auto tls (#3856)

internal/fileutil/fileutil.go

@@ -3,7 +3,10 @@
 package fileutil
 
 import (
+	"bytes"
 	"errors"
+	"fmt"
+	"io"
 	"os"
 )
 
@@ -46,3 +49,37 @@ func Getwd() string {
 	}
 	return p
 }
+
+// ReadFileUpTo reads file up to given size
+// it returns an error if file is larger than allowed maximum
+func ReadFileUpTo(fname string, maxSize int64) ([]byte, error) {
+	var buf bytes.Buffer
+	if err := CopyFileUpTo(&buf, fname, maxSize); err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}
+
+// CopyFileUpTo copies content of the file up to maxBytes
+// it returns an error if file is larger than allowed maximum
+func CopyFileUpTo(dst io.Writer, fname string, maxBytes int64) error {
+	fd, err := os.Open(fname)
+	if err != nil {
+		return fmt.Errorf("open %s: %w", fname, err)
+	}
+	defer func() { _ = fd.Close() }()
+
+	fi, err := fd.Stat()
+	if err != nil {
+		return fmt.Errorf("stat %s: %w", fname, err)
+	}
+	if fi.Size() > maxBytes {
+		return fmt.Errorf("file %s size %d > max %d", fname, fi.Size(), maxBytes)
+	}
+
+	if _, err := io.Copy(dst, fd); err != nil {
+		return fmt.Errorf("read %s: %w", fname, err)
+	}
+
+	return nil
+}