Add background package

This rewrite has better comments and returns better error messages.

background/download.go

@@ -0,0 +1,48 @@
+package background
+
+import (
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+)
+
+// Download takes path and url as input and downloads the data to a
+// file, returning an error if there is one.
+func Download(file string, url string) error {
+	o, err := os.Create(file)
+	if err != nil {
+		err = fmt.Errorf("%s%s\n%s",
+			"download.go: failed to create file: ", file,
+			err.Error())
+		return err
+	}
+	defer o.Close()
+
+	res, err := http.Get(url)
+	if err != nil {
+		err = fmt.Errorf("%s%s\n%s",
+			"download.go: failed to get response from ", url,
+			err.Error())
+		return err
+	}
+	defer res.Body.Close()
+
+	// Return an error on unexpected response code.
+	if res.StatusCode != http.StatusOK {
+		err = fmt.Errorf("Unexpected Response: %s",
+			res.Status)
+		return err
+	}
+
+	// This will not copy everything to memory but will save to
+	// disk as it progresses, ideal for big files or low memory
+	// environments.
+	_, err = io.Copy(o, res.Body)
+	if err != nil {
+		err = fmt.Errorf("%s\n%s",
+			"download.go: failed to copy body to file",
+			err.Error())
+	}
+	return err
+}

background/set_darwin.go

@@ -0,0 +1,25 @@
+// +build darwin
+
+package background
+
+import (
+	"fmt"
+	"os/exec"
+	"strconv"
+)
+
+// SetFromFile takes a string as an input, it must be absolute path to
+// the background. Checks are not made to check if the path exists or
+// it is actually an image, that must be verified before passing it to
+// SetFromFile. SetFromFile will exit returning in error if there is
+// any.
+func SetFromFile(path string) error {
+	err := exec.Command("osascript", "-e",
+		`tell application "System Events" to tell every desktop to set picture to `+strconv.Quote(path)).Run()
+	if err != nil {
+		err = fmt.Errorf("%s\n%s",
+			"set_darwin.go: failed to set background",
+			err.Error())
+	}
+	return err
+}

background/set_unix.go

@@ -0,0 +1,66 @@
+// +build linux netbsd openbsd freebsd dragonfly
+
+package background
+
+import (
+	"fmt"
+	"os"
+	"os/exec"
+)
+
+// SetFromFile takes a string as an input, it must be absolute path to
+// the background. Checks are not made to check if the path exists or
+// it is actually an image, that must be verified before passing it to
+// SetFromFile. SetFromFile will exit returning in error if there is
+// any.
+func SetFromFile(path string) error {
+	var err error
+	switch os.Getenv("XDG_CURRENT_DESKTOP") {
+	case "GNOME", "Unity", "Pantheon":
+		// GNOME, Unity & Pantheon support setting background
+		// from gsettings & have the same key.
+
+		// gsettings takes path in format of a uri
+		path = fmt.Sprintf("%s%s", "file://", path)
+
+		err = exec.Command("gsettings",
+			"set org.gnome.desktop.background picture-uri", path).Run()
+		if err != nil {
+			err = fmt.Errorf("%s\n%s",
+				"set_unix.go: failed to set background with gsettings",
+				err.Error())
+		}
+		return err
+
+	case "LXDE":
+		// Background on LXDE can be set with pcmanfm (default
+		// file manager).
+		err = exec.Command("pcmanfm", "-w", path).Run()
+		if err != nil {
+			err = fmt.Errorf("%s\n%s",
+				"set_unix.go: failed to set background with pcmanfm",
+				err.Error())
+		}
+		return err
+
+	default:
+		// If WM/DE doesn't have a case then feh is used to
+		// set the background. This is tested to work on WMs
+		// similar to i3wm.
+		feh, err := exec.LookPath("feh")
+		if err != nil {
+			err = fmt.Errorf("%s\n%s",
+				"set_unix.go: feh not found in $PATH",
+				err.Error())
+			return err
+		}
+
+		err = exec.Command(feh, "--bg-fill", path).Run()
+		if err != nil {
+			err = fmt.Errorf("%s\n%s",
+				"set_unix.go: failed to set background with feh",
+				err.Error())
+		}
+		return err
+	}
+}