fix: strip baseURL prefix before matching API routes

.changeset/fix-baseurl-api-routes.md

@@ -0,0 +1,5 @@
+---
+"@solidjs/start": patch
+---
+
+Strip baseURL prefix before matching API routes.

packages/start/src/config/index.ts

@@ -73,7 +73,7 @@ export function solidStart(options?: SolidStartOptions): Array<PluginOption> {
           },
         };
       },
-      async config(_, env) {
+      async config(config, env) {
         const clientInput = [handlers.client];
         if (env.command === "build") {
           const clientRouter: BaseFileSystemRouter = (globalThis as any).ROUTERS.client;
@@ -143,6 +143,9 @@ export function solidStart(options?: SolidStartOptions): Array<PluginOption> {
             "import.meta.env.START_CLIENT_ENTRY": JSON.stringify(handlers.client),
             "import.meta.env.START_DEV_OVERLAY": JSON.stringify(start.devOverlay),
             "import.meta.env.SEROVAL_MODE": JSON.stringify(start.serialization?.mode || "json"),
+            "import.meta.env.SERVER_BASE_URL": JSON.stringify(
+              (config as { server?: { baseURL?: string } })?.server?.baseURL ?? "",
+            ),
           },
           builder: {
             sharedPlugins: true,

packages/start/src/env.d.ts

@@ -13,5 +13,5 @@ interface SolidStartMetaEnv {
   START_CLIENT_ENTRY: string;
   START_ISLANDS: boolean;
   // START_DEV_OVERLAY: boolean;
-  // SERVER_BASE_URL: string;
+  SERVER_BASE_URL: string;
 }

packages/start/src/server/handler.ts

@@ -10,6 +10,7 @@ import { decorateHandler, decorateMiddleware } from "./fetchEvent.ts";
 import { getSsrManifest } from "./manifest/ssr-manifest.ts";
 import { matchAPIRoute } from "./routes.ts";
 import { handleServerFunction } from "./server-functions-handler.ts";
+import { stripPathBase } from "./strip-path-base.ts";
 import type { APIEvent, FetchEvent, HandlerOptions, PageEvent } from "./types.ts";
 import { getExpectedRedirectStatus } from "./util.ts";
 
@@ -254,6 +255,7 @@ function produceResponseWithEventHeaders(res: Response) {
 }
 
 function stripBaseUrl(path: string) {
-  if (import.meta.env.BASE_URL === "/" || import.meta.env.BASE_URL === "") return path;
-  return path.slice(import.meta.env.BASE_URL.length);
+  const base =
+    import.meta.env.SERVER_BASE_URL || import.meta.env.BASE_URL || "/";
+  return stripPathBase(path, base);
 }

packages/start/src/server/strip-path-base.spec.ts

@@ -0,0 +1,26 @@
+import { describe, expect, it } from "vitest";
+
+import { stripPathBase } from "./strip-path-base.ts";
+
+describe("stripPathBase", () => {
+  it("leaves path unchanged when base is root or empty", () => {
+    expect(stripPathBase("/api/hello", "/")).toBe("/api/hello");
+    expect(stripPathBase("/api/hello", "")).toBe("/api/hello");
+  });
+
+  it("strips base without trailing slash", () => {
+    expect(stripPathBase("/myapp/api/hello", "/myapp")).toBe("/api/hello");
+  });
+
+  it("strips base with trailing slash", () => {
+    expect(stripPathBase("/myapp/api/hello", "/myapp/")).toBe("/api/hello");
+  });
+
+  it("maps exact base match to /", () => {
+    expect(stripPathBase("/myapp", "/myapp")).toBe("/");
+  });
+
+  it("does not strip when path is not under base", () => {
+    expect(stripPathBase("/other/api", "/myapp")).toBe("/other/api");
+  });
+});

packages/start/src/server/strip-path-base.ts

@@ -0,0 +1,7 @@
+/** Strip deploy base path from a URL pathname so API and page routes match file routes. */
+export function stripPathBase(path: string, base: string): string {
+  if (base === "/" || base === "") return path;
+  const normalizedBase = base.endsWith("/") ? base.slice(0, -1) : base;
+  if (normalizedBase === "") return path;
+  return path.startsWith(normalizedBase) ? path.slice(normalizedBase.length) || "/" : path;
+}