Re: [go-nuts] Re: io.Copy and Writer
I don’t believe your example is correct. In order for a current wrapper to call Flush on Close on the bufio.Writer the Close would need to be defined on the Wrapper struct so there would be no name collision. I think it is best to see the proposal before commenting. I plan on addressing any code breaking issues - if there were obvious ones I wouldn’t be for the proposal either. > On May 23, 2019, at 6:14 AM, roger peppe wrote: > > I have to say that I must prefer APIs that do not take arbitrary advantage of > dynamically discovered methods. It makes things less clear, and adding a > wrapper to flush and then close the underlying writer is not hard. In fact > the idiom for doing so is probably the reason why it's not feasible to add a > Close method to `bufio.Writer`. If you do that, then you run the risk of > breaking current code that adds its own Close method: > > https://play.golang.org/p/xidNo2Z_OYB > > This would definitely break some code that I've written. > >cheers, > rog. > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/93D441AB-D98F-48F6-8BCA-E555F98919DC%40ix.netcom.com. For more options, visit https://groups.google.com/d/optout.
Re: [go-nuts] Re: io.Copy and Writer
I have to say that I must prefer APIs that do not take arbitrary advantage of dynamically discovered methods. It makes things less clear, and adding a wrapper to flush and then close the underlying writer is not hard. In fact the idiom for doing so is probably the reason why it's not feasible to add a Close method to `bufio.Writer`. If you do that, then you run the risk of breaking current code that adds its own Close method: https://play.golang.org/p/xidNo2Z_OYB This would definitely break some code that I've written. cheers, rog. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAJhgacjm-ZmpfXRfbK%3DZN26vRQsJ%3Dfn632tm0iwq%2B3sUGxEayQ%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
Re: [go-nuts] Re: io.Copy and Writer
The very fact that you downvote a proposal without reading it says a lot. > On May 22, 2019, at 8:21 AM, Jan Mercl <0xj...@gmail.com> wrote: > > On Wed, May 22, 2019 at 3:15 PM Ian Lance Taylor wrote: > >>> The bufio.Writer is badly broken and should be changed to declare Close and >>> pass this to the contained Writer if it is a WriterCloser. >> >> What to open a proposal for that? https://golang.org/s/proposal. > > As I cannot vote on proposals without having a Microsoft owned > account, please let me put my down vote on such proposal preemptively > here. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/8255A27B-74D1-435D-A8F1-F8AB1F77898D%40ix.netcom.com. For more options, visit https://groups.google.com/d/optout.
Re: [go-nuts] Re: io.Copy and Writer
Now that’s a good idea ! Hopefully sometime today. :) > On May 22, 2019, at 8:15 AM, Ian Lance Taylor wrote: > >> On Wed, May 22, 2019 at 9:02 AM Robert Engels wrote: >> >> The more I think about this, the more I believe that this is a horrible >> situation that breaks all rules of encapsulation. This requires the creator >> to maintain references to the underlying Writer. It also requires the >> creator to be the sole decider of when the Writer is closed, or the creator >> must pass the concrete class to subordinates so they can close, or the >> subordinates must do type casting. >> >> The bufio.Writer is badly broken and should be changed to declare Close and >> pass this to the contained Writer if it is a WriterCloser. > > What to open a proposal for that? https://golang.org/s/proposal. > > Ian -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/933AB061-B9BD-46C5-B114-47E8CFA0514A%40ix.netcom.com. For more options, visit https://groups.google.com/d/optout.
