添加chromium mojom调用

1,外围调用的 js方法： 

    win.webContents.session.getCacheData("http://192.168.50.206:8080/back.html1").then(
      result=>{
          console.log("getCacheData resolve:"+result);
        },
        result=>{
          console.log("getCacheData reject:"+result);
        });    
  });

2，调用到对应的c++绑定： D:develectron7srcelectronshellrowserapiatom_api_session.cc

v8::Local<v8::Promise> Session::GetCacheData(mate::Arguments* args,
                                             const std::string& url) {
  auto* isolate = v8::Isolate::GetCurrent();
  auto promise = util::Promise(isolate);
  auto handle = promise.GetHandle();

  content::BrowserContext::GetDefaultStoragePartition(browser_context_.get())
      ->GetNetworkContext()
      ->ComputeHttpCacheData(
          base::Time(), base::Time::Max(), url,
          base::BindOnce(
              [](util::Promise promise, const std::vector<int8_t>& buffer,
                 int64_t size_or_error) {
                if (size_or_error <= 0) {
                  promise.RejectWithErrorMessage(
                      "Not Found.");
                } else {
                  promise.Resolve(node::Buffer::Copy(v8::Isolate::GetCurrent(),
                                                     (const char*)buffer.data(),
                                                     buffer.size())
                                      .ToLocalChecked());
                }
              },
              std::move(promise)));

  return handle;
}

3，函数里调用的是mojo接口：D:develectron7srcservices etworkpublicmojom etwork_context.mojom

  ComputeHttpCacheData(mojo_base.mojom.Time start_time,
                       mojo_base.mojom.Time end_time,
                       string url
                       )
      => (array<int8> buffer, int64 size_or_error);

4，编译时mojo自动生成的头文件：

  void ComputeHttpCacheSize0(::base::Time start_time, ::base::Time end_time, const std::string& url, ComputeHttpCacheSize0Callback callback) final;


  using ComputeHttpCacheSize0Callback = base::OnceCallback<void(const std::vector<int8_t>&, int64_t)>;
  
  virtual void ComputeHttpCacheSize0(::base::Time start_time, ::base::Time end_time, const std::string& url, ComputeHttpCacheSize0Callback callback) = 0;

5，对mojo接口实现：D:develectron7srcservices etwork etwork_context.cc

void NetworkContext::ComputeHttpCacheData(
    base::Time start_time,
    base::Time end_time,
    const std::string& url,
    ComputeHttpCacheDataCallback callback) {  //ComputeHttpCacheDataCallback: -> base::OnceCallback<void(const std::vector<uint8_t>&, int64_t)>; 
  // It's safe to use Unretained below as the HttpCacheDataCounter is owned by
  // |this| and guarantees it won't call its callback if deleted.
  http_cache_data_counters_.push_back(HttpCacheDataCounter::CreateAndStart(
      url_request_context_, start_time, end_time,url,
      base::BindOnce(&NetworkContext::OnHttpCacheDataComputed, 
                     base::Unretained(this), std::move(callback))));
}

回调OnHttpCacheDataComputed 实现：这里的Run会回调回atom_api_session的调用

ComputeHttpCacheData（_1,_2,callback)

的第三个参数回调中。

void NetworkContext::OnHttpCacheDataComputed(
    ComputeHttpCacheDataCallback callback,
    HttpCacheDataCounter* counter,
    const std::vector<int8_t>& buffer,
    int64_t result_or_error) {
  EraseIf(http_cache_data_counters_, base::MatchesUniquePtr(counter));
  std::move(callback).Run(buffer, result_or_error);
}

对应头文件D:develectron7srcservices etwork etwork_context.h：

  void ComputeHttpCacheData(base::Time start_time,
                            base::Time end_time,
                             const std::string& url,
                            ComputeHttpCacheDataCallback callback) override;

  void OnHttpCacheDataComputed(ComputeHttpCacheDataCallback callback,
                               HttpCacheDataCounter* counter,
                                const std::vector<int8_t>& buffer,
                               int64_t result_or_error);

