From e8481260d763f8827e0188e5cd53e613aa4bd305 Mon Sep 17 00:00:00 2001
From: Serhii Kostiuk <serhii.o.kostiuk@globallogic.com>
Date: Tue, 7 Apr 2020 18:32:02 +0300
Subject: Execute system commands without invoking system shell

Added several new methods to the MTS::System class:

- ```executeBackground``` - popen alternative, creates a pipe with the specified
  mode and spawns a new process with specified arguments;
- ```closeBackground``` - pclose alternative, closes parent side of the pipe and
  waits for the child process to finish its execution;
- ```execute``` - MTS::System::cmd alternative that allows to spawn child
  processes directly without invoking system shell.
---
 include/mts/MTS_System.h | 85 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)

(limited to 'include/mts/MTS_System.h')

diff --git a/include/mts/MTS_System.h b/include/mts/MTS_System.h
index bd5fa53..6bca21b 100644
--- a/include/mts/MTS_System.h
+++ b/include/mts/MTS_System.h
@@ -31,6 +31,7 @@
 #include <mts/MTS_NonConstructable.h>
 #include <mts/MTS_Stdint.h>
 #include <string>
+#include <vector>
 
 namespace MTS {
 
@@ -38,6 +39,17 @@ namespace MTS {
 
         public:
 
+            //! Type of the pipe to be opened in executeBackground
+            enum class PipeType {
+                READ, WRITE
+            };
+
+            //! Utility structure with information about the child process
+            struct ChildHandle {
+                pid_t pid;
+                FILE* stream;
+            };
+
             //UTC (Coordinated Universal Time) : This is the standard international time or the Greenwich Mean Time.
             //EPOCH : number of seconds elapsed since 00:00:00 on January 1, 1970, Coordinated Universal Time.
 
@@ -53,6 +65,79 @@ namespace MTS {
 
             static int32_t cmd(const std::string& cmd, std::string& result);
             static int32_t readFile(const std::string& path, std::string& result);
+
+            //! Execute application with specified arguments.
+            /*!
+             * A safer alternative to System::cmd that allows to execute applications with controlled
+             * list of arguments bypasing the system shell.
+             *
+             * \param  app    name of the application to be executed
+             * \param  argv   vector of arguments (excluding argument zero)
+             * \param  result stdout output from the application is stored here
+             * \return result code as for std::system and UNIX pclose
+             */
+            static int32_t execute(const std::string& app, const std::vector<std::string>& argv, std::string& result);
+
+            //! Spawn a process and open pipe with the specified type (READ or WRITE)
+            /*!
+            * A safer alternative to POSIX popen that allows to execute applications with controlled
+            * list of arguments bypasing the system shell. If succeded, information about the spawned
+            * process is written to the \p child structure.
+            *
+            * \param  app  name of the application to be executed
+            * \param  argv vector of arguments (excluding argument zero)
+            * \param  type open pipe for read from child or write to child
+            * \return true on success, false on failure
+            */
+            static bool executeBackground(const std::string& app, const std::vector<std::string>& argv, PipeType type, ChildHandle& child);
+
+            //! Close the pipe and wait for a child to finish execution
+            /*!
+            * \param  child  name of the application to be executed
+            * \param  argv   vector of arguments (excluding argument zero)
+            * \param  result stdout output from the application is stored here
+            * \return result code as for std::system and UNIX pclose
+            */
+            static int closeBackground(ChildHandle& child);
+
+        private:
+
+            //! Spawn a process and open pipe with the specified type (READ or WRITE)
+            static bool executeBackground(const std::string& app, char* const argv[], PipeType type, ChildHandle& child);
+
+            //! Utility method. Cast argument to a C pointer required by some C-style functions.
+            static inline char* castArgument(const std::string& arg);
+
+            //! Utility method. Convert argument vector to a format required by execve and posix_spawn.
+            static std::vector<char*> castArgVector(const std::string& app, const std::vector<std::string>& argv);
+
+            //! Lightweight C++ wrapper with auto-close for file descriptors
+            class FdWrapper {
+
+                public:
+                    static const int FD_NOT_READY = -1;
+
+                    explicit FdWrapper(int fd = FD_NOT_READY);
+                    ~FdWrapper();
+
+                    inline int get() const;
+                    int release();
+                    void reset(int fd = FD_NOT_READY);
+
+                private:
+                    int m_fd;
+
+            };
+
+            //! Utility structure, used by popen wrapper
+            struct Pipe {
+                FdWrapper parent;
+                FdWrapper child;
+            };
+
+            //! Initialize UNIX pipe
+            static int initPipe(Pipe& pipe, PipeType type);
+
     };
 }
 
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