Re: [go-nuts] Re: io.Copy and Writer
Except that as the example I gave showed, it is fairly trivial to wrap the bufio.Writer into a WriteCloser that retains that reference and performs the pass-through Close as expected. So if you have a situation that needs a WriteCloser, you can manage that. Meanwhile, the bufio classes provide valuable functionality to Writers and Readers, whether or not they have a Close function, at the cost of a simple requirement to call Flush after writes finish. The current implementation *is* the more general one. So perhaps what would be better would be to add a bufio.WriteCloser that requires a WriteCloser to wrap, so that we don't have to implement one of our own in those cases. Howard On Wednesday, May 22, 2019 at 8:02:34 AM UTC-5, Robert Engels wrote: > > The more I think about this, the more I believe that this is a horrible > situation that breaks all rules of encapsulation. This requires the creator > to maintain references to the underlying Writer. It also requires the > creator to be the sole decider of when the Writer is closed, or the creator > must pass the concrete class to subordinates so they can close, or the > subordinates must do type casting. > > The bufio.Writer is badly broken and should be changed to declare Close > and pass this to the contained Writer if it is a WriterCloser. > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/da01596f-d958-46f0-9bca-18b768e49a35%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [go-nuts] Re: io.Copy and Writer
On Wed, May 22, 2019 at 3:15 PM Ian Lance Taylor wrote: > > The bufio.Writer is badly broken and should be changed to declare Close and > > pass this to the contained Writer if it is a WriterCloser. > > What to open a proposal for that? https://golang.org/s/proposal. As I cannot vote on proposals without having a Microsoft owned account, please let me put my down vote on such proposal preemptively here. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAA40n-VMTLbyU8ppeKYvKwB5nOU4xEkEZu35qO3R5sj_wd7b7g%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
Re: [go-nuts] Re: io.Copy and Writer
On Wed, May 22, 2019 at 9:02 AM Robert Engels wrote: > > The more I think about this, the more I believe that this is a horrible > situation that breaks all rules of encapsulation. This requires the creator > to maintain references to the underlying Writer. It also requires the creator > to be the sole decider of when the Writer is closed, or the creator must pass > the concrete class to subordinates so they can close, or the subordinates > must do type casting. > > The bufio.Writer is badly broken and should be changed to declare Close and > pass this to the contained Writer if it is a WriterCloser. What to open a proposal for that? https://golang.org/s/proposal. Ian -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAOyqgcXC65fYWGYS4034Gdor0_MHT9E%3DM7kp7S9nfvepR-js2A%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
Re: [go-nuts] Re: io.Copy and Writer
The more I think about this, the more I believe that this is a horrible
situation that breaks all rules of encapsulation. This requires the creator to
maintain references to the underlying Writer. It also requires the creator to
be the sole decider of when the Writer is closed, or the creator must pass the
concrete class to subordinates so they can close, or the subordinates must do
type casting.
The bufio.Writer is badly broken and should be changed to declare Close and
pass this to the contained Writer if it is a WriterCloser.
> On May 21, 2019, at 5:42 PM, Robert Engels wrote:
>
> That’s a good case of dynamic type checking and good documentation
>
>> On May 21, 2019, at 5:20 PM, roger peppe wrote:
>>
>> Probably it's not a Closer because that would imply that Close would close
>> its underlying writer too, but then it would need to take a WriteCloser
>> which would make it less general.
>>
>>> On Tue, 21 May 2019, 19:02 Robert Engels, wrote:
>>> That’s what I was saying, I incorrectly thought that the Writer was a
>>> WriterCloser.
>>>
>>> Seems it should be with a noop if the contained Writer is not a
>>> WriterCloser. This would be pretty much how every other platform does
>>> buffered IO.
>>>
On May 21, 2019, at 11:19 AM, howardcs...@gmail.com wrote:
Excuse me if I am misunderstanding something - but it certainly looks to
me like you are not at any point closing the bufio.Writer (because it is
not a WriteCloser and does not support Close function). That is why you
need to flush it! What you are closing is the underlying
file/stream/WriteCloser, but it is the bufio.Writer that has the data in
its buffer, *not* the file. This is not the same thing as flushing a file
descriptor, which happens on close.
"After all data has been written, the client should call the Flush method
to guarantee all data has been forwarded to the underlying io.Writer."
IF the bufio.Writer had been implemented as a WriteCloser, then closing it
would probably flush as well - here is a discussion where they talk about
how that could be implemented:
https://stackoverflow.com/questions/43115699/how-to-get-a-bufio-writer-that-implements-io-writecloser
Howard
> On Tuesday, May 21, 2019 at 8:42:51 AM UTC-5, Subramanian Sridharan wrote:
> I don't think so.
