[IO] Added support for a new 'TFRecordWriter' class.

RELEASE.md

@@ -2,6 +2,8 @@
 
 Other new features include:
 
+  - `io` module:
+    - Added support for a new `TFRecordWriter`.
   - `ops` module:
     - Added a new ops namespace, `sparse`, that includes all sparse ops.
     - Added support for `sparse.reorder` and `sparse.merge`.

docs/src/main/scala/installation.sh

@@ -1,7 +1,7 @@
 // #clone_repository
 git clone https://github.com/tensorflow/tensorflow.git <repository_directory>
 cd <repository_directory>
-git checkout 4b46a399d7a5a5c9cc262d08e0df1217364a5b9f
+git checkout 1aaa68d93c6b2f4151446eb211399b4330c96a09
 // #clone_repository
 
 // #compile_tf

modules/api/src/main/scala/org/platanios/tensorflow/api/io/TFRecordWriter.scala

@@ -0,0 +1,65 @@
+/* Copyright 2017-18, Emmanouil Antonios Platanios. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
+package org.platanios.tensorflow.api.io
+
+import java.io.BufferedOutputStream
+import java.nio.file.{Files, Path, StandardOpenOption}
+
+import org.platanios.tensorflow.api.utilities.{CRC32C, Coding}
+import org.tensorflow.example.Example
+
+/** Helper used to write `Example` protocol buffers to TensorFlow record files.
+  *
+  * @param  filePath TensorFlow record file path.
+  *
+  * @author Emmanouil Antonios Platanios
+  */
+class TFRecordWriter(val filePath: Path) {
+  protected var fileStream: BufferedOutputStream = {
+    new BufferedOutputStream(Files.newOutputStream(
+      filePath, StandardOpenOption.CREATE_NEW, StandardOpenOption.APPEND))
+  }
+
+  /** Appends `example` to the TensorFlow records file. */
+  def write(example: Example): Unit = {
+    val recordBytes = example.toByteArray
+    // Format of a single record:
+    //  uint64    length
+    //  uint32    masked crc of length
+    //  byte      data[length]
+    //  uint32    masked crc of data
+    val encLength = Coding.encodeFixedInt64(recordBytes.length)
+    val encLengthMaskedCrc = Coding.encodeFixedInt32(CRC32C.mask(CRC32C.value(encLength)))
+    val encDataMaskedCrc = Coding.encodeFixedInt32(CRC32C.mask(CRC32C.value(recordBytes)))
+    fileStream.write(encLength ++ encLengthMaskedCrc ++ recordBytes ++ encDataMaskedCrc)
+  }
+
+  /** Pushes outstanding examples to disk. */
+  def flush(): Unit = {
+    fileStream.flush()
+  }
+
+  /** Calls `flush()` and then closes the current TensorFlow records file. */
+  def close(): Unit = {
+    fileStream.close()
+  }
+}
+
+object TFRecordWriter {
+  def apply(filePath: Path): TFRecordWriter = {
+    new TFRecordWriter(filePath)
+  }
+}