6，mojo接口往外调用到的真正干活类：D:develectron7srcservices etworkhttp_cache_data_counter.h

回调 
 using HttpCacheDataCounterCallback0 = base::OnceCallback<void(HttpCacheDataCounter*,
                              const std::vector<int8_t>& buffer,
                              int64_t size_or_error)>;
静态方法：
static std::unique_ptr<HttpCacheDataCounter> CreateAndStart(net::URLRequestContext* url_request_context,

base::Time start_time,
base::Time end_time,
const std::string& url,
HttpCacheDataCounterCallback0 callback);

私有化构造：

HttpCacheDataCounter(base::Time start_time,
base::Time end_time,
const std::string& url,
HttpCacheDataCounterCallback0 callback); 

D:develectron7srcservices etworkhttp_cache_data_counter.cc

静态方法：

std::unique_ptr<HttpCacheDataCounter> HttpCacheDataCounter::CreateAndStart(
net::URLRequestContext* url_request_context,
base::Time start_time,
base::Time end_time,
const std::string& url,
HttpCacheDataCounterCallback0 callback) {
HttpCacheDataCounter* instance =
new HttpCacheDataCounter(start_time, end_time, std::move(callback));
net::HttpCache* http_cache =
url_request_context->http_transaction_factory()->GetCache();
if (!http_cache) {
// No cache, no space used. Posts a task, so it will run after the return.
instance->PostResult(false, 0);
} else {
std::unique_ptr<disk_cache::Backend*> backend =
std::make_unique<disk_cache::Backend*>();
disk_cache::Backend** backend_ptr = backend.get();

auto get_backend_callback =
base::BindRepeating(&HttpCacheDataCounter::GotBackend,
instance->GetWeakPtr(), base::Passed(&backend));
int rv = http_cache->GetBackend(backend_ptr, get_backend_callback);
if (rv != net::ERR_IO_PENDING) {
instance->GotBackend(std::make_unique<disk_cache::Backend*>(*backend_ptr),
rv);
}
}

return base::WrapUnique(instance);
}

私有化构造
HttpCacheDataCounter::HttpCacheDataCounter(
    base::Time start_time,
    base::Time end_time,
const std::string& url,
    HttpCacheDataCounterCallback0 callback)
    :

      index_(0),
      next_state_(STATE_NONE),
      start_time_(start_time),
      end_time_(end_time),
      callback0_(std::move(callback))

{
  std::cout << "XXXXXXXXXXXXXXXXXXXXXXXXXXXX  careate" << std::endl;
}

 h头文件：

// Copyright 2018 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.

#ifndef SERVICES_NETWORK_HTTP_CACHE_DATA_COUNTER_H_
#define SERVICES_NETWORK_HTTP_CACHE_DATA_COUNTER_H_

#include <memory>
#include <vector>
#include <utility>

#include "base/callback.h"
#include "base/component_export.h"
#include "base/macros.h"
#include "base/memory/weak_ptr.h"
#include "base/time/time.h"

#include "net/disk_cache/disk_cache.h"
namespace disk_cache {
class Backend;
}

namespace net {
class URLRequestContext;
}

namespace network {

// Helper to count data in HTTP cache.
// Export is for testing only.
class COMPONENT_EXPORT(NETWORK_SERVICE) HttpCacheDataCounter {
 public:
  using HttpCacheDataCounterCallback = base::OnceCallback<
      void(HttpCacheDataCounter*, bool upper_bound, int64_t size_or_error)>;

  // Computes the amount of disk space taken up by entries last used between
  // [start_time, end_time), and return it, or error.  Note that there may be
  // some approximation with respect to both bytes and dates.
  //
  // Furthermore, if there is no efficient way of computing this information,
  // a very loose upper bound (e.g. total disk space used by the cache) may be
  // returned; in that case |upper_bound| will be set to true.
  //
  // Once complete, invokes |callback|, passing |this| and result.
  //
  // If either |this| or |url_request_context| get destroyed, |callback|
  // will not be invoked.
  static std::unique_ptr<HttpCacheDataCounter> CreateAndStart(
      net::URLRequestContext* url_request_context,
      base::Time start_time,
      base::Time end_time,
      HttpCacheDataCounterCallback callback);

