fix: retry using remote offset

google-cloud-storage/clirr-ignored-differences.xml

@@ -26,4 +26,9 @@
         <method>com.google.cloud.storage.BucketInfo$Builder setUpdateTime(java.lang.Long)</method>
         <differenceType>7013</differenceType>
     </difference>
+    <difference>
+        <className>com/google/cloud/storage/spi/v1/StorageRpc</className>
+        <method>long getCurrentUploadOffset(java.lang.String)</method>
+        <differenceType>7012</differenceType>
+    </difference>
 </differences>

google-cloud-storage/src/main/java/com/google/cloud/storage/BlobWriteChannel.java

@@ -51,6 +51,15 @@ class BlobWriteChannel extends BaseWriteChannel<StorageOptions, BlobInfo> {
   // Contains metadata of the updated object or null if upload is not completed.
   private StorageObject storageObject;
 
+  // Detect if flushBuffer() is being retried or not.
+  // TODO: I don't think this is thread safe, and there's probably a better way to detect a retry
+  // occuring.
+  private boolean retrying = false;
+
+  boolean isRetrying() {
+    return retrying;
+  }
+
   StorageObject getStorageObject() {
     return storageObject;
   }
@@ -63,11 +72,105 @@ protected void flushBuffer(final int length, final boolean last) {
               new Runnable() {
                 @Override
                 public void run() {
-                  storageObject =
-                      getOptions()
-                          .getStorageRpcV1()
-                          .writeWithResponse(
-                              getUploadId(), getBuffer(), 0, getPosition(), length, last);
+                  if (!isRetrying()) {
+                    // Enable isRetrying state to reduce number of calls to getCurrentUploadOffset()
+                    retrying = true;
+                    storageObject =
+                        getOptions()
+                            .getStorageRpcV1()
+                            .writeWithResponse(
+                                getUploadId(), getBuffer(), 0, getPosition(), length, last);
+                  } else {
+                    // Retriable interruption occurred.
+                    // Variables:
+                    // chunk = getBuffer()
+                    // localNextByteOffset == getPosition()
+                    // chunkSize = getChunkSize()
+                    //
+                    // Case 1: localNextByteOffset == 0 && remoteNextByteOffset == 0:
+                    // we are retrying from first chunk start from 0 offset.
+                    //
+                    // Case 2: localNextByteOffset == remoteNextByteOffset:
+                    // Special case of Case 1 when a chunk is retried.
+                    //
+                    // Case 3: localNextByteOffset < remoteNextByteOffset
+                    //             && driftOffset < chunkSize:
+                    // Upload progressed and localNextByteOffset is not in-sync with
+                    // remoteNextByteOffset and driftOffset is less than chunkSize.
+                    // driftOffset must be less than chunkSize for it to retry using
+                    // chunk maintained in memory.
+                    // Find the driftOffset by subtracting localNextByteOffset from
+                    // remoteNextByteOffset.
+                    // Use driftOffset to determine where to restart from using the chunk in
+                    // memory.
+                    //
+                    // Case 4: localNextByteOffset < remoteNextByteOffset
+                    //            && driftOffset == chunkSize:
+                    // Special case of Case 3.
+                    // If chunkSize is equal to driftOffset then remoteNextByteOffset has moved on
+                    // to the next chunk.
+                    //
+                    // Case 5: localNextByteOffset < remoteNextByteOffset
+                    //            && driftOffset > chunkSize:
+                    // Throw exception as remoteNextByteOffset has drifted beyond the retriable
+                    // chunk maintained in memory. This is not possible unless there's multiple
+                    // clients uploading to the same resumable upload session.
+                    //
+                    // Case 6: localNextByteOffset > remoteNextByteOffset:
+                    // For completeness, this case is not possible because it would require retrying
+                    // a 400 status code which is not allowed.
+                    //
+                    // Get remote offset from API
+                    long remoteNextByteOffset =
+                        getOptions().getStorageRpcV1().getCurrentUploadOffset(getUploadId());
+                    long localNextByteOffset = getPosition();
+                    int driftOffset = (int) (remoteNextByteOffset - localNextByteOffset);
+                    int retryChunkLength = length - driftOffset;
+
+                    if (localNextByteOffset == 0 && remoteNextByteOffset == 0
+                        || localNextByteOffset == remoteNextByteOffset) {
+                      // Case 1 and 2
+                      storageObject =
+                          getOptions()
+                              .getStorageRpcV1()
+                              .writeWithResponse(
+                                  getUploadId(), getBuffer(), 0, getPosition(), length, last);
+                    } else if (localNextByteOffset < remoteNextByteOffset
+                        && driftOffset < getChunkSize()) {
+                      // Case 3
+                      storageObject =
+                          getOptions()
+                              .getStorageRpcV1()
+                              .writeWithResponse(
+                                  getUploadId(),
+                                  getBuffer(),
+                                  driftOffset,
+                                  remoteNextByteOffset,
+                                  retryChunkLength,
+                                  last);
+                    } else if (localNextByteOffset < remoteNextByteOffset
+                        && driftOffset == getChunkSize()) {
+                      // Case 4
+                      // Continue to next chunk
+                      retrying = false;
+                      return;
+                    } else {
+                      // Case 5
+                      StringBuilder sb = new StringBuilder();
+                      sb.append(
+                          "Remote offset has progressed beyond starting byte offset of next chunk.");
+                      sb.append(
+                          "This may be a symptom of multiple clients uploading to the same upload session.\n\n");
+                      sb.append("For debugging purposes:\n");
+                      sb.append("uploadId: ").append(getUploadId()).append('\n');
+                      sb.append("localNextByteOffset: ").append(localNextByteOffset).append('\n');
+                      sb.append("remoteNextByteOffset: ").append(remoteNextByteOffset).append('\n');
+                      sb.append("driftOffset: ").append(driftOffset).append("\n\n");
+                      throw new StorageException(0, sb.toString());
+                    }
+                  }
+                  // Request was successful and retrying state is now disabled.
+                  retrying = false;
                 }
               }),
           getOptions().getRetrySettings(),

