Move functions from process to file

Move filesystem-related functions from process.[ch] to file.[ch].

app/src/sys/unix/file.c

@@ -0,0 +1,75 @@
+#include "util/file.h"
+
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+bool
+search_executable(const char *file) {
+    char *path = getenv("PATH");
+    if (!path)
+        return false;
+    path = strdup(path);
+    if (!path)
+        return false;
+
+    bool ret = false;
+    size_t file_len = strlen(file);
+    char *saveptr;
+    for (char *dir = strtok_r(path, ":", &saveptr); dir;
+            dir = strtok_r(NULL, ":", &saveptr)) {
+        size_t dir_len = strlen(dir);
+        char *fullpath = malloc(dir_len + file_len + 2);
+        if (!fullpath)
+            continue;
+        memcpy(fullpath, dir, dir_len);
+        fullpath[dir_len] = '/';
+        memcpy(fullpath + dir_len + 1, file, file_len + 1);
+
+        struct stat sb;
+        bool fullpath_executable = stat(fullpath, &sb) == 0 &&
+            sb.st_mode & S_IXUSR;
+        free(fullpath);
+        if (fullpath_executable) {
+            ret = true;
+            break;
+        }
+    }
+
+    free(path);
+    return ret;
+}
+
+char *
+get_executable_path(void) {
+// <https://stackoverflow.com/a/1024937/1987178>
+#ifdef __linux__
+    char buf[PATH_MAX + 1]; // +1 for the null byte
+    ssize_t len = readlink("/proc/self/exe", buf, PATH_MAX);
+    if (len == -1) {
+        perror("readlink");
+        return NULL;
+    }
+    buf[len] = '\0';
+    return strdup(buf);
+#else
+    // in practice, we only need this feature for portable builds, only used on
+    // Windows, so we don't care implementing it for every platform
+    // (it's useful to have a working version on Linux for debugging though)
+    return NULL;
+#endif
+}
+
+bool
+is_regular_file(const char *path) {
+    struct stat path_stat;
+
+    if (stat(path, &path_stat)) {
+        perror("stat");
+        return false;
+    }
+    return S_ISREG(path_stat.st_mode);
+}
+