Fix: Stop treating an empty accesslist file as an error by allowing empty file pseudo mapping

1 files changed, 27 insertions, 17 deletions

diff --git a/ot_accesslist.c b/ot_accesslist.c
index 6315bc2..a199fa4 100644
--- a/ot_accesslist.c
+++ b/ot_accesslist.c
@@ -124,29 +124,37 @@ size_t accesslist_parse_hashes(ot_hash *dest, size_t capacity, const char *buf,
   return count;
 }
 
-/* Map a file read only and report its size. Returns NULL if the file cannot
-   be opened, is empty, or is too large to map, leaving maplen untouched. */
-static const char *accesslist_map(const char *filename, size_t *maplen) {
-  struct stat  st;
-  const char  *map;
-  int          fd = open(filename, O_RDONLY);
+/* Map a file read only. Returns 0 and sets map and maplen on success, -1 if
+   the file cannot be opened or mapped. */
+static int accesslist_map(const char *filename, const char **map, size_t *maplen) {
+  struct stat st;
+  void       *mapped;
+  int         fd = open(filename, O_RDONLY);
 
   if (fd < 0)
-    return NULL;
+    return -1;
 
-  if (fstat(fd, &st) < 0 || st.st_size <= 0 || (uintmax_t)st.st_size > (uintmax_t)SIZE_MAX) {
+  if (fstat(fd, &st) < 0 || st.st_size < 0 || (uintmax_t)st.st_size > (uintmax_t)SIZE_MAX) {
     close(fd);
-    return NULL;
+    return -1;
+  }
+
+  if (st.st_size == 0) {
+    close(fd);
+    *map    = NULL;
+    *maplen = 0;
+    return 0;
   }
 
-  map = mmap(NULL, (size_t)st.st_size, PROT_READ, MAP_SHARED, fd, 0);
+  mapped = mmap(NULL, (size_t)st.st_size, PROT_READ, MAP_SHARED, fd, 0);
   close(fd);
 
-  if (map == MAP_FAILED)
-    return NULL;
+  if (mapped == MAP_FAILED)
+    return -1;
 
+  *map    = mapped;
   *maplen = (size_t)st.st_size;
-  return map;
+  return 0;
 }
 
 static void accesslist_readfile(void) {
@@ -154,7 +162,7 @@ static void accesslist_readfile(void) {
   const char    *map;
   size_t         maplen, capacity, found;
 
-  if ((map = accesslist_map(g_accesslist_filename, &maplen)) == NULL) {
+  if (accesslist_map(g_accesslist_filename, &map, &maplen) < 0) {
     char *wd = getcwd(NULL, 0);
     fprintf(stderr, "Warning: Can't open accesslist file: %s (but will try to create it later, if necessary and possible).\nPWD: %s\n", g_accesslist_filename, wd);
     free(wd);
@@ -166,16 +174,18 @@ static void accesslist_readfile(void) {
   accesslist_new = accesslist_make(g_accesslist, capacity);
   if (!accesslist_new) {
     fprintf(stderr, "Warning: Not enough memory to allocate %zd bytes for accesslist buffer. May succeed later.\n", capacity * sizeof(ot_hash));
-    munmap((void *)map, maplen);
+    if (map)
+      munmap((void *)map, maplen);
     return;
   }
 
-  found = accesslist_parse_hashes(accesslist_new->list, capacity, map, maplen);
+  found = maplen ? accesslist_parse_hashes(accesslist_new->list, capacity, map, maplen) : 0;
 #ifdef _DEBUG
   fprintf(stderr, "Added %zd info_hashes to accesslist\n", found);
 #endif
 
-  munmap((void *)map, maplen);
+  if (map)
+    munmap((void *)map, maplen);
 
   qsort(accesslist_new->list, found, sizeof(ot_hash), vector_compare_hash);
   accesslist_new->size = found;