crul (version 1.5.0)

ok: check if a url is okay

Description

check if a url is okay

Usage

ok(x, status = 200L, info = TRUE, verb = "head", ua_random = FALSE, ...)

Value

a single boolean, if TRUE the URL is up and okay, if FALSE it is down; but, see Details

Arguments

x

either a URL as a character string, or an object of class HttpClient

status

(integer) one or more HTTP status codes, must be integers. default: 200L, since this is the most common signal that a URL is okay, but there may be cases in which your URL is okay if it's a 201L, or some other status code.

info

(logical) in the case of an error, do you want a message() about it? Default: TRUE

verb

(character) use "head" (default) or "get" HTTP verb for the request. note that "get" will take longer as it returns a body. however, "verb=get" may be your only option if a url blocks head requests

ua_random

(logical) use a random user agent string? default: TRUE. if you set useragent curl option it will override this setting. The random user agent string is pulled from a vector of 50 user agent strings generated from charlatan::UserAgentProvider (by executing replicate(30, UserAgentProvider$new()$user_agent()))

...

args passed on to HttpClient

Details

We internally verify that status is an integer and in the known set of HTTP status codes, and that info is a boolean

You may have to fiddle with the parameters to ok() as well as curl options to get the "right answer". If you think you are incorrectly getting FALSE, the first thing to do is to pass in verbose=TRUE to ok(). That will give you verbose curl output and will help determine what the issue may be. Here's some different scenarios:

• the site blocks head requests: some sites do this, try verb="get"

• it will be hard to determine a site that requires this, but it's worth trying a random useragent string, e.g., ok(useragent = "foobar")

• some sites are up and reachable but you could get a 403 Unauthorized error, there's nothing you can do in this case other than having access

• its possible to get a weird HTTP status code, e.g., LinkedIn gives a 999 code, they're trying to prevent any programmatic access

A FALSE result may be incorrect depending on the use case. For example, if you want to know if curl based scraping will work without fiddling with curl options, then the FALSE is probably correct, but if you want to fiddle with curl options, then first step would be to send verbose=TRUE to see whats going on with any redirects and headers. You can set headers, user agent strings, etc. to get closer to the request you want to know about. Note that a user agent string is always passed by default, but it may not be the one you want.

Examples

if (FALSE) {
# 200
ok("https://www.google.com") 
# 200
ok("https://hb.opencpu.org/status/200")
# more than one status
ok("https://www.google.com", status = c(200L, 202L))
# 404
ok("https://hb.opencpu.org/status/404")
# doesn't exist
ok("https://stuff.bar")
# doesn't exist
ok("stuff")

# use get verb instead of head
ok("http://animalnexus.ca")
ok("http://animalnexus.ca", verb = "get")

# some urls will require a different useragent string
# they probably regex the useragent string
ok("https://doi.org/10.1093/chemse/bjq042")
ok("https://doi.org/10.1093/chemse/bjq042", verb = "get", useragent = "foobar")

# with random user agent's
## here, use a request hook to print out just the user agent string so 
## we can see what user agent string is being sent off
fun_ua <- function(request) {
  message(paste0("User-agent: ", request$options$useragent), sep = "\n")
}
z <- crul::HttpClient$new("https://doi.org/10.1093/chemse/bjq042", 
 hooks = list(request = fun_ua))
z
replicate(5, ok(z, ua_random=TRUE), simplify=FALSE)
## if you set useragent option it will override ua_random=TRUE
ok("https://doi.org/10.1093/chemse/bjq042", useragent="foobar", ua_random=TRUE)

# with HttpClient
z <- crul::HttpClient$new("https://hb.opencpu.org/status/404", 
 opts = list(verbose = TRUE))
ok(z)
}