Fix remaining compiler warnings in digest.c and appimagetool.c

- Fix sign-conversion warnings in digest.c by casting unsigned long offsets to long before arithmetic
- Cast length values to ssize_t when subtracting from bytes_left_this_chunk
- Fix format-truncation warning in appimagetool.c by reducing app_name_for_filename buffer size to leave room for suffix
- Change sprintf to snprintf for app_name_for_filename to match safer pattern

All builds now compile cleanly with -Wall -Wextra -Wconversion -Werror.

Co-authored-by: probonopd <[email protected]>

Author: Copilot

src/appimagetool.c

@@ -777,16 +777,17 @@ main (int argc, char *argv[])
         gchar* arch = getArchName(archs);
         fprintf(stderr, "Using architecture %s\n", arch);
 
-        char app_name_for_filename[PATH_MAX];
+        // Reserve space for version, arch, and ".AppImage" suffix (max ~50 chars)
+        char app_name_for_filename[PATH_MAX - 50];
         {
             const char* const env_app_name = getenv("APPIMAGETOOL_APP_NAME");
             if (env_app_name != NULL) {
                 fprintf(stderr, "Using user-specified app name: %s\n", env_app_name);
-                strncpy(app_name_for_filename, env_app_name, PATH_MAX - 1);
-                app_name_for_filename[PATH_MAX - 1] = '\0';
+                strncpy(app_name_for_filename, env_app_name, sizeof(app_name_for_filename) - 1);
+                app_name_for_filename[sizeof(app_name_for_filename) - 1] = '\0';
             } else {
                 const gchar* const desktop_file_app_name = get_desktop_entry(kf, "Name");
-                sprintf(app_name_for_filename, "%s", desktop_file_app_name);
+                snprintf(app_name_for_filename, sizeof(app_name_for_filename), "%s", desktop_file_app_name);
                 replacestr(app_name_for_filename, " ", "_");
 
                 if (verbose) {

src/digest.c

@@ -57,13 +57,13 @@ bool appimage_type2_digest_md5(const char* path, char* digest) {
         }
 
         // check whether there's a section in this chunk that we need to skip
-        if (digest_md5_offset != 0 && digest_md5_length != 0 && digest_md5_offset - current_position > 0 && digest_md5_offset - current_position < chunk_size) {
-            ssize_t begin_of_section = (digest_md5_offset - current_position) % chunk_size;
+        if (digest_md5_offset != 0 && digest_md5_length != 0 && (long)digest_md5_offset - current_position > 0 && (long)digest_md5_offset - current_position < chunk_size) {
+            ssize_t begin_of_section = ((long)digest_md5_offset - current_position) % chunk_size;
             // read chunk before section
             fread(buffer, sizeof(char), (size_t) begin_of_section, fp);
 
             bytes_left_this_chunk -= begin_of_section;
-            bytes_left_this_chunk -= digest_md5_length;
+            bytes_left_this_chunk -= (ssize_t)digest_md5_length;
 
             // if bytes_left is now < 0, the section exceeds the current chunk
             // this amount of bytes needs to be skipped in the future sections
@@ -77,13 +77,13 @@ bool appimage_type2_digest_md5(const char* path, char* digest) {
         }
 
         // check whether there's a section in this chunk that we need to skip
-        if (signature_offset != 0 && signature_length != 0 && signature_offset - current_position > 0 && signature_offset - current_position < chunk_size) {
-            ssize_t begin_of_section = (signature_offset - current_position) % chunk_size;
+        if (signature_offset != 0 && signature_length != 0 && (long)signature_offset - current_position > 0 && (long)signature_offset - current_position < chunk_size) {
+            ssize_t begin_of_section = ((long)signature_offset - current_position) % chunk_size;
             // read chunk before section
             fread(buffer, sizeof(char), (size_t) begin_of_section, fp);
 
             bytes_left_this_chunk -= begin_of_section;
-            bytes_left_this_chunk -= signature_length;
+            bytes_left_this_chunk -= (ssize_t)signature_length;
 
             // if bytes_left is now < 0, the section exceeds the current chunk
             // this amount of bytes needs to be skipped in the future sections
@@ -97,13 +97,13 @@ bool appimage_type2_digest_md5(const char* path, char* digest) {
         }
 
         // check whether there's a section in this chunk that we need to skip
-        if (sig_key_offset != 0 && sig_key_length != 0 && sig_key_offset - current_position > 0 && sig_key_offset - current_position < chunk_size) {
-            ssize_t begin_of_section = (sig_key_offset - current_position) % chunk_size;
+        if (sig_key_offset != 0 && sig_key_length != 0 && (long)sig_key_offset - current_position > 0 && (long)sig_key_offset - current_position < chunk_size) {
+            ssize_t begin_of_section = ((long)sig_key_offset - current_position) % chunk_size;
             // read chunk before section
             fread(buffer, sizeof(char), (size_t) begin_of_section, fp);
 
             bytes_left_this_chunk -= begin_of_section;
-            bytes_left_this_chunk -= sig_key_length;
+            bytes_left_this_chunk -= (ssize_t)sig_key_length;
 
             // if bytes_left is now < 0, the section exceeds the current chunk
             // this amount of bytes needs to be skipped in the future sections