[chore] refactore carbonexporter to handle errors, use generic interf…

…aces (open-telemetry#29885)

Signed-off-by: Bogdan Drutu <bogdandrutu@gmail.com>

exporter/carbonexporter/exporter.go

@@ -5,21 +5,23 @@ package carbonexporter // import "github.com/open-telemetry/opentelemetry-collec
 
 import (
 	"context"
+	"io"
 	"net"
 	"sync"
 	"time"
 
 	"go.opentelemetry.io/collector/exporter"
 	"go.opentelemetry.io/collector/exporter/exporterhelper"
 	"go.opentelemetry.io/collector/pdata/pmetric"
+	"go.uber.org/multierr"
 
 	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/resourcetotelemetry"
 )
 
 // newCarbonExporter returns a new Carbon exporter.
 func newCarbonExporter(cfg *Config, set exporter.CreateSettings) (exporter.Metrics, error) {
 	sender := carbonSender{
-		connPool: newTCPConnPool(cfg.Endpoint, cfg.Timeout),
+		writer: newTCPConnPool(cfg.Endpoint, cfg.Timeout),
 	}
 
 	exp, err := exporterhelper.NewMetricsExporter(
@@ -42,13 +44,13 @@ func newCarbonExporter(cfg *Config, set exporter.CreateSettings) (exporter.Metri
 // connections into an implementations of exporterhelper.PushMetricsData so
 // the exporter can leverage the helper and get consistent observability.
 type carbonSender struct {
-	connPool *connPool
+	writer io.WriteCloser
 }
 
 func (cs *carbonSender) pushMetricsData(_ context.Context, md pmetric.Metrics) error {
 	lines := metricDataToPlaintext(md)
 
-	if _, err := cs.connPool.Write([]byte(lines)); err != nil {
+	if _, err := cs.writer.Write([]byte(lines)); err != nil {
 		// Use the sum of converted and dropped since the write failed for all.
 		return err
 	}
@@ -57,8 +59,7 @@ func (cs *carbonSender) pushMetricsData(_ context.Context, md pmetric.Metrics) e
 }
 
 func (cs *carbonSender) Shutdown(context.Context) error {
-	cs.connPool.Close()
-	return nil
+	return cs.writer.Close()
 }
 
 // connPool is a very simple implementation of a pool of net.TCPConn instances.
@@ -72,36 +73,25 @@ func (cs *carbonSender) Shutdown(context.Context) error {
 // unused connections as that was the case on the prior art mentioned above.
 type connPool struct {
 	mtx      sync.Mutex
-	conns    []*net.TCPConn
+	conns    []net.Conn
 	endpoint string
 	timeout  time.Duration
 }
 
 func newTCPConnPool(
 	endpoint string,
 	timeout time.Duration,
-) *connPool {
+) io.WriteCloser {
 	return &connPool{
 		endpoint: endpoint,
 		timeout:  timeout,
 	}
 }
 
 func (cp *connPool) Write(bytes []byte) (int, error) {
-	var conn *net.TCPConn
+	var conn net.Conn
 	var err error
 
-	// The deferred function below is what puts back connections on the pool.
-	defer func() {
-		if err == nil {
-			cp.mtx.Lock()
-			cp.conns = append(cp.conns, conn)
-			cp.mtx.Unlock()
-		} else if conn != nil {
-			conn.Close()
-		}
-	}()
-
 	start := time.Now()
 	cp.mtx.Lock()
 	lastIdx := len(cp.conns) - 1
@@ -116,6 +106,18 @@ func (cp *connPool) Write(bytes []byte) (int, error) {
 		}
 	}
 
+	// The deferred function below is what puts back connections on the pool if no error.
+	defer func() {
+		if err != nil {
+			// err already not nil, so will not influence retry logic because of the connection close.
+			err = multierr.Append(err, conn.Close())
+			return
+		}
+		cp.mtx.Lock()
+		cp.conns = append(cp.conns, conn)
+		cp.mtx.Unlock()
+	}()
+
 	// There is no way to do a call equivalent to recvfrom with an empty buffer
 	// to check if the connection was terminated (if the size of the buffer is
 	// 0 the Read call doesn't call lower level). So due to buffer sizes it is
@@ -144,20 +146,22 @@ func (cp *connPool) Write(bytes []byte) (int, error) {
 	return n, err
 }
 
-func (cp *connPool) Close() {
+func (cp *connPool) Close() error {
 	cp.mtx.Lock()
 	defer cp.mtx.Unlock()
 
+	var errs error
 	for _, conn := range cp.conns {
-		conn.Close()
+		errs = multierr.Append(errs, conn.Close())
 	}
 	cp.conns = nil
+	return errs
 }
 
-func (cp *connPool) createTCPConn() (*net.TCPConn, error) {
+func (cp *connPool) createTCPConn() (net.Conn, error) {
 	c, err := net.DialTimeout("tcp", cp.endpoint, cp.timeout)
 	if err != nil {
 		return nil, err
 	}
-	return c.(*net.TCPConn), err
+	return c, err
 }

exporter/carbonexporter/go.mod

@@ -12,6 +12,7 @@ require (
 	go.opentelemetry.io/collector/exporter v0.91.0
 	go.opentelemetry.io/collector/pdata v1.0.0
 	go.opentelemetry.io/collector/semconv v0.91.0
+	go.uber.org/multierr v1.11.0
 )
 
 require (
@@ -40,7 +41,6 @@ require (
 	go.opentelemetry.io/otel v1.21.0 // indirect
 	go.opentelemetry.io/otel/metric v1.21.0 // indirect
 	go.opentelemetry.io/otel/trace v1.21.0 // indirect
-	go.uber.org/multierr v1.11.0 // indirect
 	go.uber.org/zap v1.26.0 // indirect
 	golang.org/x/net v0.18.0 // indirect
 	golang.org/x/sys v0.15.0 // indirect