Omit adding the osd-version header when the Fetch request was expli…

…citly asked to not prepend the `basePath`

Fixes #3277

Signed-off-by: Miki <miki@amazon.com>

src/core/public/http/fetch.ts

@@ -31,6 +31,7 @@
 import { omitBy } from 'lodash';
 import { format } from 'url';
 import { BehaviorSubject } from 'rxjs';
+import { isRelativeUrl } from '@osd/std';
 
 import {
   IBasePath,
@@ -144,7 +145,6 @@ export class Fetch {
       headers: removedUndefined({
         'Content-Type': 'application/json',
         ...options.headers,
-        'osd-version': this.params.opensearchDashboardsVersion,
       }),
     };
 
@@ -158,6 +158,16 @@ export class Fetch {
       fetchOptions.headers['osd-system-request'] = 'true';
     }
 
+    /* `osd-version` is used on the server-side to make sure that an incoming request originated from a front-end
+     * of the same version; see core/server/http/lifecycle_handlers.ts
+     *
+     * If url equals `basePath,  starts with `basePath` + '/', or is relative, add `osd-version` header.
+     */
+    const basePath = this.params.basePath.get();
+    if (isRelativeUrl(url) || url === basePath || url.startsWith(`${basePath}/`)) {
+      fetchOptions.headers['osd-version'] = this.params.opensearchDashboardsVersion;
+    }
+
     return new Request(url, fetchOptions as RequestInit);
   }