Improve wfs_api() error reporting

[jlehtoma]

Currently wfs_api() passes the provided WFS URL as-is and expects a correct response. However, it is not robust against faulty URLs (404), timeouts (408) or any other unexpected situations. It would be good if it did. In principle this would be up to ows4R, but nut sure at this point how it deals with errors.

[jlehtoma]

Since we're not using ows4R, the checking responsibility is now on us (and maybe it was before too).

[jlehtoma]

@muuankarski we might be able to replace check_api_access() with little enhancements in wfs_api(). If you can figure out which HTTP status code you're receiving while behind company firewall / proxy, we could include warnings to the user here. Could you test what httr::GET() will give you (see here onwards) in case there's no access?

[muuankarski]

@jlehtoma

as we got access to geo.stat.fi from our servers yesterday, I will try to reach a layer in Paituli wfs.

# Desktop windows
httr::http_status(httr::GET("http://avaa.tdata.fi/geoserver/paituli/wfs?service=WFS&version=2.0.0&request=getFeature&typename=paituli:kotus_pitajaAll"))
Error in curl::curl_fetch_memory(url, handle = handle) : 
  Timeout was reached: [avaa.tdata.fi] Connection timed out after 10000 milliseconds```
# server
> httr::http_status(httr::GET("http://avaa.tdata.fi/geoserver/paituli/wfs?service=WFS&version=2.0.0&request=getFeature&typename=paituli:kotus_pitajaAll"))
$category
[1] "Client error"

$reason
[1] "Forbidden"

$message
[1] "Client error: (403) Forbidden"

So the problem with proxy requiring authentication is that you get no http status code from there. Therefore this download.file()-hack. But there must be more elegant way to address this?

[jlehtoma]

Right! Thanks for checking this. I had a quick look at httr/curl and it seems that although it is possible to pass a custom failure callback to curl::curl_fetch_memory() used by httr::GET(), we can't actually pass such a callback through ``httr::GET()`. Two options come to mind:

1. Do a separate probe with curl::curl_fetch_memory() (much like with download.file() now) within wfs_api() using a custom failure callback to let user know about potential issue with a proxy.
2. Use tryCatch() with GET() within wfs_api(), catch timeout error (by parsing the error message) and let user know about potential issue with a proxy.