>
> When I close the file and don't explicitly flush:
>
> package main
>
> import (
> "bufio"
> "fmt"
> "io"
> "os"
> )
>
> func main() {
> sourceFilename := "MozillaFirefox-66.0.5-741.4.x86_64.rpm"
> sourcef, err := os.Open(sourceFilename)
> if err != nil {
> fmt.Println("Error while opening source file:", err)
> return
> }
> defer sourcef.Close()
>
> destinationFilename := "CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm"
> os.Create(destinationFilename)
> destf, err := os.OpenFile(destinationFilename, os.O_APPEND|os.O_WRONLY,
> os.ModeAppend)
> if err != nil {
> fmt.Println("Error while opening destination file:", err)
> return
> }
> defer func() {
> fmt.Println("Closing file.")
> destf.Close()
> }()
>
> fReader := bufio.NewReader(sourcef)
> fWriter := bufio.NewWriter(destf)
>
> n, err := io.Copy(fWriter, fReader)
> if err != nil {
> fmt.Println("Error while copying:", err)
> return
> }
>
> fmt.Println("Copied", n, "bytes.")
> }
>
>>
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Re: [go-nuts] Re: io.Copy and Writer
That’s a good case of dynamic type checking and good documentation
> On May 21, 2019, at 5:20 PM, roger peppe wrote:
>
> Probably it's not a Closer because that would imply that Close would close
> its underlying writer too, but then it would need to take a WriteCloser which
> would make it less general.
>
>> On Tue, 21 May 2019, 19:02 Robert Engels, wrote:
>> That’s what I was saying, I incorrectly thought that the Writer was a
>> WriterCloser.
>>
>> Seems it should be with a noop if the contained Writer is not a
>> WriterCloser. This would be pretty much how every other platform does
>> buffered IO.
>>
>>> On May 21, 2019, at 11:19 AM, howardcs...@gmail.com wrote:
>>>
>>> Excuse me if I am misunderstanding something - but it certainly looks to me
>>> like you are not at any point closing the bufio.Writer (because it is not a
>>> WriteCloser and does not support Close function). That is why you need to
>>> flush it! What you are closing is the underlying file/stream/WriteCloser,
>>> but it is the bufio.Writer that has the data in its buffer, *not* the file.
>>> This is not the same thing as flushing a file descriptor, which happens on
>>> close.
>>>
>>> "After all data has been written, the client should call the Flush method
>>> to guarantee all data has been forwarded to the underlying io.Writer."
>>>
>>> IF the bufio.Writer had been implemented as a WriteCloser, then closing it
>>> would probably flush as well - here is a discussion where they talk about
>>> how that could be implemented:
>>> https://stackoverflow.com/questions/43115699/how-to-get-a-bufio-writer-that-implements-io-writecloser
>>>
>>> Howard
>>>
On Tuesday, May 21, 2019 at 8:42:51 AM UTC-5, Subramanian Sridharan wrote:
I don't think so.
When I close the file and don't explicitly flush:
package main
import (
"bufio"
"fmt"
"io"
"os"
)
func main() {
sourceFilename := "MozillaFirefox-66.0.5-741.4.x86_64.rpm"
sourcef, err := os.Open(sourceFilename)
if err != nil {
fmt.Println("Error while opening source file:", err)
return
}
defer sourcef.Close()
destinationFilename := "CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm"
os.Create(destinationFilename)
destf, err := os.OpenFile(destinationFilename, os.O_APPEND|os.O_WRONLY,
os.ModeAppend)
if err != nil {
fmt.Println("Error while opening destination file:", err)
return
}
defer func() {
fmt.Println("Closing file.")
destf.Close()
}()
fReader := bufio.NewReader(sourcef)
fWriter := bufio.NewWriter(destf)
n, err := io.Copy(fWriter, fReader)
if err != nil {
fmt.Println("Error while copying:", err)
return
}
fmt.Println("Copied", n, "bytes.")
}
>
>>>
>>> --
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>>
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>
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Re: [go-nuts] Re: io.Copy and Writer
Probably it's not a Closer because that would imply that Close would close
its underlying writer too, but then it would need to take a WriteCloser
which would make it less general.
On Tue, 21 May 2019, 19:02 Robert Engels, wrote:
> That’s what I was saying, I incorrectly thought that the Writer was a
> WriterCloser.
>
> Seems it should be with a noop if the contained Writer is not a
> WriterCloser. This would be pretty much how every other platform does
> buffered IO.
