Ensure we verify the output path before parsing the log.

Closes #2790

src/options.c

@@ -833,6 +833,8 @@ read_option_args (int argc, char **argv) {
     case 'o':
       if (!valid_output_type (optarg))
         FATAL ("Invalid filename extension. It must be any of .csv, .json, or .html\n");
+        if (!is_writable_path(optarg))
+          FATAL("Invalid or unwritable path.");
       if (conf.output_format_idx < MAX_OUTFORMATS)
         conf.output_formats[conf.output_format_idx++] = optarg;
       break;

src/util.c

@@ -47,6 +47,7 @@
 #include <inttypes.h>
 #include <regex.h>
 #include <pthread.h>
+#include <unistd.h>
 
 #include <netinet/in.h>
 #include <sys/socket.h>
@@ -1221,3 +1222,25 @@ unescape_str (const char *src) {
 
   return dest;
 }
+
+int
+is_writable_path (const char *path) {
+  if (access (path, W_OK) == 0) {
+    return 1;   // Path is writable
+  } else {
+    switch (errno) {
+    case ENOENT:
+      fprintf (stderr, "Path does not exist: %s\n", path);
+      return 0;
+    case EACCES:
+      fprintf (stderr, "No write permission for path: %s\n", path);
+      return 0;
+    case EROFS:
+      fprintf (stderr, "Path is on a read-only file system: %s\n", path);
+      return 0;
+    default:
+      fprintf (stderr, "Unknown error (errno %d) for path: %s\n", errno, path);
+      return 0;
+    }
+  }
+}

src/util.h

@@ -95,6 +95,7 @@ int intlen (uint64_t num);
 int invalid_ipaddr (const char *str, int *ipvx);
 int ip_in_range (const char *ip);
 int is_valid_http_status (int code);
+int is_writable_path (const char *path);
 int ptr2int (char *ptr);
 int str2int (const char *date);
 int str_inarray (const char *s, const char *arr[], int size);