Internal GitHub downloader doesn't configure proxy

[mmarchetti]

We saw this issue in a Connect customer environment.

They have a proxy for internet access. http_proxy and https_proxy environment variables are set when packrat is invoked. Packrat has no trouble installing packages from CRAN.

What we saw is:

• Connect configures download.file.method to be curl, and sets some curl options.
• Packrat, with devtools and httr installed, uses its internal GitHub downloader which uses httr.
• The internal downloader doesn't configure httr's proxy settings based on http_proxy and https_proxy.
• Consequently, package downloads from GitHub failed.

Some ideas for fixes include always using the configured downloader, or configuring httr's proxy settings based on the standard proxy environment variables.

[mmarchetti]

We worked around this by removing devtools from the R installations being used in Connect.

[kevinushey]

See also:

https://github.com/rstudio/packrat/blob/6dd9d597b2549cc837503916e5b166c5518dc037/R/github.R#L9-L25 https://github.com/rstudio/packrat/blob/6dd9d597b2549cc837503916e5b166c5518dc037/R/gitlab.R#L9-L11

We could provide some mechanism for overriding the default Packrat behaviors here.