chromium中HTTP网络资源的加载主要分两部分,一部分是缓存的网络资源,一部分是线上的网络资源。
我们访问http网页的时候,首先访问httpcache,看缓存中的数据是否有效,如果有效,那么我们加载这个数据,如果无效,那么我们访问网络去重新加载资源,当然chromium中HTTP网络资源的加载并没有说起来这么简单,实际上架构设计还是比较复杂的。首先我们先看看HttpCache::Transaction的相关设计及实现,研究一下缓存的处理。
HttpCache::Transaction
在源码分析之前,我们先看一个小示例,从使用者的角度看看cache的使用过程,那么就需要一个切入点。
情景分析
首先我们在windbg中启动chromium,然后设置多进程调试。
0:000> .childdbg 1
Processes created by the current process will be debugged
0:000> g
运行后待程序稳定后,中断到调试器,之后在主进程上下断
0:011> bp chrome_7feed810000!net::HttpCache::Transaction::Start
之后运行起来,然后在浏览器的地址窗口中输入一个字符“c”,这是我假定的设置的,因为浏览器的地址窗口默认设置了百度的搜索引擎,当用户输入一个字符的时候会触发一次搜索。而实际上确实是这样。当输入字符后,我的程序中断了。
0:028> kc
# Call Site
00 chrome_7feed810000!net::HttpCache::Transaction::Start
01 chrome_7feed810000!net::URLRequestHttpJob::StartTransactionInternal
02 chrome_7feed810000!net::URLRequestHttpJob::MaybeStartTransactionInternal
03 chrome_7feed810000!net::URLRequestHttpJob::StartTransaction
04 chrome_7feed810000!net::URLRequestHttpJob::SetCookieHeaderAndStart
05 chrome_7feed810000!base::internal::RunnableAdapter<void (__cdecl LocalDataContainer::*)(std::list<content::CacheStorageUsageInfo,std::allocator<content::CacheStorageUsageInfo> > const &)>::Run
06 chrome_7feed810000!base::internal::InvokeHelper<1,void,base::internal::RunnableAdapter<void (__cdecl LocalDataContainer::*)(std::list<content::CacheStorageUsageInfo,std::allocator<content::CacheStorageUsageInfo> > const &)> >::MakeItSo
07 chrome_7feed810000!base::internal::Invoker<base::IndexSequence<0>,base::internal::BindState<base::internal::RunnableAdapter<void (__cdecl LocalDataContainer::*)(std::list<content::CacheStorageUsageInfo,std::allocator<content::CacheStorageUsageInfo> > const & __ptr64) __ptr64>,void __cdecl(LocalDataContainer * __ptr64,std::list<content::CacheStorageUsageInfo,std::allocator<content::CacheStorageUsageInfo> > const & __ptr64),base::WeakPtr<LocalDataContainer> >,base::internal::InvokeHelper<1,void,base::internal::RunnableAdapter<void (__cdecl LocalDataContainer::*)(std::list<content::CacheStorageUsageInfo,std::allocator<content::CacheStorageUsageInfo> > const & __ptr64) __ptr64> >,void __cdecl(std::list<content::CacheStorageUsageInfo,std::allocator<content::CacheStorageUsageInfo> > const & __ptr64)>::Run
08 chrome_7feed810000!base::Callback<void __cdecl(void)>::Run
09 chrome_7feed810000!net::CookieMonster::CookieMonsterTask::InvokeCallback
0a chrome_7feed810000!net::CookieMonster::GetCookieListWithOptionsTask::Run
0b chrome_7feed810000!net::CookieMonster::DoCookieTaskForURL
0c chrome_7feed810000!net::CookieMonster::GetCookieListWithOptionsAsync
0d chrome_7feed810000!net::URLRequestHttpJob::AddCookieHeaderAndStart
0e chrome_7feed810000!net::URLRequestHttpJob::Start
0f chrome_7feed810000!net::URLRequest::StartJob
10 chrome_7feed810000!net::URLRequest::BeforeRequestComplete
11 chrome_7feed810000!net::URLRequest::Start
12 chrome_7feed810000!net::URLFetcherCore::StartURLRequest
13 chrome_7feed810000!net::URLFetcherCore::StartURLRequestWhenAppropriate
14 chrome_7feed810000!net::URLFetcherCore::DidInitializeWriter
15 chrome_7feed810000!net::URLFetcherCore::StartOnIOThread
16 chrome_7feed810000!base::Callback<void __cdecl(void)>::Run
17 chrome_7feed810000!base::debug::TaskAnnotator::RunTask
18 chrome_7feed810000!base::MessageLoop::RunTask
19 chrome_7feed810000!base::MessageLoop::DeferOrRunPendingTask
1a chrome_7feed810000!base::MessageLoop::DoWork
1b chrome_7feed810000!base::MessagePumpForIO::DoRunLoop
1c chrome_7feed810000!base::MessagePumpWin::Run
1d chrome_7feed810000!base::MessageLoop::RunHandler
1e chrome_7feed810000!base::RunLoop::Run
1f chrome_7feed810000!base::MessageLoop::Run
20 chrome_7feed810000!base::Thread::Run
21 chrome_7feed810000!content::BrowserThreadImpl::IOThreadRun
22 chrome_7feed810000!content::BrowserThreadImpl::Run
23 chrome_7feed810000!base::Thread::ThreadMain
24 chrome_7feed810000!base::`anonymous namespace'::ThreadFunc
25 kernel32!BaseThreadInitThunk
26 ntdll!RtlUserThreadStart
研究一下堆栈信息,其实就已经知道了大抵上的调用层次,这个请求的方式和我之前介绍过的chromium中FTP网络资源的加载 文章中很相似。
在一个IO线程中启动了URL的加载请求,这是一个内部请求,使用的是URLFetcherCore,然后启动URLRequest,之后开启一个特定的job,在这里这个job是URLRequestHttpJob,之后启动一个传输,而这个传输就是我们要说的HttpCache::Transaction,内部数据的请求基于HttpCache。
0:028> ~~[1244]s;.frame 0n0;dv /t /v
chrome_7feed810000!net::HttpCache::Transaction::Start:
000007fe`ee46c6e4 48895c2410 mov qword ptr [rsp+10h],rbx ss:00000000`0961c408=0000000012695a60
00 00000000`0961c3f8 000007fe`ee4bf027 chrome_7feed810000!net::HttpCache::Transaction::Start [c:\b\build\slave\win64\build\src\net\http\http_cache_transaction.cc @ 254]
@rcx class net::HttpCache::Transaction * this = 0x00000000`1269c170
@rdx struct net::HttpRequestInfo * request = 0x00000000`12695c28
@r8 class base::Callback<void __cdecl(int)> * callback = 0x00000000`12695d40
@r9 class net::BoundNetLog * net_log = 0x00000000`12691ec8
<unavailable> int rv = <value unavailable>
0:028> dx -id 0,0 -r1 (*((chrome_7feed810000!net::HttpRequestInfo *)0x12695c28))
