Race condition in batching leading to lost logs

[guifel]

In batching mode, clearBatch is being called after the post request:

winston-loki/src/batcher.js

Line 198 in 67e5fdf

logEntry === undefined && this.clearBatch()

Logs that came in while the post request is pending will be lost. clearBatch needs to be called before.

[guifel]

A year later the issue is still around. This is the patch I have been using ever since:

diff --git a/node_modules/winston-loki/src/batcher.js b/node_modules/winston-loki/src/batcher.js
index 5659320..879ccae 100644
--- a/node_modules/winston-loki/src/batcher.js
+++ b/node_modules/winston-loki/src/batcher.js
@@ -250,17 +250,18 @@ class Batcher {
           }
         }
 
+        const savedBatchStreams = this.batch.streams
+        logEntry === undefined && this.clearBatch()
+
         // Send the data to Grafana Loki
         req.post(this.url, this.contentType, this.options.headers, reqBody, this.options.timeout)
           .then(() => {            
-            // No need to clear the batch if batching is disabled
-            logEntry === undefined && this.clearBatch()
             this.batchSent()
             resolve()
           })
           .catch(err => {
-            // Clear the batch on error if enabled
-            this.options.clearOnError && this.clearBatch()
+            // Revert clear batch for the logs to be sent on the next iteration
+            this.batch.streams = savedBatchStreams
             
             this.options.onConnectionError !== undefined && this.options.onConnectionError(err)