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rApache Web Application Development with R and Apache: Handler Return Values and HTTP Response Codes (Chapter V).

Saturday, July 19, 2014

It is a list of lists, with the nested list giving you the "name" of the file and the "tmp_name", the location of the temporary file. For instance, to reference the uploaded file from the input tag named "FirstFile" you would use FILES$FirstFile$tmp_name. Here's a code snippet to copy the file to the '/usr/local/uploaded_files' directory:

 

destination <- file.path('/usr/local/uploaded_files',FILES$FirstFile$name)
file.copy(FILES$FirstFile$tmp_name,destination,overwrite=TRUE)

 

NOTE: the temporary files are deleted after the R handler completes handling the request. Thus, it is imperative that you copy/move this file to your desired location before the R handler returns.

rapache-small

5.5 SERVER.

As you can see from the below output, the SERVER variable contains a wealth of information about the incoming web request:

> str(SERVER)
List of 30
$ headers_in        :List of 9
  ..$ Host           : chr "localhost:8181"
  ..$ User-Agent     : chr "Mozilla/5.0 (X11; U; Linux i686; en-US; ..."
  ..$ Accept         : chr "text/xml,application/xml,application/x..."
  ..$ Accept-Language: chr "en-us,en;q=0.5"
  ..$ Accept-Encoding: chr "gzip,deflate"
  ..$ Accept-Charset : chr "ISO-8859-1,utf-8;q=0.7,*;q=0.7"
  ..$ Keep-Alive     : chr "300"
  ..$ Connection     : chr "keep-alive"
  ..$ Cache-Control  : chr "max-age=0"
$ proto_num         : int 1001
$ protocol          : chr "HTTP/1.1"
$ unparsed_uri      : chr "/brew/server.html/beetles/?foo=bar"
$ uri               : chr "/brew/server.html/beetles/"
$ filename          : chr "/home/hornerj/rapache/branches/rapache-1-0-br..."
$ canonical_filename: chr "/home/hornerj/rapache/branches/rapache-1-0-br..."
$ path_info         : chr "/beetles/"
$ args              : chr "foo=bar"
$ content_type      : chr "text/html"
$ handler           : chr "r-script"
$ content_encoding  : NULL
$ range             : NULL
$ hostname          : chr "localhost"
$ user              : NULL
$ header_only       : logi FALSE
$ no_cache          : logi FALSE
$ no_local_copy     : logi FALSE
$ assbackwards      : logi FALSE
$ status            : int 200
$ method_number     : int 0
$ eos_sent          : logi FALSE
$ the_request       : chr "GET /brew/server.html/beetles/?foo=bar HTTP/1.1"
$ method            : chr "GET"
$ status_line       : NULL
$ bytes_sent        : num 0
$ clength           : num 0
$ remaining         : num 0
$ read_length       : num 0
$ request_time      :'POSIXct', format: chr "2007-08-15 11:11:49"
$ mtime             :'POSIXct', format: chr "1969-12-31 18:00:00"

 

Here's a description of each list element:

headers_in list containing all the HTTP headers sent by the client.

proto_num Integer. Protocol version number of protocol; 1.1 = 1001

protocol Character. Protocol string, as given to us, or HTTP/0.9.

unparsed_uri Character. The URI without any parsing performed.

uri Character. The path portion of the URI.

filename Character. The name of the file with full path information.

canonical_filename Character. The true filename. Case and aliases/symbolic links have been resolved.

 

path_info Character. The suffix portion of the url after it has been matched to an asset that the web server knows about. An asset is either a file or an url defined by an Apache Location directive.

