refactor(core): use std error_code conditions

src/protocol/rtmp_output.cpp

@@ -213,7 +213,10 @@ Status write_all(int fd, std::span<const std::uint8_t> bytes) {
 			if (errno == EINTR) {
 				continue;
 			}
-			return unexpected_error(ERR_IO, std::strerror(errno));
+			const auto error = errno;
+			return unexpected_error(
+				std::error_code(error, std::generic_category()),
+				"failed to write to ffmpeg process stdin");
 		}
 		if (result == 0) {
 			return unexpected_error(ERR_IO, "short write to ffmpeg process stdin");
@@ -530,14 +533,20 @@ private:
 	Result<Session> spawn_session(const std::string &url) const {
 		int stdin_pipe[2]{-1, -1};
 		if (pipe(stdin_pipe) != 0) {
-			return unexpected_error(ERR_IO, "failed to create ffmpeg stdin pipe: " + std::string(std::strerror(errno)));
+			const auto error = errno;
+			return unexpected_error(
+				std::error_code(error, std::generic_category()),
+				"failed to create ffmpeg stdin pipe");
 		}
 
 		const auto child = fork();
 		if (child < 0) {
+			const auto error = errno;
 			close(stdin_pipe[0]);
 			close(stdin_pipe[1]);
-			return unexpected_error(ERR_CHILD_PROCESS, "failed to fork ffmpeg child: " + std::string(std::strerror(errno)));
+			return unexpected_error(
+				std::error_code(error, std::generic_category()),
+				"failed to fork ffmpeg child");
 		}
 
 		if (child == 0) {
@@ -626,7 +635,10 @@ private:
 			return {};
 		}
 		if (wait_result < 0) {
-			return unexpected_error(ERR_CHILD_PROCESS, "failed to poll ffmpeg child: " + std::string(std::strerror(errno)));
+			const auto error = errno;
+			return unexpected_error(
+				std::error_code(error, std::generic_category()),
+				"failed to poll ffmpeg child");
 		}
 
 		if (session.stdin_fd >= 0) {