Following “next” link with relative paths using rv

I am using the rvest package to scrape information from the page http://www.radiolab.org/series/podcasts. After scraping the first page, I want to follow the "Next" link at the bottom, scrape that second page, move onto the third page, etc.

The following line gives an error:

html_session("http://www.radiolab.org/series/podcasts") %>% follow_link("Next")
## Navigating to 
##     
##       ./2/  
## Error in parseURI(u) : cannot parse URI 
##     
##       ./2/

Inspecting the HTML shows there is some extra cruft around the "./2/" that rvest apparently doesn't like:

html("http://www.radiolab.org/series/podcasts") %>% html_node(".pagefooter-next a")
## <a href="&#10;    &#10;      ./2/  ">Next</a> 

.Last.value %>% html_attrs()
##                   href 
## "\n    \n      ./2/  "

Question 1: How can I get rvest::follow_link to treat this link correctly like my browser does? (I could manually grab the "Next" link and clean it up with regex, but prefer to take advantage of the automation provided with rvest.)

At the end of the follow_link code, it calls jump_to. So I tried the following:

html_session("http://www.radiolab.org/series/podcasts") %>% jump_to("./2/")
## <session> http://www.radiolab.org/series/2/
##   Status: 404
##   Type:   text/html; charset=utf-8
##   Size:   10744
## Warning message:
## In request_GET(x, url, ...) : client error: (404) Not Found

Digging into the code, it looks like the issue is with XML::getRelativeURL, which uses dirname to strip off the last part of the original path ("/podcasts"):

XML::getRelativeURL("./2/", "http://www.radiolab.org/series/podcasts/")
## [1] "http://www.radiolab.org/series/./2"

XML::getRelativeURL("../3/", "http://www.radiolab.org/series/podcasts/2/")
## [1] "http://www.radiolab.org/series/3"

Question 2: How can I get rvest::jump_to and XML::getRelativeURL to correctly handle relative paths?

Since this problem still seems to occur with RadioLab.com, your best solution is to create a custom function to handle this edge case. If you're only worried about this site - and this particular error - then you can write something like this:

library(rvest)

follow_next <- function(session, text ="Next", ...) {
    link <- html_node(session, xpath = sprintf("//*[text()[contains(.,'%s')]]", text))
    url <- html_attr(link, "href")
    url = trimws(url)
    url = gsub("^\\.{1}/", "", url)
    message("Navigating to ", url)
    jump_to(session, url, ...)
}

That would allow you to write code like this:

html_session("http://www.radiolab.org/series/podcasts") %>%
    follow_next()

#> Navigating to 2/
#> <session> http://www.radiolab.org/series/podcasts/2/
#>   Status: 200
#>   Type:   text/html; charset=utf-8
#>   Size:   61261

This is not per se an error - the URL on RadioLab is malformed, and failing to parse a malformed URL is not a bug. If you want to be liberal in how you handle the issue you need to manually work around it.

Note that you could also use RSelenium to launch an actual browser (e.g. Chrome) and have that perform the URL parsing for you.