curl_writev.cc

// Copyright 2023 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 "google/cloud/internal/curl_writev.h"
#include <cstdio>

namespace google {
namespace cloud {
namespace rest_internal {
GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_BEGIN

std::size_t WriteVector::size() const {
  std::size_t size = 0;
  for (auto const& s : writev_) {
    size += s.size();
  }
  return size;
}

std::size_t WriteVector::MoveTo(absl::Span<char> dst) {
  auto const avail = dst.size();
  while (!writev_.empty()) {
    auto& src = writev_.front();
    if (src.size() > dst.size()) {
      std::copy(src.begin(), src.begin() + dst.size(), dst.begin());
      src.remove_prefix(dst.size());
      dst.remove_prefix(dst.size());
      break;
    }
    std::copy(src.begin(), src.end(), dst.begin());
    dst.remove_prefix(src.size());
    writev_.pop_front();
  }
  return avail - dst.size();
}

bool WriteVector::Seek(std::size_t offset, int origin) {
  // libcurl claims to only require support for `SEEK_SET`, so we only support
  // that. If libcurl ever uses any other `origin` the seek operation will
  // fail, causing the libcurl request to fail with CURLE_SEND_FAIL_REWIND.
  // These errors are treated as `StatusCode::kUnavailable` and thus retryable
  // for most operations.
  if (origin != SEEK_SET) return false;
  writev_.assign(original_.begin(), original_.end());
  while (!writev_.empty()) {
    auto& src = writev_.front();
    if (src.size() >= offset) {
      src.remove_prefix(offset);
      offset = 0;
      break;
    }
    offset -= src.size();
    writev_.pop_front();
  }
  return offset == 0;
}

GOOGLE_CLOUD_CPP_INLINE_NAMESPACE_END
}  // namespace rest_internal
}  // namespace cloud
}  // namespace google