unidentified bug causing short read of chunked data

[ghost]

The problem: (drakma:http-request "http://digidb.io/digimon-list/") got an input-chunking-unexpected-end-of-file error.

Details:
After I poking around the code, I find that it is indeed a short read of (read-sequence input-buffer inner-stream :start 0 :end chunk-size) in chunga::fill-buffer. (https://github.com/edicl/chunga/blob/cb333cdba178e99b03fa60e2caa8c5d3654201d8/input.lisp#L145)

The number of bytes read is consistent most of time, but sometimes it might vary.

The bytes read is valid, and another (read-sequence big-buffer chunga::inner-stream) in the debugger can successfully read the following content left in the stream.

How to reproduce:
This error is only reproducible on Android, where only ecl is available. Can both be reproduced in cl-repl app (which is available in Play Store), and ecl compiled in Termux (a terminal for android). This error is not reproducible by curl or other tools on the same device.

This error is only observed with remote server - but I only tested with "http://digidb.io/digimon-list/" so I am uncertain about other servers. On the other hand, replaying the response on localhost does not reproduce the error.

This error is only reproducible when using drakma:http-request without :want-stream t. Even if use want-stream,

1. use read-sequence directly with the returned stream
2. use drakma:read-body on returned http-stream, or
3. use drakma::%read-body on the returned stream
   does not reproduce the error (and the request is successful).

[stassats]

The android requirement makes this harder to diagnose (don't have an android device).

[ghost]

Even though I have one, the diagnose process so far is really painful.

I am currently run out of idea. I cannot think a single reason why drakma:read-body with :want-stream work, but directly use of drakma:http-request don't.

Do you have any suggestion how can I further investigate this problem?

Thanks

edit: wording

[stassats]

Why does it do only one read-sequence and then give up?

[ghost]

`chunga::fill-buffer` reads the whole chunk, which is very big (bigger than `+buffer-size+)` in a single run and compare it with `chunk-size`. That single `read-sequence`, for some reason, does not read all of the chunk, so it caused an error.

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On Thu, Dec 10, 2020, 2:47 AM Stas Boukarev ***@***.***> wrote: Why does it do only one read-sequence and then give up? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#108 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AIAYXPUAMX4HAJFZ2QEGNEDST7A4BANCNFSM4UT276EA> .

[stassats]

read() is not guaranteed to read everything up to EOF. I'll make change to chunga for you to try.

[stassats]

Although I'm not sure how READ-SEQUENCE is implemented on ECL.

[stassats]

Can you try edicl/chunga@e83c804

And I hope I got the logic right, as I don't have anything to test it on.

[ghost]

Yes, it works. I am still curious about why use of `:want-stream nil` + read-body does not trigger the bug, though. Thanks for the fix.

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On Thu, Dec 10, 2020, 3:40 AM Stas Boukarev ***@***.***> wrote: Can you try ***@***.*** <edicl/chunga@e83c804> And I hope I got the logic right, as I don't have anything to test it on. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#108 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AIAYXPXJNL3BYEULGYP2GSDST7HBFANCNFSM4UT276EA> .

[stassats]

I'm not sure it's the right fix, maybe ECL implements read-sequence incorrectly. CLHS says that read-sequence returns fewer elements only upon reaching EOF.

[ghost]

Yeah. I doubt that too. However, with almost the same call stack, directly calling read-body with http-stream obtained from returned values from http-request with (:want-stream t) seems to be able to use the old code (read-sequence) successfully.

…

On Thu, Dec 10, 2020, 11:02 AM Stas Boukarev ***@***.***> wrote: I'm not sure it's the right fix, maybe ECL implements read-sequence incorrectly. CLHS says that read-sequence returns fewer elements only upon reaching EOF. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#108 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AIAYXPXLYGZVQVAR6U5K2KDSUA24PANCNFSM4UT276EA> .