 

cmd_path Character. The path taken from the corresponding configuration directive.

args Character. The HTTP GET data extracted from this request.

content_type Character. The content-type for the current request.

handler Character. The handler string that we use to call a handler function.

content_encoding Character. How to encode the data.

range Character. The HTTP Response header named "Range:".

hostname Character. The server hostname.

user Character. If an HTTP authentication check was made, this gets set to the user name.

header_only Logical. HEAD request, as opposed to GET.

no_cache Logical. This response can not be cached.

no_local_copy Logical. There is no local copy of this response.

assbackwards Logical. HTTP/0.9, 'simple' request (e.g. GET /foo\n w/no headers). Developers have found this a useful way to internally redirect without headers.

status Integer. Status line.

method_number Integer value of GET, POST, etc.

eos_sent Logical. A flag to determine if the eos bucket has been sent yet.

the_request Character. First line of the request.

method Character. Request method (eg. GET, HEAD, POST, etc.)

status_line Character. Status line, if set by script.

bytes_sent Numeric. Number of bytes sent.

clength Numeric. The 'real' content length.

remaining Numeric. Remaining bytes left to read from the request body.

read_length Numeric. Number of bytes that have been read from the request body.

request_time POSIXct DateTime object. Time when the request started.

mtime POSIXct DateTime object. Last modified time of the requested resource .

5.6 Handler Return Values and HTTP Response Codes.

The following table describes variables that exist as integer vectors of length 1 in the R handler environment and are proper return values for R handlers. They consist of Apache module return values and HTTP Status Codes(see Status Code Definitions from RFC2616 for more info). The most reasonable response value and the one that most handlers will return is the value DONE.
name    value    description
DECLINDED    -1    Module declines to handle
DONE    -2    Module has served response completely.
OK    -0    Module has handled this Apache response stage.
HTTP_CONTINUE    100   
HTTP_SWITCHING_PROTOCOLS    101   
HTTP_PROCESSING    102   
HTTP_OK    200   
HTTP_CREATED    201   
HTTP_ACCEPTED    202   
HTTP_NON_AUTHORITATIVE    203   
HTTP_NO_CONTENT    204   
HTTP_RESET_CONTENT    205   
HTTP_PARTIAL_CONTENT    206   
HTTP_MULTI_STATUS    207   
HTTP_MULTIPLE_CHOICES    300   
HTTP_MOVED_PERMANENTLY    301   
HTTP_MOVED_TEMPORARILY    302   
HTTP_SEE_OTHER    303   
HTTP_NOT_MODIFIED    304   
HTTP_USE_PROXY    305   
HTTP_TEMPORARY_REDIRECT    307   
HTTP_BAD_REQUEST    400   
HTTP_UNAUTHORIZED    401   
HTTP_PAYMENT_REQUIRED    402   
HTTP_FORBIDDEN    403   
HTTP_NOT_FOUND    404   
HTTP_METHOD_NOT_ALLOWED    405   
HTTP_NOT_ACCEPTABLE    406   
HTTP_PROXY_AUTHENTICATION_REQUIRED    407   
HTTP_REQUEST_TIME_OUT    408   
HTTP_CONFLICT    409   
HTTP_GONE    410   
HTTP_LENGTH_REQUIRED    411   
HTTP_PRECONDITION_FAILED    412   
HTTP_REQUEST_ENTITY_TOO_LARGE    413   
HTTP_REQUEST_URI_TOO_LARGE    414   
HTTP_UNSUPPORTED_MEDIA_TYPE    415   
HTTP_RANGE_NOT_SATISFIABLE    416   
HTTP_EXPECTATION_FAILED    417   
HTTP_UNPROCESSABLE_ENTITY    422   
HTTP_LOCKED    423   
HTTP_FAILED_DEPENDENCY    424   
HTTP_UPGRADE_REQUIRED    426   
HTTP_INTERNAL_SERVER_ERROR    500   
HTTP_NOT_IMPLEMENTED    501   
HTTP_BAD_GATEWAY    502   
HTTP_SERVICE_UNAVAILABLE    503   
HTTP_GATEWAY_TIME_OUT    504   
HTTP_VERSION_NOT_SUPPORTED    505   
HTTP_VARIANT_ALSO_VARIES    506   
HTTP_INSUFFICIENT_STORAGE    507   
HTTP_NOT_EXTENDED    510   

Another suitable value to return from a handler is an object with S3 class of 'try-error'.


6. rApache Cookbook.

