testutils/testwriter/limited.go

// Copyright (c) 2015 Uber Technologies, Inc.

// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

package testwriter

import (
	"errors"
	"io"
)

// ErrOutOfSpace is returned by Limited reader when it is out of bytes.
var ErrOutOfSpace = errors.New("out of space")

type writerFunc func([]byte) (int, error)

func (f writerFunc) Write(p []byte) (n int, err error) {
	return f(p)
}

// Limited returns an io.Writer that will only accept n bytes.
// All further calls will cause an error.
func Limited(n int) io.Writer {
	return writerFunc(func(p []byte) (int, error) {
		if n < len(p) {
			retN := n
			n = 0
			return retN, ErrOutOfSpace
		}

		n -= len(p)
		return len(p), nil
	})
}