>
> On May 21, 2019, at 11:19 AM, howardcs...@gmail.com wrote:
>
> Excuse me if I am misunderstanding something - but it certainly looks to
> me like you are not at any point closing the bufio.Writer (because it is
> not a WriteCloser and does not support Close function). That is why you
> need to flush it! What you are closing is the underlying
> file/stream/WriteCloser, but it is the bufio.Writer that has the data in
> its buffer, *not* the file. This is not the same thing as flushing a file
> descriptor, which happens on close.
>
> "After all data has been written, the client should call the Flush method
> to guarantee all data has been forwarded to the underlying io.Writer."
>
> IF the bufio.Writer had been implemented as a WriteCloser, then closing it
> would probably flush as well - here is a discussion where they talk about
> how that could be implemented:
> https://stackoverflow.com/questions/43115699/how-to-get-a-bufio-writer-that-implements-io-writecloser
>
> Howard
>
> On Tuesday, May 21, 2019 at 8:42:51 AM UTC-5, Subramanian Sridharan wrote:
>>
>> I don't think so.
>>
>> When I close the file and don't explicitly flush:
>>
>> package main
>>
>> import (
>> "bufio"
>> "fmt"
>> "io"
>> "os"
>> )
>>
>> func main() {
>> sourceFilename := "MozillaFirefox-66.0.5-741.4.x86_64.rpm"
>> sourcef, err := os.Open(sourceFilename)
>> if err != nil {
>> fmt.Println("Error while opening source file:", err)
>> return
>> }
>> defer sourcef.Close()
>>
>> destinationFilename := "CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm"
>> os.Create(destinationFilename)
>> destf, err := os.OpenFile(destinationFilename, os.O_APPEND|os.O_WRONLY,
>> os.ModeAppend)
>> if err != nil {
>> fmt.Println("Error while opening destination file:", err)
>> return
>> }
>> defer func() {
>> fmt.Println("Closing file.")
>> destf.Close()
>> }()
>>
>> fReader := bufio.NewReader(sourcef)
>> fWriter := bufio.NewWriter(destf)
>>
>> n, err := io.Copy(fWriter, fReader)
>> if err != nil {
>> fmt.Println("Error while copying:", err)
>> return
>> }
>>
>> fmt.Println("Copied", n, "bytes.")
>> }
>>
>>
>>> --
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>
> .
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>
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Re: [go-nuts] Re: io.Copy and Writer
That’s what I was saying, I incorrectly thought that the Writer was a
WriterCloser.
Seems it should be with a noop if the contained Writer is not a WriterCloser.
This would be pretty much how every other platform does buffered IO.
> On May 21, 2019, at 11:19 AM, howardcs...@gmail.com wrote:
>
> Excuse me if I am misunderstanding something - but it certainly looks to me
> like you are not at any point closing the bufio.Writer (because it is not a
> WriteCloser and does not support Close function). That is why you need to
> flush it! What you are closing is the underlying file/stream/WriteCloser, but
> it is the bufio.Writer that has the data in its buffer, *not* the file. This
> is not the same thing as flushing a file descriptor, which happens on close.
>
> "After all data has been written, the client should call the Flush method to
> guarantee all data has been forwarded to the underlying io.Writer."
>
> IF the bufio.Writer had been implemented as a WriteCloser, then closing it
> would probably flush as well - here is a discussion where they talk about how
> that could be implemented:
> https://stackoverflow.com/questions/43115699/how-to-get-a-bufio-writer-that-implements-io-writecloser
>
> Howard
>
>> On Tuesday, May 21, 2019 at 8:42:51 AM UTC-5, Subramanian Sridharan wrote:
>> I don't think so.
>>
>> When I close the file and don't explicitly flush:
>>
>> package main
>>
>> import (
>> "bufio"
>> "fmt"
>> "io"
>> "os"
>> )
>>
>> func main() {
>> sourceFilename := "MozillaFirefox-66.0.5-741.4.x86_64.rpm"
>> sourcef, err := os.Open(sourceFilename)
>> if err != nil {
>> fmt.Println("Error while opening source file:", err)
>> return
>> }
>> defer sourcef.Close()
>>
>> destinationFilename := "CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm"
>> os.Create(destinationFilename)
>> destf, err := os.OpenFile(destinationFilename, os.O_APPEND|os.O_WRONLY,
>> os.ModeAppend)
>> if err != nil {
>> fmt.Println("Error while opening destination file:", err)
>> return
>> }
>> defer func() {
>> fmt.Println("Closing file.")