For a complete look at an rApache application, download the useR2007 application which uses Hmisc and brew for power and sample size calculations.
6.1 Exercising All Functionality

The following code exercises all rApache functionality by just echoing what was sent from the browser. Copy and paste the following code to a file and then set up apache with the following configuration. You should then be able to point your browser at http://example.com/rapachetest (replacing example.com with your own hostname).

#
# Place this in your Apache config file.
#
<Location /rapachetest>
    SetHandler r-handler
    RFileHandler /var/www/R/test.R
</Location>

#
# Copy and save this code to /var/www/R/test.R
#
hrefify <- function(title) gsub('[\\.()]','_',title,perl=TRUE)
scrub <- function(str){
    if (is.null(str)) return('NULL')
    if (length(str) == 0) return('length 0 string')
    cat("\n<!-- before as.character: (",str,")-->\n",sep='')
    str <- as.character(str)
    cat("\n<!-- after as.character: (",str,")-->\n",sep='')
    str <- gsub('&','&amp;',str); str <- gsub('@','_at_',str);
    str <- gsub('<','&lt;',str); str <- gsub('>','&gt;',str);
    if (length(str) == 0 || is.null(str) || str == '')
        str <- '&nbsp;'
    str
}
cl<-'e'
zebary <- function(i){
    cl <<- ifelse(cl=='e','o','e')
    cat('<tr class="',cl,'"><td>',scrub(i),'</td></tr>\n',sep='')
}
zeblist <- function(i,l){
    cl <<- ifelse(cl=='e','o','e')
     cat('<tr class="',cl,'"><td class="l">',names(l)[i],'</td><td>')
    if(is.list(l[[i]]))
        zebra(names(l)[i],l[[i]])
    else {
        if (length(l[[i]]) > 1)
            zebary(l[[i]])
        else
            cat(scrub(l[[i]]))
    }
       
    cat('</td></tr>\n',sep='')
}
zebra <- function(title,l){
    cat('<h2><a name="',hrefify(title),'"> </a>',title,'</h2>\n<table><tbody>',sep='')
    ifelse(is.list(l),lapply(1:length(l),zeblist,l), lapply(l,zebary))
    cat('</tbody></table>\n<br/><hr/>')
}

# Output starts here
setContentType("text/html")

if(is.null(GET)){
    called <- 1
} else {
    called <- as.integer(GET$called) + 1
}

setCookie('called',called,expires=Sys.time()+100)

cat('<HTML><head><style type="text/css">\n')
cat('table { border: 1px solid #8897be; border-spacing: 0px; font-size: 10pt; }')
cat('td { border-bottom:1px solid #d9d9d9; border-left:1px solid #d9d9d9; border-spacing: 0px; padding: 3px 8px; }')
cat('td.l { font-weight: bold; width: 10%; }\n')
cat('tr.e { background-color: #eeeeee; border-spacing: 0px; }\n')
cat('tr.o { background-color: #ffffff; border-spacing: 0px; }\n')
cat('</style></head><BODY><H1>Canonical Test for rApache</H1>\n')
cat('<form enctype=multipart/form-data method=POST action="?called=',called,'">\n',sep='')
cat('Enter a string: <input type=text name=name value=""><br>\n',sep='')
cat('Enter another string: <input type=text name=name value=""><br>\n',sep='')
cat('Upload a file: <input type=file name=fileUpload><br>\n')
cat('Upload another file: <input type=file name=anotherFile><br>\n')
cat('<input type=submit name=Submit>')

cat("<hr>\n")
zebra('CGI GET Data',GET)
zebra('CGI POST Data',POST)
zebra('Cookies',COOKIES)
if (!is.null(FILES)){
    cat('<h2>Files Uploaded in POST Data</h2>\n')
    for (n in names(FILES)){
        zebra(paste("Form Variable",n),FILES[[n]])
    }
}
zebra("SERVER Variables",SERVER)
cat("</BODY></HTML>\n")

DONE

6.2 Custom Error Messages

You can have handlers create custom HTTP error responses by using the setStatus() function. For instance, here's an example that sends a custom message for 500 "Internal Server Error":

handler <- function() {
   setContentType("text/plain")
   setStatus(500L)
   cat("Hi, I'm a 'Fail Ale'!\n")
   OK
}

 

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