Azblob: DownloadBlobToWriterAt gets context cancelled

[eccles]

Bug Report

import azStorageBlob "github.com/Azure/azure-sdk-for-go/sdk/storage/azblob" 0.3.0 go version go1.17.7 linux/amd64

Attempts to download a blob with the following call:

func (rr *ReaderResponse) DownloadToWriter(ctx context.Context, w io.Writer) error {
        return rr.BlobClient.DownloadBlobToWriterAt(
                ctx,   /// context.BackGround() in most cases
                0,
                rr.CountToEnd,    /// standard MS constant
                newWriterAt(w),   /// convrets io.Writer to io.WriterAt with zero offset
                azStorageBlob.HighLevelDownloadFromBlobOptions{},
        )
}

when calling using a http.ResponseWriter as the io.Writer results in a context cancelled error most of the time. About 1 in 4 attempts are successful.

The error is "copied to out with errors: context canceled"

Expected: No context cancelled error and successful download

Similar code using the older azure-storage-blob-go repo worked. This was discovered whilst moving across to azure-sdk-for-go.

[eccles]

Ctx has the following value:

ontext: context.Background.WithValue(type *http.contextKey, val <not Stringer>).WithValue(type *http.contextKey, val 10.244.11.160:8000).WithCancel.WithCancel.WithValue(type metadata.mdIncomingKey, val <not Stringer>).WithValue(type mux.contextKey, val <not Stringer>).WithValue(type mux.contextKey, val <not Stringer>).WithCancel

[eccles]

Note that various ctx args were tried such as context.Background() to no avail

[msftbot[bot]]

Thank you for your feedback. This has been routed to the support team for assistance.

[eccles]

I have reworked the code to get the Body and feed that as a Reader to io.Copy. This still gets the context canceleld error

     resp.BlobClient = azp.containerClient.NewBlobClient(identity)
        resp.CountToEnd = int64(azStorageBlob.CountToEnd)
        get, err := resp.BlobClient.Download(
                ctx,
                &azStorageBlob.DownloadBlobOptions{
                        BlobAccessConditions: &resp.blobAccessConditions,
                        Count:                &resp.CountToEnd,
                },
        )
        if err != nil && err == io.EOF { // nolint
                logger.Sugar.Infof("cannot get blob body: %v", err)
                return nil, ErrorFromError(err)
        }
        resp.Reader = get.Body(&azStorageBlob.RetryReaderOptions{})
       _, err = io.Copy(w, resp.Reader)
        if err != nil {
                logger.Sugar.Infof("copied to out with errors: %v", err)
        }

[SaurabhSharma-MSFT]

@eccles We are looking into it and get back to you for any additional information.

[eccles]

thank you for your attention - this is not urgent but will require a fix if we are to move to the new azure-sdk as recommended by yourselves.

[jhendrixMSFT]

This might have been due to an issue in azcore which has since been fixed. https://github.com/Azure/azure-sdk-for-go/pull/17797

We've just released an updated version [email protected] that contains this (and other fixes). Note that we've refactored the public surface area. However, we feel that it makes navigating the package much easier. Can you please try it and report back?

[msftbot[bot]]

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