chore: function for checking if files are identical

See mendersoftware/mender-update-orchestrator#90

Ticket: MEN-7171

Signed-off-by: Daniel Skinstad Drabitzius <daniel.drabitzius@northern.tech>

src/common/path.hpp

@@ -71,6 +71,8 @@ error::Error DeleteRecursively(const string &path);
 
 expected::ExpectedBool IsExecutable(const string &path, const bool warn = true);
 
+expected::ExpectedBool AreFilesIdentical(const string &file_one, const string &file_two);
+
 expected::ExpectedUnorderedSet<string> ListFiles(const string &in, function<bool(string)> matcher);
 
 error::Error CreateDirectory(const string &path);

src/common/path/platform/c++17/path.cpp

@@ -12,9 +12,12 @@
 //    See the License for the specific language governing permissions and
 //    limitations under the License.
 
+#include <common/io.hpp>
 #include <common/path.hpp>
 
 #include <filesystem>
+#include <functional>
+#include <iterator>
 #include <string>
 #include <unordered_set>
 
@@ -26,6 +29,7 @@ namespace path {
 
 using namespace std;
 namespace fs = std::filesystem;
+namespace io = mender::common::io;
 
 unordered_map<Perms, fs::perms> perm_map = {
 	{Perms::Owner_exec, fs::perms::owner_exec},
@@ -112,6 +116,42 @@ expected::ExpectedBool IsExecutable(const string &file_path, const bool warn) {
 	}
 }
 
+expected::ExpectedBool AreFilesIdentical(const string &file_one, const string &file_two) {
+	auto file_one_expected_stream = io::OpenIfstream(file_one);
+	if (!file_one_expected_stream) {
+		return expected::unexpected(file_one_expected_stream.error());
+	}
+	auto file_two_expected_stream = io::OpenIfstream(file_two);
+	if (!file_two_expected_stream) {
+		return expected::unexpected(file_two_expected_stream.error());
+	}
+
+	auto &file_one_stream = file_one_expected_stream.value();
+	auto &file_two_stream = file_two_expected_stream.value();
+
+	// Compare file sizes
+	file_one_stream.seekg(0, ios::end);
+	file_two_stream.seekg(0, ios::end);
+	if (file_one_stream.tellg() != file_two_stream.tellg()) {
+		return false;
+	}
+	file_one_stream.seekg(0, ios::beg);
+	file_two_stream.seekg(0, ios::beg);
+
+	string file_one_contents {
+		istreambuf_iterator<char>(file_one_stream), istreambuf_iterator<char>()};
+	string file_two_contents {
+		istreambuf_iterator<char>(file_two_stream), istreambuf_iterator<char>()};
+
+	size_t file_one_hash = std::hash<string> {}(file_one_contents);
+	size_t file_two_hash = std::hash<string> {}(file_two_contents);
+
+	if (file_one_hash == file_two_hash) {
+		return true;
+	}
+	return false;
+}
+
 error::Error Permissions(const string &file_path, const vector<Perms> perms) {
 	if (perms.size() == 0) {
 		return error::NoError;