(*((chrome_7feed810000!net::HttpRequestInfo *)0x12695c28)) [Type: net::HttpRequestInfo]
[+0x000] url [Type: GURL]
[+0x078] method : "GET" [Type: std::basic_string<char,std::char_traits<char>,std::allocator<char> >]
[+0x098] extra_headers [Type: net::HttpRequestHeaders]
[+0x0b0] upload_data_stream : 0x0 [Type: net::UploadDataStream *]
[+0x0b8] load_flags : 64
[+0x0bc] motivation : NORMAL_MOTIVATION (2) [Type: net::HttpRequestInfo::RequestMotivation]
[+0x0c0] privacy_mode : PRIVACY_MODE_DISABLED (0) [Type: net::PrivacyMode]
0:028> dx -id 0,0 -r1 (*((chrome_7feed810000!GURL *)0x12695c28))
(*((chrome_7feed810000!GURL *)0x12695c28)) [Type: GURL]
[+0x000] spec_ : "http://suggestion.baidu.com/su?wd=c&action=opensearch&ie=UTF-8" [Type: std::basic_string<char,std::char_traits<char>,std::allocator<char> >]
[+0x020] is_valid_ : true
[+0x028] parsed_ [Type: url::Parsed]
[+0x070] inner_url_ [Type: scoped_ptr<GURL,std::default_delete<GURL> >]
接着,我们来看一下,当我们在浏览器中输入一个字符的时候,浏览器的一个URL的请求过程,上面的网址就是要请求的URL,“http://suggestion.baidu.com/su?wd=c&action=opensearch&ie=UTF-8”,这是一个http GET命令。Opensearch 字符”c”.
当然,浏览器地址栏的结果数据的提供过程并不是我们讨论的主题,我们是通过这个切入点去详细了解其中一点,http网络资源的加载过程。
源码分析
HttpCache::Transaction::Start
上面我们看到了最后一个函数栈,是一个缓存传输启动的过程,我们从这里开始,已知的一点是我们向启动函数中传递了请求信息,包含了URL和method。
int HttpCache::Transaction::Start(const HttpRequestInfo* request,
const CompletionCallback& callback,
const BoundNetLog& net_log) {
......
if (!cache_.get())
return ERR_UNEXPECTED;
SetRequest(net_log, request);
// We have to wait until the backend is initialized so we start the SM.
next_state_ = STATE_GET_BACKEND;
int rv = DoLoop(OK);
// Setting this here allows us to check for the existence of a callback_ to
// determine if we are still inside Start.
if (rv == ERR_IO_PENDING)
callback_ = callback;
return rv;
}
我们来看一下源码,这里我们设置了下一跳状态,然后启动状态机循环,这里多少和FTP资源的加载有些相似,FTP的加载要较为简单些。
HttpCache::Transaction::State
enum State {
// Normally, states are traversed in approximately this order.
STATE_NONE,
STATE_GET_BACKEND,
STATE_GET_BACKEND_COMPLETE,
STATE_INIT_ENTRY,
STATE_OPEN_ENTRY,
STATE_OPEN_ENTRY_COMPLETE,
STATE_DOOM_ENTRY,
STATE_DOOM_ENTRY_COMPLETE,
STATE_CREATE_ENTRY,
STATE_CREATE_ENTRY_COMPLETE,
STATE_ADD_TO_ENTRY,
STATE_ADD_TO_ENTRY_COMPLETE,
.....
}
HttpCache的传输过程也是状态改变的过程,状态比较多,情况就比较多。
chromium源码作者还是比较贴心的,在源码状态机循环函数前以注释的方式列出了各种情况。
// 1. Not-cached entry:
// Start():
// GetBackend* -> InitEntry -> OpenEntry* -> CreateEntry* -> AddToEntry* ->
// SendRequest* -> SuccessfulSendRequest -> OverwriteCachedResponse ->
// CacheWriteResponse* -> TruncateCachedData* -> TruncateCachedMetadata* ->
// PartialHeadersReceived
//
// Read():
// NetworkRead* -> CacheWriteData*
//
// 2. Cached entry, no validation:
// Start():
// GetBackend* -> InitEntry -> OpenEntry* -> AddToEntry* -> CacheReadResponse*
// -> CacheDispatchValidation -> BeginPartialCacheValidation() ->
// BeginCacheValidation() -> SetupEntryForRead()
//
// Read():
// CacheReadData*
//
// 3. Cached entry, validation (304):
// Start():
// GetBackend* -> InitEntry -> OpenEntry* -> AddToEntry* -> CacheReadResponse*
// -> CacheDispatchValidation -> BeginPartialCacheValidation() ->
// BeginCacheValidation() -> SendRequest* -> SuccessfulSendRequest ->
// UpdateCachedResponse -> CacheWriteUpdatedResponse* ->
// UpdateCachedResponseComplete -> OverwriteCachedResponse ->
// PartialHeadersReceived
//
// Read():
// CacheReadData*
//
// 4. Cached entry, validation and replace (200):
// Start():
// GetBackend* -> InitEntry -> OpenEntry* -> AddToEntry* -> CacheReadResponse*
// -> CacheDispatchValidation -> BeginPartialCacheValidation() ->
// BeginCacheValidation() -> SendRequest* -> SuccessfulSendRequest ->
// OverwriteCachedResponse -> CacheWriteResponse* -> DoTruncateCachedData* ->
// TruncateCachedMetadata* -> PartialHeadersReceived
//
// Read():
// NetworkRead* -> CacheWriteData*
//
// 5. Sparse entry, partially cached, byte range request:
// Start():
// GetBackend* -> InitEntry -> OpenEntry* -> AddToEntry* -> CacheReadResponse*
// -> CacheDispatchValidation -> BeginPartialCacheValidation() ->
// CacheQueryData* -> ValidateEntryHeadersAndContinue() ->
// StartPartialCacheValidation -> CompletePartialCacheValidation ->
// BeginCacheValidation() -> SendRequest* -> SuccessfulSendRequest ->
// UpdateCachedResponse -> CacheWriteUpdatedResponse* ->
// UpdateCachedResponseComplete -> OverwriteCachedResponse ->
// PartialHeadersReceived
//
// Read() 1:
// NetworkRead* -> CacheWriteData*
//
// Read() 2:
// NetworkRead* -> CacheWriteData* -> StartPartialCacheValidation ->
// CompletePartialCacheValidation -> CacheReadData* ->
//
// Read() 3:
// CacheReadData* -> StartPartialCacheValidation ->
// CompletePartialCacheValidation -> BeginCacheValidation() -> SendRequest* ->
// SuccessfulSendRequest -> UpdateCachedResponse* -> OverwriteCachedResponse
// -> PartialHeadersReceived -> NetworkRead* -> CacheWriteData*
//
// 6. HEAD. Not-cached entry:
// Pass through. Don't save a HEAD by itself.
