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libevent evhttp学习——http客户端.html
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libevent evhttp学习——http客户端.html
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<meta property="og:description" content="基本环境¶ 使用版本为libevent-2.1.5，目前为beta版，其中evhttp和旧版区别在于新增了如下接口 // 设置回调函数，在包头读取完成后回调 void evhttp_request_set_header_cb (struct evhttp_request *, int(*cb)(struct evhttp_request *, void *)) // 设置回调函数，在body有数据返回后回调 void evhttp_request_set_chunked_cb (struct evhttp_request *, void(*cb)(struct evhttp_request *, void *)) 这样的好处是可以在合适的时机回调我们注册的回调函数，比如下载1G的文件，在之前的版本只有下载完成后才会回调，现在每下载一部分数据就会回调一次，让上层应用更加灵活，尤其在http代理时，可以做到边下载边回复 2.1.5版本的完整接口文档详见http://www.wangafu.net/~nickm/libevent-2.1/doxygen/html/http_8h.html 请求流程 ..." />
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<meta name="twitter:description" content="基本环境¶ 使用版本为libevent-2.1.5，目前为beta版，其中evhttp和旧版区别在于新增了如下接口 // 设置回调函数，在包头读取完成后回调 void evhttp_request_set_header_cb (struct evhttp_request *, int(*cb)(struct evhttp_request *, void *)) // 设置回调函数，在body有数据返回后回调 void evhttp_request_set_chunked_cb (struct evhttp_request *, void(*cb)(struct evhttp_request *, void *)) 这样的好处是可以在合适的时机回调我们注册的回调函数，比如下载1G的文件，在之前的版本只有下载完成后才会回调，现在每下载一部分数据就会回调一次，让上层应用更加灵活，尤其在http代理时，可以做到边下载边回复 2.1.5版本的完整接口文档详见http://www.wangafu.net/~nickm/libevent-2.1/doxygen/html/http_8h.html 请求流程 ...">
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<h1><a href="https://chukeer.github.io/libevent evhttp学习——http客户端.html"> libevent evhttp学习——http客户端 </a></h1>
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<h4>Contents</h4>
<div class="toc">
<ul>
<li><a href="#_1">基本环境</a></li>
<li><a href="#_2">请求流程</a></li>
<li><a href="#_3">完整代码</a></li>
</ul>
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<div class="span8 article-content">
<h2 id="_1">基本环境<a class="headerlink" href="#_1" title="Permanent link">¶</a></h2>
<p>使用版本为libevent-2.1.5，目前为beta版，其中evhttp和旧版区别在于新增了如下接口</p>
<div class="highlight"><pre><span></span><span class="c1">// 设置回调函数，在包头读取完成后回调</span>
<span class="kt">void</span> <span class="n">evhttp_request_set_header_cb</span> <span class="p">(</span><span class="k">struct</span> <span class="n">evhttp_request</span> <span class="o">*</span><span class="p">,</span> <span class="kt">int</span><span class="p">(</span><span class="o">*</span><span class="n">cb</span><span class="p">)(</span><span class="k">struct</span> <span class="n">evhttp_request</span> <span class="o">*</span><span class="p">,</span> <span class="kt">void</span> <span class="o">*</span><span class="p">))</span>
<span class="c1">// 设置回调函数，在body有数据返回后回调</span>
<span class="kt">void</span> <span class="n">evhttp_request_set_chunked_cb</span> <span class="p">(</span><span class="k">struct</span> <span class="n">evhttp_request</span> <span class="o">*</span><span class="p">,</span> <span class="kt">void</span><span class="p">(</span><span class="o">*</span><span class="n">cb</span><span class="p">)(</span><span class="k">struct</span> <span class="n">evhttp_request</span> <span class="o">*</span><span class="p">,</span> <span class="kt">void</span> <span class="o">*</span><span class="p">))</span>
</pre></div>
<p>这样的好处是可以在合适的时机回调我们注册的回调函数，比如下载1G的文件，在之前的版本只有下载完成后才会回调，现在每下载一部分数据就会回调一次，让上层应用更加灵活，尤其在http代理时，可以做到边下载边回复</p>
<p>2.1.5版本的完整接口文档详见<a href="http://www.wangafu.net/~nickm/libevent-2.1/doxygen/html/http_8h.html">http://www.wangafu.net/~nickm/libevent-2.1/doxygen/html/http_8h.html</a></p>
<h2 id="_2">请求流程<a class="headerlink" href="#_2" title="Permanent link">¶</a></h2>
<p>http客户端使用到的接口函数及请求流程如下</p>
<ol>
<li>初始化event_base和evdns_base</li>
</ol>
<div class="highlight"><pre><span></span> <span class="k">struct</span> <span class="n">event_base</span> <span class="o">*</span><span class="nf">event_base_new</span><span class="p">(</span><span class="kt">void</span><span class="p">);</span>
<span class="k">struct</span> <span class="n">evdns_base</span> <span class="o">*</span> <span class="nf">evdns_base_new</span><span class="p">(</span><span class="k">struct</span> <span class="n">event_base</span> <span class="o">*</span><span class="n">event_base</span><span class="p">,</span> <span class="kt">int</span> <span class="n">initialize_nameservers</span><span class="p">);</span>
</pre></div>
<ol>
<li>
<p>创建evhttp_request对象，并设置回调函数，这里的回调函数是和数据接收相关的</p>
<p><code>cpp
struct evhttp_request *evhttp_request_new(void (*cb)(struct evhttp_request *, void *), void *arg);
void evhttp_request_set_header_cb(struct evhttp_request *, int (*cb)(struct evhttp_request *, void *));
