RCurl (version 0.9-2)

getURL: Download a URI

Description

This function downloads one or more URIs (a.k.a. URLs). It uses libcurl under the hood to perform the request and retrieve the response. There are a myriad of options that can be specified using the ...mechanism to control the creation and submission of the request and the processing of the response. The request supports any of the facilities within the version of libcurl that was installed. One can examine these via curlVersion.

Usage

getURL(url, ..., .opts = list(), write = basicTextGatherer(),
         curl = getCurlHandle(), async = length(url) > 1, .encoding = integer())
getURI(url, ..., .opts = list(), write = basicTextGatherer(),
         curl = getCurlHandle(), async = length(url) > 1, .encoding = integer())

Arguments

url

a string giving the URI

...

named values that are interpreted as CURL options governing the HTTP request.

.opts

a named list or CURLOptions object identifying the curl options for the handle. This is merged with the values of ...to create the actual options for the curl handle in the request.

write

if explicitly supplied, this is a function that is called with a single argument each time the the HTTP response handler has gathered sufficient text. The argument to the function is a single string. The default argument provides both a

curl

the previously initialized CURL context/handle which can be used for multiple requests.

async

a logical value that determines whether the download request should be done via asynchronous,concurrent downloading or a serial download. This really only arises when we are trying to download multiple URIs in a single call. There are trade-of

.encoding

an integer or a string that explicitly identifies the encoding of the content that is returned by the HTTP server in its response to our query. The possible strings are UTF-8 or ISO-8859-1 and the integers

Value

• If no value is supplied for write, the result is the text that is the HTTP response. (HTTP header information is included if the header option for CURL is set to TRUE and no handler for headerfunction is supplied in the CURL options.)

  Alternatively, if a value is supplied for the write parameter, this is returned. This allows the caller to create a handler within the call and get it back. This avoids having to explicitly create and assign it and then call getURL and then access the result. Instead, the 3 steps can be inlined in a single call.

concept

• Web
• HTTP

References

Curl homepage http://curl.haxx.se

See Also

curlPerform curlOptions

Examples

# Regular HTTP
  txt = getURL("http://www.omegahat.org/RCurl/")
   # Then we could parse the result.
  if(require(XML))
     htmlTreeParse(txt, asText = TRUE)


        # HTTPS. First check to see that we have support compiled into
        # libcurl for ssl.
  if("ssl" %in% names(curlVersion()$features)) {
     txt = tryCatch(getURL("https://sourceforge.net/"),
                    error = function(e) {
                                  getURL("https://sourceforge.net/",
                                            ssl.verifypeer = FALSE)
                              })

  }


     # Create a CURL handle that we will reuse.
  curl = getCurlHandle()
  pages = list()
  for(u in c("http://www.omegahat.org/RCurl/index.html",
             "http://www.omegahat.org/RGtk/index.html")) {
     pages[[u]] = getURL(u, curl = curl)
  }


    # Set additional fields in the header of the HTTP request.
    # verbose option allows us to see that they were included.
  getURL("http://www.omegahat.org", httpheader=c(Accept = "text/html", MyField="Duncan"), verbose = TRUE)



    # Arrange to read the header of the response from the HTTP server as
    # a separate "stream". Then we can break it into name-value
    # pairs. (The first line is the 
  h = basicTextGatherer()
  txt = getURL("http://www.omegahat.org/RCurl", header= TRUE, headerfunction = h[[1]], httpheader = c(Accept="text/html", Test=1), verbose = TRUE)
  read.dcf(textConnection(paste(h$value(NULL)[-1], collapse="")))



   # Test the passwords.
  x = getURL("http://www.omegahat.org/RCurl/testPassword/index.html",
               userpwd = "bob:duncantl")

#  Needs specific information from the cookie file on a per user basis
  #  with a registration to the NY times.
  x = getURL("http://www.nytimes.com",
                 header = TRUE, verbose = TRUE,
                 cookiefile = "/home/duncan/Rcookies",
                 netrc = TRUE,
                 maxredirs = as.integer(20),
                 netrc.file = "/home2/duncan/.netrc1",
                 followlocation = TRUE)

   d = debugGatherer()
   x = getURL("http://www.omegahat.org", debugfunction=d$update, verbose = TRUE)
   d$value()


    #############################################
    #  Using an option set in R
   opts = curlOptions(header = TRUE, userpwd = "bob:duncantl", netrc = TRUE)
   getURL("http://www.omegahat.org/RCurl/testPassword/index.html", verbose = TRUE, .opts = opts)

     # Using options in the CURL handle.
   h = getCurlHandle(header = TRUE, userpwd = "bob:duncantl", netrc = TRUE)
   getURL("http://www.omegahat.org/RCurl/testPassword/index.html",  verbose = TRUE, curl = h)



   # Use a C routine as the reader. Currently gives a warning.
  routine = getNativeSymbolInfo("R_internalWriteTest", PACKAGE = "RCurl")$address
  getURL("http://www.omegahat.org/RCurl/index.html", writefunction = routine)



  # Example
  uris = c("http://www.omegahat.org/RCurl/index.html", "http://www.omegahat.org/RCurl/philosophy.xml")
  txt = getURI(uris)
  names(txt)
  nchar(txt)

  txt = getURI(uris, async = FALSE)
  names(txt)
  nchar(txt)


  routine = getNativeSymbolInfo("R_internalWriteTest", PACKAGE = "RCurl")$address
  txt = getURI(uris, write = routine, async = FALSE)
  names(txt)
  nchar(txt)