Derive API path from frontend config URL

Dockerfile

@@ -17,6 +17,7 @@ COPY upstream/HubFrontend/ ./
 COPY docker/hcaptcha-sitekey.patch /tmp/hcaptcha-sitekey.patch
 COPY docker/remove-analytics.mjs /tmp/remove-analytics.mjs
 COPY docker/replace-fallback-avatar.mjs /tmp/replace-fallback-avatar.mjs
+COPY docker/use-config-url-api-path.mjs /tmp/use-config-url-api-path.mjs
 
 RUN if grep -q 'sitekey="1788882d-3695-4807-abac-7d7166ec6325"' src/routes/auth/login.js; then \
         patch -p1 < /tmp/hcaptcha-sitekey.patch; \
@@ -29,6 +30,7 @@ RUN if grep -q 'sitekey="1788882d-3695-4807-abac-7d7166ec6325"' src/routes/auth/
 
 RUN node /tmp/remove-analytics.mjs
 RUN node /tmp/replace-fallback-avatar.mjs
+RUN node /tmp/use-config-url-api-path.mjs
 
 ARG ASSETS_BASE=""
 ARG VITE_USE_MULTIHUB=false
@@ -45,6 +47,13 @@ ENV ASSETS_BASE=${ASSETS_BASE} \
 RUN test -n "$VITE_HCAPTCHA_SITEKEY" \
     || (echo "VITE_HCAPTCHA_SITEKEY must be set." >&2; exit 1)
 
+RUN if [ "$VITE_USE_MULTIHUB" != "true" ]; then \
+        case "$VITE_CONFIG_URL" in \
+            */client/config/global|*/client/config/global/) ;; \
+            *) echo "VITE_CONFIG_URL must end with /client/config/global." >&2; exit 1 ;; \
+        esac; \
+    fi
+
 RUN npm run build
 
 # Electron entry points are not part of the web deployment.

README.md

@@ -40,8 +40,10 @@ as `VITE_HCAPTCHA_SITEKEY`. Set the related secret in the backend
 not a secret.
 
 Enable the `client-config` external plugin in the backend configuration. The
-backend `abbr` value must match the API prefix without its leading slash. For
-example, use `"abbr": "api"` with `"prefix": "/api"`.
+single-hub build derives the API base URL from `VITE_CONFIG_URL`. The backend
+`abbr` can contain the VTC abbreviation and does not have to match the API
+prefix. This deployment-specific behavior does not apply when
+`VITE_USE_MULTIHUB` is `true`.
 
 The frontend uses the Vite values during the image build. Rebuild the image after
 you change `.env`, including the hCaptcha site key.

docker/use-config-url-api-path.mjs

@@ -0,0 +1,50 @@
+import { readFileSync, writeFileSync } from "node:fs";
+
+const loaderPath = "src/components/loader.js";
+let source = readFileSync(loaderPath, "utf8");
+
+const upstreamApiPath = "`${webConfig.api_host}/${webConfig.abbr}`";
+const deploymentApiPath = "getApiPath(webConfig)";
+const helperMarker = "function getApiPath(webConfig) {";
+const insertBefore = "function sleep(ms) {";
+const occurrences = source.split(upstreamApiPath).length - 1;
+
+if (occurrences === 3 && !source.includes(helperMarker)) {
+    const helper = `function getApiPath(webConfig) {
+  if (import.meta.env.VITE_USE_MULTIHUB == "true") {
+    return \`${upstreamApiPath.slice(1, -1)}\`;
+  }
+
+  const configUrl = new URL(import.meta.env.VITE_CONFIG_URL);
+  const endpoint = "/client/config/global";
+  const pathname = configUrl.pathname.replace(/\\/+$/, "");
+  if (!pathname.endsWith(endpoint)) {
+    throw new Error("VITE_CONFIG_URL must end with /client/config/global.");
+  }
+
+  configUrl.pathname = pathname.slice(0, -endpoint.length) || "/";
+  configUrl.search = "";
+  configUrl.hash = "";
+  return configUrl.toString().replace(/\\/$/, "");
+}
+
+`;
+
+    if (!source.includes(insertBefore)) {
+        throw new Error("Cannot locate the API path helper insertion point.");
+    }
+
+    source = source.replace(insertBefore, helper + insertBefore);
+    source = source.replaceAll(upstreamApiPath, deploymentApiPath);
+    console.log("Use VITE_CONFIG_URL as the single-hub API path source.");
+} else if (occurrences === 0 && !/api_host[^;\n]{0,80}abbr/.test(source)) {
+    console.log("Upstream does not contain the known API path dependency; skip the patch.");
+} else {
+    throw new Error(`Unsupported upstream API path implementation (${occurrences} known references).`);
+}
+
+if (source.includes(upstreamApiPath) && !source.includes("VITE_USE_MULTIHUB")) {
+    throw new Error("The upstream API path dependency remains without a multihub fallback.");
+}
+
+writeFileSync(loaderPath, source);