// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "net/http/disk_cache_based_quic_server_info.h"

#include "base/bind.h"
#include "base/callback.h"
#include "base/logging.h"
#include "base/metrics/histogram.h"
#include "net/base/completion_callback.h"
#include "net/base/io_buffer.h"
#include "net/base/net_errors.h"
#include "net/http/http_cache.h"
#include "net/http/http_network_session.h"
#include "net/quic/quic_server_id.h"

namespace net {

// Histogram for tracking down the state of disk_cache::Entry.
enum DiskCacheEntryState {
  DISK_CACHE_ENTRY_OPENED = 0,
  DISK_CACHE_ENTRY_CLOSED = 1,
  DISK_CACHE_ENTRY_NUM_STATES = 2,
};

void RecordDiskCacheEntryState(DiskCacheEntryState entry_state) {
  UMA_HISTOGRAM_ENUMERATION("Net.QuicDiskCache.EntryState", entry_state,
                            DISK_CACHE_ENTRY_NUM_STATES);
}

// Some APIs inside disk_cache take a handle that the caller must keep alive
// until the API has finished its asynchronous execution.
//
// Unfortunately, DiskCacheBasedQuicServerInfo may be deleted before the
// operation completes causing a use-after-free.
//
// This data shim struct is meant to provide a location for the disk_cache
// APIs to write into even if the originating DiskCacheBasedQuicServerInfo
// object has been deleted.  The lifetime for instances of this struct
// should be bound to the CompletionCallback that is passed to the disk_cache
// API.  We do this by binding an instance of this struct to an unused
// parameter for OnIOComplete() using base::Owned().
//
// This is a hack. A better fix is to make it so that the disk_cache APIs
// take a Callback to a mutator for setting the output value rather than
// writing into a raw handle. Then the caller can just pass in a Callback
// bound to WeakPtr for itself. This callback would correctly "no-op" itself
// when the DiskCacheBasedQuicServerInfo object is deleted.
//
// TODO(ajwong): Change disk_cache's API to return results via Callback.
struct DiskCacheBasedQuicServerInfo::CacheOperationDataShim {
  CacheOperationDataShim() : backend(NULL), entry(NULL) {}

  disk_cache::Backend* backend;
  disk_cache::Entry* entry;
};

DiskCacheBasedQuicServerInfo::DiskCacheBasedQuicServerInfo(
    const QuicServerId& server_id,
    HttpCache* http_cache)
    : QuicServerInfo(server_id),
      data_shim_(new CacheOperationDataShim()),
      state_(GET_BACKEND),
      ready_(false),
      found_entry_(false),
      server_id_(server_id),
      http_cache_(http_cache),
      backend_(NULL),
      entry_(NULL),
      weak_factory_(this) {
      io_callback_ =
          base::Bind(&DiskCacheBasedQuicServerInfo::OnIOComplete,
                     weak_factory_.GetWeakPtr(),
                     base::Owned(data_shim_));  // Ownership assigned.
}

void DiskCacheBasedQuicServerInfo::Start() {
  DCHECK(CalledOnValidThread());
  DCHECK_EQ(GET_BACKEND, state_);
  DoLoop(OK);
}

int DiskCacheBasedQuicServerInfo::WaitForDataReady(
    const CompletionCallback& callback) {
  DCHECK(CalledOnValidThread());
  DCHECK_NE(GET_BACKEND, state_);

  if (ready_)
    return OK;

  if (!callback.is_null()) {
    // Prevent a new callback for WaitForDataReady overwriting an existing
    // pending callback (|user_callback_|).
    if (!user_callback_.is_null())
      return ERR_INVALID_ARGUMENT;
    user_callback_ = callback;
  }

  return ERR_IO_PENDING;
}

bool DiskCacheBasedQuicServerInfo::IsDataReady() {
  return ready_;
}

bool DiskCacheBasedQuicServerInfo::IsReadyToPersist() {
  // TODO(rtenneti): Handle updates while a write is pending. Change
  // Persist() to save the data to be written into a temporary buffer
  // and then persist that data when we are ready to persist.
  //
  // The data can be persisted if it has been loaded from the disk cache
  // and there are no pending writes.
  return ready_ && new_data_.empty();
}

void DiskCacheBasedQuicServerInfo::Persist() {
  DCHECK(CalledOnValidThread());
  DCHECK_NE(GET_BACKEND, state_);

  DCHECK(new_data_.empty());
  CHECK(ready_);
  DCHECK(user_callback_.is_null());
  new_data_ = Serialize();

  if (!backend_)
    return;

  state_ = CREATE_OR_OPEN;
  DoLoop(OK);
}

DiskCacheBasedQuicServerInfo::~DiskCacheBasedQuicServerInfo() {
  DCHECK(user_callback_.is_null());
  if (entry_) {
    entry_->Close();
    RecordDiskCacheEntryState(DISK_CACHE_ENTRY_CLOSED);
  }
}

std::string DiskCacheBasedQuicServerInfo::key() const {
  return "quicserverinfo:" + server_id_.ToString();
}

void DiskCacheBasedQuicServerInfo::OnIOComplete(CacheOperationDataShim* unused,
                                                int rv) {
  DCHECK_NE(NONE, state_);
  rv = DoLoop(rv);
  if (rv != ERR_IO_PENDING && !user_callback_.is_null()) {
    CompletionCallback callback = user_callback_;
    user_callback_.Reset();
    callback.Run(rv);
  }
}

