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reader.go
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reader.go
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// @license
// Copyright 2023 Dynatrace LLC
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package rest
import (
"bytes"
"fmt"
"io"
)
// reusableReader is a reader that can be used multiple times to from an io.ReadCloser
type reusableReader struct {
io.Reader
readBuf *bytes.Buffer
backBuf *bytes.Buffer
}
func (r reusableReader) Close() error {
return nil
}
func ReusableReader(r io.ReadCloser) (io.ReadCloser, error) {
if r == nil {
return r, nil
}
readBuf := bytes.Buffer{}
if _, err := readBuf.ReadFrom(r); err != nil {
return nil, err
}
backBuf := bytes.Buffer{}
return reusableReader{
io.TeeReader(&readBuf, &backBuf),
&readBuf,
&backBuf,
}, nil
}
func (r reusableReader) Read(p []byte) (int, error) {
n, err := r.Reader.Read(p)
if err == io.EOF {
if err := r.reset(); err != nil {
return n, fmt.Errorf("failed to reset reader after reaching EOF: %w", err)
}
}
return n, err
}
func (r reusableReader) reset() error {
if _, err := io.Copy(r.readBuf, r.backBuf); err != nil {
return err
}
return nil
}