Return nil for items outside buffer bounds in undersized packets

openc3/ext/openc3/ext/polynomial_conversion/polynomial_conversion.c

@@ -15,7 +15,7 @@
 
 /*
 # Modified by OpenC3, Inc.
-# All changes Copyright 2022, OpenC3, Inc.
+# All changes Copyright 2026, OpenC3, Inc.
 # All Rights Reserved
 #
 # This file may also be used under the terms of a commercial license 
@@ -47,9 +47,18 @@ static VALUE polynomial_conversion_call(VALUE self, VALUE value, VALUE myself, V
   int index = 0;
   double converted = 0.0;
   double raised_to_power = 1.0;
-  volatile VALUE coeffs = rb_ivar_get(self, id_ivar_coeffs);
-  long coeffs_length = RARRAY_LEN(coeffs);
-  double double_value = RFLOAT_VALUE(rb_funcall(value, id_method_to_f, 0));
+  volatile VALUE coeffs;
+  long coeffs_length;
+  double double_value;
+
+  /* Return nil if value is nil (item outside buffer bounds) */
+  if (NIL_P(value)) {
+    return Qnil;
+  }
+
+  coeffs = rb_ivar_get(self, id_ivar_coeffs);
+  coeffs_length = RARRAY_LEN(coeffs);
+  double_value = RFLOAT_VALUE(rb_funcall(value, id_method_to_f, 0));
 
   /* Handle C0 */
   double coeff = RFLOAT_VALUE(rb_ary_entry(coeffs, 0));

openc3/ext/openc3/ext/structure/structure.c

@@ -15,7 +15,7 @@
 
 /*
 # Modified by OpenC3, Inc.
-# All changes Copyright 2024, OpenC3, Inc.
+# All changes Copyright 2026, OpenC3, Inc.
 # All Rights Reserved
 #
 # This file may also be used under the terms of a commercial license
@@ -520,7 +520,8 @@ static VALUE binary_accessor_read(VALUE self, VALUE param_bit_offset, VALUE para
 
   if (!check_bounds_and_buffer_size(bit_offset, bit_size, (int)buffer_length, param_endianness, param_data_type, &lower_bound, &upper_bound))
   {
-    rb_funcall(self, id_method_raise_buffer_error, 5, symbol_read, param_buffer, param_data_type, param_bit_offset, param_bit_size);
+    /* Return nil for out-of-bounds reads (supports undersized packets with ALLOW_SHORT) */
+    return Qnil;
   }
 
   if ((param_data_type == symbol_STRING) || (param_data_type == symbol_BLOCK))

openc3/lib/openc3/accessors/accessor.rb

@@ -85,7 +85,7 @@ def enforce_length
 
     # This sets the short_buffer_allowed flag in the Packet class
     # which allows packets that have a buffer shorter than the defined size.
-    # Note that the buffer is still resized to the defined length
+    # Items outside the buffer bounds will return nil when read.
     def enforce_short_buffer_allowed
       return false
     end

openc3/lib/openc3/accessors/binary_accessor.rb

@@ -14,7 +14,7 @@
 # GNU Affero General Public License for more details.
 
 # Modified by OpenC3, Inc.
-# All changes Copyright 2024, OpenC3, Inc.
+# All changes Copyright 2026, OpenC3, Inc.
 # All Rights Reserved
 #
 # This file may also be used under the terms of a commercial license
@@ -339,7 +339,8 @@ def self.read(bit_offset, bit_size, data_type, buffer, endianness)
         end
 
         result, lower_bound, upper_bound = check_bounds_and_buffer_size(bit_offset, bit_size, buffer.length, endianness, data_type)
-        raise_buffer_error(:read, buffer, data_type, given_bit_offset, given_bit_size) unless result
+        # Return nil for out-of-bounds reads (supports undersized packets with ALLOW_SHORT)
+        return nil unless result
 
         if (data_type == :STRING) || (data_type == :BLOCK)
           #######################################
@@ -936,6 +937,9 @@ def self.read_array(bit_offset, bit_size, data_type, array_size, buffer, endiann
       lower_bound = bit_offset / 8
       upper_bound = (bit_offset + array_size - 1) / 8
 
+      # Return nil for out-of-bounds reads (supports undersized packets with ALLOW_SHORT)
+      return nil if upper_bound >= buffer.length
+
       # Check for byte alignment
       byte_aligned = ((bit_offset % 8) == 0)
 
