R/temp_unzip.R

In NickCH-K/SafeGraphR: Package for Processing and Analyzing SafeGraph Data

#' Unzip a Data File and Read It
#'
#' SafeGraph patterns files come in \code{.csv.gz} format. \code{temp_unzip} will unzip the file, read it in using \code{fun} (usually \code{fread}), and then delete the unzipped \code{.csv} file.
#'
#' I stole this function from a StackExchange answer many years ago and have copied it so many times I no longer know where it came from. Every day we offer thanks to the author.
#'
#' @param filename The filename of the zip file to be unzipped.
#' @param fun The function to use to read in the resulting unzipped data file.
#' @param ... Additional arguments to be passed to \code{fun}. Often, this is \code{select} to only read in some of the variables.
#' @export

temp_unzip <- function(filename, fun=data.table::fread, ...){
  BFR.SIZE <- 1e7
  if (!file.exists(filename)) {
    stop("No such file: ", filename);
  }
  if (!is.function(fun)) {
    stop(sprintf("Argument 'fun' is not a function: %s", mode(fun)));
  }
  temp_dir <- tempdir()
  # test if it's zip
  files_in_zip <- try(utils::unzip(filename, list = TRUE)$Name, silent = TRUE)
  if (class(files_in_zip) == "character") {
    # hidden files can be ignored: starting with ., ending with $, __MACOSX folder
    visible_files <- files_in_zip[!grepl("((^__MACOSX\\/.*)|(^\\..*)|(^.*\\$$))",
                                         files_in_zip)]
    # will not continue for multiple non-hidden files since behavior is not well defined.
    if(length(visible_files)>1) {
      stop(paste0("Zip file contains multiple visible files:\n",
                  paste0("    ", visible_files, collapse = "\n")))
    }
    if(length(visible_files) == 0) { stop("\n  No visible file found in Zip file")}
    # proceed with single non-hidden file
    utils::unzip(filename, files = visible_files[1], exdir = temp_dir, overwrite = TRUE)
    dest_file <- file.path(temp_dir, visible_files[1])
  } else {
    dest_file <- tempfile()
    # Setup input and output connections
    inn <- gzfile(filename, open = "rb")
    out <- file(description = dest_file, open = "wb")
    # Process
    nbytes <- 0
    repeat {
      bfr <- readBin(inn, what=raw(0L), size=1L, n=BFR.SIZE)
      n <- length(bfr)
      if (n == 0L) break;
      nbytes <- nbytes + n
      writeBin(bfr, con=out, size=1L)
      bfr <- NULL  # Not needed anymore
    }
    close(inn)
    close(out)
  }
  # call fun with temp file
  res <- fun(dest_file, ...)
  file.remove(dest_file)
  return(res)
}