Apache HttpClient 未显示响应的 Content-Length 和 Content-Encoding 标头

Question

我安装了Apache httpcomponents-client-5.0.x，在查看http响应的标头时，我很震惊它没有显示Content-Length和Content-Encoding标头，这是我用于测试的代码

import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
import org.apache.hc.client5.http.impl.classic.CloseableHttpResponse;
import org.apache.hc.client5.http.impl.classic.HttpClients;
import com.sun.net.httpserver.Headers;

CloseableHttpClient httpclient = HttpClients.createDefault();
HttpGet request = new HttpGet(new URI("https://www.example.com"));
CloseableHttpResponse response = httpclient.execute(request);
Header[] responseHeaders = response.getHeaders();
for(Header header: responseHeaders) {               
    System.out.println(header.getName());
}
// this prints all the headers except 
// status code header
// Content-Length
// Content-Encoding

无论我尝试什么，我都会得到相同的结果，就像这样

Iterator<Header> headersItr = response.headerIterator();
while(headersItr.hasNext()) {
    Header header = headersItr.next();
    System.out.println(header.getName());
}

或者这个

HttpEntity entity = response.getEntity();
System.out.println(entity.getContentEncoding()); // NULL
System.out.println(entity.getContentLength());   // -1

根据 6 年前问过的this question，即使使用旧版本的 Apache HttpClient，这似乎也是一个老问题。

当然，正如 Wireshark 所确认的那样，服务器实际上正在返回这些标头，并且 Apache HttpClient 会自行记录

2020-04-03 07:59:09,106 DEBUG [org.apache.hc.client5.http.headers] http-outgoing-0 << HTTP/1.1 200 OK
2020-04-03 07:59:09,106 DEBUG [org.apache.hc.client5.http.headers] http-outgoing-0 << Content-Encoding: gzip
2020-04-03 07:59:09,106 DEBUG [org.apache.hc.client5.http.headers] http-outgoing-0 << Accept-Ranges: bytes
2020-04-03 07:59:09,107 DEBUG [org.apache.hc.client5.http.headers] http-outgoing-0 << Age: 451956
2020-04-03 07:59:09,107 DEBUG [org.apache.hc.client5.http.headers] http-outgoing-0 << Cache-Control: max-age=604800
2020-04-03 07:59:09,107 DEBUG [org.apache.hc.client5.http.headers] http-outgoing-0 << Content-Type: text/html; charset=UTF-8
2020-04-03 07:59:09,107 DEBUG [org.apache.hc.client5.http.headers] http-outgoing-0 << Date: Fri, 03 Apr 2020 05:59:09 GMT
2020-04-03 07:59:09,108 DEBUG [org.apache.hc.client5.http.headers] http-outgoing-0 << Etag: "3147526947+gzip"
2020-04-03 07:59:09,108 DEBUG [org.apache.hc.client5.http.headers] http-outgoing-0 << Expires: Fri, 10 Apr 2020 05:59:09 GMT
2020-04-03 07:59:09,108 DEBUG [org.apache.hc.client5.http.headers] http-outgoing-0 << Last-Modified: Thu, 17 Oct 2019 07:18:26 GMT
2020-04-03 07:59:09,108 DEBUG [org.apache.hc.client5.http.headers] http-outgoing-0 << Server: ECS (dcb/7EEB)
2020-04-03 07:59:09,108 DEBUG [org.apache.hc.client5.http.headers] http-outgoing-0 << Vary: Accept-Encoding
2020-04-03 07:59:09,109 DEBUG [org.apache.hc.client5.http.headers] http-outgoing-0 << X-Cache: HIT
2020-04-03 07:59:09,109 DEBUG [org.apache.hc.client5.http.headers] http-outgoing-0 << Content-Length: 648

顺便说一句，java.net.http 库称为 JDK HttpClient 效果很好，可以显示所有标题。

是我做错了什么，还是应该报告一个存在多年的错误？

Answer 1

HttpComponents 提交者在这里...

你没有密切注意戴夫 G 说的话。默认情况下HttpClientBuilder会开启透明解压，你看不到一些header的原因是here：

if (decoderFactory != null) {
  response.setEntity(new DecompressingEntity(response.getEntity(), decoderFactory));
  response.removeHeaders(HttpHeaders.CONTENT_LENGTH);
  response.removeHeaders(HttpHeaders.CONTENT_ENCODING);
  response.removeHeaders(HttpHeaders.CONTENT_MD5);
} ...

对于JDK HttpClient，它不会进行任何透明的解压，因此可以看到压缩流的长度。你必须自己解压。

在这里卷曲提交者...

我也有raised an issue。

Answer 2

在这种情况下可能会忽略内容长度。

HttpGet request = new HttpGet(new URI("https://www.example.com"));
request.setHeader("Accept-Encoding", "identity");
CloseableHttpResponse response = httpclient.execute(request);

我可以看到以下内容

HttpEntity entity = response.getEntity();
System.out.println(entity.getContentLength());
System.out.println(entity.getContentEncoding());

输出

...
2020-04-03 03:04:17.760 DEBUG 34196 --- [           main] org.apache.hc.client5.http.headers       : http-outgoing-0 << Content-Length: 1256
...
1256
null

我想请您注意正在发送的此标头：

http-outgoing-0 >> Accept-Encoding: gzip, x-gzip, deflate

这告诉服务器这个客户端可以接受 gzip、x-gzip 和 deflate 内容作为响应。响应说明它是“gzip”编码的。

http-outgoing-0 << Content-Encoding: gzip

我相信 HttpClient 正在内部透明地处理此问题并提供内容。

正如您引用的另一篇文章中所述，其中一个答案表明可以应用方法EntityUtils.toByteArray(httpResponse.getEntity()).length 来获取内容长度。