>> destf.Close()
>> }()
>>
>> fReader := bufio.NewReader(sourcef)
>> fWriter := bufio.NewWriter(destf)
>>
>> n, err := io.Copy(fWriter, fReader)
>> if err != nil {
>> fmt.Println("Error while copying:", err)
>> return
>> }
>>
>> fmt.Println("Copied", n, "bytes.")
>> }
>>
>>>
>
> --
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Re: [go-nuts] Re: io.Copy and Writer
Excuse me if I am misunderstanding something - but it certainly looks to me
like you are not at any point closing the bufio.Writer (because it is not a
WriteCloser and does not support Close function). That is why you need to
flush it! What you are closing is the underlying file/stream/WriteCloser,
but it is the bufio.Writer that has the data in its buffer, *not* the file.
This is not the same thing as flushing a file descriptor, which happens on
close.
"After all data has been written, the client should call the Flush method
to guarantee all data has been forwarded to the underlying io.Writer."
IF the bufio.Writer had been implemented as a WriteCloser, then closing it
would probably flush as well - here is a discussion where they talk about
how that could be implemented:
https://stackoverflow.com/questions/43115699/how-to-get-a-bufio-writer-that-implements-io-writecloser
Howard
On Tuesday, May 21, 2019 at 8:42:51 AM UTC-5, Subramanian Sridharan wrote:
>
> I don't think so.
>
> When I close the file and don't explicitly flush:
>
> package main
>
> import (
> "bufio"
> "fmt"
> "io"
> "os"
> )
>
> func main() {
> sourceFilename := "MozillaFirefox-66.0.5-741.4.x86_64.rpm"
> sourcef, err := os.Open(sourceFilename)
> if err != nil {
> fmt.Println("Error while opening source file:", err)
> return
> }
> defer sourcef.Close()
>
> destinationFilename := "CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm"
> os.Create(destinationFilename)
> destf, err := os.OpenFile(destinationFilename, os.O_APPEND|os.O_WRONLY,
> os.ModeAppend)
> if err != nil {
> fmt.Println("Error while opening destination file:", err)
> return
> }
> defer func() {
> fmt.Println("Closing file.")
> destf.Close()
> }()
>
> fReader := bufio.NewReader(sourcef)
> fWriter := bufio.NewWriter(destf)
>
> n, err := io.Copy(fWriter, fReader)
> if err != nil {
> fmt.Println("Error while copying:", err)
> return
> }
>
> fmt.Println("Copied", n, "bytes.")
> }
>
>
>>
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Re: [go-nuts] Re: io.Copy and Writer
Sorry, per docs, the client should call the Flush method to guarantee all data
has been forwarded to the underlying io.Writer.
Not sure why the Write doesn’t implement Closer. That’s fairly non standard way
of doing buffered io...
> On May 21, 2019, at 8:42 AM, Subramanian Sridharan
> wrote:
>
> I don't think so.
>
> When I close the file and don't explicitly flush:
>
> package main
>
> import (
> "bufio"
> "fmt"
> "io"
> "os"
> )
>
> func main() {
> sourceFilename := "MozillaFirefox-66.0.5-741.4.x86_64.rpm"
> sourcef, err := os.Open(sourceFilename)
> if err != nil {
> fmt.Println("Error while opening source file:", err)
> return
> }
> defer sourcef.Close()
>
> destinationFilename := "CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm"
> os.Create(destinationFilename)
> destf, err := os.OpenFile(destinationFilename, os.O_APPEND|os.O_WRONLY,
> os.ModeAppend)
> if err != nil {
> fmt.Println("Error while opening destination file:", err)
> return
> }
> defer func() {
> fmt.Println("Closing file.")
> destf.Close()
> }()
>
> fReader := bufio.NewReader(sourcef)
> fWriter := bufio.NewWriter(destf)
>
> n, err := io.Copy(fWriter, fReader)
> if err != nil {
> fmt.Println("Error while copying:", err)
> return
> }
>
> fmt.Println("Copied", n, "bytes.")
> }
>
>
> Output:
>
> ➜ throttle-and-resume-download go run copyTest.go
>
> Copied 46061104 bytes.