int DiskCacheBasedQuicServerInfo::DoLoop(int rv) {
  do {
    switch (state_) {
      case GET_BACKEND:
        rv = DoGetBackend();
        break;
      case GET_BACKEND_COMPLETE:
        rv = DoGetBackendComplete(rv);
        break;
      case OPEN:
        rv = DoOpen();
        break;
      case OPEN_COMPLETE:
        rv = DoOpenComplete(rv);
        break;
      case READ:
        rv = DoRead();
        break;
      case READ_COMPLETE:
        rv = DoReadComplete(rv);
        break;
      case WAIT_FOR_DATA_READY_DONE:
        rv = DoWaitForDataReadyDone();
        break;
      case CREATE_OR_OPEN:
        rv = DoCreateOrOpen();
        break;
      case CREATE_OR_OPEN_COMPLETE:
        rv = DoCreateOrOpenComplete(rv);
        break;
      case WRITE:
        rv = DoWrite();
        break;
      case WRITE_COMPLETE:
        rv = DoWriteComplete(rv);
        break;
      case SET_DONE:
        rv = DoSetDone();
        break;
      default:
        rv = OK;
        NOTREACHED();
    }
  } while (rv != ERR_IO_PENDING && state_ != NONE);

  return rv;
}

int DiskCacheBasedQuicServerInfo::DoGetBackendComplete(int rv) {
  if (rv == OK) {
    backend_ = data_shim_->backend;
    state_ = OPEN;
  } else {
    state_ = WAIT_FOR_DATA_READY_DONE;
  }
  return OK;
}

int DiskCacheBasedQuicServerInfo::DoOpenComplete(int rv) {
  if (rv == OK) {
    entry_ = data_shim_->entry;
    state_ = READ;
    found_entry_ = true;
    RecordDiskCacheEntryState(DISK_CACHE_ENTRY_OPENED);
  } else {
    state_ = WAIT_FOR_DATA_READY_DONE;
  }

  return OK;
}

int DiskCacheBasedQuicServerInfo::DoReadComplete(int rv) {
  if (rv > 0)
    data_.assign(read_buffer_->data(), rv);

  state_ = WAIT_FOR_DATA_READY_DONE;
  return OK;
}

int DiskCacheBasedQuicServerInfo::DoWriteComplete(int rv) {
  state_ = SET_DONE;
  return OK;
}

int DiskCacheBasedQuicServerInfo::DoCreateOrOpenComplete(int rv) {
  if (rv != OK) {
    state_ = SET_DONE;
  } else {
    if (!entry_) {
      entry_ = data_shim_->entry;
      found_entry_ = true;
      RecordDiskCacheEntryState(DISK_CACHE_ENTRY_OPENED);
    }
    DCHECK(entry_);
    state_ = WRITE;
  }
  return OK;
}

int DiskCacheBasedQuicServerInfo::DoGetBackend() {
  state_ = GET_BACKEND_COMPLETE;
  return http_cache_->GetBackend(&data_shim_->backend, io_callback_);
}

int DiskCacheBasedQuicServerInfo::DoOpen() {
  state_ = OPEN_COMPLETE;
  return backend_->OpenEntry(key(), &data_shim_->entry, io_callback_);
}

int DiskCacheBasedQuicServerInfo::DoRead() {
  const int32 size = entry_->GetDataSize(0 /* index */);
  if (!size) {
    state_ = WAIT_FOR_DATA_READY_DONE;
    return OK;
  }

  read_buffer_ = new IOBuffer(size);
  state_ = READ_COMPLETE;
  return entry_->ReadData(
      0 /* index */, 0 /* offset */, read_buffer_.get(), size, io_callback_);
}

int DiskCacheBasedQuicServerInfo::DoWrite() {
  write_buffer_ = new IOBuffer(new_data_.size());
  memcpy(write_buffer_->data(), new_data_.data(), new_data_.size());
  state_ = WRITE_COMPLETE;

  return entry_->WriteData(0 /* index */,
                           0 /* offset */,
                           write_buffer_.get(),
                           new_data_.size(),
                           io_callback_,
                           true /* truncate */);
}

int DiskCacheBasedQuicServerInfo::DoCreateOrOpen() {
  state_ = CREATE_OR_OPEN_COMPLETE;
  if (entry_)
    return OK;

  if (found_entry_) {
    return backend_->OpenEntry(key(), &data_shim_->entry, io_callback_);
  }

  return backend_->CreateEntry(key(), &data_shim_->entry, io_callback_);
}

int DiskCacheBasedQuicServerInfo::DoWaitForDataReadyDone() {
  DCHECK(!ready_);
  state_ = NONE;
  ready_ = true;
  // We close the entry because, if we shutdown before ::Persist is called,
  // then we might leak a cache reference, which causes a DCHECK on shutdown.
  if (entry_) {
    entry_->Close();
    RecordDiskCacheEntryState(DISK_CACHE_ENTRY_CLOSED);
  }
  entry_ = NULL;
  Parse(data_);
  return OK;
}

int DiskCacheBasedQuicServerInfo::DoSetDone() {
  if (entry_) {
    entry_->Close();
    RecordDiskCacheEntryState(DISK_CACHE_ENTRY_CLOSED);
  }
  entry_ = NULL;
  new_data_.clear();
  state_ = NONE;
  return OK;
}

}  // namespace net