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fix resumable downloads crash when gzip #6996



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@memsharded memsharded commented May 11, 2020

Changelog: Bugfix: Resumable download introduced a bug when there is a fronted (like Apache) to Artifactory or other server that gzips the returned files, returning an incorrect Content-Length header that doesn't match the real content length.
Docs: Omit

Fix: #6984

This is a fix to #6984, but it would be good to implement something more robust that handles the compression from servers in a better way.

@memsharded memsharded added this to the 1.25.1 milestone May 11, 2020
@@ -120,19 +120,17 @@ def get_total_length():

gzip = (response.headers.get("content-encoding") == "gzip")
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@flashdagger flashdagger May 12, 2020

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Should we also consider other possible compression algorithms?

Suggested change
gzip = (response.headers.get("content-encoding") == "gzip")
is_compressed = (response.headers.get("content-encoding") in {"gzip", "deflate", "br"})

You could test them e.g. here:

As an alternative you could compute the total_length with len(response.content) in those cases, ignoring the Content-Length from headers...

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@memsharded memsharded May 12, 2020

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I'd prefer to just "revert" that regression, and we could open a new ticket for improving this for next releases. These other compressions types haven't been an issue so far (they would have raised exceptions in the past, just by using them), so I think this is ok as-is.

jgsogo approved these changes May 12, 2020
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@jgsogo jgsogo left a comment

It looks like we are not the only ones with this problem and it is something we cannot fix from the client-side [1] (unless we do not request gzip from the client?). We can merge this one if we are going to release 1.25 to fix the bug/regression (excluding other compression types as @flashdagger suggests probably is needed).


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@flashdagger flashdagger commented May 12, 2020

So my understanding is this:

You can only check if you received the full data requested if:

  • Content-Encoding is "identity" (the response default)
  • Content-Length is sent in response

If the content body is sent compressed (e.g. using gzip) Content-Length represents the compressed size (what was sent over the wire) or is even omitted. In that case transmission should fail anyway if data is missing. Not a case we should consider. So we cannot resume compressed responses since we don't read from the raw socket and let the requests library do the decompression.

@memsharded memsharded merged commit 1216c50 into conan-io:release/1.25 May 12, 2020
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@memsharded memsharded deleted the fix/resumable_download_gzip branch May 12, 2020
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3 participants