// Start():
// GetBackend* -> InitEntry -> OpenEntry* -> SendRequest*
//
// 7. HEAD. Cached entry, no validation:
// Start():
// The same flow as for a GET request (example #2)
//
// Read():
// CacheReadData (returns 0)
//
// 8. HEAD. Cached entry, validation (304):
// The request updates the stored headers.
// Start(): Same as for a GET request (example #3)
//
// Read():
// CacheReadData (returns 0)
//
// 9. HEAD. Cached entry, validation and replace (200):
// Pass through. The request dooms the old entry, as a HEAD won't be stored by
// itself.
// Start():
// GetBackend* -> InitEntry -> OpenEntry* -> AddToEntry* -> CacheReadResponse*
// -> CacheDispatchValidation -> BeginPartialCacheValidation() ->
// BeginCacheValidation() -> SendRequest* -> SuccessfulSendRequest ->
// OverwriteCachedResponse
//
// 10. HEAD. Sparse entry, partially cached:
// Serve the request from the cache, as long as it doesn't require
// revalidation. Ignore missing ranges when deciding to revalidate. If the
// entry requires revalidation, ignore the whole request and go to full pass
// through (the result of the HEAD request will NOT update the entry).
//
// Start(): Basically the same as example 7, as we never create a partial_
// object for this request.
//
// 11. Prefetch, not-cached entry:
// The same as example 1. The "unused_since_prefetch" bit is stored as true in
// UpdateCachedResponse.
//
// 12. Prefetch, cached entry:
// Like examples 2-4, only CacheToggleUnusedSincePrefetch* is inserted between
// CacheReadResponse* and CacheDispatchValidation if the unused_since_prefetch
// bit is unset.
//
// 13. Cached entry less than 5 minutes old, unused_since_prefetch is true:
// Skip validation, similar to example 2.
// GetBackend* -> InitEntry -> OpenEntry* -> AddToEntry* -> CacheReadResponse*
// -> CacheToggleUnusedSincePrefetch* -> CacheDispatchValidation ->
// BeginPartialCacheValidation() -> BeginCacheValidation() ->
// SetupEntryForRead()
//
// Read():
// CacheReadData*
//
// 14. Cached entry more than 5 minutes old, unused_since_prefetch is true:
// Like examples 2-4, only CacheToggleUnusedSincePrefetch* is inserted between
// CacheReadResponse* and CacheDispatchValidation.
简要看看,一般的缓存传输基本上都要经历的过程是获取Backend,然后初始化Entry,之后打开,然后从中加载进来,之后进行验证,后面的过程就有些不一样了。自然,从地址栏中输入单个字符引发搜索,URL资源请求也就符合其中一种情况。
操作Backend准备Cache数据
base::WeakPtr<HttpCache> cache_;
int HttpCache::Transaction::DoGetBackend() {
cache_pending_ = true;
next_state_ = STATE_GET_BACKEND_COMPLETE;
net_log_.BeginEvent(NetLog::TYPE_HTTP_CACHE_GET_BACKEND);
return cache_->GetBackendForTransaction(this);
}
int HttpCache::Transaction::DoInitEntry() {
DCHECK(!new_entry_);
if (!cache_.get())
return ERR_UNEXPECTED;
if (mode_ == WRITE) {
next_state_ = STATE_DOOM_ENTRY;
return OK;
}
next_state_ = STATE_OPEN_ENTRY;
return OK;
}
int HttpCache::Transaction::DoOpenEntry() {
DCHECK(!new_entry_);
next_state_ = STATE_OPEN_ENTRY_COMPLETE;
cache_pending_ = true;
net_log_.BeginEvent(NetLog::TYPE_HTTP_CACHE_OPEN_ENTRY);
first_cache_access_since_ = TimeTicks::Now();
return cache_->OpenEntry(cache_key_, &new_entry_, this);
}
Httpcache的传输实际上操作httpCache来完成具体的功能,做前期的准备工作,最后通过cache_key_,来查询某一项。
[+0x3a0] cache_key_ : "http://suggestion.baidu.com/su?wd=c&action=opensearch&ie=UTF-8"
这里面的cache_key_其实就是URL,在HttpCache中URL唯一检索资源,就是通过这个key值来找到对应的Entry。
int HttpCache::Transaction::DoAddToEntry() {
DCHECK(new_entry_);
cache_pending_ = true;
next_state_ = STATE_ADD_TO_ENTRY_COMPLETE;
net_log_.BeginEvent(NetLog::TYPE_HTTP_CACHE_ADD_TO_ENTRY);
DCHECK(entry_lock_waiting_since_.is_null());
entry_lock_waiting_since_ = TimeTicks::Now();
int rv = cache_->AddTransactionToEntry(new_entry_, this);
if (rv == ERR_IO_PENDING) {
if (bypass_lock_for_test_) {
OnAddToEntryTimeout(entry_lock_waiting_since_);
} else {
int timeout_milliseconds = 20 * 1000;
if (partial_ && new_entry_->writer &&
new_entry_->writer->range_requested_) {
timeout_milliseconds = 25;
}
base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(
FROM_HERE,
base::Bind(&HttpCache::Transaction::OnAddToEntryTimeout,
weak_factory_.GetWeakPtr(), entry_lock_waiting_since_),
TimeDelta::FromMilliseconds(timeout_milliseconds));
}
}
return rv;
}
当我们找到对应的项后,我们具体的加载这个项的数据,如果返回IO_PENDING,那么设置超时回调函数。设置下一状态为STATE_ADD_TO_ENTRY_COMPLETE,在完成函数中,设置下一跳状态,记录处理时间。
HttpCache::Transaction Read Entry and validation
int HttpCache::Transaction::DoCacheReadResponse() {
DCHECK(entry_);
next_state_ = STATE_CACHE_READ_RESPONSE_COMPLETE;
io_buf_len_ = entry_->disk_entry->GetDataSize(kResponseInfoIndex);