void evhttp_request_set_chunked_cb(struct evhttp_request *, void (*cb)(struct evhttp_request *, void *));
void evhttp_request_set_error_cb(struct evhttp_request *, void (*)(enum evhttp_request_error, void *));</code>
3. 创建evhttp_connection对象，并设置回调函数，这里的回调函数是和连接状态相关的</p>
<p><code>cpp
struct evhttp_connection *evhttp_connection_base_new(struct event_base *base,
struct evdns_base *dnsbase, const char *address, unsigned short port);
void evhttp_connection_set_closecb(struct evhttp_connection *evcon,
void (*)(struct evhttp_connection *, void *), void *);</code>
4. 有选择的向evhttp_request添加包头字段</p>
<p><code>cpp
int evhttp_add_header(struct evkeyvalq *headers, const char *key, const char *value);</code>
5. 发送请求</p>
<p><code>cpp
int evhttp_make_request(struct evhttp_connection *evcon,
struct evhttp_request *req,
enum evhttp_cmd_type type, const char *uri);</code>
6. 派发事件</p>
<p><code>cpp
int event_base_dispatch(struct event_base *);</code></p>
</li>
</ol>
<h2 id="_3">完整代码<a class="headerlink" href="#_3" title="Permanent link">¶</a></h2>
<div class="highlight"><pre><span></span><span class="cp">#include</span> <span class="cpf">"event2/http.h"</span><span class="cp"></span>
<span class="cp">#include</span> <span class="cpf">"event2/http_struct.h"</span><span class="cp"></span>
<span class="cp">#include</span> <span class="cpf">"event2/event.h"</span><span class="cp"></span>
<span class="cp">#include</span> <span class="cpf">"event2/buffer.h"</span><span class="cp"></span>
<span class="cp">#include</span> <span class="cpf">"event2/dns.h"</span><span class="cp"></span>
<span class="cp">#include</span> <span class="cpf">"event2/thread.h"</span><span class="cp"></span>
<span class="cp">#include</span> <span class="cpf"><stdio.h></span><span class="cp"></span>
<span class="cp">#include</span> <span class="cpf"><string.h></span><span class="cp"></span>
<span class="cp">#include</span> <span class="cpf"><assert.h></span><span class="cp"></span>
<span class="cp">#include</span> <span class="cpf"><sys/queue.h></span><span class="cp"></span>
<span class="cp">#include</span> <span class="cpf"><event.h></span><span class="cp"></span>
<span class="kt">void</span> <span class="nf">RemoteReadCallback</span><span class="p">(</span><span class="k">struct</span> <span class="n">evhttp_request</span><span class="o">*</span> <span class="n">remote_rsp</span><span class="p">,</span> <span class="kt">void</span><span class="o">*</span> <span class="n">arg</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">event_base_loopexit</span><span class="p">((</span><span class="k">struct</span> <span class="n">event_base</span><span class="o">*</span><span class="p">)</span><span class="n">arg</span><span class="p">,</span> <span class="nb">NULL</span><span class="p">);</span>
<span class="p">}</span>
<span class="kt">int</span> <span class="nf">ReadHeaderDoneCallback</span><span class="p">(</span><span class="k">struct</span> <span class="n">evhttp_request</span><span class="o">*</span> <span class="n">remote_rsp</span><span class="p">,</span> <span class="kt">void</span><span class="o">*</span> <span class="n">arg</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"< HTTP/1.1 %d %s</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">evhttp_request_get_response_code</span><span class="p">(</span><span class="n">remote_rsp</span><span class="p">),</span> <span class="n">evhttp_request_get_response_code_line</span><span class="p">(</span><span class="n">remote_rsp</span><span class="p">));</span>
<span class="k">struct</span> <span class="n">evkeyvalq</span><span class="o">*</span> <span class="n">headers</span> <span class="o">=</span> <span class="n">evhttp_request_get_input_headers</span><span class="p">(</span><span class="n">remote_rsp</span><span class="p">);</span>
<span class="k">struct</span> <span class="n">evkeyval</span><span class="o">*</span> <span class="n">header</span><span class="p">;</span>
<span class="n">TAILQ_FOREACH</span><span class="p">(</span><span class="n">header</span><span class="p">,</span> <span class="n">headers</span><span class="p">,</span> <span class="n">next</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"< %s: %s</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">header</span><span class="o">-></span><span class="n">key</span><span class="p">,</span> <span class="n">header</span><span class="o">-></span><span class="n">value</span><span class="p">);</span>
<span class="p">}</span>
