WebPagetest网页前端性能测试工具和实现分析
WebPageTest 原本是由AOL开发内部使用的工具，后来在Google Code上开源， 是一款非常优秀的网页前端性能测试工具。 在线版本http://www.webpagetest.org
Google Code: http://code.google.com/p/webpagetest/
部署WebPageTest 私有实例参考资料
http://testing.etao.com/node/303
http://testing.etao.com/node如下是作者提供的客户端实现分析
the networking stack on Windows from a browser’s perspective
Function Interception
The key to how WebPagetest works is its ability to intercept arbitrary function calls
and inspect or alter the request or response before passing it on to the original imple-mentation (or choosing not to pass it on at all). Luckily someone else did most of the
heavy lifting and provided a nice open source library (http://newgre.net/ncodehook) that
can take care of the details for you but it basically works like this:
• Find the target function in memory (trivial if it is exported from a dll).
• Copy the first several bytes from the function (making sure to keep x86 instructions
intact).
• Overwrite the function entry with a jmp to the new function.
• Provide a replacement function that includes the bytes copied from the original
function along with a jmp to the remaining code.
It’s pretty hairy stuff and things tend to go very wrong if you aren’t extremely careful,
but with well-defined functions (like all of the Windows APIs), you can pretty much
intercept anything you’d like.
One catch is that you can only redirect calls to code running in the same process as the
original function, which is fine if you wrote the code but doesn’t help a lot if you are
trying to spy on software that you don’t control which leads us to…
Code Injection
Lucky for me, Windows provides several ways to inject arbitrary code into processes.
There is a good overview of several different techniques here: http://www.codeproject
.com/KB/threads/winspy.aspx, and there are actually more ways to do it than that but
it covers the basics. Some of the techniques insert your code into every process but I
wanted to be a lot more targeted and just instrument the specific browser instances
that we are interested in, so after a bunch of experimentation (and horrible failures), I
ended up using the CreateRemoteThread/LoadLibrary technique which essentially lets
you force any process to load an arbitrary dll and execute code in it (assuming you have
the necessary rights).
Resulting Browser Architecture
Get the Code
Since WebPagetest is under a BSD license you are welcome to reuse any of the code for
whatever purposes you’d like. The project lives on Google Code here: (http://code.goo
gle.com/p/webpagetest/) and some of the more interesting files are:
• Winsock API interception code (http://webpagetest.googlecode.com/svn/trunk/
agent/wpthook/hook_winsock.cc)
• Code injection (http://webpagetest.googlecode.com/svn/trunk/agent/wpthook/inject
.cc)