read_buf_ = new IOBuffer(io_buf_len_);
net_log_.BeginEvent(NetLog::TYPE_HTTP_CACHE_READ_INFO);
return entry_->disk_entry->ReadData(kResponseInfoIndex, 0, read_buf_.get(),
io_buf_len_, io_callback_);
}
当一切都准备完成后,开始从缓存中读取数据,函数中设置下一跳,然后从entry中获取到缓存的大小,申请空间,之后操作entry来读取数据。
int HttpCache::Transaction::DoCacheDispatchValidation() {
int result = ERR_FAILED;
switch (mode_) {
case READ:
UpdateTransactionPattern(PATTERN_ENTRY_USED);
result = BeginCacheRead();
break;
case READ_WRITE:
result = BeginPartialCacheValidation();
break;
case UPDATE:
result = BeginExternallyConditionalizedRequest();
break;
case WRITE:
default:
NOTREACHED();
}
return result;
}
当我们读取完数据后,就开始了验证数据的过程。这里是个读写的情况。在派发验证的过程中,跳过了验证,符合上面的情况2,Cached entry, no validation。
HttpCache::Transaction 数据读取
当我们准备cache,操作并查找到对应的项,然后读取项,之后判断是否验证项,如果这都通过了之后,下层会通知上层来提取数据。
0:026> kc
# Call Site
00 chrome_7feed900000!net::HttpCache::Transaction::DoCacheReadData
01 chrome_7feed900000!net::HttpCache::Transaction::DoLoop
02 chrome_7feed900000!net::HttpCache::Transaction::Read
03 chrome_7feed900000!net::URLRequestHttpJob::ReadRawData
04 chrome_7feed900000!net::URLRequestJob::ReadRawDataHelper
05 chrome_7feed900000!net::URLRequestJob::Read
06 chrome_7feed900000!net::URLRequest::Read
07 chrome_7feed900000!net::URLFetcherCore::ReadResponse
08 chrome_7feed900000!net::URLFetcherCore::OnResponseStarted
09 chrome_7feed900000!net::URLRequest::NotifyResponseStarted
0a chrome_7feed900000!net::URLRequestJob::NotifyHeadersComplete
0b chrome_7feed900000!net::URLRequestHttpJob::NotifyHeadersComplete
0c chrome_7feed900000!net::URLRequestHttpJob::SaveCookiesAndNotifyHeadersComplete
0d chrome_7feed900000!net::URLRequestHttpJob::OnStartCompleted
0e chrome_7feed900000!base::Callback<void __cdecl(int)>::Run
0f chrome_7feed900000!net::HttpCache::Transaction::DoLoop
10 chrome_7feed900000!base::internal::RunnableAdapter<void (__cdecl extensions::NativeMessageProcessHost::*)(int)>::Run
11 chrome_7feed900000!base::internal::InvokeHelper<1,void,base::internal::RunnableAdapter<void (__cdecl extensions::NativeMessageProcessHost::*)(int)> >::MakeItSo
12 chrome_7feed900000!base::internal::Invoker<base::IndexSequence<0>,base::internal::BindState<base::internal::RunnableAdapter<void (__cdecl extensions::NativeMessageProcessHost::*)(int) __ptr64>,void __cdecl(extensions::NativeMessageProcessHost * __ptr64,int),base::WeakPtr<extensions::NativeMessageProcessHost> >,base::internal::InvokeHelper<1,void,base::internal::RunnableAdapter<void (__cdecl extensions::NativeMessageProcessHost::*)(int) __ptr64> >,void __cdecl(int const & __ptr64)>::Run
13 chrome_7feed900000!base::Callback<void __cdecl(int)>::Run
14 chrome_7feed900000!disk_cache::InFlightBackendIO::OnOperationComplete
15 chrome_7feed900000!disk_cache::BackgroundIO::OnIOSignalled
16 chrome_7feed900000!base::Callback<void __cdecl(void)>::Run
17 chrome_7feed900000!base::debug::TaskAnnotator::RunTask
18 chrome_7feed900000!base::MessageLoop::RunTask
19 chrome_7feed900000!base::MessageLoop::DeferOrRunPendingTask
1a chrome_7feed900000!base::MessageLoop::DoWork
1b chrome_7feed900000!base::MessagePumpForIO::DoRunLoop
1c chrome_7feed900000!base::MessagePumpWin::Run
1d chrome_7feed900000!base::MessageLoop::RunHandler
1e chrome_7feed900000!base::RunLoop::Run
1f chrome_7feed900000!base::MessageLoop::Run
20 chrome_7feed900000!base::Thread::Run
21 chrome_7feed900000!content::BrowserThreadImpl::IOThreadRun
22 chrome_7feed900000!content::BrowserThreadImpl::Run
23 chrome_7feed900000!base::Thread::ThreadMain
24 chrome_7feed900000!base::`anonymous namespace'::ThreadFunc
25 kernel32!BaseThreadInitThunk
26 ntdll!RtlUserThreadStart
disk_cache 是HttpCache实际存储在硬盘上的数据组织结构,当完成后通知URLRequestHttpJob启动完成,然后再通过HttpCache进行读取数据。
int HttpCache::Transaction::DoCacheReadData() {
if (request_->method == "HEAD")
return 0;
DCHECK(entry_);
next_state_ = STATE_CACHE_READ_DATA_COMPLETE;
if (net_log_.IsCapturing())
net_log_.BeginEvent(NetLog::TYPE_HTTP_CACHE_READ_DATA);
if (partial_) {
return partial_->CacheRead(entry_->disk_entry, read_buf_.get(), io_buf_len_,
io_callback_);
}
return entry_->disk_entry->ReadData(kResponseContentIndex, read_offset_,
read_buf_.get(), io_buf_len_,
io_callback_);
}
而数据的读取操作的实际处理也是通过disk_cache进行实际的数据处理,这里HttpCache做中间的一个传输的过程。
HttpCache::Transaction 小结
这里简要介绍了HttpCache的传输过程,仅介绍了其中的一种情况(Cached entry, no validation ),当我们在地址栏中输入字符的时候,会触发一个URL的请求,而这个请求事先也是要通过HttpCache的传输的,请求去查询cache中的项,然后读取出来,在验证的时候跳过了验证机制,之后开始读取实际的数据,完成数据的传输。
HttpNetworkTransaction