<span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"< </span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
<span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
<span class="p">}</span>
<span class="kt">void</span> <span class="nf">ReadChunkCallback</span><span class="p">(</span><span class="k">struct</span> <span class="n">evhttp_request</span><span class="o">*</span> <span class="n">remote_rsp</span><span class="p">,</span> <span class="kt">void</span><span class="o">*</span> <span class="n">arg</span><span class="p">)</span>
<span class="p">{</span>
<span class="kt">char</span> <span class="n">buf</span><span class="p">[</span><span class="mi">4096</span><span class="p">];</span>
<span class="k">struct</span> <span class="n">evbuffer</span><span class="o">*</span> <span class="n">evbuf</span> <span class="o">=</span> <span class="n">evhttp_request_get_input_buffer</span><span class="p">(</span><span class="n">remote_rsp</span><span class="p">);</span>
<span class="kt">int</span> <span class="n">n</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
<span class="k">while</span> <span class="p">((</span><span class="n">n</span> <span class="o">=</span> <span class="n">evbuffer_remove</span><span class="p">(</span><span class="n">evbuf</span><span class="p">,</span> <span class="n">buf</span><span class="p">,</span> <span class="mi">4096</span><span class="p">))</span> <span class="o">></span> <span class="mi">0</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">fwrite</span><span class="p">(</span><span class="n">buf</span><span class="p">,</span> <span class="n">n</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="n">stdout</span><span class="p">);</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="kt">void</span> <span class="nf">RemoteRequestErrorCallback</span><span class="p">(</span><span class="k">enum</span> <span class="n">evhttp_request_error</span> <span class="n">error</span><span class="p">,</span> <span class="kt">void</span><span class="o">*</span> <span class="n">arg</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"request failed</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
<span class="n">event_base_loopexit</span><span class="p">((</span><span class="k">struct</span> <span class="n">event_base</span><span class="o">*</span><span class="p">)</span><span class="n">arg</span><span class="p">,</span> <span class="nb">NULL</span><span class="p">);</span>
<span class="p">}</span>
<span class="kt">void</span> <span class="nf">RemoteConnectionCloseCallback</span><span class="p">(</span><span class="k">struct</span> <span class="n">evhttp_connection</span><span class="o">*</span> <span class="n">connection</span><span class="p">,</span> <span class="kt">void</span><span class="o">*</span> <span class="n">arg</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"remote connection closed</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
<span class="n">event_base_loopexit</span><span class="p">((</span><span class="k">struct</span> <span class="n">event_base</span><span class="o">*</span><span class="p">)</span><span class="n">arg</span><span class="p">,</span> <span class="nb">NULL</span><span class="p">);</span>
<span class="p">}</span>
<span class="kt">int</span> <span class="nf">main</span><span class="p">(</span><span class="kt">int</span> <span class="n">argc</span><span class="p">,</span> <span class="kt">char</span><span class="o">**</span> <span class="n">argv</span><span class="p">)</span>
<span class="p">{</span>
<span class="k">if</span> <span class="p">(</span><span class="n">argc</span> <span class="o">!=</span> <span class="mi">2</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">printf</span><span class="p">(</span><span class="s">"usage:%s url"</span><span class="p">,</span> <span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">]);</span>
<span class="k">return</span> <span class="mi">1</span><span class="p">;</span>
<span class="p">}</span>
<span class="kt">char</span><span class="o">*</span> <span class="n">url</span> <span class="o">=</span> <span class="n">argv</span><span class="p">[</span><span class="mi">1</span><span class="p">];</span>
<span class="k">struct</span> <span class="n">evhttp_uri</span><span class="o">*</span> <span class="n">uri</span> <span class="o">=</span> <span class="n">evhttp_uri_parse</span><span class="p">(</span><span class="n">url</span><span class="p">);</span>
<span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">uri</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"parse url failed!</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
