[Security Solutions][Detection Engine] Fixes critical bug with error reporting that was doing a throw (#81549)

## Summary

Fixes an error where it was expecting some data structures on an ES error but there wasn't in some cases.

Before:
<img width="2246" alt="Screen Shot 2020-10-22 at 1 04 35 PM" src="https://user-images.githubusercontent.com/1151048/96940994-7d98a780-148e-11eb-93bd-77e4adf42896.png">

After:
<img width="2229" alt="Screen Shot 2020-10-22 at 5 45 31 PM" src="https://user-images.githubusercontent.com/1151048/96941005-84bfb580-148e-11eb-989f-1dae6892e641.png">

- [x] [Unit or functional tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html) were updated or added to match the most common scenarios

Author: FrankHassanabad

x-pack/plugins/security_solution/server/lib/detection_engine/signals/single_search_after.test.ts

@@ -105,7 +105,9 @@ describe('singleSearchAfter', () => {
       timestampOverride: undefined,
       buildRuleMessage,
     });
-    expect(searchErrors).toEqual(['reason: some reason, type: some type, caused by: some reason']);
+    expect(searchErrors).toEqual([
+      'reason: "some reason" type: "some type" caused by reason: "some reason" caused by type: "some type"',
+    ]);
   });
   test('if singleSearchAfter works with a given sort id', async () => {
     const searchAfterSortId = '1234567891111';

x-pack/plugins/security_solution/server/lib/detection_engine/signals/utils.test.ts

@@ -878,7 +878,7 @@ describe('utils', () => {
       ];
       const createdErrors = createErrorsFromShard({ errors });
       expect(createdErrors).toEqual([
-        'reason: some reason, type: some type, caused by: some reason',
+        'reason: "some reason" type: "some type" caused by reason: "some reason" caused by type: "some type"',
       ]);
     });
 
@@ -917,8 +917,54 @@ describe('utils', () => {
       ];
       const createdErrors = createErrorsFromShard({ errors });
       expect(createdErrors).toEqual([
-        'reason: some reason, type: some type, caused by: some reason',
-        'reason: some reason 2, type: some type 2, caused by: some reason 2',
+        'reason: "some reason" type: "some type" caused by reason: "some reason" caused by type: "some type"',
+        'reason: "some reason 2" type: "some type 2" caused by reason: "some reason 2" caused by type: "some type 2"',
+      ]);
+    });
+
+    test('You can have missing values for the shard errors and get the expected output of an empty string', () => {
+      const errors: ShardError[] = [
+        {
+          shard: 1,
+          index: 'index-123',
+          node: 'node-123',
+          reason: {},
+        },
+      ];
+      const createdErrors = createErrorsFromShard({ errors });
+      expect(createdErrors).toEqual(['']);
+    });
+
+    test('You can have a single value for the shard errors and get expected output without extra spaces anywhere', () => {
+      const errors: ShardError[] = [
+        {
+          shard: 1,
+          index: 'index-123',
+          node: 'node-123',
+          reason: {
+            reason: 'some reason something went wrong',
+          },
+        },
+      ];
+      const createdErrors = createErrorsFromShard({ errors });
+      expect(createdErrors).toEqual(['reason: "some reason something went wrong"']);
+    });
+
+    test('You can have two values for the shard errors and get expected output with one space exactly between the two values', () => {
+      const errors: ShardError[] = [
+        {
+          shard: 1,
+          index: 'index-123',
+          node: 'node-123',
+          reason: {
+            reason: 'some reason something went wrong',
+            caused_by: { type: 'some type' },
+          },
+        },
+      ];
+      const createdErrors = createErrorsFromShard({ errors });
+      expect(createdErrors).toEqual([
+        'reason: "some reason something went wrong" caused by type: "some type"',
       ]);
     });
   });

x-pack/plugins/security_solution/server/lib/detection_engine/signals/utils.ts

@@ -511,7 +511,23 @@ export const getSignalTimeTuples = ({
  */
 export const createErrorsFromShard = ({ errors }: { errors: ShardError[] }): string[] => {
   return errors.map((error) => {
-    return `reason: ${error.reason.reason}, type: ${error.reason.caused_by.type}, caused by: ${error.reason.caused_by.reason}`;
+    const {
+      reason: {
+        reason,
+        type,
+        caused_by: { reason: causedByReason, type: causedByType } = {
+          reason: undefined,
+          type: undefined,
+        },
+      } = {},
+    } = error;
+
+    return [
+      ...(reason != null ? [`reason: "${reason}"`] : []),
+      ...(type != null ? [`type: "${type}"`] : []),
+      ...(causedByReason != null ? [`caused by reason: "${causedByReason}"`] : []),
+      ...(causedByType != null ? [`caused by type: "${causedByType}"`] : []),
+    ].join(' ');
   });
 };
 

x-pack/plugins/security_solution/server/lib/types.ts

@@ -48,21 +48,26 @@ export interface ShardsResponse {
   failures?: ShardError[];
 }
 
-export interface ShardError {
+/**
+ * This type is being very conservative with the partials to not expect anything to
+ * be guaranteed on the type as we don't have regular and proper types of ShardError.
+ * Once we do, remove this type for the regular ShardError type from the elastic library.
+ */
+export type ShardError = Partial<{
   shard: number;
   index: string;
   node: string;
-  reason: {
+  reason: Partial<{
     type: string;
     reason: string;
     index_uuid: string;
     index: string;
-    caused_by: {
+    caused_by: Partial<{
       type: string;
       reason: string;
-    };
-  };
-}
+    }>;
+  }>;
+}>;
 
 export interface SearchResponse<T> {
   took: number;