From f00fb11977d10c05a2a0852d81ec6a4bd4163a90 Mon Sep 17 00:00:00 2001
From: nicklas dohrn <nicklas.dohrn@sap.com>
Date: Mon, 7 Oct 2024 09:25:58 +0200
Subject: [PATCH] First retry implementation

---
 src/pkg/egress/syslog/https.go            |  7 ++-
 src/pkg/egress/syslog/https_batch.go      | 16 +++++--
 src/pkg/egress/syslog/https_batch_test.go |  6 +++
 src/pkg/egress/syslog/retryer.go          | 52 +++++++++++++++++++++++
 src/pkg/egress/syslog/writer_factory.go   |  6 +++
 5 files changed, 79 insertions(+), 8 deletions(-)
 create mode 100644 src/pkg/egress/syslog/retryer.go

diff --git a/src/pkg/egress/syslog/https.go b/src/pkg/egress/syslog/https.go
index 581fb7776..d814e3dbd 100644
--- a/src/pkg/egress/syslog/https.go
+++ b/src/pkg/egress/syslog/https.go
@@ -43,7 +43,7 @@ func NewHTTPSWriter(
 	}
 }
 
-func (w *HTTPSWriter) sendHttpRequest(msg []byte, msgCount float64) error {
+func (w *HTTPSWriter) sendHttpRequest(msg []byte) error {
 	req := fasthttp.AcquireRequest()
 	req.SetRequestURI(w.url.String())
 	req.Header.SetMethod("POST")
@@ -63,8 +63,6 @@ func (w *HTTPSWriter) sendHttpRequest(msg []byte, msgCount float64) error {
 		return fmt.Errorf("syslog Writer: Post responded with %d status code", resp.StatusCode())
 	}
 
-	w.egressMetric.Add(msgCount)
-
 	return nil
 }
 
@@ -76,10 +74,11 @@ func (w *HTTPSWriter) Write(env *loggregator_v2.Envelope) error {
 	}
 
 	for _, msg := range msgs {
-		err = w.sendHttpRequest(msg, 1)
+		err = w.sendHttpRequest(msg)
 		if err != nil {
 			return err
 		}
+		w.egressMetric.Add(1)
 	}
 
 	return nil
diff --git a/src/pkg/egress/syslog/https_batch.go b/src/pkg/egress/syslog/https_batch.go
index 56bc55731..be79abaa4 100644
--- a/src/pkg/egress/syslog/https_batch.go
+++ b/src/pkg/egress/syslog/https_batch.go
@@ -15,6 +15,7 @@ const BATCHSIZE = 256 * 1024
 
 type HTTPSBatchWriter struct {
 	HTTPSWriter
+	*Retryer
 	msgs         chan []byte
 	batchSize    int
 	sendInterval time.Duration
@@ -27,6 +28,7 @@ func NewHTTPSBatchWriter(
 	tlsConf *tls.Config,
 	egressMetric metrics.Counter,
 	c *Converter,
+	retryer *Retryer,
 ) egress.WriteCloser {
 	client := httpClient(netConf, tlsConf)
 	binding.URL.Scheme = "https" // reset the scheme for usage to a valid http scheme
@@ -43,6 +45,7 @@ func NewHTTPSBatchWriter(
 		sendInterval: 1 * time.Second,
 		egrMsgCount:  0,
 		msgs:         make(chan []byte),
+		Retryer:      retryer,
 	}
 	go BatchWriter.startSender()
 	return BatchWriter
@@ -74,6 +77,13 @@ func (w *HTTPSBatchWriter) startSender() {
 		msgCount = 0
 		t.Reset(w.sendInterval)
 	}
+	sendBatch := func() {
+		err := w.Retryer.Retry(msgBatch.Bytes(), w.sendHttpRequest)
+		if err == nil {
+			w.egressMetric.Add(msgCount)
+		}
+		reset()
+	}
 	for {
 		select {
 		case msg := <-w.msgs:
@@ -84,14 +94,12 @@ func (w *HTTPSBatchWriter) startSender() {
 			} else {
 				msgCount++
 				if length >= w.batchSize {
-					w.sendHttpRequest(msgBatch.Bytes(), msgCount) //nolint:errcheck
-					reset()
+					sendBatch()
 				}
 			}
 		case <-t.C:
 			if msgBatch.Len() > 0 {
-				w.sendHttpRequest(msgBatch.Bytes(), msgCount) //nolint:errcheck
-				reset()
+				sendBatch()
 			}
 		}
 	}
diff --git a/src/pkg/egress/syslog/https_batch_test.go b/src/pkg/egress/syslog/https_batch_test.go
index 35789bcb6..149d05ab6 100644
--- a/src/pkg/egress/syslog/https_batch_test.go
+++ b/src/pkg/egress/syslog/https_batch_test.go
@@ -39,12 +39,18 @@ var _ = Describe("HTTPS_batch", func() {
 			"test-app-id",
 			"test-hostname",
 		)
+		retryer := syslog.NewBackoffRetryer(
+			b,
+			syslog.ExponentialDuration,
+			2,
+		)
 		writer = syslog.NewHTTPSBatchWriter(
 			b,
 			netConf,
 			skipSSLTLSConfig,
 			&metricsHelpers.SpyMetric{},
 			c,
+			retryer,
 		)
 	})
 
