Re: [go-nuts] cannot convert fs.FS zip file to io.ReadSeeker (missing Seek)

[Rory Campbell-Lange]

On 22/09/22, 'Dan Kortschak' via golang-nuts (golang-nuts@googlegroups.com) 
wrote:
> On Thu, 2022-09-22 at 00:58 +0100, Rory Campbell-Lange wrote:
> > interface conversion: *zip.checksumReader is not io.ReadSeeker:
> > missing method Seek
> 
> Would it be acceptable to conditionally copy the reader's contents into
> a buffer that implements io.ReadSeeker?
> 
> if rs, ok := r.(io.ReadSeeker); ok {
>       useReadSeeker(rs)
> } else {
>         b, err := io.ReadAll(r)
>       // handle err
>       useReadSeeker(bytes.NewReader(b))
> }

Thanks very much for the suggestion. The following works ok as a test (which is 
basically your code):

        fileAsReadSeeker := func(file fs.File) io.ReadSeeker {
                if rs, ok := file.(io.ReadSeeker); ok {
                        return rs
                }
                b, err := io.ReadAll(file)
                if err != nil {
                        panic(err) // to fix
                }
                return bytes.NewReader(b)
        }

I'm now thinking of adding in a bytes.Buffer field into the underlying struct 
holding the fs.File file which can be initialised (and reused) if an 
io.ReadSeeker is required and provides a clearer error path.

Thanks again,
Rory

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