msgview/save: Adapt to already decoded reader

The functionality was broken since the decoding changes.
This commit also simplifies the code (in my view) to make the application logic
easier to follow.
The docs are updated accordingly (the feature was poorly documented).

As far as I am aware there should be no breaking changes (and is certainly
still in the spec of the prior documentation)

2 files changed, 134 insertions, 74 deletions

diff --git a/commands/msgview/save.go b/commands/msgview/save.go
index c017e70..7f236cb 100644
--- a/commands/msgview/save.go
+++ b/commands/msgview/save.go
@@ -1,11 +1,9 @@
 package msgview
 
 import (
-	"encoding/base64"
 	"errors"
 	"fmt"
 	"io"
-	"mime/quotedprintable"
 	"os"
 	"path/filepath"
 	"strings"
@@ -15,6 +13,7 @@ import (
 	"github.com/mitchellh/go-homedir"
 
 	"git.sr.ht/~sircmpwn/aerc/commands"
+	"git.sr.ht/~sircmpwn/aerc/models"
 	"git.sr.ht/~sircmpwn/aerc/widgets"
 )
 
@@ -34,102 +33,158 @@ func (Save) Complete(aerc *widgets.Aerc, args []string) []string {
 }
 
 func (Save) Execute(aerc *widgets.Aerc, args []string) error {
-	if len(args) == 1 {
-		return errors.New("Usage: :save [-p] <path>")
-	}
-	opts, optind, err := getopt.Getopts(args, "p")
+	opts, optind, err := getopt.Getopts(args, "fp")
 	if err != nil {
 		return err
 	}
 
 	var (
-		mkdirs bool
-		path   string = strings.Join(args[optind:], " ")
+		force         bool
+		createDirs    bool
+		trailingSlash bool
 	)
 
 	for _, opt := range opts {
 		switch opt.Option {
+		case 'f':
+			force = true
 		case 'p':
-			mkdirs = true
+			createDirs = true
 		}
 	}
-	if defaultPath := aerc.Config().General.DefaultSavePath; defaultPath != "" {
-		path = defaultPath
+
+	defaultPath := aerc.Config().General.DefaultSavePath
+	// we either need a path or a defaultPath
+	if defaultPath == "" && len(args) == optind {
+		return errors.New("Usage: :save [-fp] <path>")
 	}
 
-	mv := aerc.SelectedTab().(*widgets.MessageViewer)
-	p := mv.SelectedMessagePart()
+	// as a convenience we join with spaces, so that the user doesn't need to
+	// quote filenames containing spaces
+	path := strings.Join(args[optind:], " ")
+
+	// needs to be determined prior to calling filepath.Clean / filepath.Join
+	// it gets stripped by Clean.
+	// we auto generate a name if a directory was given
+	if len(path) > 0 {
+		trailingSlash = path[len(path)-1] == '/'
+	} else if len(defaultPath) > 0 && len(path) == 0 {
+		// empty path, so we might have a default that ends in a trailingSlash
+		trailingSlash = defaultPath[len(defaultPath)-1] == '/'
+	}
 
-	p.Store.FetchBodyPart(p.Msg.Uid, p.Msg.BodyStructure, p.Index, func(reader io.Reader) {
-		// email parts are encoded as 7bit (plaintext), quoted-printable, or base64
+	// Absolute paths are taken as is so that the user can override the default
+	// if they want to
+	if !isAbsPath(path) {
+		path = filepath.Join(defaultPath, path)
+	}
 
-		if strings.EqualFold(p.Part.Encoding, "base64") {
-			reader = base64.NewDecoder(base64.StdEncoding, reader)
-		} else if strings.EqualFold(p.Part.Encoding, "quoted-printable") {
-			reader = quotedprintable.NewReader(reader)
-		}
+	path, err = homedir.Expand(path)
+	if err != nil {
+		return err
+	}
 
-		var pathIsDir bool
-		if path[len(path)-1:] == "/" {
-			pathIsDir = true
-		}
-		// Note: path expansion has to happen after test for trailing /,
-		// since it is stripped when path is expanded
-		path, err := homedir.Expand(path)
+	mv, ok := aerc.SelectedTab().(*widgets.MessageViewer)
+	if !ok {
+		return fmt.Errorf("SelectedTab is not a MessageViewer")
+	}
+	pi := mv.SelectedMessagePart()
+
+	if trailingSlash || isDirExists(path) {
+		filename := generateFilename(pi.Part)
+		path = filepath.Join(path, filename)
+	}
+
+	dir := filepath.Dir(path)
+	if createDirs && dir != "" {
+		err := os.MkdirAll(dir, 0755)
 		if err != nil {
-			aerc.PushError(" " + err.Error())
+			return err
 		}
+	}
 
