Introduced new --disable-serialization-buffer-check option for C & …

…CPP languages.

Allows to use a smaller buffers than otherwise it will be required. Serialization is still safe (no buffer overflows!) but it might fail during the operation with NUNAVUT_ERROR_SERIALIZATION_BUFFER_TOO_SMALL error.

src/nunavut/cli/__init__.py

@@ -809,6 +809,22 @@ def extension_type(raw_arg: str) -> str:
         ).lstrip(),
     )
 
+    ln_opt_group.add_argument(
+        "--disable-serialization-buffer-check",
+        action="store_true",
+        help=textwrap.dedent(
+            """
+
+        Instruct support header generators to disable entry buffer checks in serialization routines.
+        Serialization will be still safe (no buffer overflows) but it might fail during the operation
+        with NUNAVUT_ERROR_SERIALIZATION_BUFFER_TOO_SMALL error if provided buffer ends up being too small.
+        This option useful for systems with limited resources where messages is known to be small,
+        and so much smaller buffers can be used (comparing to the maximum possible capacity).
+
+    """
+        ).lstrip(),
+    )
+
     ln_opt_group.add_argument(
         "--language-standard",
         "-std",

src/nunavut/cli/parsers.py

@@ -366,6 +366,10 @@ def _create_language_options(cls, args: argparse.Namespace) -> Dict[str, Any]:
             True if args.enable_override_variable_array_capacity else DefaultValue(False)
         )
 
+        language_options["disable_serialization_buffer_check"] = (
+            True if args.disable_serialization_buffer_check else DefaultValue(False)
+        )
+
         if args.language_standard is not None:
             language_options["std"] = args.language_standard
 

src/nunavut/lang/c/templates/serialization.j2

@@ -27,16 +27,18 @@
 
 {# ----------------------------------------------------------------------------------------------------------------- #}
 {% macro _serialize_impl(t) %}
-    const {{ typename_unsigned_length }} capacity_bytes = *inout_buffer_size_bytes;
+{%- if not options.disable_serialization_buffer_check %}
 {%- if options.enable_override_variable_array_capacity %}
 #ifndef {{ t | full_reference_name }}_DISABLE_SERIALIZATION_BUFFER_CHECK_
 {% endif %}
+    const {{ typename_unsigned_length }} capacity_bytes = *inout_buffer_size_bytes;
     if ((8U * ({{ typename_unsigned_bit_length }}) capacity_bytes) < {{ t.inner_type.bit_length_set.max }}UL)
     {
         return -NUNAVUT_ERROR_SERIALIZATION_BUFFER_TOO_SMALL;
     }
 {%- if options.enable_override_variable_array_capacity %}
 #endif
+{% endif %}
 {% endif %}
     // Notice that fields that are not an integer number of bytes long may overrun the space allocated for them
     // in the serialization buffer up to the next byte boundary. This is by design and is guaranteed to be safe.
@@ -116,8 +118,11 @@
     {{ assert('offset_bits % 8U == 0U') }}
 {% endif %}
     {# NOTICE: If this is a delimited type, we will be requiring the buffer to be at least extent-sized.
-     # This is a bit wasteful because when serializing we can often use a smaller buffer. #}
+     # This is a bit wasteful because when serializing we can often use a smaller buffer.
+     # `disable_serialization_buffer_check` option allows to avoid such waste for variable length arrays. #}
+    {% if not (t is VariableLengthArrayType and options.disable_serialization_buffer_check) %}
     {{ assert('(offset_bits + %dULL) <= (capacity_bytes * 8U)'|format(t.bit_length_set.max)) }}
+    {% endif %}
 
 {%   if t is VoidType %}                {{- _serialize_void(t, offset) }}
 {% elif t is BooleanType %}             {{- _serialize_boolean(t, reference, offset) }}

src/nunavut/lang/cpp/templates/serialization.j2

@@ -23,17 +23,18 @@
 {# ----------------------------------------------------------------------------------------------------------------- #}
 {% macro _serialize_impl(t) %}
 
-    const {{ typename_unsigned_length }} capacity_bits = out_buffer.size();
-
+{%- if not options.disable_serialization_buffer_check %}
 {%- if options.enable_override_variable_array_capacity %}
 #ifndef {{ t | full_macro_name }}_DISABLE_SERIALIZATION_BUFFER_CHECK_
 {% endif %}
+    const {{ typename_unsigned_length }} capacity_bits = out_buffer.size();
     if ((static_cast<{{ typename_unsigned_bit_length }}>(capacity_bits)) < {{ t.inner_type.bit_length_set.max }}UL)
     {
         return -nunavut::support::Error::SerializationBufferTooSmall;
     }
 {%- if options.enable_override_variable_array_capacity %}
 #endif // ndef {{ t | full_macro_name }}_DISABLE_SERIALIZATION_BUFFER_CHECK_
+{% endif %}
 {% endif %}
 
     // Notice that fields that are not an integer number of bytes long may overrun the space allocated for them
@@ -113,8 +114,10 @@
     {{ assert('out_buffer.offset_alings_to_byte()') }}
 {% endif %}
     {# NOTICE: If this is a delimited type, we will be requiring the buffer to be at least extent-sized.
-     # This is a bit wasteful because when serializing we can often use a smaller buffer. #}
-    {% if t.bit_length_set.max > 0 %}
+     # This is a bit wasteful because when serializing we can often use a smaller buffer.
+     # `disable_serialization_buffer_check` option allows to avoid such waste for variable length arrays. #}
+    {% if (t.bit_length_set.max > 0) and
+          not (t is VariableLengthArrayType and options.disable_serialization_buffer_check) %}
     {{ assert('%dULL <= out_buffer.size()'|format(t.bit_length_set.max)) }}
     {% endif %}
 

src/nunavut/lang/properties.json

@@ -249,6 +249,7 @@
         "omit_serialization_support": false,
         "enable_serialization_asserts": false,
         "enable_override_variable_array_capacity": false,
+        "disable_serialization_buffer_check": false,
         "cast_format": "(({type}) {value})"
       }
     },
@@ -505,6 +506,7 @@
         "omit_serialization_support": false,
         "enable_serialization_asserts": false,
         "enable_override_variable_array_capacity": false,
+        "disable_serialization_buffer_check": false,
         "std": "c++14",
         "std_flavor": "std",
         "cast_format": "static_cast<{type}>({value})",

test/gentest_nnvg/templates/Any.j2

@@ -12,4 +12,7 @@
 {%- if options.enable_override_variable_array_capacity is defined %},
      "enable_override_variable_array_capacity": {{ options.enable_override_variable_array_capacity | ln.js.to_true_or_false }}
 {% endif %}
+{%- if options.disable_serialization_buffer_check is defined %},
+     "disable_serialization_buffer_check": {{ options.disable_serialization_buffer_check | ln.js.to_true_or_false }}
+{% endif %}
 }