fix: prevent 1st Read() after record() to return 0 bytes

layer4/connection.go

@@ -77,7 +77,7 @@ func (cx *Connection) Read(p []byte) (n int, err error) {
 	// if there is a buffer we should read from, start
 	// with that; we only read from the underlying conn
 	// after the buffer has been "depleted"
-	if cx.bufReader != nil {
+	if cx.bufReader != nil && cx.buf.Len() > 0 { // buf len check to prevent first read from returning 0 bytes
 		n, err = cx.bufReader.Read(p)
 		if err == io.EOF {
 			cx.bufReader = nil

layer4/connection_test.go

@@ -0,0 +1,86 @@
+package layer4
+
+import (
+	"bytes"
+	"net"
+	"testing"
+)
+
+func TestConnection_RecordAndRewind(t *testing.T) {
+	in, out := net.Pipe()
+	defer in.Close()
+	defer out.Close()
+
+	cx := WrapConnection(out, &bytes.Buffer{})
+	defer cx.Close()
+
+	matcherData := []byte("foo")
+	consumeData := []byte("bar")
+
+	buf := make([]byte, len(matcherData))
+
+	go func() {
+		in.Write(matcherData)
+		in.Write(consumeData)
+	}()
+
+	// 1st matcher
+
+	cx.record()
+
+	n, err := cx.Read(buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != len(matcherData) {
+		t.Fatalf("expected to read %d bytes but got %d", len(matcherData), n)
+	}
+	if bytes.Compare(matcherData, buf) != 0 {
+		t.Fatalf("expected %s but received %s", matcherData, buf)
+	}
+
+	cx.rewind()
+
+	// 2nd matcher (reads same data)
+
+	cx.record()
+
+	n, err = cx.Read(buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != len(matcherData) {
+		t.Fatalf("expected to read %d bytes but got %d", len(matcherData), n)
+	}
+	if bytes.Compare(matcherData, buf) != 0 {
+		t.Fatalf("expected %s but received %s", matcherData, buf)
+	}
+
+	cx.rewind()
+
+	// 1st consumer (no record call)
+
+	n, err = cx.Read(buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != len(matcherData) {
+		t.Fatalf("expected to read %d bytes but got %d", len(matcherData), n)
+	}
+	if bytes.Compare(matcherData, buf) != 0 {
+		t.Fatalf("expected %s but received %s", matcherData, buf)
+	}
+
+	// 2nd consumer (reads other data)
+
+	n, err = cx.Read(buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != len(consumeData) {
+		t.Fatalf("expected to read %d bytes but got %d", len(consumeData), n)
+	}
+	if bytes.Compare(consumeData, buf) != 0 {
+		t.Fatalf("expected %s but received %s", consumeData, buf)
+	}
+}