-		pathinfo, err := os.Stat(path)
-		if err == nil && pathinfo.IsDir() {
-			pathIsDir = true
-		} else if os.IsExist(err) && pathIsDir {
-			aerc.PushError("The given directory is an existing file")
-		}
-		var (
-			save_file string
-			save_dir  string
-		)
-		if pathIsDir {
-			save_dir = path
-			if filename, ok := p.Part.DispositionParams["filename"]; ok {
-				save_file = filename
-			} else if filename, ok := p.Part.Params["name"]; ok {
-				save_file = filename
-			} else {
-				timestamp := time.Now().Format("2006-01-02-150405")
-				save_file = fmt.Sprintf("aerc_%v", timestamp)
+	if pathExists(path) && !force {
+		return fmt.Errorf("%q already exists and -f not given", path)
+	}
+
+	ch := make(chan error, 1)
+	pi.Store.FetchBodyPart(
+		pi.Msg.Uid, pi.Msg.BodyStructure, pi.Index, func(reader io.Reader) {
+			f, err := os.Create(path)
+			if err != nil {
+				ch <- err
+				return
 			}
-		} else {
-			save_file = filepath.Base(path)
-			save_dir = filepath.Dir(path)
-		}
-		if _, err := os.Stat(save_dir); os.IsNotExist(err) {
-			if mkdirs {
-				os.MkdirAll(save_dir, 0755)
-			} else {
-				aerc.PushError("Target directory does not exist, use " +
-					":save with the -p option to create it")
+			defer f.Close()
+			_, err = io.Copy(f, reader)
+			if err != nil {
+				ch <- err
 				return
 			}
-		}
-		target := filepath.Clean(filepath.Join(save_dir, save_file))
+			ch <- nil
+		})
 
-		f, err := os.Create(target)
+	// we need to wait for the callback prior to displaying a result
+	go func() {
+		err := <-ch
 		if err != nil {
-			aerc.PushError(" " + err.Error())
+			aerc.PushError(fmt.Sprintf("Save failed: %v", err))
 			return
 		}
-		defer f.Close()
+		aerc.PushStatus("Saved to "+path, 10*time.Second)
+	}()
+	return nil
+}
 
-		_, err = io.Copy(f, reader)
-		if err != nil {
-			aerc.PushError(" " + err.Error())
-			return
-		}
+//isDir returns true if path is a directory and exists
+func isDirExists(path string) bool {
+	pathinfo, err := os.Stat(path)
+	if err != nil {
+		return false // we don't really care
+	}
+	if pathinfo.IsDir() {
+		return true
+	}
+	return false
+}
 
-		aerc.PushStatus("Saved to "+target, 10*time.Second)
-	})
+//pathExists returns true if path exists
+func pathExists(path string) bool {
+	_, err := os.Stat(path)
+	if err != nil {
+		return false // we don't really care why it failed
+	}
+	return true
+}
 
-	return nil
+//isAbsPath returns true if path given is anchored to / or . or ~
+func isAbsPath(path string) bool {
+	if len(path) == 0 {
+		return false
+	}
+	switch path[0] {
+	case '/':
+		return true
+	case '.':
+		return true
+	case '~':
+		return true
+	default:
+		return false
+	}
+}
+
+// generateFilename tries to get the filename from the given part.
+// if that fails it will fallback to a generated one based on the date
+func generateFilename(part *models.BodyStructure) string {
+	var filename string
+	if fn, ok := part.DispositionParams["filename"]; ok {
+		filename = fn
+	} else if fn, ok := part.Params["name"]; ok {
+		filename = fn
+	} else {
+		timestamp := time.Now().Format("2006-01-02-150405")
+		filename = fmt.Sprintf("aerc_%v", timestamp)
+	}
+	return filename
 }
diff --git a/doc/aerc.1.scd b/doc/aerc.1.scd
index c0e8ad4..38c0bd4 100644
--- a/doc/aerc.1.scd
+++ b/doc/aerc.1.scd
@@ -240,13 +240,18 @@ message list, the message in the message viewer, etc).
 	Saves the current message part in a temporary file and opens it
 	with the system handler.
 
-*save* [-p] <path>
+*save* [-fp] <path>
 	Saves the current message part to the given path.
+	If the path is not an absolute path, general.default-save-path will be
+	prepended to the path given.
+	If path ends in a trailing slash or if a folder exists on disc,
+	aerc assumes it to be a directory.
+	When passed a directory :save infers the filename from the mail part if
+	possible, or if that fails, uses "aerc_$DATE".
 
-	If no path is given but general.default-save-path is set, the
-	file will be saved there.
+	*-f*: Overwrite the destination whether or not it exists
 
-	*-p*: Make any directories in the path that do not exist
+	*-p*: Create any directories in the path that do not exist
 
 *mark* [-atv]
 	Marks messages. Commands will execute on all marked messages instead of the