file_hash questions

[jb]

Le 23.09.20 à 23:26, Camille Moulin a écrit :
> Hi Tom,
> On 22/09/2020 07:43, amindfv at mailbox.org wrote:


Hi,

>> Apologies if this is answered in the docs - a quick search didn't uncover the answers.
> Generally speaking, the documentation of the file format could be
> improved :-(
>
>
>> I'm wondering about the "kdenlive:file_hash" property in the file XML:
>>
>>    - Which hashing algorithm is used?
>
>  From what I understand, it's seems to be md5, but, for performance
> reasons,  it's calculated only on the first and last Mo of the file if
> the file is bigger than 2Mo
>
> In ./src/bin/projectclip.cpp, starting line 820:
>
>>          QFile file(clipUrl());
>>          if (file.open(QIODevice::ReadOnly)) { // write size and hash
>> only if resource points to a file
>>              /*
>>               * 1 MB = 1 second per 450 files (or faster)
>>               * 10 MB = 9 seconds per 450 files (or faster)
>>               */
>>              if (file.size() > 2000000) {
>>                  fileData = file.read(1000000);
>>                  if (file.seek(file.size() - 1000000)) {
>>                      fileData.append(file.readAll());
>>                  }
>>              } else {
>>                  fileData = file.readAll();
>>              }
>>              file.close();
>>             
>> ClipController::setProducerProperty(QStringLiteral("kdenlive:file_size"),
>> QString::number(file.size()));
>>              fileHash = QCryptographicHash::hash(fileData,
>> QCryptographicHash::Md5);
>>          }

That's correct.


>>    - When are the hashes checked? E.g. if I save a kdenlive file, quit, then reopen it, will the hashes of the files on disk be checked?
> Yes, I think so

That's a very good question. In fact the hash not really checked during 
normal usage. It is updated when Kdenlive is running and detects that 
the file was changed or when the user triggers reloading a clip, but 
does not seem to be checked on project opening. Thinking of it, I think 
that if the user changes a clip when Kdenlive is not running, opening 
the project will contain an incorrect hash, leading to possible bugs.


It would be much safer to check it on each project opening... I will 
investigate and come back to you.


Regards,

Jean-Baptiste

>>   Are there other points at which it's checked? Can the user manually start a check?
> I guess that if you reload the clip, it will check it and update it if
> modified.
>
> HTH,
>
> Camille
>