If I read a file through a url() connection, it seems to close or corrupt the connection on the way out. This is non-ideal, since it leaves an invalid connection just sort of sitting there:
connection <- url("http://www.iana.org/assignments/ipv4-address-space/ipv4-address-space.csv")
data <- read.csv(connection, as.is = TRUE)
Error in close.connection(connection) : invalid connection
Error in summary.connection(x) : invalid connection
The ideal behaviour is either (1) reading the file through doesn't do anything to the connection or (2) it explicitly closes the connection and has a more sensible error message than "this is invalid and that's all we're giving you".