req_perform()
will automatically convert HTTP errors (i.e. any 4xx or 5xx
status code) into R errors. Use req_error()
to either override the
defaults, or extract additional information from the response that would
be useful to expose to the user.
Arguments
- req
A httr2 request object.
- is_error
A predicate function that takes a single argument (the response) and returns
TRUE
orFALSE
indicating whether or not an R error should be signalled.- body
A callback function that takes a single argument (the response) and returns a character vector of additional information to include in the body of the error. This vector is passed along to the
message
argument ofrlang::abort()
so you can use any formatting that it supports.
Value
A modified HTTP request.
Error handling
req_perform()
is designed to succeed if and only if you get a valid HTTP
response. There are two ways a request can fail:
The HTTP request might fail, for example if the connection is dropped or the server doesn't exist. This type of error will have class
c("httr2_failure", "httr2_error")
.The HTTP request might succeed, but return an HTTP status code that represents an error, e.g. a
404 Not Found
if the specified resource is not found. This type of error will have (e.g.) classc("httr2_http_404", "httr2_http", "httr2_error")
.
These error classes are designed to be used in conjunction with R's
condition handling tools (https://adv-r.hadley.nz/conditions.html).
For example, if you want to return a default value when the server returns
a 404, use tryCatch()
:
Or if you want to re-throw the error with some additional context, use
withCallingHandlers()
, e.g.:
withCallingHandlers(
req |> req_perform() |> resp_body_json(),
httr2_http_404 = function(cnd) {
rlang::abort("Couldn't find user", parent = cnd)
}
)
Learn more about error chaining at rlang::topic-error-chaining.
See also
req_retry()
to control when errors are automatically retried.
Examples
# Performing this request usually generates an error because httr2
# converts HTTP errors into R errors:
req <- request(example_url()) |>
req_url_path("/status/404")
try(req |> req_perform())
#> Error in req_perform(req) : HTTP 404 Not Found.
# You can still retrieve it with last_response()
last_response()
#> <httr2_response>
#> GET http://127.0.0.1:42095/status/404
#> Status: 404 Not Found
#> Content-Type: text/plain
#> Body: None
# But you might want to suppress this behaviour:
resp <- req |>
req_error(is_error = \(resp) FALSE) |>
req_perform()
resp
#> <httr2_response>
#> GET http://127.0.0.1:42095/status/404
#> Status: 404 Not Found
#> Content-Type: text/plain
#> Body: None
# Or perhaps you're working with a server that routinely uses the
# wrong HTTP error codes only 500s are really errors
request("http://example.com") |>
req_error(is_error = \(resp) resp_status(resp) == 500)
#> <httr2_request>
#> GET http://example.com
#> Body: empty
#> Policies:
#> • error_is_error: a function
# Most typically you'll use req_error() to add additional information
# extracted from the response body (or sometimes header):
error_body <- function(resp) {
resp_body_json(resp)$error
}
request("http://example.com") |>
req_error(body = error_body)
#> <httr2_request>
#> GET http://example.com
#> Body: empty
#> Policies:
#> • error_body: a function
# Learn more in https://httr2.r-lib.org/articles/wrapping-apis.html