Determine the signedness of standard types

CMakeLists.txt

@@ -11,6 +11,19 @@ add_library(minitar STATIC ${SOURCES})
 
 set_target_properties(minitar PROPERTIES OUTPUT_NAME mtar)
 
+include(CheckSourceCompiles)
+
+# Check for signedness of standard types
+check_source_compiles(C "#include <sys/types.h>\nint main(int argc, char** argv){ char is_unsigned_size_type[(size_t)0 < (size_t)-1 ? 1 : -1]; }" UNSIGNED_SIZE_TYPE)
+check_source_compiles(C "#include <sys/types.h>\nint main(int argc, char** argv){ char is_unsigned_time_type[(time_t)0 < (time_t)-1 ? 1 : -1]; }" UNSIGNED_TIME_TYPE)
+check_source_compiles(C "#include <sys/types.h>\nint main(int argc, char** argv){ char is_unsigned_mode_type[(mode_t)0 < (mode_t)-1 ? 1 : -1]; }" UNSIGNED_MODE_TYPE)
+check_source_compiles(C "#include <sys/types.h>\nint main(int argc, char** argv){ char is_unsigned_gid_type[(gid_t)0 < (gid_t)-1 ? 1 : -1]; }" UNSIGNED_GID_TYPE)
+check_source_compiles(C "#include <sys/types.h>\nint main(int argc, char** argv){ char is_unsigned_uid_type[(uid_t)0 < (uid_t)-1 ? 1 : -1]; }" UNSIGNED_UID_TYPE)
+
+configure_file("${CMAKE_CURRENT_SOURCE_DIR}/src/config.h.in" "${CMAKE_CURRENT_BINARY_DIR}/config.h" @ONLY)
+
+target_include_directories(minitar PRIVATE "${CMAKE_CURRENT_BINARY_DIR}")
+
 if (MSVC)
     target_compile_options(minitar PRIVATE /W4 /WX)
 else()

src/config.h.in

@@ -0,0 +1,5 @@
+#cmakedefine UNSIGNED_SIZE_TYPE
+#cmakedefine UNSIGNED_TIME_TYPE
+#cmakedefine UNSIGNED_MODE_TYPE
+#cmakedefine UNSIGNED_GID_TYPE
+#cmakedefine UNSIGNED_UID_TYPE

src/util.c

@@ -1,5 +1,6 @@
 #define _POSIX_C_SOURCE 200809L // for strndup
 #define _IN_MINITAR
+#include "config.h"
 #include "minitar.h"
 #include "tar.h"
 #include <stdio.h>
@@ -33,18 +34,42 @@ void minitar_parse_tar_header(const struct tar_header* hdr, struct minitar_entry
         metadata->name[256] = '\0';
     }
 
+#ifdef UNSIGNED_MODE_TYPE
+    metadata->mode = (mode_t)strtoul(hdr->mode, NULL, 8);
+#else
     metadata->mode = (mode_t)strtol(hdr->mode, NULL, 8);
-    metadata->uid = (uid_t)strtoul(hdr->uid, NULL, 8);
+#endif
-    metadata->gid = (gid_t)strtoul(hdr->gid, NULL, 8);
 
-    char* sizeptr = strndup(hdr->size, 12);
+#ifdef UNSIGNED_UID_TYPE
+    metadata->uid = (uid_t)strtoul(hdr->uid, NULL, 8);
+#else
+    metadata->uid = (uid_t)strtol(hdr->uid, NULL, 8);
+#endif
+
+#ifdef UNSIGNED_GID_TYPE
+    metadata->gid = (gid_t)strtoul(hdr->gid, NULL, 8);
+#else
+    metadata->gid = (gid_t)strtol(hdr->uid, NULL, 8);
+#endif
+
+    char* sizeptr = strndup(
+        hdr->size, 12); // The hdr->size field is not null-terminated, yet strndup returns a null-terminated string.
     if (!sizeptr) minitar_panic("Failed to allocate memory to duplicate a tar header's size field");
+#ifdef UNSIGNED_SIZE_TYPE
     metadata->size = (size_t)strtoull(sizeptr, NULL, 8);
+#else
+    metadata->size = (size_t)strtoll(sizeptr, NULL, 8);
+#endif
     free(sizeptr);
 
-    char* timeptr = strndup(hdr->mtime, 12);
+    char* timeptr = strndup(
+        hdr->mtime, 12); // The hdr->mtime field is not null-terminated, yet strndup returns a null-terminated string.
     if (!timeptr) minitar_panic("Failed to allocate memory to duplicate a tar header's mtime field");
-    metadata->mtime = (time_t)strtol(timeptr, NULL, 8);
+#ifdef UNSIGNED_TIME_TYPE
+    metadata->mtime = (time_t)strtoull(timeptr, NULL, 8);
+#else
+    metadata->mtime = (time_t)strtoll(timeptr, NULL, 8);
+#endif
     free(timeptr);
 
     switch (hdr->typeflag)