@@ -1420,7 +1424,7 @@ def enforce_length
 
     # This sets the short_buffer_allowed flag in the Packet class
     # which allows packets that have a buffer shorter than the defined size.
-    # Note that the buffer is still resized to the defined length
+    # Items outside the buffer bounds will return nil when read.
     def enforce_short_buffer_allowed
       return false
     end

openc3/lib/openc3/accessors/form_accessor.rb

@@ -75,7 +75,7 @@ def enforce_length
 
     # This sets the short_buffer_allowed flag in the Packet class
     # which allows packets that have a buffer shorter than the defined size.
-    # Note that the buffer is still resized to the defined length
+    # Items outside the buffer bounds will return nil when read.
     def enforce_short_buffer_allowed
       return true
     end

openc3/lib/openc3/accessors/http_accessor.rb

@@ -164,7 +164,7 @@ def enforce_length
 
     # This sets the short_buffer_allowed flag in the Packet class
     # which allows packets that have a buffer shorter than the defined size.
-    # Note that the buffer is still resized to the defined length
+    # Items outside the buffer bounds will return nil when read.
     def enforce_short_buffer_allowed
       return @body_accessor.enforce_short_buffer_allowed
     end

openc3/lib/openc3/accessors/json_accessor.rb

@@ -158,7 +158,7 @@ def enforce_length
 
     # This sets the short_buffer_allowed flag in the Packet class
     # which allows packets that have a buffer shorter than the defined size.
-    # Note that the buffer is still resized to the defined length
+    # Items outside the buffer bounds will return nil when read.
     def enforce_short_buffer_allowed
       return true
     end

openc3/lib/openc3/accessors/template_accessor.rb

@@ -134,7 +134,7 @@ def enforce_length
 
     # This sets the short_buffer_allowed flag in the Packet class
     # which allows packets that have a buffer shorter than the defined size.
-    # Note that the buffer is still resized to the defined length
+    # Items outside the buffer bounds will return nil when read.
     def enforce_short_buffer_allowed
       return true
     end

openc3/lib/openc3/accessors/xml_accessor.rb

@@ -95,7 +95,7 @@ def enforce_length
 
     # This sets the short_buffer_allowed flag in the Packet class
     # which allows packets that have a buffer shorter than the defined size.
-    # Note that the buffer is still resized to the defined length
+    # Items outside the buffer bounds will return nil when read.
     def enforce_short_buffer_allowed
       return true
     end

openc3/lib/openc3/conversions/polynomial_conversion.rb

@@ -14,7 +14,7 @@
 # GNU Affero General Public License for more details.
 
 # Modified by OpenC3, Inc.
-# All changes Copyright 2024, OpenC3, Inc.
+# All changes Copyright 2026, OpenC3, Inc.
 # All Rights Reserved
 #
 # This file may also be used under the terms of a commercial license
@@ -45,6 +45,9 @@ def initialize(*coeffs)
       # @param (see Conversion#call)
       # @return [Float] The value with the polynomial applied
       def call(value, myself, buffer)
+        # Return nil if value is nil (item outside buffer bounds)
+        return nil if value.nil?
+
         value = value.to_f
 
         # Handle C0

openc3/lib/openc3/conversions/segmented_polynomial_conversion.rb

@@ -14,7 +14,7 @@
 # GNU Affero General Public License for more details.
 
 # Modified by OpenC3, Inc.
-# All changes Copyright 2024, OpenC3, Inc.
+# All changes Copyright 2026, OpenC3, Inc.
 # All Rights Reserved
 #
 # This file may also be used under the terms of a commercial license
@@ -116,6 +116,9 @@ def add_segment(lower_bound, *coeffs)
     # @param (see Conversion#call)
     # @return [Float] The value with the polynomial applied
     def call(value, packet, buffer)
+      # Return nil if value is nil (item outside buffer bounds)
+      return nil if value.nil?
+
       # Try to find correct segment
       @segments.each do |segment|
         return segment.calculate(value) if value >= segment.lower_bound

openc3/lib/openc3/packets/packet.rb

@@ -1049,6 +1049,9 @@ def check_limits(limits_set = :DEFAULT, ignore_persistence = false)
         if item.limits.enabled
           value = read_item(item)
 