#ifndef CUST_NO_FEATURE_CACHE_DATA  // zhibin:
  using GetCacheDataCallback = base::OnceCallback<void(HttpCacheDataCounter*,
                              const std::vector<int8_t>& buffer,
                              int64_t size_or_error)>;

  static std::unique_ptr<HttpCacheDataCounter> CreateAndStart(
      net::URLRequestContext* url_request_context,
      base::Time start_time,
      base::Time end_time,
      const std::string& url,
      GetCacheDataCallback callback);
#endif

  ~HttpCacheDataCounter();

 private:
  HttpCacheDataCounter(base::Time start_time,
                       base::Time end_time,
                       HttpCacheDataCounterCallback callback);

  void GotBackend(std::unique_ptr<disk_cache::Backend*> backend,
                  int error_code);
  void PostResult(bool is_upper_limit, int64_t result_or_error);

  base::WeakPtr<HttpCacheDataCounter> GetWeakPtr() {
    return weak_factory_.GetWeakPtr();
  }

  base::Time start_time_;
  base::Time end_time_;
  HttpCacheDataCounterCallback callback_;

#ifndef CUST_NO_FEATURE_CACHE_DATA  // zhibin:
  HttpCacheDataCounter(base::Time start_time,
                       base::Time end_time,
                       const std::string& url,
                       GetCacheDataCallback callback);

  // This will trigger the completion callback if appropriate
  void PostResult0();

  GetCacheDataCallback callback0_;
  int index_ = 0;  // 0: http header response; 1: content; 2:js compiled.

  // Tricky here: if |this| gets deleted before |http_cache| gets deleted,
  // GetBackend may still write things out (even though the callback will
  // abort due to weak pointer), so the destination for the pointer can't be
  // owned by |this|.
  //
  // While it can be transferred to the callback to GetBackend, that callback
  // also needs to be kept alive for the duration of this method in order to
  // get at the backend pointer in the synchronous result case.
  // std::unique_ptr<disk_cache::Backend*> backend;
  disk_cache::Backend* backend_;

  scoped_refptr<net::GrowableIOBuffer> iobuffer_ = nullptr;
  std::unique_ptr<std::vector<int8_t>> cacheResult_ =
      std::make_unique<std::vector<int8_t>>();
  disk_cache::EntryResult entryResult_;
  disk_cache::Entry* cache_entry_;
  std::string url_;

  enum Command {
    COMMAND_CACHE_SIZE,
    COMMAND_CACHE_DATA,
    COMMAND_CACHE_LIST,
    COMMAND_CACHE_HEAD,
    COMMAND_CACHE_CONTENT
  };
  Command cmd_;

  enum State {
    STATE_NONE,
    STATE_GET_BACKEND,
    STATE_GET_BACKEND_COMPLETE,
    STATE_OPEN_NEXT_ENTRY,
    STATE_OPEN_NEXT_ENTRY_COMPLETE,
    STATE_OPEN_ENTRY,
    STATE_OPEN_ENTRY_COMPLETE,
    STATE_READ_RESPONSE,
    STATE_READ_RESPONSE_COMPLETE,
    STATE_READ_DATA,
    STATE_READ_DATA_COMPLETE
  };
  State next_state_;

  //Runs the state transition loop.
  int DoLoop(int result);

  // Each of these methods corresponds to a State value. If there is an
  // argument, the value corresponds to the return of the previous state or
  // corresponding callback.
  // int DoGetBackend();
  // int DoGetBackendComplete(int result);
  // int DoOpenNextEntry();
  // int DoOpenNextEntryComplete(int result);
  int DoOpenEntry();
  //  int DoOpenEntryComplete(int result);
  void OpenEntryCallback(disk_cache::EntryResult result);
  int DoReadResponse();
  int DoReadResponseComplete(int result);
  int DoReadData();
  int DoReadDataComplete(int result);
  void HandleResult(int rv); 
  // Called to signal completion of asynchronous IO.
  void OnIOComplete(int result);

  void copy(const char* const p, const int& len);
#endif

  base::WeakPtrFactory<HttpCacheDataCounter> weak_factory_{this};

