Fix replication with context

The normal connection context timeout cancels the current query. That isn't
appropriate for a replication connection.

replication.go

@@ -270,16 +270,43 @@ func (rc *ReplicationConn) readReplicationMessage() (r *ReplicationMessage, err
 //
 // This returns the context error when there is no replication message before
 // the context is canceled.
-func (rc *ReplicationConn) WaitForReplicationMessage(ctx context.Context) (r *ReplicationMessage, err error) {
-	err = rc.c.initContext(ctx)
-	if err != nil {
-		return nil, err
+func (rc *ReplicationConn) WaitForReplicationMessage(ctx context.Context) (*ReplicationMessage, error) {
+	select {
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	default:
 	}
-	defer func() {
-		err = rc.c.termContext(err)
+
+	go func() {
+		select {
+		case <-ctx.Done():
+			if err := rc.c.conn.SetDeadline(time.Now()); err != nil {
+				rc.Close() // Close connection if unable to set deadline
+				return
+			}
+			rc.c.closedChan <- ctx.Err()
+		case <-rc.c.doneChan:
+		}
 	}()
 
-	return rc.readReplicationMessage()
+	r, opErr := rc.readReplicationMessage()
+
+	var err error
+	select {
+	case err = <-rc.c.closedChan:
+		if err := rc.c.conn.SetDeadline(time.Time{}); err != nil {
+			rc.Close() // Close connection if unable to disable deadline
+			return nil, err
+		}
+
+		if opErr == nil {
+			err = nil
+		}
+	case rc.c.doneChan <- struct{}{}:
+		err = opErr
+	}
+
+	return r, err
 }
 
 func (rc *ReplicationConn) sendReplicationModeQuery(sql string) (*Rows, error) {

replication_test.go

@@ -3,12 +3,13 @@ package pgx_test
 import (
 	"context"
 	"fmt"
-	"github.com/jackc/pgx"
 	"reflect"
 	"strconv"
 	"strings"
 	"testing"
 	"time"
+
+	"github.com/jackc/pgx"
 )
 
 // This function uses a postgresql 9.6 specific column
@@ -47,14 +48,19 @@ func TestSimpleReplicationConnection(t *testing.T) {
 	}
 
 	conn := mustConnect(t, *replicationConnConfig)
-	defer closeConn(t, conn)
+	defer func() {
+		// Ensure replication slot is destroyed, but don't check for errors as it
+		// should have already been destroyed.
+		conn.Exec("select pg_drop_replication_slot('pgx_test')")
+		closeConn(t, conn)
+	}()
 
 	replicationConn := mustReplicationConnect(t, *replicationConnConfig)
 	defer closeReplicationConn(t, replicationConn)
 
 	err = replicationConn.CreateReplicationSlot("pgx_test", "test_decoding")
 	if err != nil {
-		t.Logf("replication slot create failed: %v", err)
+		t.Fatalf("replication slot create failed: %v", err)
 	}
 
 	// Do a simple change so we can get some wal data