+          # Skip limits checking if value is nil (item outside buffer bounds)
+          next if value.nil?
+
           # Handle state monitoring and value monitoring differently
           if item.states
             handle_limits_states(item, value)
@@ -1526,6 +1529,9 @@ def handle_limits_values(item, value, limits_set, ignore_persistence)
     end
 
     def apply_format_string_and_units(item, value, value_type)
+      # Return nil as-is - can't format a value that doesn't exist
+      return nil if value.nil?
+
       if value_type == :FORMATTED or value_type == :WITH_UNITS
         if item.format_string && value
           value = sprintf(item.format_string, value)

openc3/lib/openc3/packets/packet_config.rb

@@ -493,8 +493,8 @@ def process_current_packet(parser, keyword, params)
           'APPEND_ARRAY_ITEM', 'APPEND_ARRAY_PARAMETER', 'STRUCTURE', 'APPEND_STRUCTURE'
         start_item(parser)
 
-      # Allow this packet to be received with less data than the defined length
-      # without generating a warning.
+      # Allow this packet to be received with less data than the defined length.
+      # Items that are beyond the buffer will return nil when read.
       when 'ALLOW_SHORT'
         @current_packet.short_buffer_allowed = true
 

openc3/lib/openc3/packets/structure.rb

@@ -14,7 +14,7 @@
 # GNU Affero General Public License for more details.
 
 # Modified by OpenC3, Inc.
-# All changes Copyright 2024, OpenC3, Inc.
+# All changes Copyright 2026, OpenC3, Inc.
 # All Rights Reserved
 #
 # This file may also be used under the terms of a commercial license
@@ -680,8 +680,12 @@ def internal_buffer_equals(buffer)
       if @accessor.enforce_length
         if @buffer.length != @defined_length
           if @buffer.length < @defined_length
-            resize_buffer()
-            raise "Buffer length less than defined length" unless @short_buffer_allowed
+            # Only resize if short_buffer_allowed is false
+            # When short_buffer_allowed is true, keep the buffer short so reads
+            # of items beyond the buffer return nil
+            unless @short_buffer_allowed
+              raise "Buffer length less than defined length"
+            end
           elsif @fixed_size and @defined_length != 0
             raise "Buffer length greater than defined length"
           end

openc3/python/openc3/accessors/binary_accessor.py

@@ -1,4 +1,4 @@
-# Copyright 2025 OpenC3, Inc.
+# Copyright 2026 OpenC3, Inc.
 # All Rights Reserved.
 #
 # This program is free software; you can modify and/or redistribute it
@@ -105,7 +105,9 @@ def raise_buffer_error(cls, read_write, buffer, data_type, given_bit_offset, giv
     def handle_read_variable_bit_size(self, item, _buffer):
         length_value = self.packet.read(item.variable_bit_size["length_item_name"], "CONVERTED")
         if item.array_size is not None:
-            item.array_size = (length_value * item.variable_bit_size["length_bits_per_count"]) + item.variable_bit_size["length_value_bit_offset"]
+            item.array_size = (length_value * item.variable_bit_size["length_bits_per_count"]) + item.variable_bit_size[
+                "length_value_bit_offset"
+            ]
         else:
             if item.data_type == "INT" or item.data_type == "UINT":
                 # QUIC encoding is currently assumed for individual variable sized integers
@@ -133,7 +135,7 @@ def read_item(self, item, buffer):
             # Structure is used to read items with parent, not accessor
             structure_buffer = self.read_item(item.parent_item, buffer)
             structure = item.parent_item.structure
-            return structure.read(item.key, 'RAW', structure_buffer)
+            return structure.read(item.key, "RAW", structure_buffer)
         else:
             if item.variable_bit_size:
                 self.handle_read_variable_bit_size(item, buffer)
@@ -291,7 +293,7 @@ def write_item(self, item, value, buffer):
             # Structure is used to write items with parent, not accessor
             structure_buffer = self.read_item(item.parent_item, buffer)
             structure = item.parent_item.structure
-            structure.write(item.key, value, 'RAW', structure_buffer)
+            structure.write(item.key, value, "RAW", structure_buffer)
             if item.parent_item.variable_bit_size:
                 self.handle_write_variable_bit_size(item.parent_item, structure_buffer, buffer)
             BinaryAccessor.class_write_item(item.parent_item, structure_buffer, buffer)
@@ -355,8 +357,9 @@ def read(cls, bit_offset, bit_size, data_type, buffer, endianness):
         result, lower_bound, upper_bound = cls.check_bounds_and_buffer_size(
             bit_offset, bit_size, len(buffer), endianness, data_type
         )
+        # Return None for out-of-bounds reads (supports undersized packets with ALLOW_SHORT)
         if not result:
-            cls.raise_buffer_error("read", buffer, data_type, given_bit_offset, given_bit_size)
+            return None
 
         if data_type in ["STRING", "BLOCK"]:
             #######################################
@@ -871,6 +874,10 @@ def read_array(cls, bit_offset, bit_size, data_type, array_size, buffer, endiann
         lower_bound = math.floor(bit_offset / 8)
         upper_bound = math.floor((bit_offset + array_size - 1) / 8)
 