google-cloud-storage/src/main/java/com/google/cloud/storage/spi/v1/HttpStorageRpc.java

@@ -747,6 +747,51 @@ public void write(
     writeWithResponse(uploadId, toWrite, toWriteOffset, destOffset, length, last);
   }
 
+  @Override
+  public long getCurrentUploadOffset(String uploadId) {
+    try {
+      GenericUrl url = new GenericUrl(uploadId);
+      HttpRequest httpRequest = storage.getRequestFactory().buildPutRequest(url, null);
+
+      httpRequest.getHeaders().setContentRange("bytes */*");
+      // Turn off automatic redirects.
+      // HTTP 308 are returned if upload is incomplete.
+      // See: https://cloud.google.com/storage/docs/performing-resumable-uploads
+      httpRequest.setFollowRedirects(false);
+
+      HttpResponse response = null;
+      try {
+        response = httpRequest.execute();
+        int code = response.getStatusCode();
+        String message = response.getStatusMessage();
+        if (code == 201 || code == 200) {
+          throw new StorageException(0, "Resumable upload is already complete.");
+        }
+        StringBuilder sb = new StringBuilder();
+        sb.append("Not sure what occurred. Here's debugging information:\n");
+        sb.append("Response:\n").append(response.toString()).append("\n\n");
+        throw new StorageException(0, sb.toString());
+      } catch (HttpResponseException ex) {
+        int code = ex.getStatusCode();
+        if (code == 308 && ex.getHeaders().getRange() == null) {
+          // No progress has been made.
+          return 0;
+        } else {
+          // API returns last byte received offset
+          String range = ex.getHeaders().getRange();
+          // Return next byte offset by adding 1 to last byte received offset
+          return Long.parseLong(range.substring(range.indexOf("-") + 1)) + 1;
+        }
+      } finally {
+        if (response != null) {
+          response.disconnect();
+        }
+      }
+    } catch (IOException ex) {
+      throw translate(ex);
+    }
+  }
+
   @Override
   public StorageObject writeWithResponse(
       String uploadId,

google-cloud-storage/src/main/java/com/google/cloud/storage/spi/v1/StorageRpc.java

@@ -328,6 +328,15 @@ void write(
       int length,
       boolean last);
 
+  /**
+   * Requests current byte offset from Cloud Storage API. Used to recover from a failure in some
+   * bytes were committed successfully to the open resumable session.
+   *
+   * @param uploadId resumable upload ID URL
+   * @throws StorageException upon failure
+   */
+  long getCurrentUploadOffset(String uploadId);
+
   /**
    * Writes the provided bytes to a storage object at the provided location. If {@code last=true}
    * returns metadata of the updated object, otherwise returns null.

