68 lines
1.3 KiB
Go
68 lines
1.3 KiB
Go
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package updater
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import (
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"fmt"
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"io"
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"golang.org/x/exp/constraints"
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)
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// LimitReachedError records the limit and the operation that caused it.
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type LimitReachedError struct {
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Limit int64
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}
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// Error implements the [error] interface for *LimitReachedError.
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//
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// TODO(a.garipov): Think about error string format.
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func (lre *LimitReachedError) Error() string {
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return fmt.Sprintf("attempted to read more than %d bytes", lre.Limit)
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}
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// limitedReader is a wrapper for [io.Reader] limiting the input and dealing
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// with errors package.
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type limitedReader struct {
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r io.Reader
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limit int64
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n int64
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}
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// Read implements the [io.Reader] interface.
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func (lr *limitedReader) Read(p []byte) (n int, err error) {
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if lr.n == 0 {
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return 0, &LimitReachedError{
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Limit: lr.limit,
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}
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}
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p = p[:Min(lr.n, int64(len(p)))]
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n, err = lr.r.Read(p)
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lr.n -= int64(n)
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return n, err
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}
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// LimitReader wraps Reader to make it's Reader stop with ErrLimitReached after
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// n bytes read.
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func LimitReader(r io.Reader, n int64) (limited io.Reader, err error) {
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if n < 0 {
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return nil, &updateError{Message: "limit must be non-negative"}
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}
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return &limitedReader{
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r: r,
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limit: n,
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n: n,
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}, nil
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}
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// Min returns the smaller of x or y.
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func Min[T constraints.Integer | ~string](x, y T) (res T) {
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if x < y {
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return x
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}
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return y
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}
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