Check if zlib is compatible.

Add a --zlib_fingerprint flag in delta_generator to check if the zlib of
source image is compatible, and only enable IMGDIFF operation if it is.

Test: Added unittest to check /etc/zlib_fingerprint
Bug: 27156099

Change-Id: Ida346a99430c95cdc8a43e1055d6efa08f07ca25
diff --git a/payload_consumer/delta_performer_unittest.cc b/payload_consumer/delta_performer_unittest.cc
index d637a7e..89182fe 100644
--- a/payload_consumer/delta_performer_unittest.cc
+++ b/payload_consumer/delta_performer_unittest.cc
@@ -56,7 +56,9 @@
 extern const char* kUnittestPrivateKeyPath;
 extern const char* kUnittestPublicKeyPath;
 
-static const char* kBogusMetadataSignature1 =
+namespace {
+
+const char kBogusMetadataSignature1[] =
     "awSFIUdUZz2VWFiR+ku0Pj00V7bPQPQFYQSXjEXr3vaw3TE4xHV5CraY3/YrZpBv"
     "J5z4dSBskoeuaO1TNC/S6E05t+yt36tE4Fh79tMnJ/z9fogBDXWgXLEUyG78IEQr"
     "YH6/eBsQGT2RJtBgXIXbZ9W+5G9KmGDoPOoiaeNsDuqHiBc/58OFsrxskH8E6vMS"
@@ -64,7 +66,13 @@
     "fjoTeLYZpt+WN65Vu7jJ0cQN8e1y+2yka5112wpRf/LLtPgiAjEZnsoYpLUd7CoV"
     "pLRtClp97kN2+tXGNBQqkA==";
 
-namespace {
+#ifdef __ANDROID__
+const char kZlibFingerprintPath[] =
+    "/data/nativetest/update_engine_unittests/zlib_fingerprint";
+#else
+const char kZlibFingerprintPath[] = "/etc/zlib_fingerprint";
+#endif  // __ANDROID__
+
 // Different options that determine what we should fill into the
 // install_plan.metadata_signature to simulate the contents received in the
 // Omaha response.
@@ -893,4 +901,14 @@
   EXPECT_EQ(DeltaPerformer::kSupportedMajorPayloadVersion, major_version);
 }
 
+// Test that we recognize our own zlib compressor implementation as supported.
+// All other equivalent implementations should be added to
+// kCompatibleZlibFingerprint.
+TEST_F(DeltaPerformerTest, ZlibFingerprintMatch) {
+  string fingerprint;
+  EXPECT_TRUE(base::ReadFileToString(base::FilePath(kZlibFingerprintPath),
+                                     &fingerprint));
+  EXPECT_TRUE(utils::IsZlibCompatible(fingerprint));
+}
+
 }  // namespace chromeos_update_engine
diff --git a/payload_consumer/payload_constants.cc b/payload_consumer/payload_constants.cc
index 3d78e0a..6078a74 100644
--- a/payload_consumer/payload_constants.cc
+++ b/payload_consumer/payload_constants.cc
@@ -33,6 +33,15 @@
 const char kDeltaMagic[4] = {'C', 'r', 'A', 'U'};
 const char kBspatchPath[] = "bspatch";
 
+// The zlib in Android and Chrome OS are currently compatible with each other,
+// so they are sharing the same array, but if in the future they are no longer
+// compatible with each other, we coule make the same change on the other one to
+// make them compatible again or use ifdef here.
+const char kCompatibleZlibFingerprint[][65] = {
+    "ea973605ccbbdb24f59f449c5f65861a1a9bc7a4353377aaaa06cb3e0f1cfbd7",
+    "3747fa404cceb00a5ec3606fc779510aaa784d5864ab1d5c28b9e267c40aad5c",
+};
+
 const char* InstallOperationTypeName(InstallOperation_Type op_type) {
   switch (op_type) {
     case InstallOperation::BSDIFF:
diff --git a/payload_consumer/payload_constants.h b/payload_consumer/payload_constants.h
index 76d740f..2dbc5fa 100644
--- a/payload_consumer/payload_constants.h
+++ b/payload_consumer/payload_constants.h
@@ -56,6 +56,15 @@
 extern const char kBspatchPath[];
 extern const char kDeltaMagic[4];
 
+// The list of compatible SHA256 hashes of zlib source code.
+// This is used to check if the source image have a compatible zlib (produce
+// same compressed result given the same input).
+// When a new fingerprint is found, please examine the changes in zlib source
+// carefully and determine if it's still compatible with previous version, if
+// yes then add the new fingerprint to this array, otherwise remove all previous
+// fingerprints in the array first, and only include the new fingerprint.
+extern const char kCompatibleZlibFingerprint[2][65];
+
 // A block number denoting a hole on a sparse file. Used on Extents to refer to
 // section of blocks not present on disk on a sparse file.
 const uint64_t kSparseHole = std::numeric_limits<uint64_t>::max();