上面我们分析了HttpCache的传输方式,如果HttpCache中没有我们要查阅的数据呢,因为我们要访问的是一个我们从没有访问过的URL,又或者我们访问的cache数据已经失效了,那么怎么办呢,此时就要通过网络来加载数据,需要通过http网络传输来完成具体的数据加载。
情景分析
现假设我们访问chromium中FTP网络资源的加载 这篇文章,我的HttpCache中并没有这个URL相关的信息,我们可以在浏览器的地址栏中输入chrome://cache/ 来看HttpCache的存储情况。
我们没有这个缓存,目前我们符合上面的情况一,当我们检索cache后发现没有数据,那么我们要启动网络传输的请求。
0:026> kc
# Call Site
00 chrome_7feed900000!net::HttpNetworkTransaction::Start
01 chrome_7feed900000!DevToolsNetworkTransaction::Start
02 chrome_7feed900000!net::HttpCache::Transaction::DoSendRequest
03 chrome_7feed900000!net::HttpCache::Transaction::DoLoop
04 chrome_7feed900000!base::internal::RunnableAdapter<void (__cdecl extensions::NativeMessageProcessHost::*)(int)>::Run
05 chrome_7feed900000!base::internal::InvokeHelper<1,void,base::internal::RunnableAdapter<void (__cdecl extensions::NativeMessageProcessHost::*)(int)> >::MakeItSo
06 chrome_7feed900000!base::internal::Invoker<base::IndexSequence<0>,base::internal::BindState<base::internal::RunnableAdapter<void (__cdecl extensions::NativeMessageProcessHost::*)(int) __ptr64>,void __cdecl(extensions::NativeMessageProcessHost * __ptr64,int),base::WeakPtr<extensions::NativeMessageProcessHost> >,base::internal::InvokeHelper<1,void,base::internal::RunnableAdapter<void (__cdecl extensions::NativeMessageProcessHost::*)(int) __ptr64> >,void __cdecl(int const & __ptr64)>::Run
07 chrome_7feed900000!base::Callback<void __cdecl(int)>::Run
08 chrome_7feed900000!net::HttpCache::WorkItem::NotifyTransaction
09 chrome_7feed900000!net::HttpCache::OnIOComplete
0a chrome_7feed900000!net::HttpCache::OnPendingOpComplete
0b chrome_7feed900000!base::Callback<void __cdecl(int)>::Run
0c chrome_7feed900000!disk_cache::InFlightBackendIO::OnOperationComplete
0d chrome_7feed900000!disk_cache::BackgroundIO::OnIOSignalled
0e chrome_7feed900000!base::Callback<void __cdecl(void)>::Run
0f chrome_7feed900000!base::debug::TaskAnnotator::RunTask
10 chrome_7feed900000!base::MessageLoop::RunTask
11 chrome_7feed900000!base::MessageLoop::DeferOrRunPendingTask
12 chrome_7feed900000!base::MessageLoop::DoWork
13 chrome_7feed900000!base::MessagePumpForIO::DoRunLoop
14 chrome_7feed900000!base::MessagePumpWin::Run
15 chrome_7feed900000!base::MessageLoop::RunHandler
16 chrome_7feed900000!base::RunLoop::Run
17 chrome_7feed900000!base::MessageLoop::Run
18 chrome_7feed900000!base::Thread::Run
19 chrome_7feed900000!content::BrowserThreadImpl::IOThreadRun
1a chrome_7feed900000!content::BrowserThreadImpl::Run
1b chrome_7feed900000!base::Thread::ThreadMain
1c chrome_7feed900000!base::`anonymous namespace'::ThreadFunc
1d kernel32!BaseThreadInitThunk
1e ntdll!RtlUserThreadStart
我们看一下局部变量信息,看看运行时的状态
0:026> ~~[10c4]s;.frame 0n0;dv /t /v
chrome_7feed900000!net::HttpNetworkTransaction::Start:
000007fe`ee58d66c 48895c2410 mov qword ptr [rsp+10h],rbx ss:00000000`0914e158=000000000aec6610
00 00000000`0914e148 000007fe`ee28f812 chrome_7feed900000!net::HttpNetworkTransaction::Start [c:\b\build\slave\win64\build\src\net\http\http_network_transaction.cc @ 191]
@rcx class net::HttpNetworkTransaction * this = 0x00000000`11a21640
@rdx struct net::HttpRequestInfo * request_info = 0x00000000`0aac8ff8
@r8 class base::Callback<void __cdecl(int)> * callback = 0x00000000`11d18b80
@r9 class net::BoundNetLog * net_log = 0x00000000`11d187a0
<unavailable> int rv = <value unavailable>
0:026> dx -id 0,0 -r1 (*((chrome_7feed900000!net::HttpRequestInfo *)0xaac8ff8))
(*((chrome_7feed900000!net::HttpRequestInfo *)0xaac8ff8)) [Type: net::HttpRequestInfo]
[+0x000] url [Type: GURL]
[+0x078] method : "GET" [Type: std::basic_string<char,std::char_traits<char>,std::allocator<char> >]
[+0x098] extra_headers [Type: net::HttpRequestHeaders]
[+0x0b0] upload_data_stream : 0x0 [Type: net::UploadDataStream *]
[+0x0b8] load_flags : 4352
[+0x0bc] motivation : NORMAL_MOTIVATION (2) [Type: net::HttpRequestInfo::RequestMotivation]
[+0x0c0] privacy_mode : PRIVACY_MODE_DISABLED (0) [Type: net::PrivacyMode]
0:026> dx -id 0,0 -r1 (*((chrome_7feed900000!GURL *)0xaac8ff8))
(*((chrome_7feed900000!GURL *)0xaac8ff8)) [Type: GURL]
[+0x000] spec_ : "http://blog.csdn.net/feiniao251314/article/details/52230012" [Type: std::basic_string<char,std::char_traits<char>,std::allocator<char> >]
[+0x020] is_valid_ : true
[+0x028] parsed_ [Type: url::Parsed]
[+0x070] inner_url_ [Type: scoped_ptr<GURL,std::default_delete<GURL> >]
在cache中没有找到URL相关的资源,那么我们将请求信息传递到HttpNetworkTransaction中,试图通过网络来请求数据。
源码分析
在源码分析之前,我们看一下HttpNetworkTransaction的状态,根据状态,我们大体上就能了解网络HttpNetworkTransaction要处理的网络情况
HttpNetworkTransaction::State
enum State {
STATE_NOTIFY_BEFORE_CREATE_STREAM,
