[Transform] extract error message from the root cause

x-pack/plugins/transform/server/routes/api/error_utils.ts

@@ -109,7 +109,9 @@ function extractCausedByChain(
  * @return Object Boom error response
  */
 export function wrapEsError(err: any, statusCodeToMessageMap: Record<string, any> = {}) {
-  const { statusCode, body } = err;
+  const {
+    meta: { body, statusCode },
+  } = err;
 
   const {
     error: {
@@ -130,6 +132,12 @@ export function wrapEsError(err: any, statusCodeToMessageMap: Record<string, any
 
     // @ts-expect-error cause is not defined on payload type
     boomError.output.payload.cause = causedByChain.length ? causedByChain : defaultCause;
+
+    // Set error message based on the root cause
+    if (root_cause?.[0]) {
+      boomError.message = extractErrorMessage(root_cause[0]);
+    }
+
     return boomError;
   }
 
@@ -138,3 +146,28 @@ export function wrapEsError(err: any, statusCodeToMessageMap: Record<string, any
   const message = statusCodeToMessageMap[statusCode];
   return new Boom(message, { statusCode });
 }
+
+interface EsError {
+  type: string;
+  reason: string;
+  line?: number;
+  col?: number;
+}
+
+/**
+ * Returns an error message based on the root cause
+ */
+function extractErrorMessage({ type, reason, line, col }: EsError): string {
+  let message = `[${type}] ${reason}`;
+
+  if (line !== undefined && col !== undefined) {
+    message +=
+      ', ' +
+      i18n.translate('xpack.transform.models.transformService.withColAndLineMessage', {
+        defaultMessage: 'with line={line} & col={col}',
+        values: { line, col },
+      });
+  }
+
+  return message;
+}

x-pack/test/api_integration/apis/transform/transforms_preview.ts

@@ -77,7 +77,7 @@ export default ({ getService }: FtrProviderContext) => {
         .expect(400);
 
       expect(body.message).to.eql(
-        '[parsing_exception] Unknown aggregation type [value_countt] did you mean [value_count]?, with { line=1 & col=43 }'
+        '[parsing_exception] Unknown aggregation type [value_countt] did you mean [value_count]?, with line=1 & col=43'
       );
     });