fix: harden GHE URL detection and extract shared GitHub helpers

server/src/services/github-fetch.ts

@@ -0,0 +1,25 @@
+import { unprocessable } from "../errors.js";
+
+function isGitHubDotCom(hostname: string) {
+  const h = hostname.toLowerCase();
+  return h === "github.com" || h === "www.github.com";
+}
+
+export function gitHubApiBase(hostname: string) {
+  return isGitHubDotCom(hostname) ? "https://api.github.com" : `https://${hostname}/api/v3`;
+}
+
+export function resolveRawGitHubUrl(hostname: string, owner: string, repo: string, ref: string, filePath: string) {
+  const p = filePath.replace(/^\/+/, "");
+  return isGitHubDotCom(hostname)
+    ? `https://raw.githubusercontent.com/${owner}/${repo}/${ref}/${p}`
+    : `https://${hostname}/raw/${owner}/${repo}/${ref}/${p}`;
+}
+
+export async function ghFetch(url: string, init?: RequestInit): Promise<Response> {
+  try {
+    return await fetch(url, init);
+  } catch {
+    throw unprocessable(`Could not connect to ${new URL(url).hostname} — ensure the URL points to a GitHub or GitHub Enterprise instance`);
+  }
+}