From 29cdb5290b532cdeb87801c41cfb2917ff7f0134 Mon Sep 17 00:00:00 2001
From: Greyson Parrelli <greyson@signal.org>
Date: Wed, 10 Apr 2019 17:05:20 -0400
Subject: [PATCH] Make headers for giphy requests random sizes.

---
 .../glide/ChunkedImageUrlLoader.java          |  1 +
 .../glide/PaddedHeadersInterceptor.java       | 46 +++++++++++++++++++
 2 files changed, 47 insertions(+)
 create mode 100644 src/org/thoughtcrime/securesms/glide/PaddedHeadersInterceptor.java

diff --git a/src/org/thoughtcrime/securesms/glide/ChunkedImageUrlLoader.java b/src/org/thoughtcrime/securesms/glide/ChunkedImageUrlLoader.java
index afd4798f80..fe0d765b8d 100644
--- a/src/org/thoughtcrime/securesms/glide/ChunkedImageUrlLoader.java
+++ b/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();
     }
 
diff --git a/src/org/thoughtcrime/securesms/glide/PaddedHeadersInterceptor.java b/src/org/thoughtcrime/securesms/glide/PaddedHeadersInterceptor.java
new file mode 100644
index 0000000000..03922b536e
--- /dev/null
+++ b/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);
+  }
+}