  DISALLOW_COPY_AND_ASSIGN(HttpCacheDataCounter);
};

}  // namespace network

#endif  // SERVICES_NETWORK_HTTP_CACHE_DATA_COUNTER_H_

cc文件源码

// Copyright 2018 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 "services/network/http_cache_data_counter.h"

#include "base/bind.h"
#include "base/callback.h"
#include "base/location.h"
#include "base/threading/sequenced_task_runner_handle.h"
#include "net/disk_cache/disk_cache.h"
#include "net/http/http_cache.h"
#include "net/url_request/url_request_context.h"

namespace network {

std::unique_ptr<HttpCacheDataCounter> HttpCacheDataCounter::CreateAndStart(
    net::URLRequestContext* url_request_context,
    base::Time start_time,
    base::Time end_time,
    HttpCacheDataCounterCallback callback) {
  HttpCacheDataCounter* instance =
      new HttpCacheDataCounter(start_time, end_time, std::move(callback));
  net::HttpCache* http_cache =
      url_request_context->http_transaction_factory()->GetCache();
  if (!http_cache) {
    // No cache, no space used. Posts a task, so it will run after the return.
    instance->PostResult(false, 0);
  } else {
    // Tricky here: if |this| gets deleted before |http_cache| gets deleted,
    // GetBackend may still write things out (even though the callback will
    // abort due to weak pointer), so the destination for the pointer can't be
    // owned by |this|.
    //
    // While it can be transferred to the callback to GetBackend, that callback
    // also needs to be kept alive for the duration of this method in order to
    // get at the backend pointer in the synchronous result case.
    auto backend = std::make_unique<disk_cache::Backend*>();
    disk_cache::Backend** backend_ptr = backend.get();

    auto get_backend_callback =
        base::BindRepeating(&HttpCacheDataCounter::GotBackend,
                            instance->GetWeakPtr(), base::Passed(&backend));
    int rv = http_cache->GetBackend(backend_ptr, get_backend_callback);
    if (rv != net::ERR_IO_PENDING) {
      instance->GotBackend(std::make_unique<disk_cache::Backend*>(*backend_ptr),
                           rv);
    }
  }

  return base::WrapUnique(instance);
}

#ifndef CUST_NO_FEATURE_CACHE_DATA  // zhibin:
std::unique_ptr<HttpCacheDataCounter> HttpCacheDataCounter::CreateAndStart(
    net::URLRequestContext* url_request_context,
    base::Time start_time,
    base::Time end_time,
    const std::string& url,
    GetCacheDataCallback callback) {
  HttpCacheDataCounter* instance =
      new HttpCacheDataCounter(start_time, end_time, url,std::move(callback));
  net::HttpCache* http_cache =
      url_request_context->http_transaction_factory()->GetCache();
  if (!http_cache) {
    // No cache, no space used. Posts a task, so it will run after the return.
    instance->PostResult(false, 0);
  } else {
    std::unique_ptr<disk_cache::Backend*> backend =
        std::make_unique<disk_cache::Backend*>();
    disk_cache::Backend** backend_ptr = backend.get();

    auto get_backend_callback =
        base::BindRepeating(&HttpCacheDataCounter::GotBackend,
                            instance->GetWeakPtr(), base::Passed(&backend));
    int rv = http_cache->GetBackend(backend_ptr, get_backend_callback);
    if (rv != net::ERR_IO_PENDING) {
      instance->GotBackend(std::make_unique<disk_cache::Backend*>(*backend_ptr),
                           rv);
    }
  }

  return base::WrapUnique(instance);
}
#endif

HttpCacheDataCounter::HttpCacheDataCounter(
    base::Time start_time,
    base::Time end_time,
    HttpCacheDataCounterCallback callback)
    : start_time_(start_time),
      end_time_(end_time),
      callback_(std::move(callback))
#ifdef CUST_NO_FEATURE_CACHE_DATA  // zhibin:
{
}
#else
      ,
      index_(0),
      cmd_(COMMAND_CACHE_SIZE),
      next_state_(STATE_NONE) {
  LOG(INFO) << "XXXXXXXXXXXXXXXXXXXXXXXXXXXX  careate" << std::endl;
}

