1 files changed, 107 insertions, 0 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/bazel/repository/HttpDownloader.java b/src/main/java/com/google/devtools/build/lib/bazel/repository/HttpDownloader.java
new file mode 100644
index 0000000000..0f9ff44a58
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/bazel/repository/HttpDownloader.java
@@ -0,0 +1,107 @@
+// Copyright 2014 Google Inc. 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 com.google.devtools.build.lib.bazel.repository;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.hash.Hasher;
+import com.google.common.hash.Hashing;
+import com.google.devtools.build.lib.vfs.Path;
+import com.google.devtools.build.lib.vfs.PathFragment;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.net.URL;
+import java.nio.ByteBuffer;
+import java.nio.channels.Channels;
+import java.nio.channels.ReadableByteChannel;
+
+/**
+ * Helper class for downloading a file from a URL.
+ */
+public class HttpDownloader {
+  private static final int BUFFER_SIZE = 2048;
+
+  private final URL url;
+  private final String sha256;
+  private final Path outputDirectory;
+
+  HttpDownloader(URL url, String sha256, Path outputDirectory) {
+    this.url = url;
+    this.sha256 = sha256;
+    this.outputDirectory = outputDirectory;
+  }
+
+  /**
+   * Attempt to download a file from the repository's URL. Returns the path to the file downloaded.
+   */
+  public Path download() throws IOException {
+    String filename = new PathFragment(url.getPath()).getBaseName();
+    if (filename.isEmpty()) {
+      filename = "temp";
+    }
+    Path destination = outputDirectory.getRelative(filename);
+
+    try (OutputStream outputStream = destination.getOutputStream()) {
+      ReadableByteChannel rbc = getChannel(url);
+      ByteBuffer byteBuffer = ByteBuffer.allocate(BUFFER_SIZE);
+      while (rbc.read(byteBuffer) > 0) {
+        byteBuffer.flip();
+        while (byteBuffer.hasRemaining()) {
+          outputStream.write(byteBuffer.get());
+        }
+      }
+    } catch (IOException e) {
+      throw new IOException(
+          "Error downloading " + url + " to " + destination + ": " + e.getMessage());
+    }
+
+    try {
+      String downloadedSha256 = getSha256(destination);
+      if (!downloadedSha256.equals(sha256)) {
+        throw new IOException(
+            "Downloaded file at " + destination + " has SHA-256 of " + downloadedSha256
+                + ", does not match expected SHA-256 (" + sha256 + ")");
+      }
+    } catch (IOException e) {
+      throw new IOException(
+          "Could not hash file " + destination + ": " + e.getMessage() + ", expected SHA-256 of "
+              + sha256 + ")");
+    }
+    return destination;
+  }
+
+  @VisibleForTesting
+  protected ReadableByteChannel getChannel(URL url) throws IOException {
+    return Channels.newChannel(url.openStream());
+  }
+
+  private String getSha256(Path path) throws IOException {
+    Hasher hasher = Hashing.sha256().newHasher();
+
+    byte byteBuffer[] = new byte[BUFFER_SIZE];
+    try (InputStream stream = path.getInputStream()) {
+      int numBytesRead = stream.read(byteBuffer);
+      while (numBytesRead != -1) {
+        if (numBytesRead != 0) {
+          // If more than 0 bytes were read, add them to the hash.
+          hasher.putBytes(byteBuffer, 0, numBytesRead);
+        }
+        numBytesRead = stream.read(byteBuffer);
+      }
+    }
+    return hasher.hash().toString();
+  }
+}