added a test case for issue gogo#587. check that we do not re-alloc a…

… buffer when we are reading a msg of the same size (gogo#592)

io/uint32_test.go

@@ -4,6 +4,7 @@ import (
 	"encoding/binary"
 	"io/ioutil"
 	"math/rand"
+	"reflect"
 	"testing"
 	"time"
 
@@ -36,3 +37,37 @@ func BenchmarkUint32DelimWriterFallback(b *testing.B) {
 		}
 	}
 }
+
+// Writing the same size messaged twice should not cause another
+// reader buffer allocation
+func TestUint32SameSizeNoAlloc(t *testing.T) {
+	buf := newBuffer()
+	writer := io.NewUint32DelimitedWriter(buf, binary.LittleEndian)
+	reader := io.NewUint32DelimitedReader(buf, binary.LittleEndian, 1024*1024)
+
+	err := writer.WriteMsg(&test.NinOptNative{Field15: []byte("numbercatinvention")})
+	if err != nil {
+		t.Fatal(err)
+	}
+	err = writer.WriteMsg(&test.NinOptNative{Field15: []byte("fastenselectionsky")})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := writer.Close(); err != nil {
+		t.Fatal(err)
+	}
+
+	msg := &test.NinOptNative{}
+	if err := reader.ReadMsg(msg); err != nil {
+		t.Fatal(err)
+	}
+	firstRead := reflect.ValueOf(reader).Elem().FieldByName("buf").Pointer()
+	if err := reader.ReadMsg(msg); err != nil {
+		t.Fatal(err)
+	}
+	secondRead := reflect.ValueOf(reader).Elem().FieldByName("buf").Pointer()
+
+	if firstRead != secondRead {
+		t.Fatalf("reader buf byte slice pointer did not stay the same after second same size read (%d != %d).", firstRead, secondRead)
+	}
+}