Fix delay filter validation: ensure delay: [0, X] returns proper error message

This fix addresses the issue where delay: [0, X] configurations were being
silently dropped instead of returning validation errors.

Changes:
- Created new utility function filter_inactive_filters() in packet_filter_validation.py
- Implemented smart filtering logic for delay filter that checks both latency and jitter:
  * delay: [0, 0] → User wants to disable delay, filter out silently
  * delay: [0, X] where X > 0 → Invalid config, keep for validation error
  * delay: [X, X] where X > 0 → Normal configuration, validate normally
- Simplified link.py update_filters() method to use the new utility function
- Added comprehensive tests for the new filtering logic

Before this fix:
- delay: [0, 100] would be silently dropped with no error message
- Users wouldn't know their configuration was invalid

After this fix:
- delay: [0, 100] returns proper error: "delay parameter Latency must be between 1 and 32767 ms, got: 0"
- delay: [0, 0] is correctly handled as intentional disable
- Normal delay configurations continue to work as expected

gns3server/controller/link.py

@@ -23,7 +23,7 @@ import html
 from .controller_error import ControllerError, ControllerNotFoundError
 from gns3server.agent.web_wireshark.manager import WebWiresharkManager
 from gns3server.config import Config
-from gns3server.utils.packet_filter_validation import validate_all_filters, FilterValidationError
+from gns3server.utils.packet_filter_validation import validate_all_filters, filter_inactive_filters, FilterValidationError
 
 import logging
 
@@ -148,19 +148,11 @@ class Link:
         """
         Modify the filters list.
 
-        Filter with value 0 will be dropped because not active
+        Filters with value 0 will be filtered out as inactive, with special
+        handling for delay filter to distinguish between "disabled" and "invalid config".
         """
-        new_filters = {}
-        for (filter, values) in filters.items():
-            new_values = []
-            for value in values:
-                if isinstance(value, str):
-                    new_values.append(value.strip("\n "))
-                else:
-                    new_values.append(int(value))
-            values = new_values
-            if len(values) != 0 and values[0] != 0 and values[0] != "":
-                new_filters[filter] = values
+        # Filter out inactive filters using the utility function
+        new_filters = filter_inactive_filters(filters)
 
         # Validate filter parameters before applying
         try:

gns3server/utils/packet_filter_validation.py

@@ -170,6 +170,69 @@ def validate_filter_parameters(filter_type: str, values: List[Any]) -> None:
                 )
 
 
+def filter_inactive_filters(filters: Dict[str, List[Any]]) -> Dict[str, List[Any]]:
+    """
+    Filter out inactive packet filters before validation.
+
+    This function implements smart filtering logic:
+    - For most filters: value 0 means "disabled" and will be filtered out
+    - For delay filter: check both latency and jitter to determine intent
+      * delay: [0, 0] → User wants to disable delay completely, filter it out
+      * delay: [0, X] where X > 0 → Invalid config (latency must be >= 1), keep for validation error
+      * delay: [X, X] where X > 0 → Normal configuration, keep for validation
+
+    Args:
+        filters: Dictionary mapping filter types to their values
+
+    Returns:
+        Filtered dictionary with only active filters for validation
+    """
+
+    if not filters:
+        return {}
+
+    active_filters = {}
+    for filter_type, values in filters.items():
+        if not values or (isinstance(values, list) and len(values) == 0):
+            continue
+
+        # Normalize values (strip strings, convert to int)
+        normalized_values = []
+        for value in values:
+            if isinstance(value, str):
+                normalized_values.append(value.strip("\n "))
+            else:
+                normalized_values.append(int(value))
+        values = normalized_values
+
+        # Skip empty filters after normalization
+        if len(values) == 0:
+            continue
+
+        # Special handling for delay filter - check both latency and jitter
+        if filter_type == "delay":
+            if len(values) >= 1 and values[0] == 0:  # latency = 0
+                if len(values) >= 2 and values[1] == 0:  # jitter = 0 too
+                    # User intentionally disabling delay completely: [0, 0]
+                    log.debug(f"Filter {filter_type} with values {values} skipped (disabled)")
+                    continue  # Skip this filter silently
+                else:
+                    # Invalid config: latency=0 but jitter>0, keep for validation error
+                    log.debug(f"Filter {filter_type} with values {values} kept for validation (invalid config)")
+                    active_filters[filter_type] = values
+            else:
+                # latency>0, normal configuration
+                active_filters[filter_type] = values
+        # For other filters, skip if first value is 0 or empty string (means "disabled")
+        elif values[0] != 0 and values[0] != "":
+            active_filters[filter_type] = values
+        else:
+            # Filters like packet_loss=0, corrupt=0, frequency_drop=0 are intentionally disabled
+            log.debug(f"Filter {filter_type} with values {values} skipped (disabled)")
+
+    return active_filters
+
+
 def validate_all_filters(filters: Dict[str, List[Any]]) -> None:
     """
     Validate all packet filters.

