Error in UseMethod("http_error") in roadoi - r

Question

I'm trying out roadoi to access Unpaywall from R, but no matter what I try to query for, I'm getting this response:
Error in UseMethod("http_error") : no applicable method for
'http_error' applied to an object of class "c('simpleError', 'error',
'condition')"
Running methods(http_error) gives me this:
[1] http_error.character* http_error.integer* http_error.response*
Could this be caused by me being behind an institutional firewall? (even so, it seems weird that this would be the response...)
Is there a way around it?

Answer 1

The http_error (actually from library httr) is a very simple function: it loads an url given by a character (http_error.character), retrieves the response (http_error.response) and ultimately looks at the response code (http_error.integer). If the response code is >=400 the function returns TRUE otherwise FALSE.
What your error says, is that you (or any function in your chain) tries to call http_error on a simpleError object. My guess is that your firewall settings block the request. Because the request is blocked the underlying httr::RETRY (which is called from oadoi_fetch) returns an error instead of a proper response object and http_error sees just this error object and breaks.
If I locally switch off my proxy (through which I can make requests) I also get an error:
library(roadoi)
Sys.unsetenv(c("HTTP_PROXY", "HTTPS_PROXY"))
oadoi_fetch("10.1038/nature12373", email = "name#whatever.com")
# Error in UseMethod("http_error") :
# no applicable method for 'http_error' applied to an object of class
# "c('simpleError', 'error', 'condition')"
As soon as my proxy is set properly I get
Sys.setenv(HTTPS_PROXY = my_proxy, HTTP_PROXY = my_proxy)
oadoi_fetch("10.1038/nature12373", email = "name#whatever.com")
# # A tibble: 1 x 16
# doi best_oa_location oa_locations data_standard is_oa genre journal_is_oa journal_is_in_d~ journal_issns journal_name publisher title year updated non_compliant authors
# <chr> <list> <list> <int> <lgl> <chr> <lgl> <lgl> <chr> <chr> <chr> <chr> <chr> <chr> <list> <list>
# 1 10.1038~ <tibble [1 x 10]> <tibble [4 x~ 2 TRUE journa~ FALSE FALSE 0028-0836,147~ Nature Springer ~ Nanometre-s~ 2013 2019-04-0~
If the problem lies indeed with the proxy, I would try the following, which helped me on my corporate Windows machine, but may be dependent on your local IT setting:
## get the proxy settings
system("netsh winhttp show proxy")
Sys.setenv(HTTP_PROXY = <the proxy from netsh>, HTTPS_PROXY = <the proxy from netsh>)
Actually, you can reproduce the error easily:
httr::http_error(simpleError("Cannot reach the page"))
# Error in UseMethod("http_error") :
# no applicable method for 'http_error' applied to an object of class
# "c('simpleError', # 'error', 'condition')"