diff --git a/src/pkg/egress/syslog/retryer.go b/src/pkg/egress/syslog/retryer.go
new file mode 100644
index 000000000..5d8700af5
--- /dev/null
+++ b/src/pkg/egress/syslog/retryer.go
@@ -0,0 +1,52 @@
+package syslog
+
+import (
+	"log"
+	"time"
+
+	"code.cloudfoundry.org/loggregator-agent-release/src/pkg/egress"
+)
+
+// RetryWriter wraps a WriteCloser and will retry writes if the first fails.
+type Retryer struct {
+	retryDuration RetryDuration
+	maxRetries    int
+	binding       *URLBinding
+}
+
+func NewBackoffRetryer(
+	urlBinding *URLBinding,
+	retryDuration RetryDuration,
+	maxRetries int,
+) *Retryer {
+	return &Retryer{
+		retryDuration: retryDuration,
+		maxRetries:    maxRetries,
+		binding:       urlBinding,
+	}
+}
+
+// Write will retry writes unitl maxRetries has been reached.
+func (r *Retryer) Retry(message []byte, fn func(msg []byte) error) error {
+	logTemplate := "failed to write to %s, retrying in %s, err: %s"
+
+	var err error
+
+	for i := 0; i < r.maxRetries; i++ {
+		err = fn(message)
+		if err == nil {
+			return nil
+		}
+
+		if egress.ContextDone(r.binding.Context) {
+			return err
+		}
+
+		sleepDuration := r.retryDuration(i)
+		log.Printf(logTemplate, r.binding.URL.Host, sleepDuration, err)
+
+		time.Sleep(sleepDuration)
+	}
+
+	return err
+}
diff --git a/src/pkg/egress/syslog/writer_factory.go b/src/pkg/egress/syslog/writer_factory.go
index 8ec8249ab..43acf57a8 100644
--- a/src/pkg/egress/syslog/writer_factory.go
+++ b/src/pkg/egress/syslog/writer_factory.go
@@ -96,6 +96,11 @@ func (f WriterFactory) NewWriter(ub *URLBinding) (egress.WriteCloser, error) {
 	}
 	converter := NewConverter(o...)
 
+	retryer := NewBackoffRetryer(
+		ub,
+		ExponentialDuration,
+		maxRetries)
+
 	var w egress.WriteCloser
 	switch ub.URL.Scheme {
 	case "https":
@@ -113,6 +118,7 @@ func (f WriterFactory) NewWriter(ub *URLBinding) (egress.WriteCloser, error) {
 			tlsCfg,
 			egressMetric,
 			converter,
+			retryer,
 		)
 	case "syslog":
 		w = NewTCPWriter(