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Finds the URL to the ‘favicon’ for a website. This is useful if you want to display the ‘favicon’ in an HTML document or web application, especially if the website is behind a firewall.
library(faviconPlease)
faviconPlease("https://github.com/")
## [1] "https://github.githubassets.com/favicons/favicon.svg"
Also check out my blog post on faviconPlease for more background and examples.
Install latest release from CRAN:
install.packages("faviconPlease")
Install development version from GitHub:
install.packages("remotes")
::install_github("jdblischak/faviconPlease") remotes
Please note that the faviconPlease project is released with a Contributor Code of Conduct. By contributing to this project, you agree to abide by its terms.
By default, faviconPlease()
uses the following strategy
to find the URL to the favicon for a given website. It stops once it
finds a URL and returns it.
Download the HTML file and search its <head>
for any <link>
elements with rel="icon"
or rel="shortcut icon"
.
Download the HTML file at the root of the server (i.e. discard
the path) and search its <head>
for any
<link>
elements with rel="icon"
or
rel="shortcut icon"
.
Attempt to download a file called favicon.ico
at the
root of the server. This is the default location that a browser looks if
the HTML file does not specify an alternative location in a
<link>
element. If the file favicon.ico
is successfully downloaded, then this URL is returned.
If the above steps fail, as a fallback, use the favicon service provided by the search engine DuckDuckGo. This provides a nice default for websites that don’t have a favicon (or can’t be easily found).
The default strategy above is designed to reliably get you a favicon URL for most websites. However, you can customize it as needed.
The default fallback function is faviconDuckDuckGo()
. To
instead use Google’s favicon service, you can set the argument
fallback = faviconGoogle
.
Note that neither DuckDuckGo nor Google have every favicon you might expect. And the availability can change over time. You can see some examples in my blog post. Fortunately they both provide a generic favicon to insert when they don’t have the favicon.
You can use your own custom fallback function instead. It must accept
one argument, which is the server, e.g. "github.com"
. The
easiest approach would be to copy-paste one of the existing fallback
functions and modify it to use your alternative favicon service.
args(faviconDuckDuckGo)
## function (server)
## NULL
body(faviconDuckDuckGo)
## {
## iconService <- "https://icons.duckduckgo.com/ip3/%s.ico"
## favicon <- sprintf(iconService, server)
## return(favicon)
## }
If you have a URL to a generic favicon file that you would like to use as a fallback, you can directly pass this as a character vector. It could also be a path to an image file on the server where your app is running.
The default strategy first checks the <head>
for a
link to the favicon file and then checks for the availability of the
file favicon.ico
. You can change this order, or only
perform one of them, by changing the argument functions
passed to faviconPlease()
. It should be a list of
functions.
# default
= list(faviconLink, faviconIco)
functions # Switch the order
= list(faviconIco, faviconLink)
functions # Only search <head>
= list(faviconLink)
functions # Only check for favicon.ico
= list(faviconIco)
functions # Skip the favicon functions entirely and just use the fallback
= NULL functions
You can also create your own custom favicon function to pass to
faviconPlease()
. By default it must accept 3 arguments. It
will be passed the URL’s scheme (e.g. "https"
), server
(e.g. "github.com"
), and path
(e.g. "/jdblischak/faviconPlease"
). Your function should
return the URL to a favicon or an empty string, ""
, if it
can’t find one.
# Favicon functions must accept at least 3 positional arguments
args(faviconLink)
## function (scheme, server, path)
## NULL
As a concrete example, here is a custom function for searching for
favicon.ico
on Ubuntu 20.04, which has increased security
settings (see troubleshooting section below).
<- function(scheme, server, path) {
faviconIcoUbuntu20 faviconIco(scheme, server, path, method = "wget",
extra = c("--no-check-certificate",
"--ciphers=DEFAULT:@SECLEVEL=1"))
}
It calls faviconIco()
with the specific settings needed
by download.file()
to work on Ubuntu 20.04. You could then
use your custom function instead of the default
faviconIco()
by calling faviconPlease()
with
functions = list(faviconLink, faviconIcoUbuntu20)
.
Note that the example function faviconIcoUbuntu20()
will
likely fail on Windows, macOS, and Ubuntu versions prior to 20.04.
Unfortunately it’s not easy to make this fool proof for all operating systems and all websites. Here are some known issues:
download.file()
, used by faviconIco()
,
is known to have cross-platform issues. Thus the official documentation
in ?download.file
recommends:
Setting the
method
should be left to the end user.
Accordingly, faviconIco()
exposes the arguments
method
, extra
, and headers
, which
are passed directly to download.file()
. Alternatively you
can set the global options "download.file.method"
or
"download.file.extra"
.
Ubuntu 20.04 increased its default security settings for
downloading files from the internet (details).
Unfortunately many websites have not updated their SSL certificates to
comply with the increased security restrictions.
faviconLink()
has a workaround for this situation, but not
faviconIco()
. As an example, here’s how you could detect
the availability of favicon.ico for the Ensembl website on Ubuntu
20.
faviconIco("https", "www.ensembl.org", "",
method = "wget", extra = c("--no-check-certificate",
"--ciphers=DEFAULT:@SECLEVEL=1"))
Alternatively, if it’s an option for you, you could avoid this
workaround by using the previous Ubuntu LTS release 18.04. Also note
that the above command will fail on Ubuntu 18.04 because the default
wget
installed doesn’t have the argument
--ciphers
.
These binaries (installable software) and packages are in development.
They may not be fully stable and should be used with caution. We make no claims about them.