// Copyright 2015 The Android Open Source Project
//
// 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.

#include "webservd/protocol_handler.h"

#include <linux/tcp.h>
#include <microhttpd.h>
#include <netinet/in.h>
#include <sys/socket.h>

#include <algorithm>
#include <limits>
#include <vector>

#include <base/bind.h>
#include <base/guid.h>
#include <base/logging.h>
#include <base/message_loop/message_loop.h>

#include "webservd/request.h"
#include "webservd/request_handler_interface.h"
#include "webservd/server_interface.h"

namespace webservd {

// Helper class to provide static callback methods to libmicrohttpd library,
// with the ability to access private methods of Server class.
class ServerHelper final {
 public:
  static int ConnectionHandler(void *cls,
                               MHD_Connection* connection,
                               const char* url,
                               const char* method,
                               const char* version,
                               const char* upload_data,
                               size_t* upload_data_size,
                               void** con_cls) {
    auto handler = reinterpret_cast<ProtocolHandler*>(cls);
    if (nullptr == *con_cls) {
      std::string request_handler_id = handler->FindRequestHandler(url, method);
      std::unique_ptr<Request> request{new Request{
          request_handler_id, url, method, version, connection, handler
      }};
      if (!request->BeginRequestData())
        return MHD_NO;

      // Pass the raw pointer here in order to interface with libmicrohttpd's
      // old-style C API.
      *con_cls = request.release();
    } else {
      auto request = reinterpret_cast<Request*>(*con_cls);
      if (*upload_data_size) {
        if (!request->AddRequestData(upload_data, upload_data_size))
          return MHD_NO;
      } else {
        request->EndRequestData();
      }
    }
    return MHD_YES;
  }

  static void RequestCompleted(void* /* cls */,
                               MHD_Connection*  /* connection */,
                               void** con_cls,
                               MHD_RequestTerminationCode toe) {
    if (toe != MHD_REQUEST_TERMINATED_COMPLETED_OK) {
      LOG(ERROR) << "Web request terminated abnormally with error code: "
                 << toe;
    }
    auto request = reinterpret_cast<Request*>(*con_cls);
    *con_cls = nullptr;
    delete request;
  }
};

ProtocolHandler::ProtocolHandler(const std::string& name,
                                 ServerInterface* server_interface)
    : id_{base::GenerateGUID()},
      name_{name},
      server_interface_{server_interface} {}

ProtocolHandler::~ProtocolHandler() {
  Stop();
}

std::string ProtocolHandler::AddRequestHandler(
    const std::string& url,
    const std::string& method,
    std::unique_ptr<RequestHandlerInterface> handler) {
  std::string handler_id = base::GenerateGUID();
  request_handlers_.emplace(handler_id,
                            HandlerMapEntry{url, method, std::move(handler)});
  return handler_id;
}

bool ProtocolHandler::RemoveRequestHandler(const std::string& handler_id) {
  return request_handlers_.erase(handler_id) == 1;
}

std::string ProtocolHandler::FindRequestHandler(
    const base::StringPiece& url,
    const base::StringPiece& method) const {
  size_t score = std::numeric_limits<size_t>::max();
  std::string handler_id;
  for (const auto& pair : request_handlers_) {
    std::string handler_url = pair.second.url;
    bool url_match = (handler_url == url);
    bool method_match = (pair.second.method == method);

    // Try exact match first. If everything matches, we have our handler.
    if (url_match && method_match)
      return pair.first;

    // Calculate the current handler's similarity score. The lower the score
    // the better the match is...
    size_t current_score = 0;
    if (!url_match && !handler_url.empty() && handler_url.back() == '/') {
      if (url.starts_with(handler_url)) {
        url_match = true;
        // Use the difference in URL length as URL match quality proxy.
        // The longer URL, the more specific (better) match is.
        // Multiply by 2 to allow for extra score point for matching the method.
        current_score = (url.size() - handler_url.size()) * 2;
      }
    }

    if (!method_match && pair.second.method.empty()) {
      // If the handler didn't specify the method it handles, this means
      // it doesn't care. However this isn't the exact match, so bump
      // the score up one point.
      method_match = true;
      ++current_score;
    }

    if (url_match && method_match && current_score < score) {
      score = current_score;
      handler_id = pair.first;
    }
  }

  return handler_id;
}

bool ProtocolHandler::Start(const Config::ProtocolHandler& config) {
  if (server_) {
    LOG(ERROR) << "Protocol handler is already running.";
    return false;
  }

  // If using TLS, the certificate, private key and fingerprint must be
  // provided.
  CHECK_EQ(config.use_tls, !config.private_key.empty());
  CHECK_EQ(config.use_tls, !config.certificate.empty());
  CHECK_EQ(config.use_tls, !config.certificate_fingerprint.empty());

  LOG(INFO) << "Starting " << (config.use_tls ? "HTTPS" : "HTTP")
            << " protocol handler on port: " << config.port;

  port_ = config.port;
  protocol_ = (config.use_tls ? "https" : "http");
  certificate_fingerprint_ = config.certificate_fingerprint;

  auto callback_addr =
      reinterpret_cast<intptr_t>(&ServerHelper::RequestCompleted);
  uint32_t flags = MHD_NO_FLAG;
  if (server_interface_->GetConfig().use_debug)
    flags |= MHD_USE_DEBUG;

  // Enable IPv6 if supported.
  if (server_interface_->GetConfig().use_ipv6)
    flags |= MHD_USE_DUAL_STACK;
  flags |= MHD_USE_TCP_FASTOPEN;  // Use TCP Fast Open (see RFC 7413).
  flags |= MHD_USE_SUSPEND_RESUME;  // Allow suspending/resuming connections.