> Closing file.
> ➜ throttle-and-resume-download diff MozillaFirefox-66.0.5-741.4.x86_64.rpm
> CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm
> Binary files MozillaFirefox-66.0.5-741.4.x86_64.rpm and
> CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm differ
> ➜ throttle-and-resume-download echo $?
> 1
>
>
> When I explicitly flush:
>
> package main
>
> import (
> "bufio"
> "fmt"
> "io"
> "os"
> )
>
> func main() {
> sourceFilename := "MozillaFirefox-66.0.5-741.4.x86_64.rpm"
> sourcef, err := os.Open(sourceFilename)
> if err != nil {
> fmt.Println("Error while opening source file:", err)
> return
> }
> defer sourcef.Close()
>
> destinationFilename := "CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm"
> os.Create(destinationFilename)
> destf, err := os.OpenFile(destinationFilename, os.O_APPEND|os.O_WRONLY,
> os.ModeAppend)
> if err != nil {
> fmt.Println("Error while opening destination file:", err)
> return
> }
> defer func() {
> fmt.Println("Closing file.")
> destf.Close()
> }()
>
> fReader := bufio.NewReader(sourcef)
> fWriter := bufio.NewWriter(destf)
>
> n, err := io.Copy(fWriter, fReader)
> if err != nil {
> fmt.Println("Error while copying:", err)
> return
> }
>
> // Flush writer to ensure all contents are written to file
> err = fWriter.Flush()
> if err != nil {
> fmt.Println("Error while flushing writer:", err)
> return
> } else {
> fmt.Println("Flushed writer.")
> }
>
> fmt.Println("Copied", n, "bytes.")
> }
>
>
> Output:
>
> ➜ throttle-and-resume-download go run copyTest.go
>
> Flushed writer.
> Copied 46061104 bytes.
> Closing file.
> ➜ throttle-and-resume-download diff MozillaFirefox-66.0.5-741.4.x86_64.rpm
> CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm
> ➜ throttle-and-resume-download echo $?
>
> 0
>
>
>
>
>
>
>> On Tuesday, May 21, 2019 at 6:39:08 PM UTC+5:30, Robert Engels wrote:
>> You do not need to flush if you call close. Close will flush. There is some
>> other bug in your code I believe.
>>
>> > On May 21, 2019, at 3:01 AM, Jan Mercl <0xj...@gmail.com> wrote:
>> >
>> >> On Tue, May 21, 2019 at 9:44 AM wrote:
>> >>
>> >> Usually though, you do not need to buffer the input or output at all.
>> >
>> > If I/O is performed in chunks comparable in size to what
>> > bufio.{Reader,Writer} uses then ok. When I/O is done in small chunks,
>> > then using bufio should improve performance.
>> >
>> > The question left is what the "usual" scenario is.
>> >
>> > --
>> > You received this message because you are subscribed to the Google Groups
>> > "golang-nuts" group.
>> > To unsubscribe from this group and stop receiving emails from it, send an
>> > email to golan...@googlegroups.com.
>> > To view this discussion on the web visit
>> >
Re: [go-nuts] Re: io.Copy and Writer
I don't think so.
When I close the file and don't explicitly flush:
package main
import (
"bufio"
"fmt"
"io"
"os"
)
func main() {
sourceFilename := "MozillaFirefox-66.0.5-741.4.x86_64.rpm"
sourcef, err := os.Open(sourceFilename)
if err != nil {
fmt.Println("Error while opening source file:", err)
return
}
defer sourcef.Close()
destinationFilename := "CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm"
os.Create(destinationFilename)
destf, err := os.OpenFile(destinationFilename, os.O_APPEND|os.O_WRONLY,
os.ModeAppend)
if err != nil {
fmt.Println("Error while opening destination file:", err)
return
}
defer func() {
fmt.Println("Closing file.")
destf.Close()
}()
fReader := bufio.NewReader(sourcef)
fWriter := bufio.NewWriter(destf)
n, err := io.Copy(fWriter, fReader)
if err != nil {
fmt.Println("Error while copying:", err)
return
}
fmt.Println("Copied", n, "bytes.")
}
Output:
➜ throttle-and-resume-download go run copyTest.go
Copied 46061104 bytes.
Closing file.
