fix(wrangler): don't proxy localhost requests during dev

.changeset/fix-proxy-localhost.md

@@ -0,0 +1,11 @@
+---
+"wrangler": patch
+---
+
+Stop proxying localhost requests when proxy environment variables are set
+
+When `HTTP_PROXY` or `HTTPS_PROXY` is configured, all fetch requests including ones to `localhost` were routed through the proxy. This caused `wrangler dev` and the Vite plugin to fail with "TypeError: fetch failed" because the proxy can't reach local addresses.
+
+This switches from `ProxyAgent` to undici's `EnvHttpProxyAgent`, which supports the `NO_PROXY` environment variable. When `NO_PROXY` is not set, it defaults to `localhost,127.0.0.1,::1` so local requests are never proxied.
+
+The `NO_PROXY` config only applies to the request destination, not the proxy server address. So a proxy running on localhost (e.g. HTTP_PROXY=http://127.0.0.1:11451) still works for outbound API calls.

packages/wrangler/src/index.ts

@@ -6,7 +6,7 @@ import {
 	experimental_readRawConfig,
 } from "@cloudflare/workers-utils";
 import chalk from "chalk";
-import { ProxyAgent, setGlobalDispatcher } from "undici";
+import { EnvHttpProxyAgent, setGlobalDispatcher } from "undici";
 import makeCLI from "yargs";
 import { version as wranglerVersion } from "../package.json";
 import { aiFineTuneNamespace, aiNamespace } from "./ai";
@@ -337,7 +337,7 @@ import {
 	logoutCommand,
 	whoamiCommand,
 } from "./user/commands";
-import { proxy } from "./utils/constants";
+import { noProxy, proxy } from "./utils/constants";
 import { debugLogFilepath } from "./utils/log-file";
 import { vectorizeCreateCommand } from "./vectorize/create";
 import { vectorizeCreateMetadataIndexCommand } from "./vectorize/createMetadataIndex";
@@ -394,7 +394,9 @@ import type { LoggerLevel } from "./logger";
 import type { CommonYargsArgv, SubHelp } from "./yargs-types";
 
 if (proxy) {
-	setGlobalDispatcher(new ProxyAgent(proxy));
+	setGlobalDispatcher(
+		new EnvHttpProxyAgent({ noProxy: noProxy || "localhost,127.0.0.1,::1" })
+	);
 	logger.log(
 		`Proxy environment variables detected. We'll use your proxy for fetch requests.`
 	);

packages/wrangler/src/utils/constants.ts

@@ -9,3 +9,5 @@ export const proxy =
 	process.env.http_proxy ||
 	process.env.HTTP_PROXY ||
 	undefined;
+export const noProxy =
+	process.env.no_proxy || process.env.NO_PROXY || undefined;

packages/wrangler/turbo.json

@@ -32,6 +32,8 @@
 				"HTTP_PROXY",
 				"https_proxy",
 				"HTTPS_PROXY",
+				"no_proxy",
+				"NO_PROXY",
 				"HYPERDRIVE_DATABASE_URL",
 				"HYPERDRIVE_MYSQL_DATABASE_URL",
 				"WRANGLER_DOCKER_BIN",