diff -r 000000000000 -r 6474c204b198 mobile/android/base/background/bagheera/DeflateHelper.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mobile/android/base/background/bagheera/DeflateHelper.java	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,77 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.gecko.background.bagheera;
+
+import java.io.UnsupportedEncodingException;
+import java.util.zip.Deflater;
+
+import ch.boye.httpclientandroidlib.HttpEntity;
+
+public class DeflateHelper {
+  /**
+   * Conservative upper bound for zlib size, equivalent to the first few lines
+   * in zlib's deflateBound function.
+   *
+   * Includes zlib header.
+   *
+   * @param sourceLen
+   *          the number of bytes to compress.
+   * @return the number of bytes to allocate for the compressed output.
+   */
+  public static int deflateBound(final int sourceLen) {
+    return sourceLen + ((sourceLen + 7) >> 3) + ((sourceLen + 63) >> 6) + 5 + 6;
+  }
+
+  /**
+   * Deflate the input into the output array, returning the number of bytes
+   * written to output.
+   */
+  public static int deflate(byte[] input, byte[] output) {
+    final Deflater deflater = new Deflater();
+    deflater.setInput(input);
+    deflater.finish();
+
+    final int length = deflater.deflate(output);
+    deflater.end();
+    return length;
+  }
+
+  /**
+   * Deflate the input, returning an HttpEntity that offers an accurate window
+   * on the output.
+   *
+   * Note that this method does not trim the output array. (Test code can use
+   * TestDeflation#deflateTrimmed(byte[]).)
+   *
+   * Trimming would be more efficient for long-term space use, but we expect this
+   * entity to be transient.
+   *
+   * Note also that deflate can require <b>more</b> space than the input.
+   * {@link #deflateBound(int)} tells us the most it will use.
+   *
+   * @param bytes the input to deflate.
+   * @return the deflated input as an entity.
+   */
+  public static HttpEntity deflateBytes(final byte[] bytes) {
+    // We would like to use DeflaterInputStream here, but it's minSDK=9, and we
+    // still target 8. It would also force us to use chunked Transfer-Encoding,
+    // so perhaps it's for the best!
+
+    final byte[] out = new byte[deflateBound(bytes.length)];
+    final int outLength = deflate(bytes, out);
+    return new BoundedByteArrayEntity(out, 0, outLength);
+  }
+
+  public static HttpEntity deflateBody(final String payload) {
+    final byte[] bytes;
+    try {
+      bytes = payload.getBytes("UTF-8");
+    } catch (UnsupportedEncodingException ex) {
+      // This will never happen. Thanks, Java!
+      throw new RuntimeException(ex);
+    }
+    return deflateBytes(bytes);
+  }
+}
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