[Solved] lNet pause download and ranged request
lazarus / 38-Networking and Web Programming

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lancilnove · 2012-03-19 16:52

Hello,
I need to download big files, isos over 2GB in size. I tried Indy,
synapse, curl, interntettools, wininet. My choice is: lNet. I love it.
It's fast (the fastest), lightweight and user friendly. Unfortunately
it lacks something I need: ranged request. To tell the truth it has
the properties RangeStart and RangeEnd but, alas, they don't work.
When these properties are set, nothing happens. Without this feature
you can't pause/resume a download. You can't accelerate a download by
segmenting it in parallel tasks (like flashget). In a previous post
Almindor wrote, answering a similar question, 'I must admit this area
of lNet is outside of my expertise (http was done by Micha Nelissen
[neli]). I'll try to figure out if this is a bug or something is
missing on your end.'
Now, is this a bug? Is something missing on my end?

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Almindor · 2012-04-13 22:18

I'm afraid this might be a bug. I wrote lNet, but the HTTP part code
was done by Micha Nelissen and I'm afraid my knowledge of it is a bit
limited. I've also fallen out of things with FPC lately (am working on
Android atm. so yeah.. java) which makes this even more difficult to
fix. The good news is, I'm currently sort of on a long vacation so I
might be able to get back into things. I'll try to get Micha to look
at this too.

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Almindor · 2012-04-14 09:03

Micha thinks it should work:

<neli> not really, it should work?
<neli>   hasRangeStart := TLHTTPClient(FCreator).RangeStart <>
high(qword);
<neli>   hasRangeEnd := TLHTTPClient(FCreator).RangeEnd <>
high(qword);
<neli> is the code to include it
<neli>   if hasRangeStart or hasRangeEnd then
<neli> ....
<neli> just set it before sending the request afaics

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lancilnove · 2012-04-16 18:12

Ciao Alminder. Thanks for having found the time to answer.
lNet is a nice little creature that deserves proper attention.

I think that The lines in lhttp.pp you're referring to are working
fine.
According to Http Analyzer, a very useful tool, the header is ok (the
server returns 206 as it should be for ranged requests).
It is as if a 206 answer triggered a disconnect event in the client.
lNet can send a range request but can't handle a 206 answer.
Look at these lines in lhttp.pp, 206 is not even contemplated:
Code: [Select]  HTTPStatusCodes: array[TLHTTPStatus] of dword =
    (0, 200, 204, 301, 302, 304, 400, 403, 404, 412, 414, 500, 501,
405);
  HTTPTexts: array[TLHTTPStatus] of string =
    ('', 'OK', 'No Content', 'Moved Permanently', 'Found', 'Not
Modified', 'Bad Request', 'Forbidden',
     'Not Found', 'Precondition Failed', 'Request Too Long', 'Internal
Error',
     'Method Not Implemented', 'Method Not Allowed');
Here's a sample of the code I used:

Code: [Select]  HTTPClient.Host := Host;
  HTTPClient.Port := Port;
  HTTPClient.URI := URI;
  HTTPClient.Method:= hmGet;
  [...]
  HTTPClient.RangeStart := 10;
  HTTPClient.RangeEnd := 100;
  //HTTPClient.AddExtraHeader('Range: bytes=start-end');
  HTTPClient.SendRequest;

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lancilnove · 2012-04-23 10:30

In 'The Fifth Element' Zorg, quoting Henry Wadsworth Longfellow or
Charles Spurgeon, says "If you want something done, do it yourself.
Yep!"

Well, I carefully perused lhttp.pp code and added a few lines.
RangeStart and RangeEnd properties are now ok. lNet works fine with
Range requests! This evening I'm going to test AddExtraHeader
property.
I'm very happy