postForm: Submit an HTML form

Description

These functions provide facilities for submitting an HTML form using either the simple GET mechanism (appending the name-value pairs of parameters in the URL) or the POST method which puts the name-value pairs as separate sections in the body of the HTTP request. The choice of action is defined by the form, not the caller.

Usage

postForm(uri, ..., .params = list(), .opts = curlOptions(url = uri),
         curl = getCurlHandle(), style = 'HTTPPOST',
          .encoding = integer(), binary = NA, .checkParams = TRUE,
          .contentEncodeFun = curlEscape)
.postForm(curl, .opts, .params, style = 'HTTPPOST')
getForm(uri, ..., .params = character(), .opts = list(), curl = getCurlHandle(),
         .encoding = integer(), binary = NA, .checkParams = TRUE)

Value

By default, the text from the HTTP response is returned.

Arguments

uri: the full URI to which the form is to be posted. This includes the host and the specific file or script which will process the form.
...: the name-value pairs of parameters. Note that these are not the CURL options.
.params: instead of specifying the name-value parameters in "free" form via the ... argument, one can specify them as named list or character vector.
.opts: an object representing the CURL options for this call.
curl: the CURLHandle object created earlier if one is reusing these objects. Otherwise, a new one is generated and discarded.
style: this is typically a string and controls how the form data is posted, specifically the value for the Content-Type header and the particular representation. Use 'httppost' to use a multipart/form-data transmission and use 'post' for application/x-www-form-urlencoded content. This string is compared to the names of (the internal) PostStyles vector using partial matching. In the future, we will use enum values within R. The default is multipart/form-data for reasons of backward compatability.
.encoding: the encoding of the result, if it is known a priori. This can be an integer between 0 and 4 or more appropriately a string identifying the encoding as one of "utf-8", or "ISO-859-1".
binary: a logical value indicating whether the caller knows whether the resulting content is binary (TRUE) or not (FALSE) or unknown (NA).
.checkParams: a logical value that indicates whether we should perform a check/test to identify if any of the arguments passed to the form correspond to Curl options. This is useful to identify potential errors in specifying the Curl options in the wrong place (in the way we would for curlPerform). This check can lead to spurious warning messages if the form has parameters with names that do conflict with Curl options. By specifying FALSE for this parameter, you can avoid this test and hence any warnings. But make certain you know what you are doing.
.contentEncodeFun: a function which encodes strings in a suitable manner. For x-www-form-encoded submissions, this should most likely should be curlPercentEncode which maps spaces to +, = to %3D, etc. We are leaving the default as curlEscape for now until we test whether applications continue to work with the correct encoding.

Details

Creating a new CURLHandle allows the C-level code to more efficiently map the R-level values to their C equivalents needed to make the call. However, reusing the handle across calls can be more efficient in that the connection to a server can be maintained and thus, the sometimes expensive task of establishing it is avoided in subsequent calls.

Examples

Run this code


if(url.exists("http://www.google.com")) withAutoprint({
   # Two ways to submit a query to google. Searching for RCurl
  getURL("http://www.google.com/search?hl=en&lr=&ie=ISO-8859-1&q=RCurl&btnG=Search")

   # Here we let getForm do the hard work of combining the names and values.
  getForm("http://www.google.com/search", hl="en", lr="",
          ie="ISO-8859-1", q="RCurl", btnG="Search")

   # And here if we already have the parameters as a list/vector.
  getForm("http://www.google.com/search", .params = c(hl="en", lr="",
          ie="ISO-8859-1",  q="RCurl", btnG="Search"))
})


   # Now looking at POST method for forms.
url <- "http://wwwx.cs.unc.edu/~jbs/aw-wwwp/docs/resources/perl/perl-cgi/programs/cgi_stdin.cgi"
if(url.exists(url)) 
 postForm(url,
           name = "Bob", "checkedbox" = "spinich",
           submitButton = "Now!",
           textarea = "Some text to send",
           selectitem = "The item",
           radiobutton = "a", style = "POST")


  # Genetic database via the Web.
if(url.exists('http://www.wormbase.org/db/searches/advanced/dumper')) withAutoprint({
 x = postForm('http://www.wormbase.org/db/searches/advanced/dumper',
         species="briggsae",
         list="",
         flank3="0",
         flank5="0",
         feature="Gene Models",
         dump = "Plain TEXT",
         orientation = "Relative to feature",
         relative = "Chromsome",
         DNA ="flanking sequences only",
         .cgifields = paste(c("feature", "orientation", "DNA", "dump","relative"), collapse=", "))


 # Note that we don't have to paste multiple values together ourselves,
 # e.g. the .cgifields can be specified as a character vector rather
 # than a string.
 x = postForm('http://www.wormbase.org/db/searches/advanced/dumper',
         species="briggsae",
         list="",
         flank3="0",
         flank5="0",
         feature="Gene Models",
         dump = "Plain TEXT",
         orientation = "Relative to feature",
         relative = "Chromsome",
         DNA ="flanking sequences only",
         .cgifields =c("feature", "orientation", "DNA", "dump", "relative"))
})