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proposal: bytes, strings: add ReadBytes(byte) ([]byte, error), ReadString(byte) (string, error) to Reader #13889

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hirochachacha opened this issue Jan 9, 2016 · 4 comments
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proposal: bytes, strings: add ReadBytes(byte) ([]byte, error), ReadString(byte) (string, error) to Reader #13889

hirochachacha opened this issue Jan 9, 2016 · 4 comments
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@hirochachacha
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One of the use-cases of byte.Reader is parsing a binary format.
There are some formats use an unpredictable length structure such as NUL-terminated string.
Unfortunately, current API set doesn't treat it well.

For example:

br := byte.NewReader(data)

func decodeCString(br *bytes.Reader, data []byte) string {
  rest := data[br.Size()-br.Len():]

  i := bytes.IndexByte(rest, 0x0)
  if i == -1 {
    panic("invalid")
  }

  br.Seek(i+1, 1)

  return string(rest[:i])
}

I think decodeCString has 2 problems.

  1. it still need to keep data variable.
  2. it manually update internal state by .Size, .Len and .Seek.

I want to write it like this:

func decodeCString(br *bytes.Reader) string {
  bs, err := br.ReadBytes(0x0)
  if err != nil {
    panic("invalid")
  }

  return string(bs[:len(bs)-1])
}

I know some people prefer bytes.Buffer because of convenience, even if data is read only.
I want to discourage such a situation.

Same things are also applicable to strings.Reader.

Thank you.

hiro
@hirochachacha hirochachacha changed the title proposal: bytes, strings, io: add ReadBytes(byte) ([]byte, error), ReadString(byte) (string, error) to Reader proposal: bytes, strings: add ReadBytes(byte) ([]byte, error), ReadString(byte) (string, error) to Reader Jan 9, 2016
@bradfitz
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bradfitz commented Jan 9, 2016

Here's a simpler, faster version:

func cstr(b []byte) string {
    if i := bytes.IndexByte(b, 0); i != -1 {
        return string(b[:i])
    }
    return ""
}

Notice that not only does it not need any changed to bytes.Reader, it also doesn't even need bytes.Reader.

And if you needed to parse these from a stream, you can use bufio.Reader.ReadBytes:

https://golang.org/pkg/bufio/#Reader.ReadBytes

I think there's nothing to do here.

@hirochachacha
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The problem in my mind is use with binary.Read.

https://github.com/golang/go/blob/master/src/debug/elf/file.go#L480-L508

And if you needed to parse these from a stream, you can use bufio.Reader.ReadBytes:

I think so, but it is bigger than problem itself, I think. That's my point.

@hirochachacha
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And if you needed to parse these from a stream, you can use bufio.Reader.ReadBytes:

I think so, but it is bigger than problem itself, I think. That's my point.

Sorry, I was mistaken.

@hirochachacha
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Thank you for commenting.

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@bradfitz @hirochachacha @gopherbot