add first fetching utilities

scraping/fetch.R

@@ -0,0 +1,33 @@
+source("../utils/helpers.R")
+library(RCurl)
+library(stringr)
+
+DOWNLOAD_DIR = "../data/" # warning: this is not created (should maybe)
+
+mk_absolute_url <- function(path) paste0("https://www.bundestag.de", path)
+
+mk_url <- function(offset) {
+    mk_absolute_url %$% sprintf("/ajax/filterlist/de/services/opendata/543410-543410?offset=%d",
+                                offset)
+}
+
+download_protocol <- function(path, name) {
+    fp <- paste0(DOWNLOAD_DIR, name)
+    try %$% download.file(mk_absolute_url(path), fp, quiet=T)
+}
+
+fetch_batch <- function(offset) {
+    url <- mk_url(offset)
+    res <- getURL(url)
+    paths <- str_match_all(res, "/resource/blob/.*?/([0-9]*-data\\.xml)")[[1]]
+    mapply(download_protocol, paths[,1], paths[,2])
+    return(length(paths) > 0)
+}
+
+# TODO: error handling
+# - what if: page not reachable
+# - wrong format, etc.
+fetch_all <- function() {
+    offset <- 0
+    while(fetch_batch(offset)) offset <- offset + 10
+}