Fix invalid JSON output for 'show ip route <protocol> json' commands (sonic-net#4111)

* Fix invalid JSON output for 'show ip route <protocol> json' commands

Commands like 'show ip route bgp json' were producing invalid JSON
with a namespace prefix (': '), breaking JSON parsers and automation.

The issue occurred because protocol filters (bgp, static, etc.) triggered
the namespace-prefix output path even when JSON was requested. On
single-ASIC systems where namespace is empty, this resulted in ': '
being printed before the JSON output.

Fixed by skipping the namespace-prefix path when JSON output is
requested, allowing proper JSON processing and formatting.

Signed-off-by: Bojun Feng <davidfeng@uchicago.edu>

* Add test for 'show ip route bgp json' command

Adds test_show_ip_route_bgp_json to verify protocol-filtered route
commands with JSON output work correctly.

Test validates:
- Command executes successfully
- Output is valid parseable JSON
- No namespace prefix bug (': ' at start)
- Output starts with '{'
- BGP routes present in filtered output

This test covers the bug fix in show/bgp_common.py where protocol
filters (bgp, static, etc.) with JSON output were producing invalid
JSON with namespace prefix on single-ASIC systems.

Signed-off-by: Bojun Feng <davidfeng@uchicago.edu>

* misc: fix new line at end of file

Signed-off-by: Bojun Feng <davidfeng@uchicago.edu>

---------

Signed-off-by: Bojun Feng <davidfeng@uchicago.edu>

Author: Bojun-Feng

show/bgp_common.py

@@ -403,7 +403,7 @@ def show_routes(args, namespace, display, verbose, ipver):
             return
 
         # Multi-asic show ip route with additional parms are handled by going to FRR directly and get those outputs from each namespace
-        if found_other_parms:
+        if found_other_parms and not found_json:
             print("{}:".format(ns))
             print(output)
             continue
@@ -429,7 +429,7 @@ def show_routes(args, namespace, display, verbose, ipver):
         else:
             print_ip_routes(combined_route, filter_by_ip)
     else:
-        new_string = json.dumps(combined_route,sort_keys=True, indent=4)
+        new_string = json.dumps(combined_route, sort_keys=True, indent=4)
         print(new_string)
 
 '''

tests/ip_show_routes_test.py

@@ -1,3 +1,4 @@
+import json
 import os
 import pytest
 
@@ -141,3 +142,30 @@ def test_show_ipv6_route_err(
         assert result.exit_code == 0
         assert result.output == show_ip_route_common.show_ipv6_route_err_expected_output + "\n"
 
+    @pytest.mark.parametrize('setup_single_bgp_instance',
+                             ['ip_route'], indirect=['setup_single_bgp_instance'])
+    def test_show_ip_route_bgp_json(
+            self,
+            setup_ip_route_commands,
+            setup_single_bgp_instance):
+        show = setup_ip_route_commands
+        runner = CliRunner()
+        result = runner.invoke(
+            show.cli.commands["ip"].commands["route"], ["bgp", "json"])
+        print("{}".format(result.output))
+        assert result.exit_code == 0
+
+        try:
+            parsed = json.loads(result.output)
+            assert isinstance(parsed, dict)
+        except json.JSONDecodeError as e:
+            pytest.fail(f"Output is not valid JSON: {e}")
+
+        bgp_routes_found = False
+        for route_data in parsed.values():
+            if isinstance(route_data, list):
+                for entry in route_data:
+                    if entry.get("protocol") == "bgp":
+                        bgp_routes_found = True
+                        break
+        assert bgp_routes_found, "BGP routes should be present in filtered output"