  // MHD uses timeout of 0 to mean there is no timeout.
  int timeout = server_interface_->GetConfig().default_request_timeout_seconds;
  if (timeout < 0)
    timeout = 0;

  std::vector<MHD_OptionItem> options{
    {MHD_OPTION_CONNECTION_LIMIT, 10, nullptr},
    {MHD_OPTION_CONNECTION_TIMEOUT, timeout, nullptr},
    {MHD_OPTION_NOTIFY_COMPLETED, callback_addr, nullptr},
  };

  if (config.socket_fd != -1) {
    int socket_fd = config.socket_fd;

    // Set some more socket options. These options were set in libmicrohttpd.
    int on = 1;
    if (setsockopt(socket_fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)) < 0) {
      // Treat this as a non-fatal failure. Just continue after logging.
      PLOG(WARNING) << "Failed to set SO_REUSEADDR option on listening socket.";
    }
    on = (MHD_USE_DUAL_STACK != (flags & MHD_USE_DUAL_STACK));
    if (setsockopt(socket_fd, IPPROTO_IPV6, IPV6_V6ONLY, &on, sizeof(on)) < 0) {
      PLOG(WARNING) << "Failed to set IPV6_V6ONLY option on listening socket.";
      close(socket_fd);
      return false;
    }

    // Bind socket to the port.
    sockaddr_in6 addr = {};
    addr.sin6_family = AF_INET6;
    addr.sin6_port = htons(config.port);
    if (bind(socket_fd, reinterpret_cast<const sockaddr*>(&addr),
             sizeof(addr)) < 0) {
      PLOG(ERROR) << "Failed to bind the socket to port " << config.port;
      close(socket_fd);
      return false;
    }
    if ((flags & MHD_USE_TCP_FASTOPEN) != 0) {
      // This is the default value from libmicrohttpd.
      int fastopen_queue_size = 10;
      if (setsockopt(socket_fd, IPPROTO_TCP, TCP_FASTOPEN,
                     &fastopen_queue_size, sizeof(fastopen_queue_size)) < 0) {
        // Treat this as a non-fatal failure. Just continue after logging.
        PLOG(WARNING) << "Failed to set TCP_FASTOPEN option on socket.";
      }
    }

    // Start listening on the socket.
    // 32 connections is the value used by libmicrohttpd.
    if (listen(socket_fd, 32) < 0) {
      PLOG(ERROR) << "Failed to listen for connections on the socket.";
      close(socket_fd);
      return false;
    }

    // Finally, pass the socket to libmicrohttpd.
    options.push_back(
        MHD_OptionItem{MHD_OPTION_LISTEN_SOCKET, socket_fd, nullptr});
  }

  // libmicrohttpd expects both the key and certificate to be zero-terminated
  // strings. Make sure they are terminated properly.
  brillo::SecureBlob private_key_copy = config.private_key;
  brillo::Blob certificate_copy = config.certificate;
  private_key_copy.push_back(0);
  certificate_copy.push_back(0);

  if (config.use_tls) {
    flags |= MHD_USE_SSL;
    options.push_back(
        MHD_OptionItem{MHD_OPTION_HTTPS_MEM_KEY, 0, private_key_copy.data()});
    options.push_back(
        MHD_OptionItem{MHD_OPTION_HTTPS_MEM_CERT, 0, certificate_copy.data()});
  }

  options.push_back(MHD_OptionItem{MHD_OPTION_END, 0, nullptr});

  server_ = MHD_start_daemon(flags, config.port, nullptr, nullptr,
                             &ServerHelper::ConnectionHandler, this,
                             MHD_OPTION_ARRAY, options.data(), MHD_OPTION_END);
  if (!server_) {
    PLOG(ERROR) << "Failed to create protocol handler on port " << config.port;
    return false;
  }
  server_interface_->ProtocolHandlerStarted(this);
  DoWork();
  LOG(INFO) << "Protocol handler started";
  return true;
}

bool ProtocolHandler::Stop() {
  if (server_) {
    LOG(INFO) << "Shutting down the protocol handler...";
    MHD_stop_daemon(server_);
    server_ = nullptr;
    server_interface_->ProtocolHandlerStopped(this);
    LOG(INFO) << "Protocol handler shutdown complete";
  }
  port_ = 0;
  protocol_.clear();
  certificate_fingerprint_.clear();
  return true;
}

void ProtocolHandler::AddRequest(Request* request) {
  requests_.emplace(request->GetID(), request);
}

void ProtocolHandler::RemoveRequest(Request* request) {
  requests_.erase(request->GetID());
}

