Scrape website with R by navigating doPostBack - r

Question

I want to extract a table periodicaly from below site.
price list changes when clicked building block names(BLOK 16 A, BLOK 16 B, BLOK 16 C, ...) . URL doesn't change, page changes by trigering
javascript:__doPostBack('ctl00$ContentPlaceHolder1$DataList2$ctl04$lnk_blok','')
I've tried 3 ways after searching google and starckoverflow.
what I've tried no 1: this doesn't triger doPostBack event.
postForm( "http://www.kentkonut.com.tr/tr/modul/projeler/daire_fiyatlari.aspx?id=44", ctl00_ContentPlaceHolder1_DataList2_ctl03_lnk_blok="ctl00$ContentPlaceHolder1$DataList2$ctl03$lnk_blok")
what I've tried no 2: selenium remote seem to works on (http://localhost:4444/) but remotedriver doesn't navigate. returns this error. (Error in checkError(res) :
Undefined error in httr call. httr output: length(url) == 1 is not TRUE)
library(RSelenium)
startServer()
remDr <- remoteDriver()
remDr <- remoteDriver(remoteServerAddr = "localhost"
, port = 4444L, browserName = "firefox")
remDr$open()
remDr$getStatus()
remDr$navigate("http://www.kentkonut.com.tr/tr/modul/projeler/daire_fiyatlari.aspx?id=44")
what I've tried no 3: this another way to triger dopostback event. it doesn't navigate.
base.url <- "http://www.kentkonut.com.tr/tr/modul/projeler/",
event.target <- 'ctl00$ContentPlaceHolder1$DataList2$ctl03$lnk_blok',
action <- "daire_fiyatlari.aspx?id=44"
ftarget <- paste0(base.url, action)
dum <- getURL(ftarget)
event.val <- unlist(strsplit(dum,"__EVENTVALIDATION\" value=\""))[2]
event.val <- unlist(strsplit(event.val,"\" />\r\n\r\n<script"))[1]
view.state <- unlist(strsplit(dum,"id=\"__VIEWSTATE\" value=\""))[2]
view.state <- unlist(strsplit(view.state,"\" />\r\n\r\n\r\n<script"))[1]
web.data <- postForm(ftarget, "form name" = "ctl00_ContentPlaceHolder1_DataList2_ctl03_lnk_blok",
"method" = "POST",
"action" = action,
"id" = "ctl00_ContentPlaceHolder1_DataList2_ctl03_lnk_blok",
"__EVENTTARGET"=event.target,
"__EVENTVALIDATION"=event.val,
"__VIEWSTATE"=view.state)
thanks for your help.

Answer 1

library(rvest)
url<-"http://www.kentkonut.com.tr/tr/modul/projeler/daire_fiyatlari.aspx?id=44"
pgsession<-html_session(url)
t<-html_table(html_nodes(read_html(pgsession), css = "#ctl00_ContentPlaceHolder1_DataList1"), fill= TRUE)[[1]]
even_indices<-seq(2,length(t$X1),2)
t<-t[even_indices,]
t<-t[2:(length(t$X1)),]
EDITED CODE:
library(rvest)
url<-"http://www.kentkonut.com.tr/tr/modul/projeler/daire_fiyatlari.aspx?id=44"
pgsession<-html_session(url)
pgform<-html_form(pgsession)[[1]]
page<-rvest:::request_POST(pgsession,"http://www.kentkonut.com.tr/tr/modul/projeler/daire_fiyatlari.aspx?id=44",
body=list(
`__VIEWSTATE`=pgform$fields$`__VIEWSTATE`$value,
`__EVENTTARGET`="ctl00$ContentPlaceHolder1$DataList2$ctl01$lnk_blok",
`__EVENTARGUMENT`="",
`__VIEWSTATEGENERATOR`=pgform$fields$`__VIEWSTATEGENERATOR`$value,
`__VIEWSTATEENCRYPTED`=pgform$fields$`__VIEWSTATEENCRYPTED`$value,
`__EVENTVALIDATION`=pgform$fields$`__EVENTVALIDATION`$value
),
encode="form"
)
# in the above example change eventtarget as "ctl00$ContentPlaceHolder1$DataList2$ctl02$lnk_blok" to get different table
t<-html_table(html_nodes(read_html(page), css = "#ctl00_ContentPlaceHolder1_DataList1"), fill= TRUE)[[1]]
even_indices<-seq(2,length(t$X1),2)
t<-t[even_indices,]
t<-t[2:(length(t$X1)),]