HttpCacheDataCounter::HttpCacheDataCounter(
    base::Time start_time,
    base::Time end_time,
    const std::string& url,
    GetCacheDataCallback callback)
    : start_time_(start_time),
      end_time_(end_time),
      callback0_(std::move(callback)),
      index_(0),
      url_(url),
      cmd_(COMMAND_CACHE_DATA),
      next_state_(STATE_NONE) {
  LOG(INFO) << "XXXXXXXXXXXXXXXXXXXXXXXXXXXX  careate" << std::endl;
}
#endif

HttpCacheDataCounter::~HttpCacheDataCounter() {
  LOG(INFO) << "XXXXXXXXXXXXXXXXXXXXXXXXXXXX   You got to kill me" << std::endl;
}

void HttpCacheDataCounter::GotBackend(
    std::unique_ptr<disk_cache::Backend*> backend,
    int error_code) {
  DCHECK_LE(error_code, 0);

#ifndef CUST_NO_FEATURE_CACHE_DATA  // zhibin:
  backend_ = *backend;
  if (cmd_ == COMMAND_CACHE_SIZE) {
#endif
    bool is_upper_limit = false;
    if (error_code != net::OK) {
      PostResult(is_upper_limit, error_code);
      return;
    }

    if (!*backend) {
      PostResult(is_upper_limit, 0);
      return;
    }

    int64_t rv;
    disk_cache::Backend* cache = *backend;

    // Handle this here since some backends would DCHECK on this.
    if (start_time_ > end_time_) {
      PostResult(is_upper_limit, 0);
      return;
    }

    if (start_time_.is_null() && end_time_.is_max()) {
      rv = cache->CalculateSizeOfAllEntries(base::BindOnce(
          &HttpCacheDataCounter::PostResult, GetWeakPtr(), is_upper_limit));
    } else {
      rv = cache->CalculateSizeOfEntriesBetween(
          start_time_, end_time_,
          base::BindOnce(&HttpCacheDataCounter::PostResult, GetWeakPtr(),
                         is_upper_limit));
      if (rv == net::ERR_NOT_IMPLEMENTED) {
        is_upper_limit = true;
        rv = cache->CalculateSizeOfAllEntries(base::BindOnce(
            &HttpCacheDataCounter::PostResult, GetWeakPtr(), is_upper_limit));
      }
    }
    if (rv != net::ERR_IO_PENDING)
      PostResult(is_upper_limit, rv);
#ifndef CUST_NO_FEATURE_CACHE_DATA  // zhibin:  
  } else if (cmd_ == COMMAND_CACHE_DATA) {
    if (error_code != net::OK) {
      PostResult0();
      return;
    }

    if (!*backend) {
      PostResult0();
      return;
    }
    backend_ = *backend;

    // Handle this here since some backends would DCHECK on this.
    if (start_time_ > end_time_) {
      PostResult0();
      return;
    }

    if (start_time_.is_null() && end_time_.is_max()) {
      next_state_ = STATE_OPEN_ENTRY;
      DoLoop(net::OK);
    } else {
      // todo:
    }
  } else if (cmd_ == COMMAND_CACHE_LIST) {
    // todo:
  }
#endif 
}

void HttpCacheDataCounter::PostResult(bool is_upper_limit,
                                      int64_t result_or_error) {
  base::SequencedTaskRunnerHandle::Get()->PostTask(
      FROM_HERE, base::BindOnce(std::move(callback_), this, is_upper_limit,
                                result_or_error));
}

