fauxpas – HTTP conditions package

HTTP, or Hypertext Transfer Protocol is a protocol by which most of us interact with the web. When we do requests to a website in a browser on desktop or mobile, or get some data from a server in R, all of that is using HTTP.

HTTP has a rich suite of status codes describing different HTTP conditions, ranging from Success to various client errors, to server errors. R has a few HTTP client libraries – crul, curl, httr, and RCurl – each of which is slightly different. I thought it would be nice if there was a single way to do HTTP exception handling across these libraries.

fauxpas is a package to handle HTTP conditions. Methods are included for general purpose HTTP error handling, as well as individual methods for every HTTP status code, both via status code numbers as well as their descriptive names. fauxpas allows flexibility to have stop, message or warning behavior.

In addition, you can use custom whisker template to have any configuration of status code, short description, and verbose message.

fauxpas currently supports integration with crul, curl, and httr.

It will be interesting to see how people use fauxpas. It may be that users really like being able to handle individual HTTP conditions separately, or it may be that most users simply want a general purpose handler.

Installation

install.packages("fauxpas")

library("fauxpas")

Generic http condition handler

Error() is the most generic handler in fuaxpas

First, let's make an HTTP request, here with crul, using the wonderful https://httpbin.org site.

library("crul")
res <- HttpClient$new("https://httpbin.org/status/418")$get()

Next, we'll constrct an error object

(x <- Error$new(behavior = "stop"))
#> <HTTP Error>
#>   behavior: stop
#>   message_template:  (HTTP ).

The default behavior is stop – you can also choose warning or message.

The object is of class Error and is an R6 object. You can inspect parts of the object

x$behavior
#> [1] "stop"
x$behavior_type
#> [1] "error"
x$call.
#> [1] FALSE
x$message_template
#> [1] " (HTTP )."

Check the response

x$do(res)
#> Error: I'm a teapot (HTTP 418).

HTTP* R6 methods

In addition to Error(), there's a method for every HTTP code – they start with HTTP, followed by the http code name. For example, HTTPBadGateway for the 502 code.

These are R6 methods as well, but inherit from the Error class. So they implement do(), but also do_verbose() to include a verbose explanation of the http condition.

Make an HTTP request:

res <- HttpClient$new("https://httpbin.org/status/414")$get()

x <- HTTPRequestURITooLong$new()

x$do(res)
#> Error: Request-URI Too Long (HTTP 414).

x$do_verbose(res)
#> Error: Request-URI Too Long (HTTP 414).
#>  - The server is refusing to service the request because the Request-URI is longer 
#> than the server is willing to interpret. This rare condition is only likely to occur 
#> when a client has improperly converted a POST request to a GET request with long 
#> query information, when the client has descended into a URI 'black hole' of 
#> redirection (e.g., a redirected URI prefix that points to a suffix of itself), or 
#> when the server is under attack by a client attempting to exploit security holes 
#> present in some servers using fixed-length buffers for reading or manipulating
#> the Request-URI.

http* methods

There's a series of simpler to use functions for every http condition that wrap the above HTTP* methods that follow the form http*, where the * is the status code number. For example, http404 for the 404 code.

Make an HTTP request:

library("crul")
res <- HttpClient$new("https://httpbin.org/status/418")$get()

Default behavior is to stop()

http(res)
#> Error: I'm a teapot (HTTP 418).

But you can easily do warning()

http(res, behavior = "warning")
#> Warning message:
#> I'm a teapot (HTTP 418). 

Or message()

http(res, behavior = "message")
#> I'm a teapot (HTTP 418).

Custom templates

The default way that conditions are handled is with the template:

" (HTTP )."

Named elements that are used for do() are:

• reason
• status

Named elements that are used for do_verbose() are:

• reason
• status
• message

All other named elements are ignored.

First, make an HTTP request:

library("crul")
res <- HttpClient$new("https://httpbin.org/status/418")$get()

Then, run a handler with a custom template:

http418(res, message_template = "\n  --> ")
#> Error: 418
#>   --> I'm a teapot

Future work

Even more customizeable messages

Right now, you can use a hack to customize the do_verbose() method to replace the mssg string (which holds the verbose explanation of the HTTP condition from the HTTP spec) with your own message. For example, servers often return custom messages explaining why a request failed (e.g., page must be a number). Ideally, you'd want to return that message along with the HTTP code (presumably 400 or similar) and the HTTP name (Bad Request).

I'm going to make this easier, so you don't have to replace the verbose HTTP condition explanation, so you can still expose that if you want.

Support RCurl

I hope to support RCurl at some point.

Feedback?

I'd love to know what people think about this package.

• Does the package API make sense?
  
• Any additional exported methods you'd like?

I know documentation can be better, e.g., there's no vignette yet (but adding that soon).