
+    srcs = [
+        "RecordReadWriteTest.java",
+    ],
+    deps = [
+        ":loader",
+        ":wrapper",
+        "@junit_long",
+        "@org_hamcrest_core",
+    ],
+)
+
+java_test(
+    name = "RecordReadWriteTest",
+    runtime_deps = [
+        ":tests",
+    ],
+)

java/com/google/riegeli/Loader.java

@@ -0,0 +1,19 @@
+package com.google.riegeli;
+
+import com.github.fmeum.rules_jni.RulesJni;
+
+public class Loader {
+  // Not sure whether it's worth the redirection to put JNI native lib loading logic in a single class.
+  static {
+    RulesJni.loadLibrary("riegeli_jni", RecordReader.class);
+    RulesJni.loadLibrary("riegeli_jni", RecordWriter.class);
+  }
+
+  public final static RecordWriter newWriter() {
+    return new RecordWriter();
+  }
+
+  public static RecordReader newReader() {
+    return new RecordReader();
+  }
+}

java/com/google/riegeli/RecordReadWriteTest.java

@@ -0,0 +1,46 @@
+package com.google.riegeli;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import java.io.IOException;
+
+import static org.junit.Assert.assertEquals;
+
+public class RecordReadWriteTest {
+
+    @Before
+    public void setUp() {
+    }
+
+    private String createTestString(int length) {
+        // String.repeat is only available from Java 11, so create a
+        // helper method instead.
+        return String.join("", java.util.Collections.nCopies(length, "a"));
+    }
+
+    @Test
+    public void writeWriteString() throws IOException {
+        // TODO: create a random file on TEST_TEMP directory.
+        final String filename = "/tmp/test.rg";
+        RecordWriter writer = Loader.newWriter();
+        writer.open(filename, "default");
+        final int kNumRecords = 4096;
+        for (int i = 0; i < kNumRecords; i++) {
+            final String s = createTestString(i+1);
+            writer.writeRecord(s);
+        }
+        writer.close();
+
+        RecordReader reader = Loader.newReader();
+        reader.open(filename);
+        for (int i = 0; i < kNumRecords; i++) {
+            byte[] record = reader.readRecord();
+            final String s = createTestString(i+1);
+            assertEquals(new String(record), s);
+        }
+        byte[] record = reader.readRecord();
+        assertEquals(null, record);
+        reader.close();
+    }
+}

java/com/google/riegeli/RecordReader.java

@@ -0,0 +1,19 @@
+package com.google.riegeli;
+
+import java.io.IOException;
+
+// JNI wrapper for riegeli record reader.
+public class RecordReader {
+
+  public final static class Options {
+    // Nothing is supported for now.
+  }
+
+  private long recordReaderPtr;
+
+  public native void open(String filename) throws IOException;
+
+  public native byte[] readRecord();
+
+  public native void close() throws IOException;
+}

java/com/google/riegeli/RecordWriter.java

@@ -0,0 +1,50 @@
+package com.google.riegeli;
+
+import java.io.IOException;
+
+// JNI wrapper for riegeli record writer.
+public class RecordWriter {
+
+  public final static class Options {
+    // Nothing is supported for now.
+  }
+
+  // Pointer to the C++ object.
+  private long recordWriterPtr;
+
+  // Options could be:
+  // ```
+  //   options ::= option? ("," option?)*
+  //   option ::=
+  //     "default" |
+  //     "transpose" (":" ("true" | "false"))? |
+  //     "uncompressed" |
+  //     "brotli" (":" brotli_level)? |
+  //     "zstd" (":" zstd_level)? |
+  //     "snappy" |
+  //     "window_log" ":" window_log |
+  //     "chunk_size" ":" chunk_size |
+  //     "bucket_fraction" ":" bucket_fraction |
+  //     "pad_to_block_boundary" (":" ("true" | "false"))? |
+  //     "parallelism" ":" parallelism
+  //   brotli_level ::= integer in the range [0..11] (default 6)
+  //   zstd_level ::= integer in the range [-131072..22] (default 3)
+  //   window_log ::= "auto" or integer in the range [10..31]
+  //   chunk_size ::= "auto" or positive integer expressed as real with
+  //     optional suffix [BkKMGTPE]
+  //   bucket_fraction ::= real in the range [0..1]
+  //   parallelism ::= non-negative integer
+  // ```
+  public native void open(String filename, String options) throws IOException;
+
+  public void writeRecord(String record) throws IOException {
+    writeRecord(record.getBytes());
+  }
+
+  public native void writeRecord(byte[] record) throws IOException;
+
+  // Flush the data into disk, more `writeRecord` can be called.
+  public native void flush() throws IOException;
+
+  public native void close() throws IOException;
+}

