Resolve "Sharing Plattform: Prüfung: Gitlab Login für Simon in Produktion funktioniert nicht zuverlässig."

Related to #501 (closed)

src/main/java/at/ac/uibk/gitsearch/config/EduSharingApiConfiguration.java

@@ -3,6 +3,7 @@ package at.ac.uibk.gitsearch.config;
 import at.ac.uibk.gitsearch.edu_sharing.model.Authority;
 import at.ac.uibk.gitsearch.properties.ApplicationProperties;
 import at.ac.uibk.gitsearch.service.edu_sharing.EduSharingConfiguration;
+import at.ac.uibk.gitsearch.service.edu_sharing.EduSharingUnavailableException;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.beans.factory.annotation.Autowired;
@@ -64,6 +65,21 @@ public class EduSharingApiConfiguration {
       .builder()
       .baseUrl(eduSharingUrl)
       .filter(new EduSharingLogger())
+      .filter((request, next) ->
+        next
+          .exchange(request)
+          .flatMap(response -> {
+            if (response.statusCode().value() == 503) {
+              return response
+                .bodyToMono(String.class)
+                .flatMap(errorBody -> {
+                  return Mono.error(new EduSharingUnavailableException("Error response: " + errorBody));
+                });
+            } else {
+              return Mono.just(response);
+            }
+          })
+      )
       .defaultHeaders(header -> header.setBasicAuth(user, password))
       .build();
   }