Move the RDE PGP file encoding to a dedicated file

The "file encoding" saves the file + metadata (filename and modification) in a "blob" format that PGP knows how to read.

Merges the file-encoder creation between RyDE and Ghostryde.

The new file - RydeFileEncoding.java - is a merge of the removed functions in
Ghostryde.java and the RydePgpFileOutputStream.java.

This is one of a series of CLs - each merging a single "part" of the encoding.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=205295756

java/google/registry/rde/RydeFileEncoding.java

@@ -0,0 +1,107 @@
+// Copyright 2018 The Nomulus Authors. 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 google.registry.rde;
+
+import static org.bouncycastle.openpgp.PGPLiteralData.BINARY;
+import static org.joda.time.DateTimeZone.UTC;
+
+import google.registry.util.ImprovedInputStream;
+import google.registry.util.ImprovedOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import javax.annotation.CheckReturnValue;
+import javax.annotation.WillNotClose;
+import org.bouncycastle.openpgp.PGPLiteralData;
+import org.bouncycastle.openpgp.PGPLiteralDataGenerator;
+import org.joda.time.DateTime;
+
+/**
+ * Input/Output stream for reading/writing PGP literal data layer.
+ *
+ * <p>OpenPGP messages are like an onion; there can be many layers like compression and encryption.
+ * It's important to wrap out plaintext in a literal data layer such as this so the code that's
+ * unwrapping the onion knows when to stop.
+ *
+ * <p>According to escrow spec, the PGP message should contain a single tar file.
+ */
+final class RydeFileEncoding {
+
+  private static final int BUFFER_SIZE = 64 * 1024;
+
+  /**
+   * Creates an OutputStream that encodes the data as a PGP file blob.
+   *
+   * <p>TODO(b/110465964): document where the input comes from / output goes to. Something like
+   * documenting that os is the result of openCompressor and the result is used for the actual file
+   * data (Ghostryde) / goes in to openTarEncoder (RyDE).
+   *
+   * @param os where to write the file blob. Is not closed by this object.
+   * @param filename the filename to set in the file's metadata.
+   * @param modified the modification time to set in the file's metadata.
+   */
+  @CheckReturnValue
+  static ImprovedOutputStream openPgpFileWriter(
+      @WillNotClose OutputStream os, String filename, DateTime modified) {
+    try {
+      return new ImprovedOutputStream(
+          "PgpFileWriter",
+          new PGPLiteralDataGenerator()
+              .open(os, BINARY, filename, modified.toDate(), new byte[BUFFER_SIZE]));
+    } catch (IOException e) {
+      throw new RuntimeException(e);
+    }
+  }
+
+  /** Input stream to a PGP file's data that also holds the file's metadata. */
+  static class PgpFileInputStream extends ImprovedInputStream {
+    private final String filename;
+    private final DateTime modified;
+
+    private PgpFileInputStream(PGPLiteralData literal) {
+      super("PgpFileReader", literal.getDataStream());
+      filename = literal.getFileName();
+      modified = new DateTime(literal.getModificationTime(), UTC);
+    }
+
+    /** Returns the name of the original file. */
+    String getFilename() {
+      return filename;
+    }
+
+    /** Returns the time this file was created or modified. */
+    DateTime getModified() {
+      return modified;
+    }
+  }
+
+  /**
+   * Opens an InputStream to a PGP file blob's data.
+   *
+   * <p>The result includes the file's metadata - the file name and modification time.
+   *
+   * <p>TODO(b/110465964): document where the input comes from / output goes to. Something like
+   * documenting that input is the result of openDecompressor and the result is the final file
+   * (Ghostryde) / goes into openTarDecoder (RyDE).
+   *
+   * @param input from where to read the file blob.
+   */
+  @CheckReturnValue
+  static PgpFileInputStream openPgpFileReader(@WillNotClose InputStream input) {
+    return new PgpFileInputStream(PgpUtils.readSinglePgpObject(input, PGPLiteralData.class));
+  }
+
+  private RydeFileEncoding() {}
+}