fix #53

Signed-off-by: Edzer Pebesma <edzer.pebesma@uni-muenster.de>

R/read.R

@@ -76,14 +76,16 @@ st_read = function(dsn, layer, ..., options = NULL, quiet = FALSE, iGeomField =
 #'    layer_options = "OVERWRITE=true")
 #' }
 #' nc = st_read(system.file("shape/nc.shp", package="sf"), "nc", crs = 4267)
-#' st_write(nc, ".", "nc")
+#' st_write(nc, "nc.shp")
 #' @export
-st_write = function(obj, dsn, layer = basename(dsn), driver = "ESRI Shapefile", ..., dataset_options = NULL,
-		layer_options = NULL, quiet = FALSE, factorsAsCharacter = TRUE) {
+st_write = function(obj, dsn, layer = basename(dsn), driver = guess_driver(dsn), ..., 
+		dataset_options = NULL, layer_options = NULL, quiet = FALSE, factorsAsCharacter = TRUE) {
 
 	if (inherits(obj, "sfc"))
 		obj = st_sf(id = 1:length(obj), geom = obj)
 	stopifnot(inherits(obj, "sf"))
+	if (missing(dsn))
+		stop("dsn should specify a data source or filename")
 	geom = st_geometry(obj)
 	obj[[attr(obj, "sf_column")]] = NULL
 	if (factorsAsCharacter)
@@ -251,3 +253,32 @@ print.sf_layers = function(x, ...) {
 st_list = function(dsn, options = character(0), do_count = FALSE) {
 	CPL_get_layers(dsn, options, do_count)
 }
+
+guess_driver = function(dsn) {
+    ext_map <- matrix (c(
+                       "e00",    "AVCE00",
+					   "geojson","GeoJSON",
+					   "gpkg",   "GPKG",
+                       "gps",    "GPSBabel",
+                       "gtm",    "GPSTrackMaker",   
+                       "gxt",    "Geoconcept",
+                       "map",    "WAsP",
+                       "nc",     "netCDF",
+                       "osm",    "OSM",  # NO WRITE
+                       "pbf",    "OSM",  # NO WRITE
+                       "shp",    "ESRI Shapefile"
+					   ),
+                       ncol = 2, byrow = TRUE)
+	drv = ext_map[,2]
+	names(drv) = ext_map[,1]
+	drv = drv[tolower(tools::file_ext(dsn))]
+	if (is.na(drv))
+		stop("no driver specified, cannot guess driver from dsn extension")
+	drivers = st_drivers()
+	i = match(drv, drivers$name)
+	if (is.na(i))
+		stop(paste("guess_driver:", drv, "not available in supported drivers, see `st_drivers()'"))
+	if (! drivers[i, "write"])
+		warning(paste("guess_driver", drv, "is available but reports it will not allow writing"))
+	drv
+}

src/gdal_write.cpp

@@ -129,8 +129,8 @@ void CPL_write_ogr(Rcpp::List obj, Rcpp::CharacterVector dsn, Rcpp::CharacterVec
 		Rcpp::Rcout << driver[0] << " driver not available." << std::endl;
 		throw std::invalid_argument("Driver not available.\n");
 	}  else if (! quiet)
-		Rcpp::Rcout << "Writing layer " << layer[0] << " to data source " << dsn[0] <<
-			" using driver " << driver << std::endl;
+		Rcpp::Rcout << "Writing layer `" << layer[0] << "' to data source `" << dsn[0] <<
+			"' using driver `" << driver[0] << "'" << std::endl;
 
 	// open data set:
 	std::vector <char *> options = create_options(dco, quiet);

tests/gdal_geom.Rout.save

@@ -330,7 +330,7 @@ LINESTRING(1 3, 2 4)
 [1] 1
 > 
 > st_length(st_polygon(list(rbind(c(0,0), c(1,0), c(1,1), c(0,1), c(0,0)))))
-[1] 0
+[1] NA
 > 
 > st_area(st_multilinestring(list(rbind(c(0,0),c(0,1)))))
 [1] 0
@@ -348,4 +348,4 @@ MULTILINESTRING((0 0, 0.5 0.5), (0.5 0.5, 1 1),...
 > 
 > proc.time()
    user  system elapsed 
-  0.672   0.276   0.649 
+  0.680   0.276   0.648 