STATE_CREATE_STREAM,
STATE_CREATE_STREAM_COMPLETE,
STATE_INIT_STREAM,
STATE_INIT_STREAM_COMPLETE,
STATE_GENERATE_PROXY_AUTH_TOKEN,
STATE_GENERATE_PROXY_AUTH_TOKEN_COMPLETE,
STATE_GENERATE_SERVER_AUTH_TOKEN,
STATE_GENERATE_SERVER_AUTH_TOKEN_COMPLETE,
STATE_GET_TOKEN_BINDING_KEY,
STATE_GET_TOKEN_BINDING_KEY_COMPLETE,
STATE_INIT_REQUEST_BODY,
STATE_INIT_REQUEST_BODY_COMPLETE,
STATE_BUILD_REQUEST,
STATE_BUILD_REQUEST_COMPLETE,
STATE_SEND_REQUEST,
STATE_SEND_REQUEST_COMPLETE,
STATE_READ_HEADERS,
STATE_READ_HEADERS_COMPLETE,
STATE_READ_BODY,
STATE_READ_BODY_COMPLETE,
STATE_DRAIN_BODY_FOR_AUTH_RESTART,
STATE_DRAIN_BODY_FOR_AUTH_RESTART_COMPLETE,
STATE_NONE
};
状态要比HttpCache要少许多,和ftp网络传输状态相当。分创建,初始化,生成key,初始化请求,建立请求,发送请求,读取请求等等。我们从中简要分析其中的过程。
启动与初始化
int HttpNetworkTransaction::Start(const HttpRequestInfo* request_info,
const CompletionCallback& callback,
const BoundNetLog& net_log) {
net_log_ = net_log;
request_ = request_info;
.......
next_state_ = STATE_NOTIFY_BEFORE_CREATE_STREAM;
int rv = DoLoop(OK);
if (rv == ERR_IO_PENDING)
callback_ = callback;
return rv;
}
int HttpNetworkTransaction::DoNotifyBeforeCreateStream() {
next_state_ = STATE_CREATE_STREAM;
bool defer = false;
if (!before_network_start_callback_.is_null())
before_network_start_callback_.Run(&defer);
if (!defer)
return OK;
return ERR_IO_PENDING;
}
int HttpNetworkTransaction::DoCreateStream() {
// TODO(mmenke): Remove ScopedTracker below once crbug.com/424359 is fixed.
tracked_objects::ScopedTracker tracking_profile(
FROM_HERE_WITH_EXPLICIT_FUNCTION(
"424359 HttpNetworkTransaction::DoCreateStream"));
response_.network_accessed = true;
next_state_ = STATE_CREATE_STREAM_COMPLETE;
if (ForWebSocketHandshake()) {
stream_request_.reset(
session_->http_stream_factory_for_websocket()
->RequestWebSocketHandshakeStream(
*request_,
priority_,
server_ssl_config_,
proxy_ssl_config_,
this,
websocket_handshake_stream_base_create_helper_,
net_log_));
} else {
stream_request_.reset(
session_->http_stream_factory()->RequestStream(
*request_,
priority_,
server_ssl_config_,
proxy_ssl_config_,
this,
net_log_));
}
DCHECK(stream_request_.get());
return ERR_IO_PENDING;
}
创建比较简单,使用会话session_来创建一个请求Stream,内部创建了socket,我们暂且不向下深挖,暂时先分析http这一层次的传输过程,下面给出创建socket的堆栈示意:
0:026> kc
# Call Site
00 chrome_7feed900000!net::CreatePlatformSocket
01 chrome_7feed900000!net::UDPSocketWin::Open
02 chrome_7feed900000!net::UDPClientSocket::Connect
03 chrome_7feed900000!net::`anonymous namespace'::IsGloballyReachable
04 chrome_7feed900000!net::HostResolverImpl::IsIPv6Reachable
05 chrome_7feed900000!net::HostResolverImpl::GetEffectiveKeyForRequest
06 chrome_7feed900000!net::HostResolverImpl::Resolve
07 chrome_7feed900000!net::SingleRequestHostResolver::Resolve
08 chrome_7feed900000!net::TransportConnectJobHelper::DoResolveHost
09 chrome_7feed900000!net::TransportConnectJob::DoResolveHost
0a chrome_7feed900000!net::TransportConnectJobHelper::DoLoop<net::TransportConnectJob>
0b chrome_7feed900000!net::ConnectJob::Connect
0c chrome_7feed900000!net::internal::ClientSocketPoolBaseHelper::RequestSocketInternal
0d chrome_7feed900000!net::internal::ClientSocketPoolBaseHelper::RequestSocket
0e chrome_7feed900000!net::ClientSocketPoolBase<net::TransportSocketParams>::RequestSocket
0f chrome_7feed900000!net::ClientSocketHandle::Init<net::SSLClientSocketPool>
10 chrome_7feed900000!net::`anonymous namespace'::InitSocketPoolHelper
11 chrome_7feed900000!net::InitSocketHandleForHttpRequest
12 chrome_7feed900000!net::HttpStreamFactoryImpl::Job::DoInitConnection
13 chrome_7feed900000!net::HttpStreamFactoryImpl::Job::DoLoop
14 chrome_7feed900000!net::HttpStreamFactoryImpl::Job::RunLoop
15 chrome_7feed900000!net::HttpStreamFactoryImpl::RequestStreamInternal
16 chrome_7feed900000!net::HttpStreamFactoryImpl::RequestStream
17 chrome_7feed900000!net::HttpNetworkTransaction::DoCreateStream
18 chrome_7feed900000!net::HttpNetworkTransaction::DoLoop
19 chrome_7feed900000!net::HttpNetworkTransaction::Start
1a chrome_7feed900000!DevToolsNetworkTransaction::Start
1b chrome_7feed900000!net::HttpCache::Transaction::DoSendRequest
1c chrome_7feed900000!net::HttpCache::Transaction::DoLoop
1d chrome_7feed900000!base::internal::RunnableAdapter<void (__cdecl extensions::NativeMessageProcessHost::*)(int)>::Run
1e chrome_7feed900000!base::internal::InvokeHelper<1,void,base::internal::RunnableAdapter<void (__cdecl extensions::NativeMessageProcessHost::*)(int)> >::MakeItSo
