LambdaMail/services/protocols/internal/application/usecase/inbound_system_message_test.go

package usecase

import (
	"bytes"
	"context"
	"strings"
	"testing"

	"github.com/google/uuid"

	"lambdamail/protocols/internal/application/port"
	"lambdamail/protocols/internal/domain/valueobject"
)

// junkingScanner files everything as spam, standing in for the real scanner
// scoring a bounce-shaped message with no SPF result.
type junkingScanner struct{ called bool }

func (s *junkingScanner) Scan(_ context.Context, _ port.ScanInput) (*valueobject.ScanResult, error) {
	s.called = true
	return &valueobject.ScanResult{
		Verdict:      valueobject.ScanVerdictSpamJunk,
		Score:        12.0,
		Symbols:      map[string]float64{},
		HeadersToAdd: map[string]string{},
	}, nil
}

// A delivery status notification this server wrote itself must never be
// spam-filtered.
//
// The report goes through the same inbound path as mail from the internet, but
// it is injected with no client IP, so SPF can only be "none" and the content
// looks exactly like a bounce. The result was that "your message to X was
// delayed" arrived in the sender's own Junk folder - the single notification
// they most need to see, filed where they will not look.
func TestSystemGeneratedMessageIsNotSpamFiltered(t *testing.T) {
	blobs := &stubBlobStorage{ref: port.BlobRef{ID: uuid.New(), SHA256: "dsn", SizeBytes: 10}}
	messages := &recordingMessageRepository{}
	scanner := &junkingScanner{}

	uc := NewProcessInboundEmailUseCase(nil, blobs, messages)
	uc.SetScanner(scanner)

	err := uc.Handle(context.Background(), ProcessInboundEmailInput{
		Sender:             "postmaster@mail.example.test",
		Recipients:         []port.MailboxRecord{{ID: uuid.New(), MaxMessageBytes: 100000}},
		RecipientAddresses: []string{"user@example.test"},
		Body:               bytes.NewReader([]byte("Subject: Delivery Delay Notification\r\n\r\ndelayed\r\n")),
		SystemGenerated:    true,
	})
	if err != nil {
		t.Fatalf("Handle: %v", err)
	}

	if scanner.called {
		t.Error("the scanner ran on a message this server generated itself")
	}
	if len(messages.persisted) != 1 {
		t.Fatalf("want 1 persisted message, got %d", len(messages.persisted))
	}
	if folder := messages.persisted[0].TargetFolderName; folder == "Junk" {
		t.Errorf("a postmaster notification was filed as Junk")
	}
}

// The exemption must be narrow: anything actually received from a peer is
// still scanned, or marking a message "system generated" would be a way past
// the spam filter.
func TestOrdinaryMessageIsStillScanned(t *testing.T) {
	blobs := &stubBlobStorage{ref: port.BlobRef{ID: uuid.New(), SHA256: "x", SizeBytes: 10}}
	messages := &recordingMessageRepository{}
	scanner := &junkingScanner{}

	uc := NewProcessInboundEmailUseCase(nil, blobs, messages)
	uc.SetScanner(scanner)

	err := uc.Handle(context.Background(), ProcessInboundEmailInput{
		Sender:             "stranger@spam.test",
		Recipients:         []port.MailboxRecord{{ID: uuid.New(), MaxMessageBytes: 100000}},
		RecipientAddresses: []string{"user@example.test"},
		Body:               bytes.NewReader([]byte("Subject: buy pills\r\n\r\nspam\r\n")),
	})
	if err != nil {
		t.Fatalf("Handle: %v", err)
	}
	if !scanner.called {
		t.Fatal("an ordinary inbound message skipped the scanner")
	}
	if messages.persisted[0].TargetFolderName != "Junk" {
		t.Errorf("a message the scanner called spam was not filed as Junk, got %q",
			messages.persisted[0].TargetFolderName)
	}
}

// A DSN announces itself as automatic so the far side's vacation responder
// does not answer it. RFC 3834 section 5 distinguishes the two values, and
// filters read the header.
func TestDsnDeclaresItselfAutoGenerated(t *testing.T) {
	payload, loop := valueobject.BuildDsnReport(
		valueobject.DsnActionDelayed, "mail.example.test",
		"sender@example.test", "far@remote.test", "abc", "timeout",
	)
	if loop {
		t.Fatal("unexpected loop prevention")
	}
	if !strings.Contains(string(payload), "Auto-Submitted: auto-generated") {
		t.Errorf("a delivery report is auto-generated, not auto-replied:\n%s", payload)
	}
}