Add support for incoming emails (#22056)

closes #13585
fixes #9067
fixes #2386
ref #6226
ref #6219
fixes #745

This PR adds support to process incoming emails to perform actions.
Currently I added handling of replies and unsubscribing from
issues/pulls. In contrast to #13585 the IMAP IDLE command is used
instead of polling which results (in my opinion 😉) in cleaner code.

Procedure:
- When sending an issue/pull reply email, a token is generated which is
present in the Reply-To and References header.
- IMAP IDLE waits until a new email arrives
- The token tells which action should be performed

A possible signature and/or reply gets stripped from the content.

I added a new service to the drone pipeline to test the receiving of
incoming mails. If we keep this in, we may test our outgoing emails too
in future.

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

2 files changed, 259 insertions, 0 deletions

diff --git a/tests/integration/incoming_email_test.go b/tests/integration/incoming_email_test.go
new file mode 100644
index 000000000..b4478f578
--- /dev/null
+++ b/tests/integration/incoming_email_test.go
@@ -0,0 +1,249 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package integration
+
+import (
+	"io"
+	"net"
+	"net/smtp"
+	"strings"
+	"testing"
+	"time"
+
+	"code.gitea.io/gitea/models/db"
+	issues_model "code.gitea.io/gitea/models/issues"
+	"code.gitea.io/gitea/models/unittest"
+	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/services/mailer/incoming"
+	incoming_payload "code.gitea.io/gitea/services/mailer/incoming/payload"
+	token_service "code.gitea.io/gitea/services/mailer/token"
+	"code.gitea.io/gitea/tests"
+
+	"github.com/stretchr/testify/assert"
+	"gopkg.in/gomail.v2"
+)
+
+func TestIncomingEmail(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	user := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 2})
+	issue := unittest.AssertExistsAndLoadBean(t, &issues_model.Issue{ID: 1})
+
+	t.Run("Payload", func(t *testing.T) {
+		defer tests.PrintCurrentTest(t)()
+
+		comment := unittest.AssertExistsAndLoadBean(t, &issues_model.Comment{ID: 1})
+
+		_, err := incoming_payload.CreateReferencePayload(user)
+		assert.Error(t, err)
+
+		issuePayload, err := incoming_payload.CreateReferencePayload(issue)
+		assert.NoError(t, err)
+		commentPayload, err := incoming_payload.CreateReferencePayload(comment)
+		assert.NoError(t, err)
+
+		_, err = incoming_payload.GetReferenceFromPayload(db.DefaultContext, []byte{1, 2, 3})
+		assert.Error(t, err)
+
+		ref, err := incoming_payload.GetReferenceFromPayload(db.DefaultContext, issuePayload)
+		assert.NoError(t, err)
+		assert.IsType(t, ref, new(issues_model.Issue))
+		assert.EqualValues(t, issue.ID, ref.(*issues_model.Issue).ID)
+
+		ref, err = incoming_payload.GetReferenceFromPayload(db.DefaultContext, commentPayload)
+		assert.NoError(t, err)
+		assert.IsType(t, ref, new(issues_model.Comment))
+		assert.EqualValues(t, comment.ID, ref.(*issues_model.Comment).ID)
+	})
+
+	t.Run("Token", func(t *testing.T) {
+		defer tests.PrintCurrentTest(t)()
+
+		payload := []byte{1, 2, 3, 4, 5}
+
+		token, err := token_service.CreateToken(token_service.ReplyHandlerType, user, payload)
+		assert.NoError(t, err)
+		assert.NotEmpty(t, token)
+
+		ht, u, p, err := token_service.ExtractToken(db.DefaultContext, token)
+		assert.NoError(t, err)
+		assert.Equal(t, token_service.ReplyHandlerType, ht)
+		assert.Equal(t, user.ID, u.ID)
+		assert.Equal(t, payload, p)
+	})
+
+	t.Run("Handler", func(t *testing.T) {
+		t.Run("Reply", func(t *testing.T) {
+			t.Run("Comment", func(t *testing.T) {
+				defer tests.PrintCurrentTest(t)()
+
+				handler := &incoming.ReplyHandler{}
+
+				payload, err := incoming_payload.CreateReferencePayload(issue)
+				assert.NoError(t, err)
+
+				assert.Error(t, handler.Handle(db.DefaultContext, &incoming.MailContent{}, nil, payload))
+				assert.NoError(t, handler.Handle(db.DefaultContext, &incoming.MailContent{}, user, payload))
+
+				content := &incoming.MailContent{
+					Content: "reply by mail",
+					Attachments: []*incoming.Attachment{
+						{
+							Name:    "attachment.txt",
+							Content: []byte("test"),
+						},
+					},
+				}
+
+				assert.NoError(t, handler.Handle(db.DefaultContext, content, user, payload))
+
+				comments, err := issues_model.FindComments(db.DefaultContext, &issues_model.FindCommentsOptions{
+					IssueID: issue.ID,
+					Type:    issues_model.CommentTypeComment,
+				})
+				assert.NoError(t, err)
+				assert.NotEmpty(t, comments)
+				comment := comments[len(comments)-1]
+				assert.Equal(t, user.ID, comment.PosterID)
+				assert.Equal(t, content.Content, comment.Content)
