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/*
* util.go - Various helpers used throughout fscrypt
*
* Copyright 2017 Google Inc.
* Author: Joe Richey (joerichey@google.com)
*
* 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 util contains useful components for simplifying Go code.
//
// The package contains common error types (errors.go) and functions for
// converting arrays to pointers.
package util
import (
"io"
"unsafe"
)
// ErrReader wraps an io.Reader, passing along calls to Read() until a read
// fails. Then, the error is stored, and all subsequent calls to Read() do
// nothing. This allows you to write code which has many subsequent reads and
// do all of the error checking at the end. For example:
//
// r := NewErrReader(reader)
// r.Read(foo)
// io.ReadFull(r, bar)
// if r.Err() != nil {
// // Handle error
// }
//
// Taken from https://blog.golang.org/errors-are-values by Rob Pike.
type ErrReader struct {
r io.Reader
err error
}
// NewErrReader creates an ErrReader which wraps the provided reader.
func NewErrReader(reader io.Reader) *ErrReader {
return &ErrReader{r: reader, err: nil}
}
// Read runs ReadFull on the wrapped reader if no errors have occurred.
// Otherwise, the previous error is just returned and no reads are attempted.
func (e *ErrReader) Read(p []byte) (n int, err error) {
if e.err == nil {
n, e.err = io.ReadFull(e.r, p)
}
return n, e.err
}
// Err returns the first encountered err (or nil if no errors occurred).
func (e *ErrReader) Err() error {
return e.err
}
// ErrWriter works exactly like ErrReader, except with io.Writer.
type ErrWriter struct {
w io.Writer
err error
}
// NewErrWriter creates an ErrWriter which wraps the provided reader.
func NewErrWriter(writer io.Writer) *ErrWriter {
return &ErrWriter{w: writer, err: nil}
}
// Write runs the wrapped writer's Write if no errors have occurred. Otherwise,
// the previous error is just returned and no writes are attempted.
func (e *ErrWriter) Write(p []byte) (n int, err error) {
if e.err == nil {
n, e.err = e.w.Write(p)
}
return n, e.err
}
// Err returns the first encountered err (or nil if no errors occurred).
func (e *ErrWriter) Err() error {
return e.err
}
// Ptr converts an Go byte array to a pointer to the start of the array.
func Ptr(slice []byte) unsafe.Pointer {
return unsafe.Pointer(&slice[0])
}
// Index returns the first index i such that inVal == inArray[i].
// ok is true if we find a match, false otherwise.
func Index(inVal int64, inArray []int64) (index int, ok bool) {
for index, val := range inArray {
if val == inVal {
return index, true
}
}
return 0, false
}
// Lookup finds inVal in inArray and returns the corresponding element in
// outArray. Specifically, if inVal == inArray[i], outVal == outArray[i].
// ok is true if we find a match, false otherwise.
func Lookup(inVal int64, inArray, outArray []int64) (outVal int64, ok bool) {
index, ok := Index(inVal, inArray)
if !ok {
return 0, false
}
return outArray[index], true
}
// MinInt returns the lesser of a and b.
func MinInt(a, b int) int {
if a < b {
return a
}
return b
}
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