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package iolimit
import (
"bytes"
"fmt"
"lindenii.org/go/lgo/intconv"
)
// CappedCaptureWriter captures written bytes up to a fixed limit.
//
// Once the total written bytes would exceed the limit,
// capture is disabled and Bytes returns nil.
// Write still reports success for the full input length.
type CappedCaptureWriter struct {
limit uint64
buf bytes.Buffer
full bool
}
// NewCappedCaptureWriter constructs one capped capture writer.
func NewCappedCaptureWriter(limit uint64) *CappedCaptureWriter {
return &CappedCaptureWriter{limit: limit}
}
// Write captures up to the configured limit
// and always reports len(src) bytes written.
func (writer *CappedCaptureWriter) Write(src []byte) (int, error) {
if writer.full {
return len(src), nil
}
used, err := intconv.IntToUint64(writer.buf.Len())
if err != nil {
return 0, fmt.Errorf("iolimit: %w", err)
}
if used >= writer.limit {
writer.full = true
return len(src), nil
}
room := writer.limit - used
if uint64(len(src)) > room {
take, err := intconv.Uint64ToInt(room)
if err != nil {
return 0, fmt.Errorf("iolimit: %w", err)
}
_, _ = writer.buf.Write(src[:take])
writer.full = true
return len(src), nil
}
_, _ = writer.buf.Write(src)
return len(src), nil
}
// Bytes returns captured bytes,
// or nil when capture exceeded the limit.
func (writer *CappedCaptureWriter) Bytes() []byte {
if writer.full {
return nil
}
return writer.buf.Bytes()
}
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