#ifndef CUST_NO_FEATURE_CACHE_DATA  // zhibin:
int HttpCacheDataCounter::DoLoop(int result) {
  DCHECK(next_state_ != STATE_NONE);
  LOG(INFO) << "========  DoLoop begin result=" << result << std::endl;
  int rv = result;
  do {
    State state = next_state_;
    next_state_ = STATE_NONE;
    switch (state) {
      case STATE_GET_BACKEND:
        // DCHECK_EQ(net::OK, rv);
        // rv = DoGetBackend();
        break;
      case STATE_GET_BACKEND_COMPLETE:
        // rv = DoGetBackendComplete(rv);
        break;
      case STATE_OPEN_NEXT_ENTRY:
        // DCHECK_EQ(net::OK, rv);
        // rv = DoOpenNextEntry();
        break;
      case STATE_OPEN_NEXT_ENTRY_COMPLETE:
        // rv = DoOpenNextEntryComplete(rv);
        break;
      case STATE_OPEN_ENTRY:
        DCHECK_EQ(net::OK, rv);
        rv = DoOpenEntry();
        break;
      case STATE_OPEN_ENTRY_COMPLETE:
        // rv = DoOpenEntryComplete(rv);
        break;
      case STATE_READ_RESPONSE:
        DCHECK_EQ(net::OK, rv);
        rv = DoReadResponse();
        break;
      case STATE_READ_RESPONSE_COMPLETE:
        rv = DoReadResponseComplete(rv);
        break;
      case STATE_READ_DATA:
        DCHECK_EQ(net::OK, rv);
        rv = DoReadData();
        break;
      case STATE_READ_DATA_COMPLETE:
        rv = DoReadDataComplete(rv);
        break;

      default:
        NOTREACHED() << "bad state";
        rv = net::ERR_FAILED;
        break;
    }
  } while (rv != net::ERR_IO_PENDING && next_state_ != STATE_NONE);

  if (rv != net::ERR_IO_PENDING)
    HandleResult(rv);
  LOG(INFO) << "========DoLoop end  " << std::endl;
  return rv;
}

int HttpCacheDataCounter::DoOpenEntry() {
  LOG(INFO) << "========    DoOpenEntry" << std::endl;
  entryResult_ = backend_->OpenEntry(
      url_, net::HIGHEST,
      base::BindOnce(&HttpCacheDataCounter::OpenEntryCallback, GetWeakPtr()));
  return net::ERR_IO_PENDING;
}

void HttpCacheDataCounter::OpenEntryCallback(disk_cache::EntryResult result) {
  next_state_ = STATE_READ_RESPONSE;
  LOG(INFO) << "=== OpenEntryCallback " << std::endl;
  cache_entry_ = result.ReleaseEntry();
  LOG(INFO) << "=== OpenEntryCallback " << cache_entry_ << std::endl;
  if (!cache_entry_)
    PostResult0();
  else
    DoLoop(net::OK);
}

int HttpCacheDataCounter::DoReadResponse() {
  LOG(INFO) << "========  STATE_READ_RESPONSE  begin" << std::endl;
  next_state_ = STATE_READ_RESPONSE_COMPLETE;

  if (iobuffer_ == nullptr) {
    // init
    const int kInitBufferSize = cache_entry_->GetDataSize(0);
    if (kInitBufferSize < 1) {
      NOTREACHED() << "cache_entry_->GetDataSize(0) return less than 1.";
      return net::ERR_FAILED;
    }
    iobuffer_ = base::MakeRefCounted<net::GrowableIOBuffer>();
    iobuffer_->SetCapacity(kInitBufferSize);  // size of header
  }

  return cache_entry_->ReadData(
      index_, iobuffer_->offset(), iobuffer_.get(),
      iobuffer_->capacity() - iobuffer_->offset(),
      base::BindRepeating(&HttpCacheDataCounter::OnIOComplete, GetWeakPtr()));
}

int HttpCacheDataCounter::DoReadResponseComplete(int result) {
  if (result > 0) {
    iobuffer_->set_offset(iobuffer_->offset() + result);
  }
  // http response must be returned in once call.
  if (result && result == cache_entry_->GetDataSize(index_)) {
    net::HttpResponseInfo response_info;
    bool truncated_response_info = false;
    if (!net::HttpCache::ParseResponseInfo(iobuffer_->StartOfBuffer(),
                                           iobuffer_->offset(), &response_info,
                                           &truncated_response_info)) {
      // This can happen when reading data stored by content::CacheStorage.
      std::cerr << "WARNING: Returning empty response info for key: "
                << std::endl;
      return net::ERR_FAILED;
    }
    if (truncated_response_info) {
      std::cerr << "WARNING: Truncated HTTP response." << std::endl;
      return net::ERR_FAILED;
    }
    auto resp = net::HttpUtil::ConvertHeadersBackToHTTPResponse(
        response_info.headers->raw_headers());

