Redirection heuristic for #113

[Mrmaxmeier]

I've tried to keep the heuristic general and avoid false-negatives as it only interferes if the last segment of the URL doesn't contain a .
(This will separates hash-like URLs from ones that contain a file extension)

Closes #113

[pkgw]

@Mrmaxmeier Thanks for tackling this! Do you understand the problem that's occurring in #113, then? I've been puzzled since I simply don't get that amount of redirection when I run the program myself. It doesn't seem like the redirects should be location-dependent, but I don't know a lot about how modern CDNs work.

[Mrmaxmeier]

@pkgw I guess Bintray only redirects to a CDN if it knows of a server that's in the general location of the request IP.
I'm not really sure though as I've used tectonic from my location (Europe) before and have not experienced this problem until now.

For reference: Here's the chain of redirects I get when resolving the URL:

curl -v -L https://purl.org/net/pkgwpub/tectonic-default
> GET /net/pkgwpub/tectonic-default HTTP/1.1
< HTTP/1.1 302 FOUND
< Location: https://dl.bintray.com/pkgw/tectonic/tl2016extras/2016.0r4/tlextras-2016.0r4.tar
...
> GET /pkgw/tectonic/tl2016extras/2016.0r4/tlextras-2016.0r4.tar HTTP/1.1
< HTTP/1.1 302 
< Location: https://akamai.bintray.com/59/59eecf9d49e259191ef66cb68b274c7c50fa20a75f593130d2603176418422eb?__gda__=exp=1499264990~hmac=bd70aaa3f2249e31aca70cf040e04d21132e19d1f9c27b63e9664ea8bd2f23fb&response-content-disposition=attachment%3Bfilename%3D%22tlextras-2016.0r4.tar%22&response-content-type=application%2Fx-tar&requestInfo=U2FsdGVkX19GOYzRiCoj7rRz6RTs24E4yUI2Wc3mKyq97fRbWcXx6QUWVJIpPjGn_2vPkzFEFkf_CNb6McWXfn2ickRChp6BZ4EwYa7POzj6lDugKNwDm4waK5LUo210UPGRCWIzzBooxHoj1ie5Kg
...
> GET /59/59eecf9d49e259191ef66cb68b274c7c50fa20a75f593130d2603176418422eb?__gda__=exp=1499265082~hmac=9297d5a6259c63dc9d1c58ef972177e228f5912143ea8631513b420bdff17c57&response-content-disposition=attachment%3Bfilename%3D%22tlextras-2016.0r4.tar%22&response-content-type=application%2Fx-tar&requestInfo=U2FsdGVkX1-fRImzfVxqor3YiRC3T5jXzJDLfhnflJi3TPK60FLOJ0GbGJZ6xbrEsTH85PlaOZVG492ak-kzjAA-1XasiputOmb1wJyjxoxy18bZjv2QUKuRhb07RMxaEwwAiYRLjKq3iejxpm7EBA HTTP/1.1
> Host: akamai.bintray.com
< HTTP/1.1 200 OK

[19h]

Yes, this is it. And yes, this fixes it. Good job and -- thanks.

🍻

[pkgw]

Ah, interesting. I've been blocking the 0.1.6 release on writing a skeleton manual but this seems like an important enough fix to be worth cutting a release even if I can't complete that task, which is looking like it's going to take a long time due to non-Tectonic obligations. I will aim to do so this weekend.

Thanks for the very rapid fix!