Request* ProtocolHandler::GetRequest(const std::string& request_id) const {
  auto p = requests_.find(request_id);
  return (p != requests_.end()) ? p->second : nullptr;
}

// A file descriptor watcher class that oversees I/O operation notification
// on particular socket file descriptor.
class ProtocolHandler::Watcher final : public base::MessageLoopForIO::Watcher {
 public:
  Watcher(ProtocolHandler* handler, int fd) : fd_{fd}, handler_{handler} {}

  void Watch(bool read, bool write) {
    if (read == watching_read_ && write == watching_write_ && !triggered_)
      return;

    controller_.StopWatchingFileDescriptor();
    watching_read_ = read;
    watching_write_ = write;
    triggered_ = false;

    auto mode = base::MessageLoopForIO::WATCH_READ_WRITE;
    if (watching_read_ && watching_write_)
      mode = base::MessageLoopForIO::WATCH_READ_WRITE;
    else if (watching_read_)
      mode = base::MessageLoopForIO::WATCH_READ;
    else if (watching_write_)
      mode = base::MessageLoopForIO::WATCH_WRITE;
    base::MessageLoopForIO::current()->WatchFileDescriptor(fd_, false, mode,
                                                           &controller_, this);
  }

  // Overrides from base::MessageLoopForIO::Watcher.
  void OnFileCanReadWithoutBlocking(int /* fd */) override {
    triggered_ = true;
    handler_->ScheduleWork();
  }

  void OnFileCanWriteWithoutBlocking(int /* fd */) override {
    triggered_ = true;
    handler_->ScheduleWork();
  }

  int GetFileDescriptor() const { return fd_; }

 private:
  int fd_{-1};
  ProtocolHandler* handler_{nullptr};
  bool watching_read_{false};
  bool watching_write_{false};
  bool triggered_{false};
  base::MessageLoopForIO::FileDescriptorWatcher controller_;

  DISALLOW_COPY_AND_ASSIGN(Watcher);
};

void ProtocolHandler::ScheduleWork() {
  if (work_scheduled_)
    return;

  work_scheduled_ = true;
  base::MessageLoopForIO::current()->PostTask(
      FROM_HERE,
      base::Bind(&ProtocolHandler::DoWork, weak_ptr_factory_.GetWeakPtr()));
}

void ProtocolHandler::DoWork() {
  work_scheduled_ = false;
  weak_ptr_factory_.InvalidateWeakPtrs();

  // Check if there is any pending work to be done in libmicrohttpd.
  MHD_run(server_);

  // Get all the file descriptors from libmicrohttpd and watch for I/O
  // operations on them.
  fd_set rs;
  fd_set ws;
  fd_set es;
  int max_fd = MHD_INVALID_SOCKET;
  FD_ZERO(&rs);
  FD_ZERO(&ws);
  FD_ZERO(&es);
  CHECK_EQ(MHD_YES, MHD_get_fdset(server_, &rs, &ws, &es, &max_fd));

  for (auto& watcher : watchers_) {
    int fd = watcher->GetFileDescriptor();
    if (FD_ISSET(fd, &rs) || FD_ISSET(fd, &ws)) {
      watcher->Watch(FD_ISSET(fd, &rs), FD_ISSET(fd, &ws));
      FD_CLR(fd, &rs);
      FD_CLR(fd, &ws);
    } else {
      watcher.reset();
    }
  }

  watchers_.erase(std::remove(watchers_.begin(), watchers_.end(), nullptr),
                  watchers_.end());

  for (int fd = 0; fd <= max_fd; fd++) {
    // libmicrohttpd is not using exception FDs, so lets put our expectations
    // upfront.
    CHECK(!FD_ISSET(fd, &es));
    if (FD_ISSET(fd, &rs) || FD_ISSET(fd, &ws)) {
      // libmicrohttpd should never use any of stdin/stdout/stderr descriptors.
      CHECK_GT(fd, STDERR_FILENO);
      std::unique_ptr<Watcher> watcher{new Watcher{this, fd}};
      watcher->Watch(FD_ISSET(fd, &rs), FD_ISSET(fd, &ws));
      watchers_.push_back(std::move(watcher));
    }
  }

  // Schedule a time-out timer, if asked by libmicrohttpd.
  MHD_UNSIGNED_LONG_LONG mhd_timeout = 0;
  if (MHD_get_timeout(server_, &mhd_timeout) == MHD_YES) {
    base::MessageLoopForIO::current()->PostDelayedTask(
        FROM_HERE,
        base::Bind(&ProtocolHandler::DoWork, weak_ptr_factory_.GetWeakPtr()),
        base::TimeDelta::FromMilliseconds(mhd_timeout));
  }
}

}  // namespace webservd