Fix WS connection getting closed

app/common/UserAPI.ts

@@ -755,7 +755,7 @@ export class UserAPIImpl extends BaseAPI implements UserAPI {
       method: 'GET',
       credentials: 'include'
     });
-    return getDocWorkerUrl(this._homeUrl, json);
+    return getPublicDocWorkerUrl(this._homeUrl, json);
   }
 
   public async getWorkerAPI(key: string): Promise<DocWorkerAPI> {
@@ -1112,6 +1112,22 @@ export class DocAPIImpl extends BaseAPI implements DocAPI {
   }
 }
 
+interface DocWorkerInfo {
+  docWorkerUrl: string|null;
+  internalDocWorkerUrl: string|null;
+  selfPrefix?: string;
+}
+
+function getUrlFromPrefix(homeUrl: string, prefix?: string) {
+  if (!prefix) {
+    // This should never happen.
+    throw new Error('missing selfPrefix for docWorkerUrl');
+  }
+  const url = new URL(homeUrl);
+  url.pathname = prefix + url.pathname;
+  return url.href;
+}
+
 /**
  * Get a docWorkerUrl from information returned from backend. When the backend
  * is fully configured, and there is a pool of workers, this is straightforward,
@@ -1120,20 +1136,32 @@ export class DocAPIImpl extends BaseAPI implements DocAPI {
  * use the homeUrl of the backend, with extra path prefix information
  * given by selfPrefix. At the time of writing, the selfPrefix contains a
  * doc-worker id, and a tag for the codebase (used in consistency checks).
+ *
+ * @param {string} homeUrl
+ * @param {object} docWorkerInfo
+ * @param {string} docWorkerInfo.docWorkerUrl The public doc Worker URL
+ * @param {string} docWorkerInfo.internalDocWorkerUrl The internal doc Worker URL
+ * @param {string|undefined} docWorkerInfo.selfPrefix
+ * @param {string} urlType The type of doc worker url to extract from the docWorkerInfo
  */
-export function getDocWorkerUrl(homeUrl: string, docWorkerInfo: {
-  docWorkerUrl: string|null,
-  internalDocWorkerUrl: string|null,
-  selfPrefix?: string,
-}): string {
-  if (!docWorkerInfo.docWorkerUrl) {
-    if (!docWorkerInfo.selfPrefix) {
-      // This should never happen.
-      throw new Error('missing selfPrefix for docWorkerUrl');
-    }
-    const url = new URL(homeUrl);
-    url.pathname = docWorkerInfo.selfPrefix + url.pathname;
-    return url.href;
-  }
-  return docWorkerInfo.internalDocWorkerUrl || docWorkerInfo.docWorkerUrl;
+export function getPublicDocWorkerUrl(homeUrl: string, docWorkerInfo: DocWorkerInfo) {
+  const publicUrl = docWorkerInfo.docWorkerUrl;
+  return publicUrl || getUrlFromPrefix(homeUrl, docWorkerInfo.selfPrefix);
+}
+
+/**
+ * @see getPublicDocWorkerUrl
+ * Like getPublicDocWorkerUrl but returns the URL resolvable internally (behind a Reverse Proxy).
+ * Especially useful when and where the public url cannot be resolved.
+ *
+ * @param {string} homeUrl
+ * @param {object} docWorkerInfo
+ * @param {string} docWorkerInfo.docWorkerUrl The public doc Worker URL
+ * @param {string} docWorkerInfo.internalDocWorkerUrl The internal doc Worker URL
+ * @param {string|undefined} docWorkerInfo.selfPrefix
+ * @param {string} urlType The type of doc worker url to extract from the docWorkerInfo
+ */
+export function getInternalDocWorkerUrl(homeUrl: string, docWorkerInfo: DocWorkerInfo) {
+  const internalUrl = docWorkerInfo.internalDocWorkerUrl;
+  return internalUrl || getUrlFromPrefix(homeUrl, docWorkerInfo.selfPrefix);
 }

app/server/lib/uploads.ts

@@ -1,7 +1,7 @@
 import {ApiError} from 'app/common/ApiError';
 import {InactivityTimer} from 'app/common/InactivityTimer';
 import {FetchUrlOptions, FileUploadResult, UPLOAD_URL_PATH, UploadResult} from 'app/common/uploads';
-import {getDocWorkerUrl} from 'app/common/UserAPI';
+import {getInternalDocWorkerUrl} from 'app/common/UserAPI';
 import {getAuthorizedUserId, getTransitiveHeaders, getUserId, isSingleUserMode,
         RequestWithLogin} from 'app/server/lib/Authorizer';
 import {expressWrap} from 'app/server/lib/expressWrap';
@@ -415,7 +415,7 @@ export async function fetchDoc(server: GristServer, docId: string, req: Request,
   const fetchUrl = new URL(`/api/worker/${docId}`, homeUrl);
   const response: FetchResponse = await Deps.fetch(fetchUrl.href, {headers});
   await _checkForError(response);
-  const docWorkerUrl = getDocWorkerUrl(server.getOwnUrl(), await response.json());
+  const docWorkerUrl = getInternalDocWorkerUrl(server.getOwnUrl(), await response.json());
   // Download the document, in full or as a template.
   const url = new URL(`api/docs/${docId}/download?template=${Number(template)}`,
                       docWorkerUrl.replace(/\/*$/, '/'));