Throughput oddities with some downloads

[Lanigiro]

All of these are long-standing issues with downloads that continue in 2.7.4.0. All of them could be the uploader's fault. Most of them affect downloads from ED2K.

* Downloads sometimes begin and then sit there showing as "Active" with 0 throughput, without any volume being added, so it really is zero and not just low. Eventually these time out. With a given source for a given file, the behavior is consistent. It usually happens with partial sources (have some part of the file we do need, but don't have the whole file). Shareaza seems to request a range that the source has and that is needed, but after that, nothing seems to be transferred. This happens most commonly with ED2K partial sources, but sometimes with Gnutella ones as well.

* Downloads sometimes begin, transfer a small volume, and then languish for a while, before abruptly downloading most of the rest of the file, undownloading(!) the initial bit transferred, and then forgetting the source(!???). This only happens with DC++. Re-adding the source (hope you kept the tab with the search result around) usually results in the rest of the file downloading successfully, and the file verifying. When a large number of DC++ hits on a common source appear, downloading more than one of them almost invariably produces this syndrome, but upon re-adding the source for the first file, not only does it typically complete normally but the others on that source then tend to follow, without any further hiccups, and usually very quickly even for largish files.

* Downloads sometimes go extremely slowly, showing a distinctive square-wave throughput pattern with a roughly 50% duty cycle and a peak throughput well below 1 measly KB/s, with a trough throughput of precisely zero. See attached image for an example. (Boy, was I glad that file was not a long HD video instead.) This seems to happen mainly, perhaps exclusively, with ED2K transfers. The file tends to download successfully ... eventually.

* Once in a while I find a file that downloads quickly and completely, only the downloaded volume disappears and Shareaza forgets the source(s). Adding the source back results in the same thing repeating. Shareaza seems incapable of actually downloading the file in these instances, or rather, seems incapable of downloading it and keeping it. This seems to also be an ED2K-source-exclusive issue. (The partials that "download" at 0b/s from partial sources at least can be successfully downloaded when a complete source connects, and the other two cases above require manually adding sources back and/or just waiting patiently, but this one appears to be an outright show-stopper.)

[Lanigiro]

Oh, here's another one. Download sometimes goes into a state where it keeps slowing down. When this happens, the speed drop seems to be a slow exponential decay ... not slow enough for it not to extrapolate to stopping before the file is completely downloaded, though, as evidenced by the countdown becoming a countup. Sometimes it recovers on its own; sometimes the speed ramps down all the way to zero, followed after a minute or so by a timeout.

This happens with G2 sources, and can happen when both the uploader and the downloader are running Shareaza 2.7.4.0, which means this particular buggy behavior is Shareaza's fault (but might be in either the upload code or the download code) and is not fixed in the current version (whichever side of the upload/download divide it's on).