1f chrome_7feed900000!base::internal::Invoker<base::IndexSequence<0>,base::internal::BindState<base::internal::RunnableAdapter<void (__cdecl extensions::NativeMessageProcessHost::*)(int) __ptr64>,void __cdecl(extensions::NativeMessageProcessHost * __ptr64,int),base::WeakPtr<extensions::NativeMessageProcessHost> >,base::internal::InvokeHelper<1,void,base::internal::RunnableAdapter<void (__cdecl extensions::NativeMessageProcessHost::*)(int) __ptr64> >,void __cdecl(int const & __ptr64)>::Run
20 chrome_7feed900000!base::Callback<void __cdecl(int)>::Run
21 chrome_7feed900000!net::HttpCache::WorkItem::NotifyTransaction
22 chrome_7feed900000!net::HttpCache::OnIOComplete
23 chrome_7feed900000!net::HttpCache::OnPendingOpComplete
24 chrome_7feed900000!base::Callback<void __cdecl(int)>::Run
25 chrome_7feed900000!disk_cache::InFlightBackendIO::OnOperationComplete
26 chrome_7feed900000!disk_cache::BackgroundIO::OnIOSignalled
27 chrome_7feed900000!base::Callback<void __cdecl(void)>::Run
28 chrome_7feed900000!base::debug::TaskAnnotator::RunTask
29 chrome_7feed900000!base::MessageLoop::RunTask
2a chrome_7feed900000!base::MessageLoop::DeferOrRunPendingTask
2b chrome_7feed900000!base::MessageLoop::DoWork
2c chrome_7feed900000!base::MessagePumpForIO::DoRunLoop
2d chrome_7feed900000!base::MessagePumpWin::Run
2e chrome_7feed900000!base::MessageLoop::RunHandler
2f chrome_7feed900000!base::RunLoop::Run
30 chrome_7feed900000!base::MessageLoop::Run
31 chrome_7feed900000!base::Thread::Run
32 chrome_7feed900000!content::BrowserThreadImpl::IOThreadRun
33 chrome_7feed900000!content::BrowserThreadImpl::Run
34 chrome_7feed900000!base::Thread::ThreadMain
35 chrome_7feed900000!base::`anonymous namespace'::ThreadFunc
36 kernel32!BaseThreadInitThunk
37 ntdll!RtlUserThreadStart
int HttpNetworkTransaction::DoInitStream() {
DCHECK(stream_.get());
next_state_ = STATE_INIT_STREAM_COMPLETE;
stream_->GetRemoteEndpoint(&remote_endpoint_);
return stream_->InitializeStream(request_, priority_, net_log_, io_callback_);
}
创建请求完成后,初始化Stream,然后生成服务器和客户端的Token.
发送请求
int HttpNetworkTransaction::DoSendRequest() {
// TODO(mmenke): Remove ScopedTracker below once crbug.com/424359 is fixed.
tracked_objects::ScopedTracker tracking_profile(
FROM_HERE_WITH_EXPLICIT_FUNCTION(
"424359 HttpNetworkTransaction::DoSendRequest"));
send_start_time_ = base::TimeTicks::Now();
next_state_ = STATE_SEND_REQUEST_COMPLETE;
return stream_->SendRequest(request_headers_, &response_, io_callback_);
}
这里我们可以查看一下request_headers_的相关信息,目前是connection请求。
0:025> dx -id 0,0 -r1 (*((chrome_7fee4550000!net::HttpRequestHeaders::HeaderKeyValuePair *)0x114f49e0))
(*((chrome_7fee4550000!net::HttpRequestHeaders::HeaderKeyValuePair *)0x114f49e0)) [Type: net::HttpRequestHeaders::HeaderKeyValuePair]
[+0x000] key : "Host" [Type: std::basic_string<char,std::char_traits<char>,std::allocator<char> >]
[+0x020] value : "blog.csdn.net" [Type: std::basic_string<char,std::char_traits<char>,std::allocator<char> >]
0:025> dx -id 0,0 -r1 (*((chrome_7fee4550000!net::HttpRequestHeaders::HeaderKeyValuePair *)0x114f4a20))
(*((chrome_7fee4550000!net::HttpRequestHeaders::HeaderKeyValuePair *)0x114f4a20)) [Type: net::HttpRequestHeaders::HeaderKeyValuePair]
[+0x000] key : "Connection" [Type: std::basic_string<char,std::char_traits<char>,std::allocator<char> >]
[+0x020] value : "keep-alive" [Type: std::basic_string<char,std::char_traits<char>,std::allocator<char> >]
0:025> dx -id 0,0 -r1 (*((chrome_7fee4550000!net::HttpRequestHeaders::HeaderKeyValuePair *)0x114f4a60))
(*((chrome_7fee4550000!net::HttpRequestHeaders::HeaderKeyValuePair *)0x114f4a60)) [Type: net::HttpRequestHeaders::HeaderKeyValuePair]
[+0x000] key : "Accept" [Type: std::basic_string<char,std::char_traits<char>,std::allocator<char> >]
[+0x020] value : "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8" [Type: std::basic_string<char,std::char_traits<char>,std::allocator<char> >]
接收数据
int HttpNetworkTransaction::DoSendRequestComplete(int result) {
send_end_time_ = base::TimeTicks::Now();
if (result < 0)
return HandleIOError(result);
next_state_ = STATE_READ_HEADERS;
return OK;
}
int HttpNetworkTransaction::DoReadHeaders() {
next_state_ = STATE_READ_HEADERS_COMPLETE;
return stream_->ReadResponseHeaders(io_callback_);
}
当发送请求完成后,会设置下一跳状态为读取头部状态,然后返回状态循环,开始读取头部信息。
HttpNetworkTransaction 小结
当在HttpCache中无法获取到有效信息的时候,那么就会生成一个HttpNetworkTransaction请求,通过网络来请求最新数据,HttpNetworkTransaction负责建立连接,初始化终端,发送和接收数据,将数据组织好。
网络请求结果的转储
上面我们说了HttpCache::transaction和HttpNetworkTransaction的情况,一个是本地缓存传输,一个是网络数据传输,当本地数据无效的时候,会请求网络传输,而当网络传输完毕的时候会通知本地缓存处理。
情景分析
我们可以如下下断
