Replace bundled hashlib with gcrypt

The commit also adds a minimalistic, idiomatic C++ wrapper for gcrypt, which can be used in projects that use libzsync2 (e.g., libappimageupdate).

Author: TheAssassin

CMakeLists.txt

@@ -83,6 +83,13 @@ else()
     message(FATAL_ERROR "Unsupported platform: ${CMAKE_SYSTEM_NAME}")
 endif()
 
+# doing this on project level allows all subdirs to use the imported targets
+find_package(PkgConfig)
+
+# we used to ship a minimal, zlib-licensed hash lib as part of zsync2
+# now, we use a system provided crypto library for this purpose
+pkg_check_modules(libgcrypt REQUIRED IMPORTED_TARGET libgcrypt)
+
 # add libraries shipped along with the project
 add_subdirectory(lib)
 

cmake/zsync2Config.cmake.in

@@ -1,3 +1,10 @@
 @PACKAGE_INIT@
 
-include ( "${CMAKE_CURRENT_LIST_DIR}/zsync2Targets.cmake" )
+# doing this on project level allows all subdirs to use the imported targets
+find_package(PkgConfig)
+
+# we used to ship a minimal, zlib-licensed hash lib as part of zsync2
+# now, we use a system provided crypto library for this purpose
+pkg_check_modules(libgcrypt REQUIRED IMPORTED_TARGET libgcrypt)
+
+include ("${CMAKE_CURRENT_LIST_DIR}/zsync2Targets.cmake")

include/zshash.h

@@ -0,0 +1,61 @@
+#ifndef ZSYNC2_ZSHASH_H
+#define ZSYNC2_ZSHASH_H
+
+// system headers
+#include <assert.h>
+#include <memory>
+#include <sstream>
+
+// library headers
+#include <gcrypt.h>
+
+// own headers
+#include "zsutil.h"
+
+namespace zsync2 {
+    /**
+     * Minimal idiomatic C++ wrapper around libgcrypt's hashing library.
+     */
+    template<gcry_md_algos _algorithm>
+    class ZSyncHash {
+    private:
+        static void _assertGcryptNoError(gcry_error_t error) {
+            if (error != 0) {
+                throw std::runtime_error(std::to_string(error));
+            }
+        }
+
+    public:
+        ZSyncHash() {
+            _assertGcryptNoError(gcry_md_open(&_handle, _algorithm, 0));
+        };
+
+        explicit ZSyncHash(const std::string& data) : ZSyncHash() {
+            add(data);
+        }
+
+        template<typename Vector>
+        void add(const Vector& vector) {
+            gcry_md_write(_handle, vector.data(), vector.size());
+        }
+
+        // this function may be called only once, the result will not change once the digest has been calculated
+        std::string getHash() {
+            const auto* buffer = gcry_md_read(_handle, _algorithm);
+            const auto len = gcry_md_get_algo_dlen(_algorithm);
+
+            assert(buffer != nullptr);
+
+            return bytesToHex(buffer, len);
+        }
+
+        ~ZSyncHash() noexcept {
+            gcry_md_close(_handle);
+        }
+
+    private:
+        gcry_md_hd_t _handle{};
+    };
+}
+
+#endif //ZSYNC2_ZSHASH_H

include/zsutil.h

@@ -41,5 +41,5 @@ namespace zsync2 {
 
     std::string base64Decode(const std::string& in);
 
-    std::string bytesToHex(unsigned char *data, int len);
+    std::string bytesToHex(const unsigned char *data, size_t len);
 }

lib/CMakeLists.txt

@@ -1,4 +1,5 @@
-set(CMAKE_MINIMUM_REQUIRED_VERSION 3.2)
+# for pkg-config IMPORTED_TARGET
+cmake_minimum_required(VERSION 3.6)
 
 include_directories(.)
 
@@ -25,6 +26,3 @@ target_include_directories(args INTERFACE args)
 if(NOT TARGET gtest)
     add_subdirectory(gtest EXCLUDE_FROM_ALL)
 endif()
-
-# minimal zlib-licensed hash library
-add_subdirectory(hashlib)