plugins/experimental/cache_fill/background_fetch.h

/** @file

    Plugin to perform background fetches of certain content that would
    otherwise not be cached. For example, Range: requests / responses.

    @section license License

    Licensed to the Apache Software Foundation (ASF) under one
    or more contributor license agreements.  See the NOTICE file
    distributed with this work for additional information
    regarding copyright ownership.  The ASF licenses this file
    to you 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.
*/

#pragma once
#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <cstdarg>

#include <string>
#include <iostream>
#include <unordered_map>
#include <cinttypes>
#include <string_view>
#include <array>
#include <netinet/in.h>
#include <arpa/inet.h>

#include "ts/ts.h"
#include "ts/remap.h"

using OutstandingRequests = std::unordered_map<std::string, bool>;
const char PLUGIN_NAME[]  = "cache_fill";

// This is the list of all headers that must be removed when we make the actual background
// fetch request for range requests.
static const std::array<const std::string_view, 6> FILTER_HEADERS{
  {{TS_MIME_FIELD_RANGE, static_cast<size_t>(TS_MIME_LEN_RANGE)},
   {TS_MIME_FIELD_IF_MATCH, static_cast<size_t>(TS_MIME_LEN_IF_MATCH)},
   {TS_MIME_FIELD_IF_MODIFIED_SINCE, static_cast<size_t>(TS_MIME_LEN_IF_MODIFIED_SINCE)},
   {TS_MIME_FIELD_IF_NONE_MATCH, static_cast<size_t>(TS_MIME_LEN_IF_NONE_MATCH)},
   {TS_MIME_FIELD_IF_RANGE, static_cast<size_t>(TS_MIME_LEN_IF_RANGE)},
   {TS_MIME_FIELD_IF_UNMODIFIED_SINCE, static_cast<size_t>(TS_MIME_LEN_IF_UNMODIFIED_SINCE)}}
};

namespace cache_fill_ns
{
extern DbgCtl dbg_ctl;
}
using namespace cache_fill_ns;
class BgFetchState
{
public:
  BgFetchState()                       = default;
  BgFetchState(BgFetchState const &)   = delete;
  void operator=(BgFetchState const &) = delete;

  static BgFetchState &
  getInstance()
  {
    static BgFetchState _instance;
    return _instance;
  }

  ~BgFetchState() { TSMutexDestroy(_lock); }

  bool
  acquire(const std::string &url)
  {
    bool ret;

    TSMutexLock(_lock);
    if (_urls.end() == _urls.find(url)) {
      _urls[url] = true;
      ret        = true;
    } else {
      ret = false;
    }
    TSMutexUnlock(_lock);

    Dbg(dbg_ctl, "BgFetchState.acquire(): ret = %d, url = %s", ret, url.c_str());

    return ret;
  }

  bool
  release(const std::string &url)
  {
    bool ret;

    TSMutexLockGuard lock(_lock);
    if (_urls.end() == _urls.find(url)) {
      ret = false;
    } else {
      _urls.erase(url);
      ret = true;
    }

    return ret;
  }

private:
  OutstandingRequests _urls;
  TSMutex             _lock = TSMutexCreate();
};

//////////////////////////////////////////////////////////////////////////////
// Hold and manage some state for the TXN background fetch continuation.
// This is necessary, because the TXN is likely to not be available
// during the time we fetch from origin.
struct BgFetchData {
  BgFetchData() { memset(&client_ip, 0, sizeof(client_ip)); }

  ~BgFetchData()
  {
    TSHandleMLocRelease(mbuf, TS_NULL_MLOC, hdr_loc);
    TSHandleMLocRelease(mbuf, TS_NULL_MLOC, url_loc);

    TSMBufferDestroy(mbuf);

    if (vc) {
      TSError("[%s] Destroyed BgFetchDATA while VC was alive", PLUGIN_NAME);
      TSVConnClose(vc);
      vc = nullptr;
    }

    // If we got schedule, also clean that up
    if (_cont) {
      releaseUrl();

      TSContDestroy(_cont);
      _cont = nullptr;
      TSIOBufferReaderFree(req_io_buf_reader);
      TSIOBufferDestroy(req_io_buf);
      TSIOBufferReaderFree(resp_io_buf_reader);
      TSIOBufferDestroy(resp_io_buf);
    }
  }

  bool
  acquireUrl() const
  {
    return BgFetchState::getInstance().acquire(_url);
  }
  bool
  releaseUrl() const
  {
    return BgFetchState::getInstance().release(_url);
  }

  const char *
  getUrl() const
  {
    return _url.c_str();
  }

  void
  addBytes(int64_t b)
  {
    _bytes += b;
  }

  bool initialize(TSMBuffer request, TSMLoc req_hdr, TSHttpTxn txnp);
  void schedule();

  TSMBuffer mbuf    = TSMBufferCreate();
  TSMLoc    hdr_loc = TS_NULL_MLOC;
  TSMLoc    url_loc = TS_NULL_MLOC;

  struct sockaddr_storage client_ip;

  // This is for the actual background fetch / NetVC
  TSVConn          vc                 = nullptr;
  TSIOBuffer       req_io_buf         = nullptr;
  TSIOBuffer       resp_io_buf        = nullptr;
  TSIOBufferReader req_io_buf_reader  = nullptr;
  TSIOBufferReader resp_io_buf_reader = nullptr;
  TSVIO            r_vio              = nullptr;
  TSVIO            w_vio              = nullptr;

private:
  std::string _url;
  int64_t     _bytes = 0;
  TSCont      _cont  = nullptr;
};