Support payload offsets

Support sending a file or stream payload from a non-zero offset.
This allows the clients to resume a transfer. Upper layers should use
this feature only when both sides support it.

PiperOrigin-RevId: 385137570

cpp/platform/base/BUILD

@@ -19,6 +19,7 @@ cc_library(
     srcs = [
         "base64_utils.cc",
         "bluetooth_utils.cc",
+        "input_stream.cc",
         "prng.cc",
     ],
     hdrs = [

cpp/platform/base/base_input_stream.h

@@ -32,6 +32,12 @@ class BaseInputStream : public InputStream {
 
   ExceptionOr<ByteArray> Read(std::int64_t size) override;
 
+  ExceptionOr<size_t> Skip(size_t offset) override {
+    size_t real_offset = std::min(offset, buffer_.size() - position_);
+    position_ += real_offset;
+    return ExceptionOr<size_t>(real_offset);
+  }
+
   Exception Close() override {
     // Do nothing.
     return {Exception::kSuccess};

cpp/platform/base/feature_flags.h

@@ -40,6 +40,8 @@ class FeatureFlags {
     // with the exp backoff, retry intervals in seconds: 3, 6, 12, 24...
     absl::Duration bwu_retry_exp_backoff_initial_delay = absl::Seconds(3);
     absl::Duration bwu_retry_exp_backoff_maximum_delay = absl::Seconds(300);
+    // Support sending file and stream payloads starting from a non-zero offset.
+    bool enable_send_payload_offset = true;
   };
 
   static const FeatureFlags& GetInstance() {

cpp/platform/base/input_stream.cc

@@ -0,0 +1,42 @@
+// Copyright 2020 Google LLC
+//
+// 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
+//
+//     https://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.
+
+#include "platform/base/input_stream.h"
+
+#include <cstddef>
+#include <cstdint>
+
+#include "platform/base/byte_array.h"
+#include "platform/base/exception.h"
+
+namespace location {
+namespace nearby {
+
+constexpr size_t kSkipBufferSize = 64 * 1024;
+
+ExceptionOr<size_t> InputStream::Skip(size_t offset) {
+  size_t bytes_left = offset;
+  while (bytes_left > 0) {
+    size_t chunk_size = std::min(bytes_left, kSkipBufferSize);
+    ExceptionOr<ByteArray> result = Read(chunk_size);
+    if (!result.ok()) {
+      return result.GetException();
+    }
+    bytes_left -= chunk_size;
+  }
+  return ExceptionOr<size_t>(offset);
+}
+
+}  // namespace nearby
+}  // namespace location

cpp/platform/base/input_stream.h

@@ -32,6 +32,10 @@ class InputStream {
 
   // throws Exception::kIo
   virtual ExceptionOr<ByteArray> Read(std::int64_t size) = 0;
+
+  // throws Exception::kIo
+  virtual ExceptionOr<size_t> Skip(size_t offset);
+
   // throws Exception::kIo
   virtual Exception Close() = 0;
 };

cpp/platform/public/file.h

@@ -50,6 +50,8 @@ class InputFile final {
   // Returns total size of this file in bytes.
   std::int64_t GetTotalSize() const { return impl_->GetTotalSize(); }
 
+  ExceptionOr<size_t> Skip(size_t offset) { return impl_->Skip(offset); }
+
   // Disallows further reads from the file and frees system resources,
   // associated with it.
   Exception Close() { return impl_->Close(); }