Make headers for giphy requests random sizes.

src/org/thoughtcrime/securesms/glide/ChunkedImageUrlLoader.java

@@ -41,6 +41,7 @@ public class ChunkedImageUrlLoader implements ModelLoader<ChunkedImageUrl, Input
       this.client  = new OkHttpClient.Builder()
                                      .proxySelector(new ContentProxySelector())
                                      .cache(null)
+                                     .addNetworkInterceptor(new PaddedHeadersInterceptor())
                                      .build();
     }
 

src/org/thoughtcrime/securesms/glide/PaddedHeadersInterceptor.java

@@ -0,0 +1,46 @@
+package org.thoughtcrime.securesms.glide;
+
+import android.support.annotation.NonNull;
+
+import java.io.IOException;
+import java.security.SecureRandom;
+
+import okhttp3.Headers;
+import okhttp3.Interceptor;
+import okhttp3.Request;
+import okhttp3.Response;
+
+/**
+ * An interceptor that adds a header with a random amount of bytes to disguise header length.
+ */
+public class PaddedHeadersInterceptor implements Interceptor {
+
+  private static final String PADDING_HEADER   = "X-SignalPadding";
+  private static final int    MIN_RANDOM_BYTES = 1;
+  private static final int    MAX_RANDOM_BYTES = 64;
+
+  @Override
+  public Response intercept(@NonNull Chain chain) throws IOException {
+    Request padded = chain.request().newBuilder()
+                                    .headers(getPaddedHeaders(chain.request().headers()))
+                                    .build();
+
+    return chain.proceed(padded);
+  }
+
+  private @NonNull Headers getPaddedHeaders(@NonNull Headers headers) {
+    return headers.newBuilder()
+                  .add(PADDING_HEADER, getRandomString(new SecureRandom(), MIN_RANDOM_BYTES, MAX_RANDOM_BYTES))
+                  .build();
+  }
+
+  private static @NonNull String getRandomString(@NonNull SecureRandom secureRandom, int minLength, int maxLength) {
+    char[] buffer = new char[secureRandom.nextInt(maxLength - minLength) + minLength];
+
+    for (int i = 0 ; i  < buffer.length; i++) {
+      buffer[i] = (char) (secureRandom.nextInt(74) + 48); // Random char from 0-Z
+    }
+
+    return new String(buffer);
+  }
+}