add a common one way override function

Author: gagik

src/common/config/configUtils.ts

@@ -125,3 +125,14 @@ export function parseBoolean(val: unknown): unknown {
     }
     return false;
 }
+
+/** Allow overriding only to the allowed value */
+export function oneWayOverride<T>(allowedValue: T): CustomOverrideLogic {
+    return (oldValue, newValue) => {
+        // Only allow override if setting to true from false
+        if (newValue === allowedValue) {
+            return newValue;
+        }
+        throw new Error(`Can only set to ${allowedValue ? "true" : "false"}`);
+    };
+}

src/common/config/userConfig.ts

@@ -5,6 +5,7 @@ import {
     commaSeparatedToArray,
     getExportsPath,
     getLogPath,
+    oneWayOverride,
     parseBoolean,
 } from "./configUtils.js";
 import { previewFeatureValues, similarityValues } from "../schemas.js";
@@ -86,13 +87,7 @@ export const UserConfigSchema = z4.object({
             "When set to true, only allows read, connect, and metadata operation types, disabling create/update/delete operations."
         )
         .register(configRegistry, {
-            overrideBehavior: (oldValue, newValue) => {
-                // Only allow override if setting to true from false
-                if (oldValue === false && newValue === true) {
-                    return newValue;
-                }
-                throw new Error("Cannot disable readOnly mode");
-            },
+            overrideBehavior: oneWayOverride(true),
         }),
     indexCheck: z4
         .preprocess(parseBoolean, z4.boolean())
@@ -101,13 +96,7 @@ export const UserConfigSchema = z4.object({
             "When set to true, enforces that query operations must use an index, rejecting queries that perform a collection scan."
         )
         .register(configRegistry, {
-            overrideBehavior: (oldValue, newValue) => {
-                // Only allow override if setting to true from false
-                if (newValue === true) {
-                    return newValue;
-                }
-                throw new Error("Cannot disable indexCheck mode");
-            },
+            overrideBehavior: oneWayOverride(true),
         }),
     telemetry: z4
         .enum(["enabled", "disabled"])
@@ -198,13 +187,7 @@ export const UserConfigSchema = z4.object({
         .default(false)
         .describe("When set to true, disables validation of embeddings dimensions.")
         .register(configRegistry, {
-            overrideBehavior: (oldValue, newValue) => {
-                // Only allow override if setting to false from true (making more restrictive)
-                if (newValue === false) {
-                    return newValue;
-                }
-                throw new Error("Cannot disable disableEmbeddingsValidation");
-            },
+            overrideBehavior: oneWayOverride(false),
         }),
     vectorSearchDimensions: z4.coerce
         .number()

tests/integration/transports/configOverrides.test.ts

@@ -330,7 +330,7 @@ describe("Config Overrides via HTTP", () => {
                 }
                 expect(error.message).toContain("Error POSTing to endpoint (HTTP 400)");
                 expect(error.message).toContain(
-                    `Cannot apply override for readOnly from true to false: Cannot disable readOnly mode`
+                    `Cannot apply override for readOnly from true to false: Can only set to true`
                 );
             }
         });

tests/unit/common/config/configOverrides.test.ts

@@ -202,7 +202,7 @@ describe("configOverrides", () => {
                 const request: RequestContext = { headers: { "x-mongodb-mcp-read-only": "false" } };
                 expect(() =>
                     applyConfigOverrides({ baseConfig: { ...baseConfig, readOnly: true } as UserConfig, request })
-                ).toThrow("Cannot apply override for readOnly from true to false: Cannot disable readOnly mode");
+                ).toThrow("Cannot apply override for readOnly from true to false: Can only set to true");
             });
 
             it("should allow indexCheck override from false to true", () => {
@@ -218,7 +218,7 @@ describe("configOverrides", () => {
                 const request: RequestContext = { headers: { "x-mongodb-mcp-index-check": "false" } };
                 expect(() =>
                     applyConfigOverrides({ baseConfig: { ...baseConfig, indexCheck: true } as UserConfig, request })
-                ).toThrow("Cannot apply override for indexCheck from true to false: Cannot disable indexCheck mode");
+                ).toThrow("Cannot apply override for indexCheck from true to false: Can only set to true");
             });
 
             it("should allow disableEmbeddingsValidation override from true to false", () => {
@@ -238,7 +238,7 @@ describe("configOverrides", () => {
                         request,
                     })
                 ).toThrow(
-                    "Cannot apply override for disableEmbeddingsValidation from false to true: Cannot disable disableEmbeddingsValidation"
+                    "Cannot apply override for disableEmbeddingsValidation from false to true: Can only set to false"
                 );
             });
         });