tests/read.R

@@ -19,3 +19,15 @@ class(st_geometry(tst)[[1]])
 tst = st_read(system.file("shape/storms_xyzm_feature.shp", package="sf"), quiet = TRUE)
 class(st_geometry(tst))
 class(st_geometry(tst)[[1]])
+
+sf:::guess_driver("nc.e00")
+sf:::guess_driver("nc.shp")
+sf:::guess_driver("nc.gxt")
+sf:::guess_driver("nc.gps")
+sf:::guess_driver("nc.gtm")
+sf:::guess_driver("nc.nc")
+sf:::guess_driver("nc.map")
+try(sf:::guess_driver("nc.sh"))
+try(sf:::guess_driver("nc.osm"))
+try(sf:::guess_driver("nc.pbf"))
+try(sf:::guess_driver("nc"))

tests/read.Rout.save

@@ -59,6 +59,49 @@ proj4string:    +proj=longlat +datum=NAD27 +no_defs
 > class(st_geometry(tst)[[1]])
 [1] "XYM"        "LINESTRING" "sfg"       
 > 
+> sf:::guess_driver("nc.e00")
+     e00 
+"AVCE00" 
+Warning message:
+In sf:::guess_driver("nc.e00") :
+  guess_driver AVCE00 is available but reports it will not allow writing
+> sf:::guess_driver("nc.shp")
+             shp 
+"ESRI Shapefile" 
+> sf:::guess_driver("nc.gxt")
+         gxt 
+"Geoconcept" 
+> sf:::guess_driver("nc.gps")
+       gps 
+"GPSBabel" 
+> sf:::guess_driver("nc.gtm")
+            gtm 
+"GPSTrackMaker" 
+> sf:::guess_driver("nc.nc")
+      nc 
+"netCDF" 
+> sf:::guess_driver("nc.map")
+   map 
+"WAsP" 
+> try(sf:::guess_driver("nc.sh"))
+Error in sf:::guess_driver("nc.sh") : 
+  no driver specified, cannot guess driver from dsn extension
+> try(sf:::guess_driver("nc.osm"))
+  osm 
+"OSM" 
+Warning message:
+In sf:::guess_driver("nc.osm") :
+  guess_driver OSM is available but reports it will not allow writing
+> try(sf:::guess_driver("nc.pbf"))
+  pbf 
+"OSM" 
+Warning message:
+In sf:::guess_driver("nc.pbf") :
+  guess_driver OSM is available but reports it will not allow writing
+> try(sf:::guess_driver("nc"))
+Error in sf:::guess_driver("nc") : 
+  no driver specified, cannot guess driver from dsn extension
+> 
 > proc.time()
    user  system elapsed 
-  0.448   0.264   0.404 
+  0.424   0.260   0.402 

tests/write.R

@@ -3,7 +3,7 @@ demo(meuse, ask = FALSE, echo = FALSE)
 library(sf)
 meuse = st_as_sf(meuse)
 # write shapefile:
-st_write(meuse, ".", "meuse")
+st_write(meuse, "meuse.shp")
 library(RPostgreSQL)
 # -- doesn't work on appveyor:
 #cn = dbConnect(PostgreSQL(), dbname = "postgis")

tests/write.Rout.save

@@ -1,5 +1,5 @@
 
-R version 3.3.1 (2016-06-21) -- "Bug in Your Hair"
+R version 3.3.2 (2016-10-31) -- "Sincere Pumpkin Patch"
 Copyright (C) 2016 The R Foundation for Statistical Computing
 Platform: x86_64-pc-linux-gnu (64-bit)
 
@@ -21,8 +21,8 @@ Type 'q()' to quit R.
 Linking to GEOS 3.5.0, GDAL 2.1.0
 > meuse = st_as_sf(meuse)
 > # write shapefile:
-> st_write(meuse, ".", "meuse")
-Writing layer meuse to data source . using driver "ESRI Shapefile"
+> st_write(meuse, "meuse.shp")
+Writing layer `meuse.shp' to data source `meuse.shp' using driver `ESRI Shapefile'
 features:       155
 fields:         12
 geometry type:  POINT
@@ -36,4 +36,4 @@ Loading required package: DBI
 > 
 > proc.time()
    user  system elapsed 
-  0.636   0.304   0.633 
+  0.648   0.312   0.645