To reproduce, try running the following code on a version with R without libcurl support (e.g. the Snow Leopard build of R 3.2.1):

> suppressMessages(library(BiocInstaller))
Error : .onLoad failed in loadNamespace() for 'BiocInstaller', details:
  call: url(paste0(.protocol(), "//bioconductor.org/BiocInstaller.dcf"))
  error: https:// URLs are not supported
Error: package or namespace load failed for ‘BiocInstaller’

The interaction occurs when 'BiocInstaller:::.protocol' attempts to ascertain whether `https://` or `http://` should be used. The implementation has:

        con <- file(fl <- tempfile(), "a")
        on.exit(close(con))
        sink(con, type = "message")
        tryCatch({
            fcon <- file("https://bioconductor.org/index.html")
            on.exit(close(fcon), add = TRUE)
            readLines(fcon, 1L)
        }, error = function(e) {
            message(conditionMessage(e))
        })
        sink(type = "message")
        flush(con)
        useHTTPS <- length(readLines(fl)) == 0L
        PROTOCOL <<- if (useHTTPS) 
            "https:"
        else "http:"

And that attempt to populate a message sink fails when executed within a suppressMessages() context. Although the above example is artificial, most other examples may not be -- it's easy to imagine that the BiocInstaller namespace might be implicitly loaded deep within the bowels of some code; for example, 'packrat::snapshot()' will query 'BiocInstaller::biocinstallRepos()', and a user calling 'packrat::snapshot()' wrapped in 'suppressMessages()' will then see the BiocInstaller load error.

There are a lot of safer ways this check for https could be implemented:

1. Attempt to read a URL with known contents, and check for expected output.
2. Check 'capabilities("libcurl")'.
3. Check for a specific version of R.

Thanks,
Kevin

---

> sessionInfo()
R version 3.2.1 (2015-06-18)
Platform: x86_64-apple-darwin10.8.0 (64-bit)
Running under: OS X 10.12 (unknown)

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] utils   methods base   

loaded via a namespace (and not attached):
[1] BiocInstaller_1.20.3 graphics_3.2.1       tools_3.2.1          grDevices_3.2.1      stats_3.2.1       

Hi Kevin -- I've been digesting this and should have replied earlier. First the use of sink was 'necessary' because of the way that version of R handled failed connections (via message or print rather than warning / error). Second, that version of Bioconductor is frozen and won't be changed. Third, the current check does not need to and so does not use sink (see BiocInstaller::.protocol). And finally, I guess the code is an attempt at 1. (try the connection); 2. is inadequate in general because e.g., on my Linux libcurl("capabilities") simply returns TRUE without additional information about https support; 3. is not sufficient because the version of R does not determine https support. I believe that there is code in RStudio that tests for https support, but I've lost track of where that is, so any info would be appreciated.