[MacPorts] #55502: Use size from checksums for curl progress bar when server does not supply length header

[MacPorts]

#55502: Use size from checksums for curl progress bar when server does not supply
length header
-------------------------+-----------------
 Reporter:  ryandesign   |      Owner:
     Type:  enhancement  |     Status:  new
 Priority:  Normal       |  Milestone:
Component:  base         |    Version:
 Keywords:               |       Port:
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 When MacPorts is fetching a distfile using libcurl, and the web server
 does not supply a `Length` header, MacPorts does not know how big the file
 is, so it can't display a determinate progress bar and has to fall back on
 an indeterminate progress bar. GitHub's automatically generated tarballs
 are a common example of when this happens.

 MacPorts now has support for portfile authors to indicate the filesize in
 the `checksums` line, using the checksum type `size`.

 For distfiles that indicate their size in this way, MacPorts should be
 able to use that information to display a determinate progress bar, even
 if the server doesn't supply the length.

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Ticket URL: <https://trac.macports.org/ticket/55502>
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