Move file hashing into its own class, Hash.

Test: hidl output remains the same.
Bug: 34178341
Merged-In: Ic8c5de61ebba3bd556d343c4f2c12af4bafb8d6b
Change-Id: Ic8c5de61ebba3bd556d343c4f2c12af4bafb8d6b
diff --git a/Android.bp b/Android.bp
index d969017..5c03b03 100644
--- a/Android.bp
+++ b/Android.bp
@@ -40,6 +40,7 @@
         "DeathRecipientType.cpp",
         "EnumType.cpp",
         "HandleType.cpp",
+        "Hash.cpp",
         "HidlTypeAssertion.cpp",
         "Interface.cpp",
         "MemoryType.cpp",
diff --git a/Hash.cpp b/Hash.cpp
new file mode 100644
index 0000000..348a79f
--- /dev/null
+++ b/Hash.cpp
@@ -0,0 +1,75 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "Hash.h"
+
+#include <fstream>
+#include <iomanip>
+#include <map>
+#include <sstream>
+
+#include <openssl/sha.h>
+
+namespace android {
+
+const Hash &Hash::getHash(const std::string &path) {
+    static std::map<std::string, Hash> hashes;
+
+    auto it = hashes.find(path);
+
+    if (hashes.find(path) == hashes.end()) {
+        it = hashes.insert(it, {path, Hash(path)});
+    }
+
+    return it->second;
+}
+
+static std::vector<uint8_t> sha256File(const std::string &path) {
+    std::ifstream stream(path);
+    std::stringstream fileStream;
+    fileStream << stream.rdbuf();
+    std::string fileContent = fileStream.str();
+
+    std::vector<uint8_t> ret = std::vector<uint8_t>(SHA256_DIGEST_LENGTH);
+
+    SHA256(reinterpret_cast<const uint8_t *>(fileContent.c_str()),
+            fileContent.size(), ret.data());
+
+    return ret;
+}
+
+Hash::Hash(const std::string &path)
+  : mPath(path),
+    mHash(sha256File(path)) {}
+
+std::string Hash::hexString() const {
+    std::ostringstream s;
+    s << std::hex << std::setfill('0');
+    for (uint8_t i : mHash) {
+        s << std::setw(2) << static_cast<int>(i);
+    }
+    return s.str();
+}
+
+const std::vector<uint8_t> &Hash::raw() const {
+    return mHash;
+}
+
+const std::string &Hash::getPath() const {
+    return mPath;
+}
+
+}  // android
\ No newline at end of file
diff --git a/Hash.h b/Hash.h
new file mode 100644
index 0000000..99dea31
--- /dev/null
+++ b/Hash.h
@@ -0,0 +1,44 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef HASH_H_
+
+#define HASH_H_
+
+#include <string>
+#include <vector>
+
+namespace android {
+
+struct Hash {
+    static const Hash &getHash(const std::string &path);
+
+    std::string hexString() const;
+
+    const std::vector<uint8_t> &raw() const;
+    const std::string &getPath() const;
+
+private:
+    Hash(const std::string &path);
+
+    const std::string mPath;
+    const std::vector<uint8_t> mHash;
+};
+
+}  // namespace android
+
+#endif  // HASH_H_
+
diff --git a/Interface.cpp b/Interface.cpp
index d326703..99c13e1 100644
--- a/Interface.cpp
+++ b/Interface.cpp
@@ -20,6 +20,7 @@
 #include "ArrayType.h"
 #include "ConstantExpression.h"
 #include "DeathRecipientType.h"
+#include "Hash.h"
 #include "Method.h"
 #include "ScalarType.h"
 #include "StringType.h"
@@ -27,14 +28,12 @@
 
 #include <unistd.h>
 
-#include <fstream>
 #include <iostream>
 #include <sstream>
 
 #include <android-base/logging.h>
 #include <hidl-util/Formatter.h>
 #include <hidl-util/StringHelper.h>
-#include <openssl/sha.h>
 
 namespace android {
 
@@ -288,36 +287,22 @@
     return true;
 }
 
-static void sha256File(const std::string &path, uint8_t *outDigest) {
-    std::ifstream stream(path);
-    std::stringstream fileStream;
-    fileStream << stream.rdbuf();
-    std::string fileContent = fileStream.str();
-    SHA256(reinterpret_cast<const uint8_t *>(fileContent.c_str()),
-            fileContent.size(), outDigest);
-}
-
 static void emitDigestChain(
         Formatter &out,
         const std::string &prefix,
         const std::vector<const Interface *> &chain,
         std::function<std::string(const ConstantExpression &)> byteToString) {
     out.join(chain.begin(), chain.end(), ",\n", [&] (const auto &iface) {
-        const std::string &filename = iface->location().begin().filename();
-        uint8_t digest[SHA256_DIGEST_LENGTH];
-        sha256File(filename, digest);
+        const Hash &hash = Hash::getHash(iface->location().begin().filename());
         out << prefix;
         out << "{";
-        out.join(digest, digest + SHA256_DIGEST_LENGTH, ",", [&](const auto &e) {
+        out.join(hash.raw().begin(), hash.raw().end(), ",", [&](const auto &e) {
             // Use ConstantExpression::cppValue / javaValue
             // because Java used signed byte for uint8_t.
             out << byteToString(ConstantExpression::ValueOf(ScalarType::Kind::KIND_UINT8, e));
         });
         out << "} /* ";
-        out.join(digest, digest + SHA256_DIGEST_LENGTH, "", [&](const auto &e) {
-            static const char hexes[] = "0123456789abcdef";
-            out << hexes[e >> 4] << hexes[e & 0xF];
-        });
+        out << hash.hexString();
         out << " */";
     });
 }
diff --git a/utils/include/hidl-util/Formatter.h b/utils/include/hidl-util/Formatter.h
index 513efad..bb4288b 100644
--- a/utils/include/hidl-util/Formatter.h
+++ b/utils/include/hidl-util/Formatter.h
@@ -105,7 +105,7 @@
     //     out << toString(e);
     // });
     template<typename I>
-    Formatter &join(I begin, I end, const std::string &separator,
+    Formatter &join(const I begin, const I end, const std::string &separator,
             std::function<void(const typename std::iterator_traits<I>::value_type &)> func);
 
     Formatter &operator<<(const std::string &out);
@@ -151,7 +151,7 @@
 };
 
 template<typename I>
-Formatter &Formatter::join(I begin, I end, const std::string &separator,
+Formatter &Formatter::join(const I begin, const I end, const std::string &separator,
         std::function<void(const typename std::iterator_traits<I>::value_type &)> func) {
     for (I iter = begin; iter != end; ++iter) {
         if (iter != begin) {