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reader.go
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/
reader.go
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package nbt
import (
"io"
)
// offsetReader is a wrapper around an io.Reader, used to track the offset (amount of bytes read) of the data
// that is being read, so that errors may have offset data.
type offsetReader struct {
io.Reader
off int64
// ReadByte is a function provided by offsetReader if the io.Reader does not implement io.ByteReader.
ReadByte func() (byte, error)
// Next is a function provided by offsetReader if the io.Reader does not have a Next method.
Next func(n int) []byte
}
// newOffsetReader returns a new offset reader for the io.Reader passed, setting the ReadByte and Next
// functions as appropriate for that particular reader.
func newOffsetReader(r io.Reader) *offsetReader {
reader := &offsetReader{Reader: r}
if byteReader, ok := r.(io.ByteReader); ok {
reader.ReadByte = func() (byte, error) {
reader.off++
return byteReader.ReadByte()
}
} else {
reader.ReadByte = func() (byte, error) {
data := make([]byte, 1)
_, err := io.ReadAtLeast(reader, data, 1)
return data[0], err
}
}
if r, ok := r.(interface {
Next(n int) []byte
}); ok {
reader.Next = func(n int) []byte {
data := r.Next(n)
reader.off += int64(len(data))
return data
}
} else {
reader.Next = func(n int) []byte {
data := make([]byte, n)
_, _ = io.ReadAtLeast(reader, data, n)
return data
}
}
return reader
}
// Read reads from the io.Reader and increases the reader's offset by exactly n.
func (b *offsetReader) Read(p []byte) (n int, err error) {
n, err = io.ReadAtLeast(b.Reader, p, len(p))
b.off += int64(n)
return
}