add webmail

it was far down on the roadmap, but implemented earlier, because it's
interesting, and to help prepare for a jmap implementation. for jmap we need to
implement more client-like functionality than with just imap. internal data
structures need to change. jmap has lots of other requirements, so it's already
a big project. by implementing a webmail now, some of the required data
structure changes become clear and can be made now, so the later jmap
implementation can do things similarly to the webmail code. the webmail
frontend and webmail are written together, making their interface/api much
smaller and simpler than jmap.

one of the internal changes is that we now keep track of per-mailbox
total/unread/unseen/deleted message counts and mailbox sizes.  keeping this
data consistent after any change to the stored messages (through the code base)
is tricky, so mox now has a consistency check that verifies the counts are
correct, which runs only during tests, each time an internal account reference
is closed. we have a few more internal "changes" that are propagated for the
webmail frontend (that imap doesn't have a way to propagate on a connection),
like changes to the special-use flags on mailboxes, and used keywords in a
mailbox. more changes that will be required have revealed themselves while
implementing the webmail, and will be implemented next.

the webmail user interface is modeled after the mail clients i use or have
used: thunderbird, macos mail, mutt; and webmails i normally only use for
testing: gmail, proton, yahoo, outlook. a somewhat technical user is assumed,
but still the goal is to make this webmail client easy to use for everyone. the
user interface looks like most other mail clients: a list of mailboxes, a
search bar, a message list view, and message details. there is a top/bottom and
a left/right layout for the list/message view, default is automatic based on
screen size. the panes can be resized by the user. buttons for actions are just
text, not icons. clicking a button briefly shows the shortcut for the action in
the bottom right, helping with learning to operate quickly. any text that is
underdotted has a title attribute that causes more information to be displayed,
e.g. what a button does or a field is about. to highlight potential phishing
attempts, any text (anywhere in the webclient) that switches unicode "blocks"
(a rough approximation to (language) scripts) within a word is underlined
orange. multiple messages can be selected with familiar ui interaction:
clicking while holding control and/or shift keys.  keyboard navigation works
with arrows/page up/down and home/end keys, and also with a few basic vi-like
keys for list/message navigation. we prefer showing the text instead of
html (with inlined images only) version of a message. html messages are shown
in an iframe served from an endpoint with CSP headers to prevent dangerous
resources (scripts, external images) from being loaded. the html is also
sanitized, with javascript removed. a user can choose to load external
resources (e.g. images for tracking purposes).

the frontend is just (strict) typescript, no external frameworks. all
incoming/outgoing data is typechecked, both the api request parameters and
response types, and the data coming in over SSE. the types and checking code
are generated with sherpats, which uses the api definitions generated by
sherpadoc based on the Go code. so types from the backend are automatically
propagated to the frontend.  since there is no framework to automatically
propagate properties and rerender components, changes coming in over the SSE
connection are propagated explicitly with regular function calls.  the ui is
separated into "views", each with a "root" dom element that is added to the
visible document. these views have additional functions for getting changes
propagated, often resulting in the view updating its (internal) ui state (dom).
we keep the frontend compilation simple, it's just a few typescript files that
get compiled (combined and types stripped) into a single js file, no additional
runtime code needed or complicated build processes used.  the webmail is served
is served from a compressed, cachable html file that includes style and the
javascript, currently just over 225kb uncompressed, under 60kb compressed (not
minified, including comments). we include the generated js files in the
repository, to keep Go's easily buildable self-contained binaries.

authentication is basic http, as with the account and admin pages. most data
comes in over one long-term SSE connection to the backend. api requests signal
which mailbox/search/messages are requested over the SSE connection. fetching
individual messages, and making changes, are done through api calls. the
operations are similar to imap, so some code has been moved from package
imapserver to package store. the future jmap implementation will benefit from
these changes too. more functionality will probably be moved to the store
package in the future.

the quickstart enables webmail on the internal listener by default (for new
installs). users can enable it on the public listener if they want to. mox
localserve enables it too. to enable webmail on existing installs, add settings
like the following to the listeners in mox.conf, similar to AccountHTTP(S):

	WebmailHTTP:
		Enabled: true
	WebmailHTTPS:
		Enabled: true

special thanks to liesbeth, gerben, andrii for early user feedback.

there is plenty still to do, see the list at the top of webmail/webmail.ts.
feedback welcome as always.

