[MacPorts] #25128: Avoid checksum errors due to helpful DNS servers

[MacPorts]

#25128: Avoid checksum errors due to helpful DNS servers
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 Reporter:  ryandesign@…             |       Owner:  macports-tickets@…                   
     Type:  defect                   |      Status:  new                                  
 Priority:  Normal                   |   Milestone:  MacPorts 1.9.1                       
Component:  base                     |     Version:  1.8.2                                
 Keywords:                           |        Port:                                       
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 We've had quite a lot of tickets filed lately about checksum errors, and I
 have a feeling a fair number of them are because of the "helpful" DNS
 servers ISPs seem to be so fond of providing these days. When asking such
 DNS servers about a hostname that does not exist, they do not respond that
 the hostname does not exist; instead, they respond with the IP address of
 the ISP's search page, and if you are trying to connect to it over HTTP,
 they do a web search for you and send you the results. OpenDNS does this
 by default, so does Time Warner's Roadrunner service and probably others.
 MacPorts can't currently recognize this, so it saves that search results
 page as the distfile, which then of course doesn't match the expected
 checksums.

 The attached patch fixes this by using the "file" command to check if the
 downloaded file is an HTML page, and if so, discarding it and trying
 another mirror. I have tested this on Snow Leopard only. Before
 committing, I would like to verify that the "file" command on Leopard and
 preferably Tiger works the same way (i.e. accepts the same flags).

 There is already special-case code in this procedure for dealing with
 SourceForge mirrors. Possibly the new code I propose could replace the old
 SourceForge code; I was unable to locate a test case that triggered the
 SourceForge special-case code.

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Ticket URL: <http://trac.macports.org/ticket/25128>
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