add copy by count bytes && io.EOF

Author: markus621

ioutils.go

@@ -7,6 +7,7 @@ package ioutils
 
 import (
 	"bytes"
+	"fmt"
 	"io"
 
 	"go.osspkg.com/errors"
@@ -108,3 +109,24 @@ func WriteBytes(v io.Writer, b []byte, divide string) error {
 	}
 	return nil
 }
+
+const copyBufferSize = 512
+
+func Copy(w io.Writer, r io.Reader) (int, error) {
+	n := 0
+	buff := make([]byte, copyBufferSize)
+	for {
+		m, err1 := r.Read(buff)
+		if m < 0 {
+			return 0, fmt.Errorf("reader err: negative read bytes")
+		}
+		n += m
+		_, err2 := w.Write(buff[:m])
+		if err2 != nil {
+			return 0, fmt.Errorf("writer err: %w", err2)
+		}
+		if m == 0 || m < copyBufferSize || errors.Is(err1, io.EOF) {
+			return n, nil
+		}
+	}
+}

ioutils_test.go

@@ -11,6 +11,7 @@ import (
 	"reflect"
 	"testing"
 
+	"go.osspkg.com/casecheck"
 	"go.osspkg.com/errors"
 )
 
@@ -103,3 +104,15 @@ func TestUnit_ReadAll(t *testing.T) {
 		})
 	}
 }
+
+func TestUnit_Copy(t *testing.T) {
+	b := make([]byte, 521, 1024)
+	in := bytes.NewBuffer(b)
+	out := bytes.NewBuffer(nil)
+	n, err := Copy(out, in)
+	casecheck.NoError(t, err)
+	casecheck.Equal(t, 521, n)
+	bb, err := io.ReadAll(out)
+	casecheck.NoError(t, err)
+	casecheck.Equal(t, 521, len(bb))
+}