<span class="k">return</span> <span class="mi">1</span><span class="p">;</span>
<span class="p">}</span>
<span class="k">struct</span> <span class="n">event_base</span><span class="o">*</span> <span class="n">base</span> <span class="o">=</span> <span class="n">event_base_new</span><span class="p">();</span>
<span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">base</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"create event base failed!</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
<span class="k">return</span> <span class="mi">1</span><span class="p">;</span>
<span class="p">}</span>
<span class="k">struct</span> <span class="n">evdns_base</span><span class="o">*</span> <span class="n">dnsbase</span> <span class="o">=</span> <span class="n">evdns_base_new</span><span class="p">(</span><span class="n">base</span><span class="p">,</span> <span class="mi">1</span><span class="p">);</span>
<span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">dnsbase</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"create dns base failed!</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
<span class="p">}</span>
<span class="n">assert</span><span class="p">(</span><span class="n">dnsbase</span><span class="p">);</span>
<span class="k">struct</span> <span class="n">evhttp_request</span><span class="o">*</span> <span class="n">request</span> <span class="o">=</span> <span class="n">evhttp_request_new</span><span class="p">(</span><span class="n">RemoteReadCallback</span><span class="p">,</span> <span class="n">base</span><span class="p">);</span>
<span class="n">evhttp_request_set_header_cb</span><span class="p">(</span><span class="n">request</span><span class="p">,</span> <span class="n">ReadHeaderDoneCallback</span><span class="p">);</span>
<span class="n">evhttp_request_set_chunked_cb</span><span class="p">(</span><span class="n">request</span><span class="p">,</span> <span class="n">ReadChunkCallback</span><span class="p">);</span>
<span class="n">evhttp_request_set_error_cb</span><span class="p">(</span><span class="n">request</span><span class="p">,</span> <span class="n">RemoteRequestErrorCallback</span><span class="p">);</span>
<span class="k">const</span> <span class="kt">char</span><span class="o">*</span> <span class="n">host</span> <span class="o">=</span> <span class="n">evhttp_uri_get_host</span><span class="p">(</span><span class="n">uri</span><span class="p">);</span>
<span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">host</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"parse host failed!</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
<span class="k">return</span> <span class="mi">1</span><span class="p">;</span>
<span class="p">}</span>
<span class="kt">int</span> <span class="n">port</span> <span class="o">=</span> <span class="n">evhttp_uri_get_port</span><span class="p">(</span><span class="n">uri</span><span class="p">);</span>
<span class="k">if</span> <span class="p">(</span><span class="n">port</span> <span class="o"><</span> <span class="mi">0</span><span class="p">)</span> <span class="n">port</span> <span class="o">=</span> <span class="mi">80</span><span class="p">;</span>
<span class="k">const</span> <span class="kt">char</span><span class="o">*</span> <span class="n">request_url</span> <span class="o">=</span> <span class="n">url</span><span class="p">;</span>
<span class="k">const</span> <span class="kt">char</span><span class="o">*</span> <span class="n">path</span> <span class="o">=</span> <span class="n">evhttp_uri_get_path</span><span class="p">(</span><span class="n">uri</span><span class="p">);</span>
<span class="k">if</span> <span class="p">(</span><span class="n">path</span> <span class="o">==</span> <span class="nb">NULL</span> <span class="o">||</span> <span class="n">strlen</span><span class="p">(</span><span class="n">path</span><span class="p">)</span> <span class="o">==</span> <span class="mi">0</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">request_url</span> <span class="o">=</span> <span class="s">"/"</span><span class="p">;</span>
<span class="p">}</span>
<span class="n">printf</span><span class="p">(</span><span class="s">"url:%s host:%s port:%d path:%s request_url:%s</span><span class="se">\n</span><span class="s">"</span><span class="p">,</span> <span class="n">url</span><span class="p">,</span> <span class="n">host</span><span class="p">,</span> <span class="n">port</span><span class="p">,</span> <span class="n">path</span><span class="p">,</span> <span class="n">request_url</span><span class="p">);</span>
