Extract process handling into separate class

Needed for plugins' subprocess handling.

include/linuxdeploy/subprocess/process.h

@@ -0,0 +1,71 @@
+// system headers
+#include <unordered_map>
+#include <vector>
+
+// local headers
+#include "linuxdeploy/subprocess/subprocess.h"
+
+namespace linuxdeploy {
+    namespace subprocess {
+        class process {
+        private:
+            // child process ID
+            int child_pid_;
+
+            // pipes to child process's stdout/stderr
+            int stdout_fd_;
+            int stderr_fd_;
+
+            // process exited
+            bool exited_ = false;
+            // exit code -- will be initialized by close()
+            int exit_code_;
+
+            // these constants help make the pipe code more readable
+            static constexpr int READ_END_ = 0, WRITE_END_ = 1;
+
+            static std::vector<char*> make_args_vector_(const std::vector<std::string>& args) ;
+
+            static std::vector<char*> make_env_vector_(const subprocess_env_map_t& env) ;
+
+        public:
+            /**
+             * Create a child process.
+             * @param args parameters for process
+             * @param env additional environment variables (current environment will be copied)
+             */
+            process(std::initializer_list<std::string> args, const subprocess_env_map_t& env);
+
+            /**
+             * Create a child process.
+             * @param args parameters for process
+             * @param env additional environment variables (current environment will be copied)
+             */
+            process(const std::vector<std::string>& args, const subprocess_env_map_t& env);
+
+            ~process();
+
+            /**
+             * @return child process's ID
+             */
+            int pid() const;
+
+            /**
+             * @return child process's stdout file descriptor ID
+             */
+            int stdout_fd() const;
+
+
+            /**
+             * @return child process's stderr file descriptor ID
+             */
+            int stderr_fd() const;
+
+            /**
+             * Close all pipes and wait for process to exit. If process was closed already, just returns exit code.
+             * @return child process's exit code
+             */
+            int close();
+        };
+    }
+}

include/linuxdeploy/subprocess/subprocess.h

@@ -19,12 +19,6 @@ namespace linuxdeploy {
             std::vector<std::string> args_{};
             std::unordered_map<std::string, std::string> env_{};
 
-            void assert_args_not_empty_() const;
-
-            std::vector<char*> make_args_vector_() const;
-
-            std::vector<char*> make_env_vector_() const;
-
         public:
             subprocess(std::initializer_list<std::string> args, subprocess_env_map_t env = {});