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https://github.com/jdblischak/faviconplease

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https://github.com/jdblischak/faviconplease

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output: github_document

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# faviconPlease



[![CRAN status](https://www.r-pkg.org/badges/version/faviconPlease)](https://cran.r-project.org/package=faviconPlease)

[![R-CMD-check](https://github.com/jdblischak/faviconPlease/workflows/R-CMD-check/badge.svg)](https://github.com/jdblischak/faviconPlease/actions)



```{r description, results='asis', echo=FALSE}

cat(read.dcf("DESCRIPTION", fields = "Description"))

```



```{r example}

library(faviconPlease)

faviconPlease("https://github.com/")

```



Also check out my [blog post on faviconPlease][blog-post] for more background

and examples.



[blog-post]: https://blog.jdblischak.com/posts/faviconplease/



## Installation



Install latest release from CRAN:



```{r installation-cran, eval=FALSE}

install.packages("faviconPlease")

```



Install development version from GitHub:



```{r installation-github, eval=FALSE}

install.packages("remotes")

remotes::install_github("jdblischak/faviconPlease")

```



## Code of Conduct

  

Please note that the faviconPlease project is released with a [Contributor Code

of Conduct](https://contributor-covenant.org/version/2/0/CODE_OF_CONDUCT.html).

By contributing to this project, you agree to abide by its terms.



## Default strategy



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.



1. Download the HTML file and search its `` for any `` elements with

`rel="icon"` or `rel="shortcut icon"`.



1. Download the HTML file at the root of the server (i.e. discard the path) and

search its `` for any `` elements with `rel="icon"` or

`rel="shortcut icon"`.



1. 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 `` element. If the file `favicon.ico`

is successfully downloaded, then this URL is returned.



1. If the above steps fail, as a fallback, use the [favicon service][ddg-icon]

provided by the search engine [DuckDuckGo][ddg]. This provides a nice default

for websites that don't have a favicon (or can't be easily found).



[ddg]: https://duckduckgo.com/

[ddg-icon]: https://duckduckgo.com/duckduckgo-help-pages/privacy/favicons/



## Extending faviconPlease



The default strategy above is designed to reliably get you a favicon URL for

most websites. However, you can customize it as needed.



### Change the fallback to use Google's favicon service



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][blog-post]. Fortunately they both provide a generic favicon to insert when

they don't have the favicon.



### Use a custom fallback function



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.



```{r custom-fallback}

args(faviconDuckDuckGo)

body(faviconDuckDuckGo)

```



### Use a custom fallback 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.



### Change the order of the favicon functions



The default strategy first checks the `` 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.



```{r order, eval=FALSE}

# default

functions = list(faviconLink, faviconIco)

# Switch the order

functions = list(faviconIco, faviconLink)

# Only search 

functions = list(faviconLink)

# Only check for favicon.ico

functions = list(faviconIco)

# Skip the favicon functions entirely and just use the fallback

functions = NULL

```



### Use a custom favicon function



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.



```{r faviconLink-signature}

# Favicon functions must accept at least 3 positional arguments

args(faviconLink)

```



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).



```{r faviconIcoUbuntu20}

faviconIcoUbuntu20 <- function(scheme, server, path) {

  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.



## Troubleshooting



Unfortunately it's not easy to make this fool proof for all operating systems

and all websites. Here are some known issues:



1. `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"`.



1. Ubuntu 20.04 increased its default security settings for downloading files

from the internet ([details][openssl-ticket]). 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.



    ```{r ubuntu20, eval=FALSE}

    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`.



    [openssl-ticket]: https://bugs.launchpad.net/ubuntu/+source/openssl/+bug/1864689