Don't abort program if next_key is NULL in ebpf_map_get_next_key()

On Linux it is valid to pass NULL as next_key for queue type maps, since
that map type doesn't really have a key. Return EINVAL instead of aborting
the process via an assert.

libs/api/api_internal.h

@@ -415,7 +415,7 @@ ebpf_map_lookup_and_delete_element_batch(
  * @retval EBPF_NO_MORE_KEYS previous_key was the last key.
  */
 _Must_inspect_result_ ebpf_result_t
-ebpf_map_get_next_key(fd_t map_fd, _In_opt_ const void* previous_key, _Out_ void* next_key) noexcept;
+ebpf_map_get_next_key(fd_t map_fd, _In_opt_ const void* previous_key, _Out_opt_ void* next_key) noexcept;
 
 /**
  * @brief Detach a link given a file descriptor.

libs/api/ebpf_api.cpp

@@ -1142,7 +1142,10 @@ ebpf_map_get_next_key(fd_t map_fd, _In_opt_ const void* previous_key, _Out_ void
  uint32_t type;
  ebpf_handle_t map_handle = ebpf_handle_invalid;
 
- ebpf_assert(next_key);
+ if (next_key == NULL) {
+ result = EBPF_INVALID_ARGUMENT;
+ goto Exit;
+ }
 
  map_handle = _get_handle_from_file_descriptor(map_fd);
  if (map_handle == ebpf_handle_invalid) {

tests/unit/libbpf_test.cpp

@@ -1005,6 +1005,11 @@ TEST_CASE("libbpf map", "[libbpf]")
  REQUIRE(result < 0);
  REQUIRE(errno == EINVAL);
 
+ // next_key is NULL.
+ result = bpf_map_get_next_key(map_fd, NULL, &value);
+ REQUIRE(result < 0);
+ REQUIRE(errno == EINVAL);
+
  bpf_object__close(object);
 }
 #endif