wip

src/spx_utils.c

@@ -21,6 +21,52 @@
 #include <string.h>
 #include "spx_utils.h"
 
+char * spx_utils_resolve_confined_file_absolute_path(
+    const char * root_dir,
+    const char * relative_path,
+    const char * suffix,
+    char * dst,
+    size_t size
+) {
+    if (size < PATH_MAX) {
+        spx_utils_die("size < PATH_MAX");
+    }
+
+    char absolute_file_path[PATH_MAX];
+
+    snprintf(
+        absolute_file_path,
+        sizeof(absolute_file_path),
+        "%s%s%s",
+        root_dir,
+        relative_path,
+        suffix == NULL ? "" : suffix
+    );
+
+    if (realpath(absolute_file_path, dst) == NULL) {
+        return NULL;
+    }
+
+    char root_dir_real_path[PATH_MAX];
+    if (realpath(root_dir, root_dir_real_path) == NULL) {
+        return NULL;
+    }
+
+    char expected_path_prefix[PATH_MAX + 1];
+    snprintf(
+        expected_path_prefix,
+        sizeof(expected_path_prefix),
+        "%s/",
+        root_dir_real_path
+    );
+
+    if (! spx_utils_str_starts_with(dst, expected_path_prefix)) {
+        return NULL;
+    }
+
+    return dst;
+}
+
 char * spx_utils_json_escape(char * dst, const char * src, size_t limit)
 {
     size_t i = 0;

src/spx_utils.h

@@ -50,6 +50,14 @@ do {                                                              \
     }                                                             \
 } while (0)
 
+char * spx_utils_resolve_confined_file_absolute_path(
+    const char * root_dir,
+    const char * relative_path,
+    const char * suffix,
+    char * dst,
+    size_t size
+);
+
 char * spx_utils_json_escape(char * dst, const char * src, size_t limit);
 int spx_utils_str_starts_with(const char * str, const char * prefix);
 int spx_utils_str_ends_with(const char * str, const char * suffix);