handle message unknown charset error

This change handles message parse errors by printing the error when the
user tries to view the message. Specifically only handling unknown
charset errors in this patch, but there are many types of invalid
messages that can be handled in this way.

aerc currently leaves certain messages in the msglist in the pending
(spinner) state, and I'm unable to view or modify the message. aerc also
only prints parse errors with message when they are initially loaded.
This UX is a little better, because you can still see the header info
about the message, and if you try to view it, you will see the specific
error.

commands/account/view.go

@@ -38,6 +38,10 @@ func (ViewMessage) Execute(aerc *widgets.Aerc, args []string) error {
 	if deleted {
 		return nil
 	}
+	if msg.Error != nil {
+		aerc.PushError(msg.Error.Error())
+		return nil
+	}
 	lib.NewMessageStoreView(msg, store, aerc.DecryptKeys,
 		func(view lib.MessageView, err error) {
 			if err != nil {

models/models.go

@@ -65,6 +65,7 @@ type MessageInfo struct {
 	RFC822Headers *mail.Header
 	Size          uint32
 	Uid           uint32
+	Error         error
 }
 
 // A MessageBodyPart can be displayed in the message viewer

worker/lib/parse.go

@@ -94,7 +94,7 @@ func ParseEntityStructure(e *message.Entity) (*models.BodyStructure, error) {
 			}
 			ps, err := ParseEntityStructure(part)
 			if err != nil {
-				return nil, fmt.Errorf("could not parse child entity structure: %v", err)
+				return nil, fmt.Errorf("could not parse child entity structure: %w", err)
 			}
 			body.Parts = append(body.Parts, ps)
 		}
@@ -224,6 +224,7 @@ type RawMessage interface {
 // MessageInfo populates a models.MessageInfo struct for the message.
 // based on the reader returned by NewReader
 func MessageInfo(raw RawMessage) (*models.MessageInfo, error) {
+	var parseErr error
 	r, err := raw.NewReader()
 	if err != nil {
 		return nil, err
@@ -233,7 +234,9 @@ func MessageInfo(raw RawMessage) (*models.MessageInfo, error) {
 		return nil, fmt.Errorf("could not read message: %v", err)
 	}
 	bs, err := ParseEntityStructure(msg)
-	if err != nil {
+	if errors.As(err, new(message.UnknownEncodingError)) {
+		parseErr = err
+	} else if err != nil {
 		return nil, fmt.Errorf("could not get structure: %v", err)
 	}
 	h := &mail.Header{msg.Header}
@@ -268,5 +271,6 @@ func MessageInfo(raw RawMessage) (*models.MessageInfo, error) {
 		RFC822Headers: &mail.Header{msg.Header},
 		Size:          0,
 		Uid:           raw.UID(),
+		Error:         parseErr,
 	}, nil
 }

worker/lib/parse_test.go

@@ -0,0 +1,65 @@
+package lib
+
+import (
+	"bytes"
+	"io"
+	"io/ioutil"
+	"path/filepath"
+	"testing"
+
+	"git.sr.ht/~sircmpwn/aerc/models"
+)
+
+func TestMessageInfoHandledError(t *testing.T) {
+	rootDir := "testdata/message/invalid"
+	msgFiles, err := ioutil.ReadDir(rootDir)
+	die(err)
+
+	for _, fi := range msgFiles {
+		if fi.IsDir() {
+			continue
+		}
+
+		p := fi.Name()
+		t.Run(p, func(t *testing.T) {
+			m := newMockRawMessageFromPath(filepath.Join(rootDir, p))
+			mi, err := MessageInfo(m)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			if perr := mi.Error; perr == nil {
+				t.Fatal("Expected MessageInfo.Error, got none")
+			}
+		})
+	}
+}
+
+type mockRawMessage struct {
+	body []byte
+}
+
+func newMockRawMessage(body []byte) *mockRawMessage {
+	return &mockRawMessage{
+		body: body,
+	}
+}
+
+func newMockRawMessageFromPath(p string) *mockRawMessage {
+	b, err := ioutil.ReadFile(p)
+	die(err)
+	return newMockRawMessage(b)
+}
+
+func (m *mockRawMessage) NewReader() (io.Reader, error) {
+	return bytes.NewReader(m.body), nil
+}
+func (m *mockRawMessage) ModelFlags() ([]models.Flag, error) { return nil, nil }
+func (m *mockRawMessage) Labels() ([]string, error)          { return nil, nil }
+func (m *mockRawMessage) UID() uint32                        { return 0 }
+
+func die(err error) {
+	if err != nil {
+		panic(err)
+	}
+}

worker/lib/testdata/message/invalid/hexa

@@ -0,0 +1,28 @@
+Subject: Confirmation Needed gUdVJQBhsd
+Content-Type: multipart/mixed; boundary="Nextpart_1Q2YJhd197991794467076Pgfa"
+To:  <BORK@example.com>
+From: ""REGISTRAR"" <zdglopi-1Q2YJhd-noReply@example.com>
+
+--Nextpart_1Q2YJhd197991794467076Pgfa
+Content-Type: multipart/parallel; boundary="sg54sd54g54sdg54"
+
+--sg54sd54g54sdg54
+Content-Type: multipart/alternative; boundary="54qgf54q546f46qsf46qsf"
+
+--54qgf54q546f46qsf46qsf
+Content-Type: text/plain; charset=utf-8
+Content-Transfer-Encoding: Hexa
+
+
+
+--54qgf54q546f46qsf46qsf
+Content-Type: text/html; charset=utf-8
+
+
+<CeNteR><a hRef="https://example.com-ap-southeast-example.com.com/example.com#qs=r-acacaeehdiebadgdhgghcaegckhabababaggacihaccajfbacccgaehhbkacb"><b><h2>Congratulations Netflix Customer!</h2></b></a><br>
+<HeaD>
+<ObJECT>
+
+--Nextpart_1Q2YJhd197991794467076Pgfa--
+
+