ensure syslog parser gets an EOF-terminated reader on udp receive (#5297

)

Co-authored-by: Robert Fratto <[email protected]>

CHANGELOG.md

@@ -96,6 +96,8 @@ Main (unreleased)
 
 - Mark `password` argument of `loki.source.kafka` as a `secret` rather than a `string`. (@harsiddhdave44)
 
+- Fixed a bug where UDP syslog messages were never processed (@joshuapare)
+
 ### Enhancements
 
 - The `loki.write` WAL now has snappy compression enabled by default. (@thepalbi)
@@ -122,7 +124,7 @@ Main (unreleased)
 
 - Support clustering in `loki.source.podlogs` (@rfratto).
 
-- Adds new metrics (`mssql_server_total_memory_bytes`, `mssql_server_target_memory_bytes`, 
+- Adds new metrics (`mssql_server_total_memory_bytes`, `mssql_server_target_memory_bytes`,
   and `mssql_available_commit_memory_bytes`) for `mssql` integration.
 
 v0.37.3 (2023-10-26)

component/loki/source/syslog/internal/syslogtarget/transport.go

@@ -5,6 +5,7 @@ package syslogtarget
 // to other loki components.
 
 import (
+	"bytes"
 	"context"
 	"crypto/tls"
 	"crypto/x509"
@@ -430,16 +431,32 @@ func (t *UDPTransport) handleRcv(c *ConnPipe) {
 	defer t.openConnections.Done()
 
 	lbs := t.connectionLabels(c.addr.String())
-	err := syslogparser.ParseStream(c, func(result *syslog.Result) {
-		if err := result.Error; err != nil {
-			t.handleMessageError(err)
-		} else {
-			t.handleMessage(lbs.Copy(), result.Message)
+
+	for {
+		datagram := make([]byte, t.maxMessageLength())
+		n, err := c.Read(datagram)
+		if err != nil {
+			if err == io.EOF {
+				break
+			}
+
+			level.Warn(t.logger).Log("msg", "error reading from pipe", "err", err)
+			continue
 		}
-	}, t.maxMessageLength())
 
-	if err != nil {
-		level.Warn(t.logger).Log("msg", "error parsing syslog stream", "err", err)
+		r := bytes.NewReader(datagram[:n])
+
+		err = syslogparser.ParseStream(r, func(result *syslog.Result) {
+			if err := result.Error; err != nil {
+				t.handleMessageError(err)
+			} else {
+				t.handleMessage(lbs.Copy(), result.Message)
+			}
+		}, t.maxMessageLength())
+
+		if err != nil {
+			level.Warn(t.logger).Log("msg", "error parsing syslog stream", "err", err)
+		}
 	}
 }