Signed trailers for signature v4 (#16484)

internal/ioutil/hardlimitreader.go

@@ -0,0 +1,56 @@
+// Copyright (c) 2015-2023 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+// Package ioutil implements some I/O utility functions which are not covered
+// by the standard library.
+package ioutil
+
+import (
+	"errors"
+	"io"
+)
+
+// ErrOverread is returned to the reader when the hard limit of HardLimitReader is exceeded.
+var ErrOverread = errors.New("input provided more bytes than specified")
+
+// HardLimitReader returns a Reader that reads from r
+// but returns an error if the source provides more data than allowed.
+// This means the source *will* be overread unless EOF is returned prior.
+// The underlying implementation is a *HardLimitedReader.
+// This will ensure that at most n bytes are returned and EOF is reached.
+func HardLimitReader(r io.Reader, n int64) io.Reader { return &HardLimitedReader{r, n} }
+
+// A HardLimitedReader reads from R but limits the amount of
+// data returned to just N bytes. Each call to Read
+// updates N to reflect the new amount remaining.
+// Read returns EOF when N <= 0 or when the underlying R returns EOF.
+type HardLimitedReader struct {
+	R io.Reader // underlying reader
+	N int64     // max bytes remaining
+}
+
+func (l *HardLimitedReader) Read(p []byte) (n int, err error) {
+	if l.N < 0 {
+		return 0, ErrOverread
+	}
+	n, err = l.R.Read(p)
+	l.N -= int64(n)
+	if l.N < 0 {
+		return 0, ErrOverread
+	}
+	return
+}