+        # Return None for out-of-bounds reads (supports undersized packets with ALLOW_SHORT)
+        if upper_bound >= len(buffer):
+            return None
+
         # Check for byte alignment
         byte_aligned = (bit_offset % 8) == 0
 
@@ -936,9 +943,7 @@ def read_array(cls, bit_offset, bit_size, data_type, array_size, buffer, endiann
                             )
                         )
                     else:
-                        raise ValueError(
-                            f"bit_size is {given_bit_size} but must be 32 or 64 for data_type {data_type}"
-                        )
+                        raise ValueError(f"bit_size is {given_bit_size} but must be 32 or 64 for data_type {data_type}")
 
                 else:
                     raise ValueError(f"bit_offset {given_bit_offset} is not byte aligned for data_type {data_type}")
@@ -1149,9 +1154,7 @@ def write_array(
                             *values,
                         )
                     else:
-                        raise ValueError(
-                            f"bit_size is {given_bit_size} but must be 32 or 64 for data_type {data_type}"
-                        )
+                        raise ValueError(f"bit_size is {given_bit_size} but must be 32 or 64 for data_type {data_type}")
                 else:
                     raise ValueError(f"bit_offset {given_bit_offset} is not byte aligned for data_type {data_type}")
 

openc3/python/openc3/accessors/form_accessor.py

@@ -63,7 +63,7 @@ def enforce_length(self):
 
     # This sets the short_buffer_allowed flag in the Packet class
     # which allows packets that have a buffer shorter than the defined size.
-    # Note that the buffer is still resized to the defined length
+    # Items outside the buffer bounds will return None when read.
     def enforce_short_buffer_allowed(self):
         return True
 

openc3/python/openc3/accessors/http_accessor.py

@@ -163,7 +163,7 @@ def enforce_length(self):
 
     # This sets the short_buffer_allowed flag in the Packet class
     # which allows packets that have a buffer shorter than the defined size.
-    # Note that the buffer is still resized to the defined length
+    # Items outside the buffer bounds will return None when read.
     def enforce_short_buffer_allowed(self):
         return self.body_accessor.enforce_short_buffer_allowed()
 

openc3/python/openc3/accessors/template_accessor.py

@@ -157,7 +157,7 @@ def enforce_length(self):
 
     # This sets the short_buffer_allowed flag in the Packet class
     # which allows packets that have a buffer shorter than the defined size.
-    # Note that the buffer is still resized to the defined length
+    # Items outside the buffer bounds will return None when read.
     def enforce_short_buffer_allowed(self):
         return True
 

openc3/python/openc3/conversions/polynomial_conversion.py

@@ -1,4 +1,4 @@
-# Copyright 2024 OpenC3, Inc.
+# Copyright 2026 OpenC3, Inc.
 # All Rights Reserved.
 #
 # This program is free software; you can modify and/or redistribute it
@@ -34,6 +34,10 @@ def __init__(self, *coeffs):
     # @param (see Conversion#call)
     # @return [Float] The value with the polynomial applied
     def call(self, value, myself, buffer):
+        # Return None if value is None (item outside buffer bounds)
+        if value is None:
+            return None
+
         value = float(value)
 
         # Handle C0

openc3/python/openc3/conversions/segmented_polynomial_conversion.py

@@ -1,4 +1,4 @@
-# Copyright 2023 OpenC3, Inc.
+# Copyright 2026 OpenC3, Inc.
 # All Rights Reserved.
 #
 # This program is free software; you can modify and/or redistribute it
@@ -92,6 +92,10 @@ def add_segment(self, lower_bound, *coeffs):
     # @param (see Conversion#call)
     # @return [Float] The value with the polynomial applied
     def call(self, value, packet, buffer):
+        # Return None if value is None (item outside buffer bounds)
+        if value is None:
+            return None
+
         # Try to find correct segment
         for segment in self.segments:
             if value >= segment.lower_bound: