AdGuardHome/internal/aghio/limitedreader.go

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// Package aghio contains extensions for io package's types and methods
package aghio
import (
"fmt"
"io"
)
// LimitReachedError records the limit and the operation that caused it.
type LimitReachedError struct {
Limit int64
}
// Error implements error interface for LimitReachedError.
//
// TODO(a.garipov): Think about error string format.
func (lre *LimitReachedError) Error() string {
return fmt.Sprintf("attempted to read more than %d bytes", lre.Limit)
}
// limitedReader is a wrapper for io.Reader with limited reader and dealing with
// errors package.
type limitedReader struct {
r io.Reader
limit int64
n int64
}
// Read implements Reader interface.
func (lr *limitedReader) Read(p []byte) (n int, err error) {
if lr.n == 0 {
return 0, &LimitReachedError{
Limit: lr.limit,
}
}
if int64(len(p)) > lr.n {
p = p[0:lr.n]
}
n, err = lr.r.Read(p)
lr.n -= int64(n)
return n, err
}
// LimitReader wraps Reader to make it's Reader stop with ErrLimitReached after
// n bytes read.
func LimitReader(r io.Reader, n int64) (limited io.Reader, err error) {
if n < 0 {
return nil, fmt.Errorf("aghio: invalid n in LimitReader: %d", n)
}
return &limitedReader{
r: r,
limit: n,
n: n,
}, nil
}