Use /v3/index.json for NuGet feed check

Author: mbg

lib/start-proxy-action.js

@@ -7,6 +7,17 @@ import { getErrorMessage } from "../util";
 
 import { getAddressString, ProxyInfo, Registry } from "./types";
 
+/** Represents registry-specific connection test configurations. */
+export interface ConnectionTestConfig {
+  /** An optional path to append to the end of the base url. */
+  path?: string;
+}
+
+/** A partial mapping of registry types to extra connection test configurations. */
+const connectionTestConfig: Partial<Record<string, ConnectionTestConfig>> = {
+  nuget_feed: { path: "/v3/index.json" },
+};
+
 export class ReachabilityError extends Error {
   constructor(public readonly statusCode?: number | undefined) {
     super();
@@ -92,6 +103,7 @@ export async function checkConnections(
     }
 
     for (const registry of proxy.registries) {
+      const config = connectionTestConfig[registry.type];
       const address = getAddressString(registry);
       const url = URL.parse(address);
 
@@ -102,18 +114,25 @@ export async function checkConnections(
         continue;
       }
 
+      const testUrl =
+        config?.path === undefined ? url : new URL(config.path, url);
+
       try {
-        logger.debug(`Testing connection to ${url}...`);
-        const statusCode = await backend.checkConnection(url);
+        logger.debug(`Testing connection to ${testUrl}...`);
+        const statusCode = await backend.checkConnection(testUrl);
 
-        logger.info(`Successfully tested connection to ${url} (${statusCode})`);
+        logger.info(
+          `Successfully tested connection to ${testUrl} (${statusCode})`,
+        );
         result.add(registry);
       } catch (e) {
         if (e instanceof ReachabilityError && e.statusCode !== undefined) {
-          logger.info(`Connection test to ${url} failed. (${e.statusCode})`);
+          logger.info(
+            `Connection test to ${testUrl} failed. (${e.statusCode})`,
+          );
         } else {
           logger.warning(
-            `Connection test to ${url} failed: ${getErrorMessage(e)}`,
+            `Connection test to ${testUrl} failed: ${getErrorMessage(e)}`,
           );
         }
       }