    copy(resp.data(), resp.length());
    // LOG(INFO) << resp << std::endl;
  }

  // enter next loop directly.
  index_ = 1;  // read content
  next_state_ = STATE_READ_DATA;
  return net::OK;
}

int HttpCacheDataCounter::DoReadData() {
  next_state_ = STATE_READ_DATA_COMPLETE;
  int buf_len_ = cache_entry_->GetDataSize(index_);
  if (!buf_len_)
    return buf_len_;

  iobuffer_->SetCapacity(buf_len_);  // iobuffer_->capacity() +
  iobuffer_->set_offset(0);
  return cache_entry_->ReadData(
      index_, iobuffer_->offset(), iobuffer_.get(),
      iobuffer_->capacity() - iobuffer_->offset(),
      base::BindRepeating(&HttpCacheDataCounter::OnIOComplete, GetWeakPtr()));
}

int HttpCacheDataCounter::DoReadDataComplete(int result) {
  LOG(INFO) << "========       DoReadDataComplete  len=" << result << std::endl;
  if (result > 0) {
    iobuffer_->set_offset(iobuffer_->offset() + result);
  }

  if (iobuffer_->capacity() <= iobuffer_->offset()) {
    return net::OK;
  } else {
    return net::ERR_FAILED;
  }
}

void HttpCacheDataCounter::OnIOComplete(int rv) {
  LOG(INFO) << "========       OnIOComplete  len=" << rv << std::endl;
  DoLoop(rv);
}

#if 0
int ViewCacheHelper::DoReadResponseComplete(int result) {
  HandleResult(rv);

  index_ = 0;
  next_state_ = STATE_NONE;
  return OK;
}

int HttpCacheDataCounter::DoOpenEntryComplete(int result) {
  LOG(INFO) << "========  DoOpenEntryComplete" << std::endl;

  return OK;
}
#endif

void HttpCacheDataCounter::HandleResult(int rv) {
  DCHECK_NE(net::ERR_IO_PENDING, rv);
  // DCHECK_NE(net::ERR_FAILED, rv);
  LOG(INFO) << "========  HandleResult" << std::endl;
  // LOG(INFO).write(iobuffer_->StartOfBuffer(), iobuffer_->offset());
  if (cache_entry_) {
    LOG(INFO) << "========    XXX  cache_entry_->Close()" << std::endl;
    cache_entry_->Close();
    cache_entry_ = NULL;
  }

  if (rv == net::ERR_FAILED) {
    LOG(INFO) << "Stream read error.." << std::endl;
  } else if (rv == net::OK) {  // suc
    copy(iobuffer_->StartOfBuffer(), iobuffer_->offset());
  }

  PostResult0();
}

void HttpCacheDataCounter::PostResult0() {
  base::SequencedTaskRunnerHandle::Get()->PostTask(
      FROM_HERE, base::BindOnce(std::move(callback0_), this,
                                *(cacheResult_.get()), cacheResult_->size()));
}

void HttpCacheDataCounter::copy(const char* const p, const int& len) {
  LOG(INFO) << "========  copy len=" << len << std::endl;
  int8_t* initPtr = (int8_t*)(p);
  int8_t* ptr = (int8_t*)(p);
  while (ptr < initPtr + len) {
    cacheResult_->push_back(*ptr);
    ptr++;
  }
}
#endif

}  // namespace network

---

参考：

1，Mojo C++ System API

file:///D:/dev/electron7/src/mojo/public/cpp/system/README.md

2，Mojo C++ Bindings API

file:///D:/dev/electron7/src/mojo/public/cpp/bindings/README.md 

3，Mojo

file:///D:/dev/electron7/src/mojo/README.md