Modify gcs_upload to also use an extension on the tempfile

[himanshu-sikaria]

Usecase:
Write raster files (.tif format) using the gcs_upload function. Using the function writeRaster from raster package.

Error:
Problem writing file using object_function

Possible solution:
Adding an extension to the tempfile. Looks very similar to the closed issue (#226) in aws.s3 package.

[MarkEdmondson1234]

Is this not possible by providing your own write function? From the examples:

f <- function(input, output){
   write.csv2(input, file = output)
 }

gcs_upload(mtcars, name = "mtcars_csv2.csv", object_function = f)

...so for your use case:

f <- function(input, output){
   # change this to write tif files
  raster::writeRaster(input, file = output)  # a guess, don't know this function :)
 }

gcs_upload(your_raster, name = "raster.tif", object_function = f)

[himanshu-sikaria]

Did exactly the same thing:

f <- function(input, output){
  raster::writeRaster(input, filename = output, format="GTiff", overwrite=TRUE)
}
gcs_upload(my_raster, name = "raster.tif", object_function = f)

Which resulted in the above mentioned error:
Problem writing file using object_function

Internally what gcs_upload is doing (from what I could understand) is using the f function to first write to a tempfile and then uploads to the GCS. While writing it to a tempfile, it ignores the file extension which results to the error.

[MarkEdmondson1234]

Hmm ok, I guess an error raised with rasterthen - would you mind outputting the whole stack trace of the error?

I think a work around would be to save the raster to a .tif file yourself, then pass in the filename to gcs_upload

But I will also look at making a change, where the temporary file is created with the same file extension as what is passed to name, as you suggested.

[MarkEdmondson1234]

@himanshu-sikaria could you download the latest GitHub version and see if it fixes the issue? You will need to specify your name argument to have .tif at the end.

remotes::install_github("cloudyr/googleCloudStorageR")

[himanshu-sikaria]

Thanks for adding the patch. We are very close to solving this.

## take file extension of name, fix #91
    temp <- tempfile(fileext = tools::file_ext(name))

In the above code (line 135) fileext by default doesn't consider the . after the filename. Could you please change it to

temp <- tempfile(fileext = paste0(".", tools::file_ext(name)))

[MarkEdmondson1234]

Ah thanks, that change is live now.

[himanshu-sikaria]

@MarkEdmondson1234 After your latest modifications, I have started getting this error for the following code. I am running the latest dev version for this package.

library(raster)
test = raster("~/Downloads/final/green_tn.tif")
f <- function(input, output){
  writeRaster(input, filename = output,format="GTiff", overwrite=TRUE)
}
gcs_upload(test, name = "tests/test.tif", object_function = f)

I get this error:

Error in value[[3L]](cond) : 
  object_function error: unable to find an inherited method for function ‘writeRaster’ for signature ‘"gcs_cf", "character"’
In addition: Warning message:
In class(file) <- c("gcs_cf", class(file)) :
  Setting class(x) to multiple strings ("gcs_cf", "RasterLayer", ...); result will no longer be an S4 object

[MarkEdmondson1234]

Hmm ok, I don't know how to deal with S4 objects, only S3.

This will work, as it uploads from disk:

library(raster)
gcs_upload("~/Downloads/final/green_tn.tif", name = "tests/test.tif")

In fact there is nothing to gain from passing in a raster object if uploading already from disk, is this your use case or do you need it to upload the objects directly?

[himanshu-sikaria]

Thanks for the quick response. This is just an example, I would ideally like to download multiple rasters from GCS, do some operations and upload the final raster back to GCS. What could be the best way to solve for this?

[MarkEdmondson1234]

I think downloading and uploading to file, then using raster as you would normally on files. The custom function only saves the object to a temporary file anyway, so you would gain in speed and memory not having temporary files.

Something like (not tested):

# upload all .tif files
my_rasters <- list.files(pattern = ".tif$")
lapply(my_rasters, function(x){
  gcs_upload(x, name = x)
})

# download all .tif files
objs <- gcs_list_objects("my_bucket")
tif_objs <- objs$name[grepl(".tif$",objs$name)]

lapply(tif_objs, function(x) {
  gcs_get_object(x, saveToDisk = paste0("download/", x), overwrite = TRUE)
})

Or put it in one function something like:

# download all .tif files
objs <- gcs_list_objects("my_bucket")
tif_objs <- objs$name[grepl(".tif$",objs$name)]

## loop over the tif files
lapply(tif_objs, function(x) {
  # download to a download folder
  gcs_get_object(x, saveToDisk = paste0("download/", x), overwrite = TRUE)
  tif <- raster::raster(paste0("download/", x))
  # do stuff to tifs
  new_tif <- idontknow(tif)
  # write modified to disk
  raster::writeRaster(new_tif, filename = paste0("upload",x),format="GTiff", overwrite=TRUE)
  # upload to upload folder
  gcs_upload(paste0("upload",x))
})