java/com/google/riegeli/jni_record_reader.cc

@@ -0,0 +1,82 @@
+#include "com_google_riegeli_RecordReader.h"
+
+#include "riegeli/bytes/fd_reader.h"
+#include "riegeli/records/record_reader.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+/*
+ * Class:     com_google_riegeli_RecordReader
+ * Method:    open
+ * Signature: (Ljava/lang/String;)V
+ */
+using ReaderType = riegeli::RecordReader<riegeli::FdReader<>>;
+
+JNIEXPORT void JNICALL Java_com_google_riegeli_RecordReader_open(JNIEnv* env, jobject reader, jstring filename) {
+  /* Obtain a C-copy of the Java string */ 
+  const char* fname = env->GetStringUTFChars(filename, nullptr); 
+
+  /* Create the recorder */
+  riegeli::RecordReaderBase::Options record_reader_options;
+  auto* record_reader = new ReaderType(
+      std::forward_as_tuple(fname, O_RDONLY),
+      record_reader_options);
+
+  env->ReleaseStringUTFChars(filename, fname);   
+
+  /* Get the Field ID of the instance variables "recordReaderPtr" */
+  jfieldID fid = env->GetFieldID(env->GetObjectClass(reader), "recordReaderPtr", "J");
+
+  // Save the pointer as member.
+  env->SetLongField(reader, fid, reinterpret_cast<jlong>(record_reader));
+}
+
+namespace {
+ReaderType* getRecordReader(JNIEnv* env, jobject reader) {
+  jfieldID fid = env->GetFieldID(env->GetObjectClass(reader), "recordReaderPtr", "J");
+  jlong ptr = env->GetLongField(reader, fid);
+  return reinterpret_cast<ReaderType*>(ptr);
+}
+}
+
+/*
+ * Class:     com_google_riegeli_RecordReader
+ * Method:    readRecord
+ * Signature: ()[B
+ */
+JNIEXPORT jbyteArray JNICALL Java_com_google_riegeli_RecordReader_readRecord(JNIEnv* env, jobject obj) {
+  auto* record_reader = getRecordReader(env, obj);
+  if (!record_reader) {
+    return nullptr;
+  }
+  std::string record;
+  if (record_reader->ReadRecord(record)) {
+    jbyteArray ret = env->NewByteArray(record.size());
+    env->SetByteArrayRegion(ret, 0, record.size(), reinterpret_cast<const jbyte*>(record.data()));
+    return ret;
+  } else {
+    return nullptr;
+  }
+}
+
+/*
+ * Class:     com_google_riegeli_RecordReader
+ * Method:    close
+ * Signature: ()V
+ */
+JNIEXPORT void JNICALL Java_com_google_riegeli_RecordReader_close(JNIEnv* env, jobject reader) {
+  auto* record_reader = getRecordReader(env, reader);
+  if (record_reader) {
+    record_reader->Close();
+    delete record_reader;
+
+    jfieldID fid = env->GetFieldID(env->GetObjectClass(reader), "recordReaderPtr", "J");
+    env->SetLongField(reader, fid, 0L);
+  }
+}
+
+#ifdef __cplusplus
+}
+#endif
+