add modified version of Native File Dialog

it will replace portable-file-dialogs on Windows, and perhaps in
the rest of operating systems (maybe not Linux) as well.

extern/nfd-modified/src/simple_exec.h

@@ -0,0 +1,218 @@
+// copied from: https://github.com/wheybags/simple_exec/blob/5a74c507c4ce1b2bb166177ead4cca7cfa23cb35/simple_exec.h
+
+// simple_exec.h, single header library to run external programs + retrieve their status code and output (unix only for now)
+//
+// do this:
+// #define SIMPLE_EXEC_IMPLEMENTATION
+//   before you include this file in *one* C or C++ file to create the implementation.
+// i.e. it should look like this:
+// #define SIMPLE_EXEC_IMPLEMENTATION
+// #include "simple_exec.h"
+
+#ifndef SIMPLE_EXEC_H
+#define SIMPLE_EXEC_H
+
+int runCommand(char** stdOut, int* stdOutByteCount, int* returnCode, int includeStdErr, char* command, ...);
+int runCommandArray(char** stdOut, int* stdOutByteCount, int* returnCode, int includeStdErr, char* const* allArgs);
+
+#endif // SIMPLE_EXEC_H
+
+#ifdef SIMPLE_EXEC_IMPLEMENTATION
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <assert.h>
+#include <sys/wait.h>
+#include <stdarg.h>
+#include <fcntl.h>
+
+#define release_assert(exp) { if (!(exp)) { abort(); } }
+
+enum PIPE_FILE_DESCRIPTORS
+{
+  READ_FD  = 0,
+  WRITE_FD = 1
+};
+
+enum RUN_COMMAND_ERROR
+{
+    COMMAND_RAN_OK = 0,
+    COMMAND_NOT_FOUND = 1
+};
+
+int runCommandArray(char** stdOut, int* stdOutByteCount, int* returnCode, int includeStdErr, char* const* allArgs)
+{
+    // adapted from: https://stackoverflow.com/a/479103
+
+    int bufferSize = 256;
+    char buffer[bufferSize + 1];
+
+    int dataReadFromChildDefaultSize = bufferSize * 5;
+    int dataReadFromChildSize = dataReadFromChildDefaultSize;
+    int dataReadFromChildUsed = 0;
+    char* dataReadFromChild = (char*)malloc(dataReadFromChildSize);
+
+
+    int parentToChild[2];
+    release_assert(pipe(parentToChild) == 0);
+
+    int childToParent[2];
+    release_assert(pipe(childToParent) == 0);
+
+    int errPipe[2];
+    release_assert(pipe(errPipe) == 0);
+
+    pid_t pid;
+    switch( pid = fork() )
+    {
+        case -1:
+        {
+            release_assert(0 && "Fork failed");
+            break;
+        }
+
+        case 0: // child
+        {
+            release_assert(dup2(parentToChild[READ_FD ], STDIN_FILENO ) != -1);
+            release_assert(dup2(childToParent[WRITE_FD], STDOUT_FILENO) != -1);
+            
+            if(includeStdErr)
+            {
+                release_assert(dup2(childToParent[WRITE_FD], STDERR_FILENO) != -1);
+            }
+            else
+            {
+                int devNull = open("/dev/null", O_WRONLY);
+                release_assert(dup2(devNull, STDERR_FILENO) != -1);
+            }
+
+            // unused
+            release_assert(close(parentToChild[WRITE_FD]) == 0);
+            release_assert(close(childToParent[READ_FD ]) == 0);
+            release_assert(close(errPipe[READ_FD]) == 0);
+            
+            const char* command = allArgs[0];
+            execvp(command, allArgs);
+
+            char err = 1;
+            ssize_t result = write(errPipe[WRITE_FD], &err, 1);
+            release_assert(result != -1);
+            
+            close(errPipe[WRITE_FD]);
+            close(parentToChild[READ_FD]);
+            close(childToParent[WRITE_FD]);
+
+            exit(0);
+        }
+
+
+        default: // parent
+        {
+            // unused
+            release_assert(close(parentToChild[READ_FD]) == 0);
+            release_assert(close(childToParent[WRITE_FD]) == 0);
+            release_assert(close(errPipe[WRITE_FD]) == 0);
+
+            while(1)
+            {
+                ssize_t bytesRead = 0;
+                switch(bytesRead = read(childToParent[READ_FD], buffer, bufferSize))
+                {
+                    case 0: // End-of-File, or non-blocking read.
+                    {
+                        int status = 0;
+                        release_assert(waitpid(pid, &status, 0) == pid);
+
+                        // done with these now
+                        release_assert(close(parentToChild[WRITE_FD]) == 0);
+                        release_assert(close(childToParent[READ_FD]) == 0);
+
+                        char errChar = 0;
+                        ssize_t result = read(errPipe[READ_FD], &errChar, 1);
+                        release_assert(result != -1);
+                        close(errPipe[READ_FD]);
+
+                        if(errChar)
+                        {
+                            free(dataReadFromChild); 
+                            return COMMAND_NOT_FOUND;
+                        }
+                        
+                        // free any un-needed memory with realloc + add a null terminator for convenience
+                        dataReadFromChild = (char*)realloc(dataReadFromChild, dataReadFromChildUsed + 1);
+                        dataReadFromChild[dataReadFromChildUsed] = '\0';
+                        
+                        if(stdOut != NULL)
+                            *stdOut = dataReadFromChild;
+                        else
+                            free(dataReadFromChild);
+
+                        if(stdOutByteCount != NULL)
+                            *stdOutByteCount = dataReadFromChildUsed;
+                        if(returnCode != NULL)
+                            *returnCode = WEXITSTATUS(status);
+
+                        return COMMAND_RAN_OK;
+                    }
+                    case -1:
+                    {
+                        release_assert(0 && "read() failed");
+                        break;
+                    }
+
+                    default:
+                    {
+                        if(dataReadFromChildUsed + bytesRead + 1 >= dataReadFromChildSize)
+                        {
+                            dataReadFromChildSize += dataReadFromChildDefaultSize;
+                            dataReadFromChild = (char*)realloc(dataReadFromChild, dataReadFromChildSize);
+                        }
+
+                        memcpy(dataReadFromChild + dataReadFromChildUsed, buffer, bytesRead);
+                        dataReadFromChildUsed += bytesRead;
+                        break;
+                    }
+                }
+            }
+        }
+    }
+}
+
+int runCommand(char** stdOut, int* stdOutByteCount, int* returnCode, int includeStdErr, char* command, ...)
+{
+    va_list vl;
+    va_start(vl, command);
+      
+    char* currArg = NULL;
+      
+    int allArgsInitialSize = 16;
+    int allArgsSize = allArgsInitialSize;
+    char** allArgs = (char**)malloc(sizeof(char*) * allArgsSize);
+    allArgs[0] = command;
+        
+    int i = 1;
+    do
+    {
+        currArg = va_arg(vl, char*);
+        allArgs[i] = currArg;
+
+        i++;
+
+        if(i >= allArgsSize)
+        {
+            allArgsSize += allArgsInitialSize;
+            allArgs = (char**)realloc(allArgs, sizeof(char*) * allArgsSize);
+        }
+
+    } while(currArg != NULL);
+
+    va_end(vl);
+
+    int retval = runCommandArray(stdOut, stdOutByteCount, returnCode, includeStdErr, allArgs);
+    free(allArgs);
+    return retval;
+}
+
+#endif //SIMPLE_EXEC_IMPLEMENTATION