➜ throttle-and-resume-download diff MozillaFirefox-66.0.5-741.4.x86_64.rpm
CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm
Binary files MozillaFirefox-66.0.5-741.4.x86_64.rpm and
CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm differ
➜ throttle-and-resume-download echo $?
1
When I explicitly flush:
package main
import (
"bufio"
"fmt"
"io"
"os"
)
func main() {
sourceFilename := "MozillaFirefox-66.0.5-741.4.x86_64.rpm"
sourcef, err := os.Open(sourceFilename)
if err != nil {
fmt.Println("Error while opening source file:", err)
return
}
defer sourcef.Close()
destinationFilename := "CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm"
os.Create(destinationFilename)
destf, err := os.OpenFile(destinationFilename, os.O_APPEND|os.O_WRONLY,
os.ModeAppend)
if err != nil {
fmt.Println("Error while opening destination file:", err)
return
}
defer func() {
fmt.Println("Closing file.")
destf.Close()
}()
fReader := bufio.NewReader(sourcef)
fWriter := bufio.NewWriter(destf)
n, err := io.Copy(fWriter, fReader)
if err != nil {
fmt.Println("Error while copying:", err)
return
}
// Flush writer to ensure all contents are written to file
err = fWriter.Flush()
if err != nil {
fmt.Println("Error while flushing writer:", err)
return
} else {
fmt.Println("Flushed writer.")
}
fmt.Println("Copied", n, "bytes.")
}
Output:
➜ throttle-and-resume-download go run copyTest.go
Flushed writer.
Copied 46061104 bytes.
Closing file.
➜ throttle-and-resume-download diff MozillaFirefox-66.0.5-741.4.x86_64.rpm
CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm
➜ throttle-and-resume-download echo $?
0
On Tuesday, May 21, 2019 at 6:39:08 PM UTC+5:30, Robert Engels wrote:
>
> You do not need to flush if you call close. Close will flush. There is
> some other bug in your code I believe.
>
> > On May 21, 2019, at 3:01 AM, Jan Mercl <0xj...@gmail.com >
> wrote:
> >
> >> On Tue, May 21, 2019 at 9:44 AM >
> wrote:
> >>
> >> Usually though, you do not need to buffer the input or output at all.
> >
> > If I/O is performed in chunks comparable in size to what
> > bufio.{Reader,Writer} uses then ok. When I/O is done in small chunks,
> > then using bufio should improve performance.
> >
> > The question left is what the "usual" scenario is.
> >
> > --
> > You received this message because you are subscribed to the Google
> Groups "golang-nuts" group.
> > To unsubscribe from this group and stop receiving emails from it, send
> an email to golan...@googlegroups.com .
> > To view this discussion on the web visit
> https://groups.google.com/d/msgid/golang-nuts/CAA40n-WsWkLtnP19DUwHNSrjDNBncbVepqNxVj%3DUF6MFV8ARLA%40mail.gmail.com.
>
>
> > For more options, visit https://groups.google.com/d/optout.
>
>
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Re: [go-nuts] Re: io.Copy and Writer
I don't think so.
Closing file without flushing:
package main
import (
"bufio"
"fmt"
"io"
"os"
)
func main() {
sourceFilename := "MozillaFirefox-66.0.5-741.4.x86_64.rpm"
sourcef, err := os.Open(sourceFilename)
if err != nil {
fmt.Println("Error while opening source file:", err)
return
}
defer sourcef.Close()
destinationFilename := "CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm"
os.Create(destinationFilename)
destf, err := os.OpenFile(destinationFilename, os.O_APPEND|os.O_WRONLY,
os.ModeAppend)
if err != nil {
fmt.Println("Error while opening destination file:", err)
return
}
defer func() {
fmt.Println("Closing file.")
destf.Close()
}()
fReader := bufio.NewReader(sourcef)
fWriter := bufio.NewWriter(destf)
n, err := io.Copy(fWriter, fReader)
if err != nil {
fmt.Println("Error while copying:", err)
return
}
fmt.Println("Copied", n, "bytes.")
}
Output:
➜ throttle-and-resume-download go run copyTest.go
Copied 46061104 bytes.
Closing file.
