bufio.Reader.Buffered returns 0

[Archos]

Why bufio.Reader.Buffered() returns 0?

It should returns the number of bytes to read from buffer

Note that I've to read the first byte (ReadByte) for then to can use
Buffered()

* * *
package main

import (
"bufio"
"os"
"fmt"
)

func ChangeHeader(fname string) os.Error {
inputFile, err := os.Open(fname, os.O_RDWR, 0644)
if err != nil {
return err
}

defer inputFile.Close()

input := bufio.NewReader(inputFile)
println(input.Buffered()) // *** It returns 0

return nil
}


func main() {
var fname = "src"

ChangeHeader(fname)
}

[Evan Shaw]

On Tue, Aug 24, 2010 at 4:50 PM, Archos <raul...@sent.com> wrote:
> Why bufio.Reader.Buffered() returns 0?
>
> It should returns the number of bytes to read from buffer
>
> Note that I've to read the first byte (ReadByte) for then to can use
> Buffered()

I think you're misunderstanding the documentation of the Buffered
method. It returns the number of bytes it's read into its buffer,
*not* the number of bytes that are in the underlying io.Reader. Since
you haven't read anything yet in your code, the bufio.Reader hasn't
read anything into its buffer.

- Evan

[Archos]

Well, the doc. *on this case* didn't help me much:

"Buffered returns the number of bytes that can be read from the
current buffer."[1]

[1]: http://golang.org/pkg/bufio/#Reader.Buffered

On Aug 24, 9:55 pm, Evan Shaw <chicken...@gmail.com> wrote:

[Evan Shaw]

On Tue, Aug 24, 2010 at 5:17 PM, Archos <raul...@sent.com> wrote:
> Well, the doc. *on this case* didn't help me much:
>
> "Buffered returns the number of bytes that can be read from the
> current buffer."[1]

I find that to be a pretty clear description. Consider that it could
be impossible or at least expensive to find the number of bytes in the
underlying io.Reader when all you have to go off of is the Read
method. How would you propose to do it with this type, for example:

type nullReader struct{}

func (r *nullReader) Read(p []byte) (int, os.Error) {
for i := range p {
p[i] = 0
}
return len(p), nil
}

- Evan

[smog...@gmail.com]

I'm having a similar problem as the original poster. I expect Buffered() to return the number of bytes that can be read from the current buffer, like the documentation states. However a call to Buffered() returns 0 both before and after a call to any Read() that finds bytes in the buffer. In my case the Reader is a net.Conn. 

How do we use Buffered() properly? This is the only google result I could find that even mentions using the function.

I ended up solving my problem without using bufio.

   -Sam

On Tuesday, August 24, 2010 at 6:21:20 PM UTC-4, Evan Shaw wrote:

[Ian Lance Taylor]

On Sun, Dec 15, 2019 at 7:56 PM <smog...@gmail.com> wrote:
>
> I'm having a similar problem as the original poster. I expect Buffered() to return the number of bytes that can be read from the current buffer, like the documentation states. However a call to Buffered() returns 0 both before and after a call to any Read() that finds bytes in the buffer. In my case the Reader is a net.Conn.
>
> How do we use Buffered() properly? This is the only google result I could find that even mentions using the function.
>
> I ended up solving my problem without using bufio.

Note that you are replying to an e-mail from over nine years ago.

The Buffered method is fairly special purpose. It just tells you how
many bytes you can Read without causing a call to the underlying
Reader. What are you really trying to do? Can you show us some code
that does not work as you expect?

Ian

> On Tuesday, August 24, 2010 at 6:21:20 PM UTC-4, Evan Shaw wrote:
>>
>> On Tue, Aug 24, 2010 at 5:17 PM, Archos <rau...@sent.com> wrote:
>> > Well, the doc. *on this case* didn't help me much:
>> >
>> > "Buffered returns the number of bytes that can be read from the
>> > current buffer."[1]
>>
>> I find that to be a pretty clear description. Consider that it could
>> be impossible or at least expensive to find the number of bytes in the
>> underlying io.Reader when all you have to go off of is the Read
>> method. How would you propose to do it with this type, for example:
>>
>> type nullReader struct{}
>>
>> func (r *nullReader) Read(p []byte) (int, os.Error) {
>> for i := range p {
>> p[i] = 0
>> }
>> return len(p), nil
>> }
>>
>> - Evan
>

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[Marvin Renich]

* Ian Lance Taylor <ia...@golang.org> [191215 23:05]:
> The Buffered method [snip] tells you how

> many bytes you can Read without causing a call to the underlying
> Reader.

I think this would be a significant improvement over the current
ambiguous documentation. It should adequately dispel any unrealistic
expectations on the part of programmers who are reading the
documentation.

...Marvin

[Sam]

Thanks Marvin, I think I understand now.

Sorry Ian I didn't even notice, but still...

I was using a net.Conn as the underlying reader. What I really needed was the Peek() function but the documentation for Buffered() made it seem more appropriate. I only needed to know the number of bytes received over the connection before evicting and interpreting them. 

intBytes, err := reader.Peek(4)
if err == nil {

// Decode integer

reader.Discard(4)

}

   -Sam

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