<span class="k">struct</span> <span class="n">evhttp_connection</span><span class="o">*</span> <span class="n">connection</span> <span class="o">=</span> <span class="n">evhttp_connection_base_new</span><span class="p">(</span><span class="n">base</span><span class="p">,</span> <span class="n">dnsbase</span><span class="p">,</span> <span class="n">host</span><span class="p">,</span> <span class="n">port</span><span class="p">);</span>
<span class="k">if</span> <span class="p">(</span><span class="o">!</span><span class="n">connection</span><span class="p">)</span>
<span class="p">{</span>
<span class="n">fprintf</span><span class="p">(</span><span class="n">stderr</span><span class="p">,</span> <span class="s">"create evhttp connection failed!</span><span class="se">\n</span><span class="s">"</span><span class="p">);</span>
<span class="k">return</span> <span class="mi">1</span><span class="p">;</span>
<span class="p">}</span>
<span class="n">evhttp_connection_set_closecb</span><span class="p">(</span><span class="n">connection</span><span class="p">,</span> <span class="n">RemoteConnectionCloseCallback</span><span class="p">,</span> <span class="n">base</span><span class="p">);</span>
<span class="n">evhttp_add_header</span><span class="p">(</span><span class="n">evhttp_request_get_output_headers</span><span class="p">(</span><span class="n">request</span><span class="p">),</span> <span class="s">"Host"</span><span class="p">,</span> <span class="n">host</span><span class="p">);</span>
<span class="n">evhttp_make_request</span><span class="p">(</span><span class="n">connection</span><span class="p">,</span> <span class="n">request</span><span class="p">,</span> <span class="n">EVHTTP_REQ_GET</span><span class="p">,</span> <span class="n">request_url</span><span class="p">);</span>
<span class="n">event_base_dispatch</span><span class="p">(</span><span class="n">base</span><span class="p">);</span>
<span class="k">return</span> <span class="mi">0</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
<p>编译</p>
<div class="highlight"><pre><span></span>g++ http_client.cpp -I/opt/local/libevent-2.1.5/include -L/opt/local/libevent-2.1.5/lib -levent -g -o http_client
</pre></div>
<p>运行示例，这里只打印了包头字段</p>
<div class="highlight"><pre><span></span> <span class="o">$</span> <span class="o">./</span><span class="nt">http_client</span> <span class="nt">http</span><span class="o">://</span><span class="nt">www</span><span class="nc">.qq.com</span> <span class="o">>/</span><span class="nt">dev</span><span class="o">/</span><span class="nt">null</span>
<span class="o"><</span> <span class="nt">HTTP</span><span class="o">/</span><span class="nt">1</span><span class="nc">.1</span> <span class="nt">200</span> <span class="nt">OK</span>
<span class="o"><</span> <span class="nt">Server</span><span class="o">:</span> <span class="nt">squid</span><span class="o">/</span><span class="nt">3</span><span class="nc">.4.3</span>
<span class="o"><</span> <span class="nt">Content-Type</span><span class="o">:</span> <span class="nt">text</span><span class="o">/</span><span class="nt">html</span><span class="o">;</span> <span class="nt">charset</span><span class="o">=</span><span class="nt">GB2312</span>
<span class="o"><</span> <span class="nt">Cache-Control</span><span class="o">:</span> <span class="nt">max-age</span><span class="o">=</span><span class="nt">60</span>
<span class="o"><</span> <span class="nt">Expires</span><span class="o">:</span> <span class="nt">Fri</span><span class="o">,</span> <span class="nt">05</span> <span class="nt">Aug</span> <span class="nt">2016</span> <span class="nt">08</span><span class="nd">:48:31</span> <span class="nt">GMT</span>
<span class="o"><</span> <span class="nt">Date</span><span class="o">:</span> <span class="nt">Fri</span><span class="o">,</span> <span class="nt">05</span> <span class="nt">Aug</span> <span class="nt">2016</span> <span class="nt">08</span><span class="nd">:47:31</span> <span class="nt">GMT</span>
<span class="o"><</span> <span class="nt">Transfer-Encoding</span><span class="o">:</span> <span class="nt">chunked</span>
<span class="o"><</span> <span class="nt">Connection</span><span class="o">:</span> <span class="nt">keep-alive</span>
<span class="o"><</span> <span class="nt">Connection</span><span class="o">:</span> <span class="nt">Transfer-Encoding</span>
<span class="o"><</span>
</pre></div>
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