tests/utils/test_packet_filter_validation.py

@@ -6,6 +6,7 @@ import pytest
 from gns3server.utils.packet_filter_validation import (
     validate_filter_parameters,
     validate_all_filters,
+    filter_inactive_filters,
     FilterValidationError
 )
 
@@ -160,4 +161,105 @@ class TestPacketFilterValidation:
     def test_unknown_filter_type(self):
         """Test unknown filter type."""
         with pytest.raises(FilterValidationError, match="Unknown filter type"):
-            validate_filter_parameters("unknown_filter", [1])
+            validate_filter_parameters("unknown_filter", [1])
+
+
+class TestFilterInactiveFilters:
+    """Test filter_inactive_filters function for smart filter filtering logic."""
+
+    def test_filter_inactive_delay_disabled(self):
+        """Test delay [0, 0] is filtered out (user wants to disable delay)."""
+        filters = {"delay": [0, 0]}
+        result = filter_inactive_filters(filters)
+        assert result == {}  # Should be filtered out
+
+    def test_filter_inactive_delay_invalid_config(self):
+        """Test delay [0, 100] is kept for validation (invalid config)."""
+        filters = {"delay": [0, 100]}
+        result = filter_inactive_filters(filters)
+        assert result == {"delay": [0, 100]}  # Should be kept for validation error
+
+    def test_filter_inactive_delay_normal_config(self):
+        """Test delay [100, 20] is kept (normal configuration)."""
+        filters = {"delay": [100, 20]}
+        result = filter_inactive_filters(filters)
+        assert result == {"delay": [100, 20]}  # Should be kept
+
+    def test_filter_inactive_delay_zero_jitter(self):
+        """Test delay [100, 0] is kept (normal config with zero jitter)."""
+        filters = {"delay": [100, 0]}
+        result = filter_inactive_filters(filters)
+        assert result == {"delay": [100, 0]}  # Should be kept
+
+    def test_filter_inactive_packet_loss_zero(self):
+        """Test packet_loss [0] is filtered out (disabled)."""
+        filters = {"packet_loss": [0]}
+        result = filter_inactive_filters(filters)
+        assert result == {}  # Should be filtered out
+
+    def test_filter_inactive_packet_loss_active(self):
+        """Test packet_loss [5] is kept (active)."""
+        filters = {"packet_loss": [5]}
+        result = filter_inactive_filters(filters)
+        assert result == {"packet_loss": [5]}  # Should be kept
+
+    def test_filter_inactive_corrupt_zero(self):
+        """Test corrupt [0] is filtered out (disabled)."""
+        filters = {"corrupt": [0]}
+        result = filter_inactive_filters(filters)
+        assert result == {}  # Should be filtered out
+
+    def test_filter_inactive_corrupt_active(self):
+        """Test corrupt [2] is kept (active)."""
+        filters = {"corrupt": [2]}
+        result = filter_inactive_filters(filters)
+        assert result == {"corrupt": [2]}  # Should be kept
+
+    def test_filter_inactive_frequency_drop_zero(self):
+        """Test frequency_drop [0] is filtered out (disabled)."""
+        filters = {"frequency_drop": [0]}
+        result = filter_inactive_filters(filters)
+        assert result == {}  # Should be filtered out
+
+    def test_filter_inactive_frequency_drop_active(self):
+        """Test frequency_drop [10] is kept (active)."""
+        filters = {"frequency_drop": [10]}
+        result = filter_inactive_filters(filters)
+        assert result == {"frequency_drop": [10]}  # Should be kept
+
+    def test_filter_inactive_bpf_empty(self):
+        """Test BPF empty string is filtered out."""
+        filters = {"bpf": [""]}
+        result = filter_inactive_filters(filters)
+        assert result == {}  # Should be filtered out
+
+    def test_filter_inactive_bpf_active(self):
+        """Test BPF with expression is kept."""
+        filters = {"bpf": ["tcp port 80"]}
+        result = filter_inactive_filters(filters)
+        assert result == {"bpf": ["tcp port 80"]}  # Should be kept
+
+    def test_filter_inactive_multiple_filters_mixed(self):
+        """Test multiple filters with mixed active/inactive states."""
+        filters = {
+            "delay": [0, 0],           # Disabled: [0, 0]
+            "packet_loss": [0],         # Disabled: 0%
+            "corrupt": [2],             # Active: 2%
+            "frequency_drop": [10]      # Active: every 10th packet
+        }
+        result = filter_inactive_filters(filters)
+        assert result == {
+            "corrupt": [2],
+            "frequency_drop": [10]
+        }
+
+    def test_filter_inactive_empty_filters(self):
+        """Test empty filters dictionary."""
+        filters = {}
+        result = filter_inactive_filters(filters)
+        assert result == {}
+
+    def test_filter_inactive_none_filters(self):
+        """Test None filters."""
+        result = filter_inactive_filters(None)
+        assert result == {}