don't clobber error output, append worker output

src/worker.js

@@ -73,12 +73,15 @@ export default class Job extends events.EventEmitter {
   _failJob(job, msg) {
     this.debug(`Failing job ${job._id}`);
     const doc = {
-      status: jobStatuses.JOB_STATUS_FAILED,
+      status: jobStatuses.JOB_STATUS_FAILED
-      output: {
+    };
+
+    if (!job._source.output) {
+      doc.output = {
         content_type: 'text/plain',
         content: msg
-      }
+      };
-    };
+    }
 
     return this.client.update({
       index: job._index,
@@ -94,8 +97,57 @@ export default class Job extends events.EventEmitter {
   }
 
   _performJob(job) {
-    this.debug(`Performing job ${job._id}`);
+    this.debug(`Starting job ${job._id}`);
-    return Promise.reject('mock es failure');
+
+    return Bluebird.try(() => {
+      return this.workerFn(job._source.payload);
+    })
+    .then((output) => {
+      const unknownMime = false;
+      const docOutput = {};
+      if (typeof output === 'object' && output.content) {
+        docOutput.content = output.content;
+        docOutput.content_type = output.content_type || unknownMime;
+      } else {
+        docOutput.content = output || '';
+        docOutput.content_type = unknownMime;
+      }
+
+      const doc = {
+        status: jobStatuses.JOB_STATUS_COMPLETED,
+        output: docOutput
+      };
+
+      return this.client.update({
+        index: job._index,
+        type: job._type,
+        id: job._id,
+        version: job._version,
+        body: { doc }
+      })
+      .catch((err) => {
+        if (err.statusCode === 409) return false;
+        throw err;
+      });
+    }, (err) => {
+      console.error('err', err);
+      const doc = {
+        output: {
+          content_type: false,
+          content: err.toString()
+        }
+      };
+
+      return this.client.update({
+        index: job._index,
+        type: job._type,
+        id: job._id,
+        version: job._version,
+        body: { doc }
+      })
+      .catch(() => false)
+      .then(() => { throw err; });
+    });
   }
 
   _startJobPolling() {
@@ -138,7 +190,6 @@ export default class Job extends events.EventEmitter {
     .then((claimedJobs) => {
       if (claimedJobs.length !== 1) return;
       const job = claimedJobs[0];
-      this.debug(`Beginning work on ${job._id}`);
       return this._performJob(job);
     })
     .finally(() => this._startJobPolling());