Install or uninstall a callback function
Supported callback functions:
This callback is called before an HTTP request
is performed, with the request object as an argument.
If the callback returns a value other than NULL, the HTTP
request is not performed at all, and the return value of the callback
is returned. This mechanism can be used to replay previously
recorded HTTP responses.
This callback is called after an HTTP request
is performed. The callback is called with two arguments: the
request object and the response object of the HTTP
request. If this callback returns a value other than NULL,
then this value is returned by httr.
get_callback(name) set_callback(name, new_callback = NULL)
name |
Character scalar, name of the callback to query or set. |
new_callback |
The callback function to install, a function object;
or |
Note that it is not possible to install multiple callbacks of the same
type. The installed callback overwrites the previously intalled one.
To uninstall a callback function, set it to NULL with
set_callback().
See the httrmock package for a proper example that uses
callbacks.
get_callback returns the currently installed
callback, or NULL if none is installed.
set_callback returns the previously installed callback,
or NULL if none was installed.
## Not run:
## Log all HTTP requests to the screeen
req_logger <- function(req) {
cat("HTTP request to", sQuote(req$url), "\n")
}
old <- set_callback("request", req_logger)
g1 <- GET("https://httpbin.org")
g2 <- GET("https://httpbin.org/ip")
set_callback("request", old)
## Log all HTTP requests and response status codes as well
req_logger2 <- function(req) {
cat("HTTP request to", sQuote(req$url), "... ")
}
res_logger <- function(req, res) {
cat(res$status_code, "\n")
}
old_req <- set_callback("request", req_logger2)
old_res <- set_callback("response", res_logger)
g3 <- GET("https://httpbin.org")
g4 <- GET("https://httpbin.org/ip")
set_callback("request", old_req)
set_callback("response", old_res)
## Return a recorded response, without performing the HTTP request
replay <- function(req) {
if (req$url == "https://httpbin.org") g3
}
old_req <- set_callback("request", replay)
grec <- GET("https://httpbin.org")
grec$date == g3$date
set_callback("request", old_req)
## End(Not run)Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.