Better error handling for using external images

This fixes #241

src/go/splib/splib.go

@@ -16,6 +16,10 @@ import (
 	"splibaux"
 )
 
+var (
+	errorpattern = `**err`
+)
+
 // Convert a string slice to a C char* array and add a NULL pointer.
 func toCharArray(s []string) **C.char {
 	cArray := C.malloc(C.size_t(len(s)+1) * C.size_t(unsafe.Sizeof(uintptr(0))))
@@ -138,7 +142,7 @@ func addDir(p string) {
 func lookupFile(path string) *C.char {
 	ret, err := splibaux.GetFullPath(path)
 	if err != nil {
-		fmt.Println(err)
+		return s2c(errorpattern + err.Error())
 	}
 	return s2c(ret)
 }
@@ -153,7 +157,7 @@ func listFonts() **C.char {
 func convertSVGImage(path string) *C.char {
 	ret, err := splibaux.ConvertSVGImage(path)
 	if err != nil {
-		fmt.Println(err)
+		return s2c(errorpattern + err.Error())
 	}
 	return s2c(ret)
 }

src/go/splibaux/splibaux.go

@@ -49,7 +49,10 @@ func saveFileFromUrl(parsedURL *url.URL, rawURL string) (string, error) {
 			return "", fmt.Errorf("Image cache %q exists but is not a directory", rawimgcache)
 		}
 	} else {
-		os.MkdirAll(rawimgcache, 0755)
+		err = os.MkdirAll(rawimgcache, 0755)
+		if err != nil {
+			return "", err
+		}
 	}
 
 	destfile := parsedURL.Hostname() + parsedURL.Path

src/lua/splib.lua

@@ -53,6 +53,7 @@ extern char* convertSVGImage(GoString p0);
 ]]
 
 ld = ffi.load("libsplib")
+errorpattern = "^%*%*err"
 
 local function c(str)
     return ffi.new("GoString",str,#str)
@@ -104,9 +105,13 @@ end
 local function lookupfile(filename)
     local ret = ld.lookupFile(c(filename))
     local _ret = ffi.string(ret)
+    if string.match( _ret,errorpattern ) then
+        err(string.gsub( _ret,errorpattern ,"" ))
+        return
+    end
     if _ret == "" then return nil end
 
-    return ffi.string(ret)
+    return _ret
 end
 
 local function listfonts()
@@ -123,9 +128,15 @@ end
 local function convertSVGImage(filename)
     local ret = ld.convertSVGImage(c(filename))
     local _ret = ffi.string(ret)
+
+    if string.match( _ret,errorpattern ) then
+        err(string.gsub( _ret,errorpattern ,"" ))
+        return
+    end
+
     if _ret == "" then return nil end
 
-    return ffi.string(ret)
+    return _ret
 end