Fresco使用HttpURLConnection支持加载https链接图片

文章目录

1. 1. 查找原因
2. 2. 解决方法

前几天使用Fresco加载图片时遇到图片加载不出来的问题，然后调试了一下，发现出现如下错误：

javax.net.ssl.SSLException: Connection closed by peer

debug时的截图如下图所示：

查找原因

上面的截图是在给Fresco中的展示图片的类SimpleDraweeView调用如下代码时出现的：

// SimpileDraweeView sdv = ...;
sdv.setController(Fresco.newDraweeControllerBuilder().setControllerListener(new BaseControllerListener<ImageInfo>() {
        @Override
        public void onFinalImageSet(String id, ImageInfo imageInfo, Animatable animatable) {
            File file = getCacheFile(request);
            if (file != null && callback != null) {
                callback.onImageLoadFinish(file);
            }
        }

        @Override
        public void onFailure(String id, Throwable throwable) {
            // 这里throwable就是javax.net.ssl.SSLException: Connection closed by peer
            super.onFailure(id, throwable);
            if (callback != null) {
                callback.onFailure(uri, throwable);
            }
        }
    })
    .setImageRequest(request)
    .build());

看到上面的错误提示，马上反应是不是因为https证书的原因？原来请求的图片链接是https地址。到网上一搜，果然，Fresco默认不支持https，需要自己设置。一看网上的解决方法，都是使用Okhttp库来解决的，由于项目比较老，还没有使用Okhttp库，总不能为了解决这个问题而引入一个库吧？感觉代价太大了。所以跑去看了一下Okhttp默认请求加载图片的实现。

Okhttp库加载图片的网络请求处理在这个类com.facebook.imagepipeline.producers.HttpUrlConnectionNetworkFetcher中，关键的请求处理是在downloadFrom(Uri uri, int maxRedirects)这个方法中，代码如下所示：

private HttpURLConnection downloadFrom(Uri uri, int maxRedirects) throws IOException {
  HttpURLConnection connection = openConnectionTo(uri);
  int responseCode = connection.getResponseCode(); // 请求是在这一步发出的，在这之前设置HTTPS即可

  if (isHttpSuccess(responseCode)) {
      return connection;

  } else if (isHttpRedirect(responseCode)) {
      String nextUriString = connection.getHeaderField("Location");
      connection.disconnect();

      Uri nextUri = (nextUriString == null) ? null : Uri.parse(nextUriString);
      String originalScheme = uri.getScheme();

      if (maxRedirects > 0 && nextUri != null && !nextUri.getScheme().equals(originalScheme)) {
        return downloadFrom(nextUri, maxRedirects - 1);
      } else {
        String message = maxRedirects == 0
            ? error("URL %s follows too many redirects", uri.toString())
            : error("URL %s returned %d without a valid redirect", uri.toString(), responseCode);
        throw new IOException(message);
      }

  } else {
      connection.disconnect();
      throw new IOException(String
          .format("Image URL %s returned HTTP code %d", uri.toString(), responseCode));
  }
}

@VisibleForTesting
static HttpURLConnection openConnectionTo(Uri uri) throws IOException {
  URL url = new URL(uri.toString());
  return (HttpURLConnection) url.openConnection();
}

解决方法

从上面的代码可以看出来，请求是从int responseCode = connection.getResponseCode();这行代码发出去的，但是又没有对https的证书进行处理，所以在这之前增加处理即可。于是想到继承这个类来扩展处理https的情况，结果从上面的代码来看，想从继承的角度增加https的处理是不可能的。干脆把整个类的代码复制一份，修改类名为HttpsUrlConnectionNetworkFetcher，修改downloadFrom这个方法，增加https证书处理，代码如下所示：

public class HttpsUrlConnectionNetworkFetcher extends BaseNetworkFetcher<FetchState> {

    // 中间代码忽略...

    private HttpURLConnection downloadFrom(Uri uri, int maxRedirects) throws IOException {
        HttpURLConnection connection = openConnectionTo(uri);
        // 增加https支持
        String scheme = uri.getScheme();
        if ("https".equals(scheme)) {
            HttpsURLConnection httpsURLConnection = (HttpsURLConnection) connection;
            SSLContext sslContext = SSLContextUtils.getSSLContext();
            if (sslContext != null) {
                SSLSocketFactory sslSocketFactory = sslContext.getSocketFactory();
                httpsURLConnection.setSSLSocketFactory(sslSocketFactory);
                httpsURLConnection.setHostnameVerifier(SSLContextUtils.getHostnameVerifier());
            }
        }

        int responseCode = connection.getResponseCode(); 
        // 其它代码忽略...
    }

}

SSLContextUtils类中忽略对证书的处理，信任所有证书，这种做法很不安全，仅供参考。代码如下所示：

import android.util.Log;

import java.security.SecureRandom;
import java.security.cert.X509Certificate;

import javax.net.ssl.HostnameVerifier;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLSession;
import javax.net.ssl.TrustManager;
import javax.net.ssl.X509TrustManager;

/**
 * SSL工具类
 */
public class SSLContextUtils {

    private static HostnameVerifier hostnameVerifier = new HostnameVerifier() {
        @Override
        public boolean verify(String hostname, SSLSession session) {
            return true;
        }
    };

    public static HostnameVerifier getHostnameVerifier() {
        return hostnameVerifier;
    }

    public static SSLContext getSSLContext() {
        SSLContext sslContext = null;
        try {
            sslContext = SSLContext.getInstance("TLS");
            sslContext.init(null, new TrustManager[]{new X509TrustManager() {
                @Override
                public void checkClientTrusted(X509Certificate[] chain, String authType)  {}

                @Override
                public void checkServerTrusted(X509Certificate[] chain, String authType) {}

                @Override
                public X509Certificate[] getAcceptedIssuers() {
                    return new X509Certificate[0];
                }
            }}, new SecureRandom());
        } catch (Exception e) {
            Log.e("SSLContextUtils", e.getMessage(), e);
        }
        return sslContext;
    }

}

最后需要把这个自定义的类的通过调用ImagePipelineConfig.Builder#setNetworkFetcher()方法设置进来，指定加载图片时使用新的网络请求策略。具体代码如下所示：

ImagePipelineConfig config = ImagePipelineConfig.newBuilder(context)
        .setDownsampleEnabled(true)
        .setNetworkFetcher(new HttpsUrlConnectionNetworkFetcher()) // 这里设置自定义类
        .build();
Fresco.initialize(context, config);

再重新运行App，图片加载出来了，问题解决。