0:025> bp chrome_7fee4550000!net::HttpCache::Transaction::DoSuccessfulSendRequest
这样,当HttpNetworkTransaction传输完成的时候,会中断到调试器,这样跟踪一下,看看实际的运行过程。
下面是堆栈示意。
0:025> kc
# Call Site
00 chrome_7fee4550000!net::HttpCache::Transaction::DoSuccessfulSendRequest
01 chrome_7fee4550000!net::HttpCache::Transaction::DoLoop
02 chrome_7fee4550000!base::internal::RunnableAdapter<void (__cdecl extensions::NativeMessageProcessHost::*)(int)>::Run
03 chrome_7fee4550000!base::internal::InvokeHelper<1,void,base::internal::RunnableAdapter<void (__cdecl extensions::NativeMessageProcessHost::*)(int)> >::MakeItSo
04 chrome_7fee4550000!base::internal::Invoker<base::IndexSequence<0>,base::internal::BindState<base::internal::RunnableAdapter<void (__cdecl extensions::NativeMessageProcessHost::*)(int) __ptr64>,void __cdecl(extensions::NativeMessageProcessHost * __ptr64,int),base::WeakPtr<extensions::NativeMessageProcessHost> >,base::internal::InvokeHelper<1,void,base::internal::RunnableAdapter<void (__cdecl extensions::NativeMessageProcessHost::*)(int) __ptr64> >,void __cdecl(int const & __ptr64)>::Run
05 chrome_7fee4550000!base::Callback<void __cdecl(int)>::Run
06 chrome_7fee4550000!net::HttpNetworkTransaction::DoCallback
07 chrome_7fee4550000!net::HttpNetworkTransaction::OnIOComplete
08 chrome_7fee4550000!net::HttpNetworkTransaction::OnStreamReady
09 chrome_7fee4550000!net::HttpStreamFactoryImpl::Job::OnStreamReadyCallback
0a chrome_7fee4550000!base::internal::RunnableAdapter<void (__cdecl browser_sync::BookmarkModelAssociator::*)(void)>::Run
0b chrome_7fee4550000!base::internal::InvokeHelper<1,void,base::internal::RunnableAdapter<void (__cdecl browser_sync::BookmarkModelAssociator::*)(void)> >::MakeItSo
0c chrome_7fee4550000!base::internal::Invoker<base::IndexSequence<0>,base::internal::BindState<base::internal::RunnableAdapter<void (__cdecl browser_sync::BookmarkModelAssociator::*)(void) __ptr64>,void __cdecl(browser_sync::BookmarkModelAssociator * __ptr64),base::WeakPtr<browser_sync::BookmarkModelAssociator> >,base::internal::InvokeHelper<1,void,base::internal::RunnableAdapter<void (__cdecl browser_sync::BookmarkModelAssociator::*)(void) __ptr64> >,void __cdecl(void)>::Run
0d chrome_7fee4550000!base::Callback<void __cdecl(void)>::Run
0e chrome_7fee4550000!base::debug::TaskAnnotator::RunTask
0f chrome_7fee4550000!base::MessageLoop::RunTask
10 chrome_7fee4550000!base::MessageLoop::DeferOrRunPendingTask
11 chrome_7fee4550000!base::MessageLoop::DoWork
12 chrome_7fee4550000!base::MessagePumpForIO::DoRunLoop
13 chrome_7fee4550000!base::MessagePumpWin::Run
14 chrome_7fee4550000!base::MessageLoop::RunHandler
15 chrome_7fee4550000!base::RunLoop::Run
16 chrome_7fee4550000!base::MessageLoop::Run
17 chrome_7fee4550000!base::Thread::Run
18 chrome_7fee4550000!content::BrowserThreadImpl::IOThreadRun
19 chrome_7fee4550000!content::BrowserThreadImpl::Run
1a chrome_7fee4550000!base::Thread::ThreadMain
1b chrome_7fee4550000!base::`anonymous namespace'::ThreadFunc
1c kernel32!BaseThreadInitThunk
1d ntdll!RtlUserThreadStart
在HttpNetworkTransaction完成的时候会调用callback,这个是在启动HttpNetworkTransaction请求的时候设置的,完成时回调到HttpCache::transaction,进行数据的转储处理。
源码分析
调用过程
// 1. Not-cached entry:
// Start():
// GetBackend* -> InitEntry -> OpenEntry* -> CreateEntry* -> AddToEntry* ->
// SendRequest* -> SuccessfulSendRequest -> OverwriteCachedResponse ->
// CacheWriteResponse* -> TruncateCachedData* -> TruncateCachedMetadata* ->
// PartialHeadersReceived
//
// Read():
// NetworkRead* -> CacheWriteData*
我们回顾一下情况一,如上,我们收到了HttpNetworkTransaction请求完成后,会重写缓存,但是我们的缓存中并没有这一项,就没有实际的重写操作,而是进行下一状态,STATE_CACHE_WRITE_RESPONSE.
int HttpCache::Transaction::DoCacheWriteResponse() {
next_state_ = STATE_CACHE_WRITE_RESPONSE_COMPLETE;
return WriteResponseInfoToEntry(truncated_);
}
这一状态的处理就是实际的写响应信息到HttpCache的Entry中。
int HttpCache::Transaction::WriteResponseInfoToEntry(bool truncated) {
if (!entry_)
return OK;
......
bool skip_transient_headers = true;
scoped_refptr<PickledIOBuffer> data(new PickledIOBuffer());
response_.Persist(data->pickle(), skip_transient_headers, truncated);
data->Done();
io_buf_len_ = data->pickle()->size();
return entry_->disk_entry->WriteData(kResponseInfoIndex, 0, data.get(),
io_buf_len_, io_callback_, true);
}
在这个函数中实际的写数据操作通过Entry来实现,将数据写到disk_cache中。
转储小结
就是这样,当HttpCache中没有有效数据的时候,就通过HttpNetworkTransaction请求网络数据,当网络数据请求完毕时,回调到HttpCache::transaction中将数据存储到HttpCache中,以便下次读取。
样本的版本信息
chrome 50.0.2661.87
符号路径:
https://chromium-browser-symsrv.commondatastorage.googleapis.com
源码网站:
www.chromium.org
感谢chromium项目相关作者及人员。