Support client configs with "." in json keys (#1258)

Signed-off-by: Chris Gernon <[email protected]>

Author: while1fork

pkg/client/config_editor.go

@@ -156,6 +156,13 @@ func (jcu *JSONConfigUpdater) Remove(serverName string) error {
 // This is necessary because the MCP client config file is a JSON object,
 // and we need to ensure that the path exists before we can add a new key to it.
 func ensurePathExists(content []byte, path string) []byte {
+	// Special case: if path is root ("/"), just return everything (formatted)
+	if path == "/" {
+		v, _ := hujson.Parse(content)
+		formatted, _ := hujson.Format(v.Pack())
+		return formatted
+	}
+
 	segments := strings.Split(path, "/")
 
 	// Navigate through the JSON structure
@@ -172,12 +179,18 @@ func ensurePathExists(content []byte, path string) []byte {
 		// The "/" is added to the path for the patch operation because the path
 		// is a JSON pointer, and JSON pointers are prefixed with "/".
 		// The "." is added to the path for the retrieval operation.
+		// - gjson (used for retrieval) treats `.` as a special (traversal) character,
+		// so any json keys which contain `.` must have the `.` "escaped" with a single
+		// '\'. In it, key `a.b` would be matched by `a\.b` but not `a.b`.
+		// - hujson (used for the patch) treats "." and "\" as ordinary characters in a
+		// json key. In it, key `a.b` would be matched by `a.b` but not `a\.b`.
+		// So we need to "escape" json keys this way for retrieval, but not for patch.
 		if len(pathSoFarForPatch) == 0 {
 			pathSoFarForPatch = "/" + segment
-			pathSoFarForRetrieval = segment
+			pathSoFarForRetrieval = strings.ReplaceAll(segment, ".", `\.`)
 		} else {
 			pathSoFarForPatch = pathSoFarForPatch + "/" + segment
-			pathSoFarForRetrieval = pathSoFarForRetrieval + "." + segment
+			pathSoFarForRetrieval = pathSoFarForRetrieval + "." + strings.ReplaceAll(segment, ".", `\.`)
 		}
 
 		// We retrieve the segment from the content so that we can check if it exists

pkg/client/config_editor_test.go

@@ -224,3 +224,63 @@ func getMCPServerFromFile(t *testing.T, configPath string, key string) MCPServer
 
 	return testMcpServer
 }
+
+func TestEnsurePathExists(t *testing.T) {
+	t.Parallel()
+
+	logger.Initialize()
+
+	tests := []struct {
+		name           string
+		description    string
+		content        []byte
+		path           string
+		expectedResult []byte
+	}{
+		{
+			name:           "EmptyContent",
+			description:    "Should create path in empty JSON object",
+			content:        []byte("{}"),
+			path:           "/mcp/servers",
+			expectedResult: []byte("{\"mcp\": {\"servers\": {}}}\n"),
+		},
+		{
+			name:           "ExistingPath",
+			description:    "Should return existing path",
+			content:        []byte(`{"mcp": {"servers": {"existing": "value"}}}`),
+			path:           "/mcp/servers",
+			expectedResult: []byte("{\"mcp\": {\"servers\": {\"existing\": \"value\"}}}\n"),
+		},
+		{
+			name:           "PartialExistingPath",
+			description:    "Should create missing nested path when parent exists",
+			content:        []byte(`{"misc": {}}`),
+			path:           "/misc/mcp/servers",
+			expectedResult: []byte("{\"misc\": {\"mcp\": {\"servers\": {}}}}\n"),
+		},
+		{
+			name:           "PathWithDots",
+			description:    "Should handle paths with dots correctly",
+			content:        []byte(`{"agent.support": {"mcp.servers": {"existing": "value"}}}`),
+			path:           "/agent.support/mcp.servers",
+			expectedResult: []byte("{\"agent.support\": {\"mcp.servers\": {\"existing\": \"value\"}}}\n"),
+		},
+		{
+			name:           "RootPath",
+			description:    "Should handle root path",
+			content:        []byte(`{"server1": {"some": "config"}, "server2": {"some": "other_config"}}`),
+			path:           "/",
+			expectedResult: []byte("{\"server1\": {\"some\": \"config\"}, \"server2\": {\"some\": \"other_config\"}}\n"),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			result := ensurePathExists(tt.content, tt.path)
+
+			assert.DeepEqual(t, tt.expectedResult, result)
+		})
+	}
+}