Re: How to determine when to stop receiving pack content

["Farhan Khan" <farhan@farhan.codes>]

August 11, 2019 11:04 AM, "Pratyush Yadav" <me@yadavpratyush.com> wrote:

> On 10/08/19 11:47PM, Farhan Khan wrote:
> 
>> Hi,
>> 
>> I am trying to write an implementation of git clone over ssh and am a little confused how to
>> determine a server response has ended. Specifically, after a client sends its requested 'want', the
>> server sends the pack content over. However, how does the client know to stop reading data? If I
>> run a simple read() of the file descriptor:
>> 
>> A. If I use reading blocking, the client will wait until new data is available, potentially
>> forever.
>> B. If I use non-blocking, the client might terminate reading for new data, when in reality new data
>> is in transit.
>> 
>> I do not see a mechanism to specify the size or to indicate the end of the pack content. Am I
>> missing something?
> 
> Well, I am not very familiar with git-clone internals, but I did some
> digging around, and I think I know what answer to your problem is.
> 
> Looking at Documentation/technical/protocol-v2.txt:34, the flush packet
> indicates the end of a message. Looking in the output section of the
> fetch command (protocol-v2.txt:342), it sends you some optional
> sections, and then the packfile and then sends a flush packet.
> 
> So your read should stop reading data when it sees the flush packet.
> 
> Another way would be to look at the packfile contents. Looking at
> Documentation/technical/pack-format.txt, the packfile contains the
> number of objects in the packfile, and each object entry has the object
> size. So you can stop reading after you have received the last object in
> the packfile (plus the 20-byte trailer).
> 
> I don't know which is the better way, but the former seems like a better
> choice to me.
> 
> --
> Regards,
> Pratyush Yadav

Hi Pratyush,

Thanks for your reply!

Unless I am mistaken, a pack file does not end in a flush_pkt. I ran some tests and did not see the stream end in "0000". Is there is a mistake somewhere on my end?

---
Farhan Khan
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