Libevhtp小试牛刀——使用Libevhtp实现http服务

从不浪费时间的人，没有工夫抱怨时间不够。 —— 杰弗逊

本来是打算写一个入门的介绍使用Libevhtp的小文章和大家分享，发现官方的文档已经写的很好了，就翻译了一下。但是限于自己能力有限，翻译的不是很好，大家可以对应着官方的介绍看。对于英语比较好的建议还是直接看英文吧。

LOGO	Libevhtp

Libevhtp简介

Libevhtp was created as a replacement API for Libevent's current HTTP API. The reality of libevent's http interface is that it was created as a JIT server, meaning the developer never thought of it being used for creating a full-fledged HTTP service. Infact I am under the impression that the libevent http API was designed almost as an example of what you can do with libevent. It's not Apache in a box, but more and more developers are attempting to use it as so.

简而言之，作者之所以开发这个基于Libevent HTTP的库，是为了解决Libevent HTTP不太好用的特性，下面列举了一系列Libevent HTTP的瑕疵。

It was not designed to be a fully functional HTTP server.

The code is messy, abstractions are almost non-existent, and feature-creep has made long-term maintainability very hard.

The parsing code is slow and requires data to be buffered before a full parse can be completed. This results in extranious memory usage and lots of string comparison functions.

There is no method for a user to access various parts of the request processing cycle. For example if the "Content-Length" header has a value of 50000, your callback is not executed until all 50000 bytes have been read.

Setting callback URI's do exact matches; meaning if you set a callback for "/foo/", requests for "/foo/bar/" are ignored.

Creating an HTTPS server is hard, it requires a bunch of work to be done on the underlying bufferevents.

As far as I know, streaming data back to a client is hard, if not impossible without messing with underlying bufferevents.

It's confusing to work with, this is probably due to the lack of proper documentation.

翻译过来，总结一下大致如下，

不是为全功能的HTTP服务而设计。
代码有点糟糕，几乎没有抽象，很难维护。
解析数据慢，而且需要数据缓存之后才能完成完整解析。
很难创建HTTP服务。
流数据返回客户端很困难。
缺少文档，很难上手使用。

下载安装

需要的依赖

gcc
Libevent2
OpenSSL（可选）
pthreads（可选）

使用步骤

创建一个 parent evhtp_t 结构。

Assign callbacks to the parent for specific URIs or posix-regex based URI's（设置特定的URIs）。

（可选）为回调函数声明连接前的hooks。

（可选）声明连接前、后的回调函数。

（可选）开启内置的线程池处理连接。

（可选）设置服务类型为HTTPS方式。

开始evhtp服务监听。

代码实现

客户端

#!/usr/bin/python
# -*- coding: UTF-8 -*-

import urllib
import urllib2
import time



def parseText():
    data_urlencode = urllib.urlencode("Hello World!")
    requrl = "http://127.0.0.1:8090/test/"
    req = urllib2.Request(url = requrl, data_urlencode)
    res_data = urllib2.urlopen(req)
    res = res_data.read()
    print res

def main():
        time1 = time.time()
        parseText()
        time2 = time.time()
        print time2 - time1

if __name__ == '__main__':
        main()

服务端

最简代码

#include 
#include 

void
testcb(evhtp_request_t * req, void * a) {
    evbuffer_add_reference(req->buffer_out, "foobar", 6, NULL, NULL);
    evhtp_send_reply(req, EVHTP_RES_OK);
}

int
main(int argc, char ** argv) {
    evbase_t * evbase = event_base_new();
    evhtp_t  * htp    = evhtp_new(evbase, NULL);

    evhtp_set_cb(htp, "/test", testcb, NULL);
    evhtp_bind_socket(htp, "0.0.0.0", 8080, 1024);
    event_base_loop(evbase, 0);
    return 0;
}

总结

通过学习，对Libevhtp有了一个简单的认识，学习到了Libevhtp设计开发的初衷，Libevhtp在Linux上下载、安装的方法，书写一个最简单的Libevhtp服务的方法。

参考文献

https://github.com/criticalstack/libevhtp
http://blog.chinaunix.net/uid-24567872-id-3860909.html
http://www.ruanyifeng.com/blog/2015/02/make.html