➜ throttle-and-resume-download diff MozillaFirefox-66.0.5-741.4.x86_64.rpm
CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm
Binary files MozillaFirefox-66.0.5-741.4.x86_64.rpm and
CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm differ
When I flush:
package main
import (
"bufio"
"fmt"
"io"
"os"
)
func main() {
sourceFilename := "MozillaFirefox-66.0.5-741.4.x86_64.rpm"
sourcef, err := os.Open(sourceFilename)
if err != nil {
fmt.Println("Error while opening source file:", err)
return
}
defer sourcef.Close()
destinationFilename := "CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm"
os.Create(destinationFilename)
destf, err := os.OpenFile(destinationFilename, os.O_APPEND|os.O_WRONLY,
os.ModeAppend)
if err != nil {
fmt.Println("Error while opening destination file:", err)
return
}
defer func() {
fmt.Println("Closing file.")
destf.Close()
}()
fReader := bufio.NewReader(sourcef)
fWriter := bufio.NewWriter(destf)
n, err := io.Copy(fWriter, fReader)
if err != nil {
fmt.Println("Error while copying:", err)
return
}
// Flush writer to ensure all contents are written to file
err = fWriter.Flush()
if err != nil {
fmt.Println("Error while flushing writer:", err)
return
} else {
fmt.Println("Flushed writer.")
}
fmt.Println("Copied", n, "bytes.")
}
Output:
➜ throttle-and-resume-download go run copyTest.go
Flushed writer.
Copied 46061104 bytes.
Closing file.
➜ throttle-and-resume-download diff MozillaFirefox-66.0.5-741.4.x86_64.rpm
CopiedMozillaFirefox-66.0.5-741.4.x86_64.rpm
➜ throttle-and-resume-download
On Tuesday, May 21, 2019 at 6:39:08 PM UTC+5:30, Robert Engels wrote:
>
> You do not need to flush if you call close. Close will flush. There is
> some other bug in your code I believe.
>
> > On May 21, 2019, at 3:01 AM, Jan Mercl <0xj...@gmail.com >
> wrote:
> >
> >> On Tue, May 21, 2019 at 9:44 AM >
> wrote:
> >>
> >> Usually though, you do not need to buffer the input or output at all.
> >
> > If I/O is performed in chunks comparable in size to what
> > bufio.{Reader,Writer} uses then ok. When I/O is done in small chunks,
> > then using bufio should improve performance.
> >
> > The question left is what the "usual" scenario is.
> >
> > --
> > You received this message because you are subscribed to the Google
> Groups "golang-nuts" group.
> > To unsubscribe from this group and stop receiving emails from it, send
> an email to golan...@googlegroups.com .
> > To view this discussion on the web visit
> https://groups.google.com/d/msgid/golang-nuts/CAA40n-WsWkLtnP19DUwHNSrjDNBncbVepqNxVj%3DUF6MFV8ARLA%40mail.gmail.com.
>
>
> > For more options, visit https://groups.google.com/d/optout.
>
>
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Re: [go-nuts] Re: io.Copy and Writer
You do not need to flush if you call close. Close will flush. There is some
other bug in your code I believe.
> On May 21, 2019, at 3:01 AM, Jan Mercl <0xj...@gmail.com> wrote:
>
>> On Tue, May 21, 2019 at 9:44 AM wrote:
>>
>> Usually though, you do not need to buffer the input or output at all.
>
> If I/O is performed in chunks comparable in size to what
> bufio.{Reader,Writer} uses then ok. When I/O is done in small chunks,
> then using bufio should improve performance.
>
> The question left is what the "usual" scenario is.
>
> --
> You received this message because you are subscribed to the Google Groups
> "golang-nuts" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to golang-nuts+unsubscr...@googlegroups.com.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/golang-nuts/CAA40n-WsWkLtnP19DUwHNSrjDNBncbVepqNxVj%3DUF6MFV8ARLA%40mail.gmail.com.
> For more options, visit https://groups.google.com/d/optout.
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Re: [go-nuts] Re: io.Copy and Writer
On Tue, May 21, 2019 at 9:44 AM wrote:
> Usually though, you do not need to buffer the input or output at all.
If I/O is performed in chunks comparable in size to what
bufio.{Reader,Writer} uses then ok. When I/O is done in small chunks,
then using bufio should improve performance.
The question left is what the "usual" scenario is.
--
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