google-cloud-storage/src/main/java/com/google/cloud/storage/testing/StorageRpcTestBase.java

@@ -139,6 +139,11 @@ public void write(
     throw new UnsupportedOperationException("Not implemented yet");
   }
 
+  @Override
+  public long getCurrentUploadOffset(String uploadId) {
+    throw new UnsupportedOperationException("Not implemented yet");
+  }
+
   @Override
   public StorageObject writeWithResponse(
       String uploadId,

google-cloud-storage/src/test/java/com/google/cloud/storage/BlobWriteChannelTest.java

@@ -134,6 +134,74 @@ public void testWriteWithoutFlush() throws IOException {
     assertEquals(MIN_CHUNK_SIZE, writer.write(ByteBuffer.allocate(MIN_CHUNK_SIZE)));
   }
 
+  @Test
+  public void testWriteWithFlushRetryChunk() throws IOException {
+    StorageException exception = new StorageException(new SocketException("Socket closed"));
+    ByteBuffer buffer = randomBuffer(MIN_CHUNK_SIZE);
+    Capture<byte[]> capturedBuffer = Capture.newInstance();
+    expect(storageRpcMock.open(BLOB_INFO.toPb(), EMPTY_RPC_OPTIONS)).andReturn(UPLOAD_ID);
+    expect(
+            storageRpcMock.writeWithResponse(
+                eq(UPLOAD_ID),
+                capture(capturedBuffer),
+                eq(0),
+                eq(0L),
+                eq(MIN_CHUNK_SIZE),
+                eq(false)))
+        .andThrow(exception);
+    expect(storageRpcMock.getCurrentUploadOffset(eq(UPLOAD_ID))).andReturn(0L);
+    expect(
+            storageRpcMock.writeWithResponse(
+                eq(UPLOAD_ID),
+                capture(capturedBuffer),
+                eq(0),
+                eq(0L),
+                eq(MIN_CHUNK_SIZE),
+                eq(false)))
+        .andReturn(null);
+    replay(storageRpcMock);
+    writer = new BlobWriteChannel(options, BLOB_INFO, EMPTY_RPC_OPTIONS);
+    writer.setChunkSize(MIN_CHUNK_SIZE);
+    assertEquals(MIN_CHUNK_SIZE, writer.write(buffer));
+    assertTrue(writer.isOpen());
+    assertNull(writer.getStorageObject());
+    assertArrayEquals(buffer.array(), capturedBuffer.getValue());
+  }
+
+  @Test
+  public void testWriteWithFlushRetryChunkWithDrift() throws IOException {
+    StorageException exception = new StorageException(new SocketException("Socket closed"));
+    ByteBuffer buffer = randomBuffer(MIN_CHUNK_SIZE);
+    Capture<byte[]> capturedBuffer = Capture.newInstance();
+    expect(storageRpcMock.open(BLOB_INFO.toPb(), EMPTY_RPC_OPTIONS)).andReturn(UPLOAD_ID);
+    expect(
+            storageRpcMock.writeWithResponse(
+                eq(UPLOAD_ID),
+                capture(capturedBuffer),
+                eq(0),
+                eq(0L),
+                eq(MIN_CHUNK_SIZE),
+                eq(false)))
+        .andThrow(exception);
+    expect(storageRpcMock.getCurrentUploadOffset(eq(UPLOAD_ID))).andReturn(10L);
+    expect(
+            storageRpcMock.writeWithResponse(
+                eq(UPLOAD_ID),
+                capture(capturedBuffer),
+                eq(10),
+                eq(10L),
+                eq(MIN_CHUNK_SIZE - 10),
+                eq(false)))
+        .andReturn(null);
+    replay(storageRpcMock);
+    writer = new BlobWriteChannel(options, BLOB_INFO, EMPTY_RPC_OPTIONS);
+    writer.setChunkSize(MIN_CHUNK_SIZE);
+    assertEquals(MIN_CHUNK_SIZE, writer.write(buffer));
+    assertTrue(writer.isOpen());
+    assertNull(writer.getStorageObject());
+    assertArrayEquals(buffer.array(), capturedBuffer.getValue());
+  }
+
   @Test
   public void testWriteWithFlush() throws IOException {
     expect(storageRpcMock.open(BLOB_INFO.toPb(), EMPTY_RPC_OPTIONS)).andReturn(UPLOAD_ID);