fix: address review findings — sendfile EINTR, path traversal check

src/shared/file.c

@@ -1,4 +1,5 @@
 #include <dirent.h>
+#include <errno.h>
 #include <fcntl.h>
 #include <libgen.h>
 #include <stddef.h>
@@ -199,10 +200,25 @@ bool file_send_single_calls(File* file, int file_descriptor, bool use_metadata,
   return true;
 }
 
+static bool has_path_traversal(const char* path) {
+  // Check if ".." appears as a path component — at start, end, or between '/'
+  const char* p = path;
+  while ((p = strstr(p, "..")) != NULL) {
+    bool at_start = (p == path);
+    bool after_slash = (p > path && p[-1] == '/');
+    bool at_end = (p[2] == '\0');
+    bool before_slash = (p[2] == '/');
+    if ((at_start || after_slash) && (at_end || before_slash))
+      return true;
+    p += 2;
+  }
+  return false;
+}
+
 bool file_save_to_disk(const char* root_directory, File* file) {
   if (file->type == FILE_TYPE_SYMLINK && file->link_target) {
     // Validate link_target — reject absolute paths or traversal
-    if (file->link_target[0] == '/' || strstr(file->link_target, "..") != NULL) {
+    if (file->link_target[0] == '/' || has_path_traversal(file->link_target)) {
       log_message(LOG_LEVEL_ERROR, "Path traversal blocked in symlink target: %s",
                   file->link_target);
       return false;
@@ -210,7 +226,7 @@ bool file_save_to_disk(const char* root_directory, File* file) {
     char* disk_path = path_cat((char*)root_directory, file->path);
     if (disk_path == NULL)
       return false;
-    if (strstr(disk_path, "..") != NULL) {
+    if (has_path_traversal(disk_path)) {
       log_message(LOG_LEVEL_ERROR, "Path traversal blocked: %s", disk_path);
       free(disk_path);
       return false;
@@ -226,7 +242,7 @@ bool file_save_to_disk(const char* root_directory, File* file) {
   char* disk_path = path_cat((char*)root_directory, file->path);
   if (disk_path == NULL)
     return false;
-  if (strstr(disk_path, "..") != NULL) {
+  if (has_path_traversal(disk_path)) {
     log_message(LOG_LEVEL_ERROR, "Path traversal blocked: %s", disk_path);
     free(disk_path);
     return false;
@@ -625,6 +641,8 @@ bool file_send_sendfile(File* file, int file_descriptor, bool use_metadata, int
   while ((unsigned long long)offset < file_size) {
     ssize_t sent = sendfile(file_descriptor, fd, &offset, file_size - offset);
     if (sent == -1) {
+      if (errno == EINTR)
+        continue;
       perror("sendfile failed");
       close(fd);
       return false;