+				assert.NoError(t, comment.LoadAttachments(db.DefaultContext))
+				assert.Len(t, comment.Attachments, 1)
+				attachment := comment.Attachments[0]
+				assert.Equal(t, content.Attachments[0].Name, attachment.Name)
+				assert.EqualValues(t, 4, attachment.Size)
+			})
+
+			t.Run("CodeComment", func(t *testing.T) {
+				defer tests.PrintCurrentTest(t)()
+
+				comment := unittest.AssertExistsAndLoadBean(t, &issues_model.Comment{ID: 6})
+				issue := unittest.AssertExistsAndLoadBean(t, &issues_model.Issue{ID: comment.IssueID})
+
+				handler := &incoming.ReplyHandler{}
+				content := &incoming.MailContent{
+					Content: "code reply by mail",
+					Attachments: []*incoming.Attachment{
+						{
+							Name:    "attachment.txt",
+							Content: []byte("test"),
+						},
+					},
+				}
+
+				payload, err := incoming_payload.CreateReferencePayload(comment)
+				assert.NoError(t, err)
+
+				assert.NoError(t, handler.Handle(db.DefaultContext, content, user, payload))
+
+				comments, err := issues_model.FindComments(db.DefaultContext, &issues_model.FindCommentsOptions{
+					IssueID: issue.ID,
+					Type:    issues_model.CommentTypeCode,
+				})
+				assert.NoError(t, err)
+				assert.NotEmpty(t, comments)
+				comment = comments[len(comments)-1]
+				assert.Equal(t, user.ID, comment.PosterID)
+				assert.Equal(t, content.Content, comment.Content)
+				assert.NoError(t, comment.LoadAttachments(db.DefaultContext))
+				assert.Empty(t, comment.Attachments)
+			})
+		})
+
+		t.Run("Unsubscribe", func(t *testing.T) {
+			defer tests.PrintCurrentTest(t)()
+
+			watching, err := issues_model.CheckIssueWatch(user, issue)
+			assert.NoError(t, err)
+			assert.True(t, watching)
+
+			handler := &incoming.UnsubscribeHandler{}
+
+			content := &incoming.MailContent{
+				Content: "unsub me",
+			}
+
+			payload, err := incoming_payload.CreateReferencePayload(issue)
+			assert.NoError(t, err)
+
+			assert.NoError(t, handler.Handle(db.DefaultContext, content, user, payload))
+
+			watching, err = issues_model.CheckIssueWatch(user, issue)
+			assert.NoError(t, err)
+			assert.False(t, watching)
+		})
+	})
+
+	if setting.IncomingEmail.Enabled {
+		// This test connects to the configured email server and is currently only enabled for MySql integration tests.
+		// It sends a reply to create a comment. If the comment is not detected after 10 seconds the test fails.
+		t.Run("IMAP", func(t *testing.T) {
+			defer tests.PrintCurrentTest(t)()
+
+			payload, err := incoming_payload.CreateReferencePayload(issue)
+			assert.NoError(t, err)
+			token, err := token_service.CreateToken(token_service.ReplyHandlerType, user, payload)
+			assert.NoError(t, err)
+
+			msg := gomail.NewMessage()
+			msg.SetHeader("To", strings.Replace(setting.IncomingEmail.ReplyToAddress, setting.IncomingEmail.TokenPlaceholder, token, 1))
+			msg.SetHeader("From", user.Email)
+			msg.SetBody("text/plain", token)
+			err = gomail.Send(&smtpTestSender{}, msg)
+			assert.NoError(t, err)
+
+			assert.Eventually(t, func() bool {
+				comments, err := issues_model.FindComments(db.DefaultContext, &issues_model.FindCommentsOptions{
+					IssueID: issue.ID,
+					Type:    issues_model.CommentTypeComment,
+				})
+				assert.NoError(t, err)
+				assert.NotEmpty(t, comments)
+
+				comment := comments[len(comments)-1]
+
+				return comment.PosterID == user.ID && comment.Content == token
+			}, 10*time.Second, 1*time.Second)
+		})
+	}
+}
+
+// A simple SMTP mail sender used for integration tests.
+type smtpTestSender struct{}
+
+func (s *smtpTestSender) Send(from string, to []string, msg io.WriterTo) error {
+	conn, err := net.Dial("tcp", net.JoinHostPort(setting.IncomingEmail.Host, "25"))
+	if err != nil {
+		return err
+	}
+	defer conn.Close()
+
+	client, err := smtp.NewClient(conn, setting.IncomingEmail.Host)
+	if err != nil {
+		return err
+	}
+
+	if err = client.Mail(from); err != nil {
+		return err
+	}
+
+	for _, rec := range to {
+		if err = client.Rcpt(rec); err != nil {
+			return err
+		}
+	}
+
+	w, err := client.Data()
+	if err != nil {
+		return err
+	}
+	if _, err := msg.WriteTo(w); err != nil {
+		return err
+	}
+	if err := w.Close(); err != nil {
+		return err
+	}
+
+	return client.Quit()
+}
diff --git a/tests/mysql.ini.tmpl b/tests/mysql.ini.tmpl
index 24a9a02dc..44914d087 100644
--- a/tests/mysql.ini.tmpl
+++ b/tests/mysql.ini.tmpl
@@ -124,3 +124,13 @@ INTERNAL_TOKEN = eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJuYmYiOjE0OTU1NTE2MTh9.h
 
 [packages]
 ENABLED = true
+
+[email.incoming]
+ENABLED = true
+HOST = smtpimap
+PORT = 993
+USERNAME = debug@localdomain.test
+PASSWORD = debug
+USE_TLS = true
+SKIP_TLS_VERIFY = true
+REPLY_TO_ADDRESS = incoming+%{token}@localhost