message/authresults.go

@@ -0,0 +1,119 @@
+package message
+
+import (
+	"fmt"
+)
+
+// ../rfc/8601:577
+
+// Authentication-Results header, see RFC 8601.
+type AuthResults struct {
+	Hostname string
+	Comment  string // If not empty, header comment without "()", added after Hostname.
+	Methods  []AuthMethod
+}
+
+// ../rfc/8601:598
+
+// AuthMethod is a result for one authentication method.
+//
+// Example encoding in the header: "spf=pass smtp.mailfrom=example.net".
+type AuthMethod struct {
+	// E.g. "dkim", "spf", "iprev", "auth".
+	Method  string
+	Result  string // Each method has a set of known values, e.g. "pass", "temperror", etc.
+	Comment string // Optional, message header comment.
+	Reason  string // Optional.
+	Props   []AuthProp
+}
+
+// ../rfc/8601:606
+
+// AuthProp describes properties for an authentication method.
+// Each method has a set of known properties.
+// Encoded in the header as "type.property=value", e.g. "smtp.mailfrom=example.net"
+// for spf.
+type AuthProp struct {
+	// Valid values maintained at https://www.iana.org/assignments/email-auth/email-auth.xhtml
+	Type     string
+	Property string
+	Value    string
+	// Whether value is address-like (localpart@domain, or domain). Or another value,
+	// which is subject to escaping.
+	IsAddrLike bool
+	Comment    string // If not empty, header comment withtout "()", added after Value.
+}
+
+// MakeAuthProp is a convenient way to make an AuthProp.
+func MakeAuthProp(typ, property, value string, isAddrLike bool, Comment string) AuthProp {
+	return AuthProp{typ, property, value, isAddrLike, Comment}
+}
+
+// todo future: we could store fields as dns.Domain, and when we encode as non-ascii also add the ascii version as a comment.
+
+// Header returns an Authentication-Results header, possibly spanning multiple
+// lines, always ending in crlf.
+func (h AuthResults) Header() string {
+	// Escaping of values: ../rfc/8601:684 ../rfc/2045:661
+
+	optComment := func(s string) string {
+		if s != "" {
+			return " (" + s + ")"
+		}
+		return s
+	}
+
+	w := &HeaderWriter{}
+	w.Add("", "Authentication-Results:"+optComment(h.Comment)+" "+value(h.Hostname)+";")
+	for i, m := range h.Methods {
+		tokens := []string{}
+		addf := func(format string, args ...any) {
+			s := fmt.Sprintf(format, args...)
+			tokens = append(tokens, s)
+		}
+		addf("%s=%s", m.Method, m.Result)
+		if m.Comment != "" && (m.Reason != "" || len(m.Props) > 0) {
+			addf("(%s)", m.Comment)
+		}
+		if m.Reason != "" {
+			addf("reason=%s", value(m.Reason))
+		}
+		for _, p := range m.Props {
+			v := p.Value
+			if !p.IsAddrLike {
+				v = value(v)
+			}
+			addf("%s.%s=%s%s", p.Type, p.Property, v, optComment(p.Comment))
+		}
+		for j, t := range tokens {
+			if j == len(tokens)-1 && i < len(h.Methods)-1 {
+				t += ";"
+			}
+			w.Add(" ", t)
+		}
+	}
+	return w.String()
+}
+
+func value(s string) string {
+	quote := s == ""
+	for _, c := range s {
+		// utf-8 does not have to be quoted. ../rfc/6532:242
+		if c == '"' || c == '\\' || c <= ' ' || c == 0x7f {
+			quote = true
+			break
+		}
+	}
+	if !quote {
+		return s
+	}
+	r := `"`
+	for _, c := range s {
+		if c == '"' || c == '\\' {
+			r += "\\"
+		}
+		r += string(c)
+	}
+	r += `"`
+	return r
+}

message/authresults_test.go

@@ -0,0 +1,26 @@
+package message
+
+import (
+	"testing"
+
+	"github.com/mjl-/mox/dns"
+)
+
+func TestAuthResults(t *testing.T) {
+	dom, err := dns.ParseDomain("møx.example")
+	if err != nil {
+		t.Fatalf("parsing domain: %v", err)
+	}
+	authRes := AuthResults{
+		Hostname: dom.XName(true),
+		Comment:  dom.ASCIIExtra(true),
+		Methods: []AuthMethod{
+			{"dkim", "pass", "", "", []AuthProp{{"header", "d", dom.XName(true), true, dom.ASCIIExtra(true)}}},
+		},
+	}
+	s := authRes.Header()
+	const exp = "Authentication-Results: (xn--mx-lka.example) møx.example; dkim=pass\r\n\theader.d=møx.example (xn--mx-lka.example)\r\n"
+	if s != exp {
+		t.Fatalf("got %q, expected %q", s, exp)
+	}
+}

message/hdrcmtdomain.go

@@ -0,0 +1,21 @@
+package message
+
+import (
+	"github.com/mjl-/mox/dns"
+)
+
+// HeaderCommentDomain returns domain name optionally followed by a message
+// header comment with ascii-only name.
+//
+// The comment is only present when smtputf8 is true and the domain name is unicode.
+//
+// Caller should make sure the comment is allowed in the syntax. E.g. for Received,
+// it is often allowed before the next field, so make sure such a next field is
+// present.
+func HeaderCommentDomain(domain dns.Domain, smtputf8 bool) string {
+	s := domain.XName(smtputf8)
+	if smtputf8 && domain.Unicode != "" {
+		s += " (" + domain.ASCII + ")"
+	}
+	return s
+}

message/part.go

@@ -85,6 +85,10 @@ type Part struct {
 	bound           []byte               // Only set if valid multipart with boundary, includes leading --, excludes \r\n.
 }
 
+// todo: have all Content* fields in Part?
+// todo: make Address contain a type Localpart and dns.Domain?
+// todo: if we ever make a major change and reparse all parts, switch to lower-case values if not too troublesome.
+
 // Envelope holds the basic/common message headers as used in IMAP4.
 type Envelope struct {
 	Date      time.Time

message/qp.go

@@ -0,0 +1,17 @@
+package message
+
+import (
+	"strings"
+)
+
+// NeedsQuotedPrintable returns whether text should be encoded with
+// quoted-printable. If not, it can be included as 7bit or 8bit encoding.
+func NeedsQuotedPrintable(text string) bool {
+	// ../rfc/2045:1025
+	for _, line := range strings.Split(text, "\r\n") {
+		if len(line) > 78 || strings.Contains(line, "\r") || strings.Contains(line, "\n") {
+			return true
+		}
+	}
+	return false
+}

message/tlsrecv.go

@@ -0,0 +1,46 @@
+package message
+
+import (
+	"crypto/tls"
+	"fmt"
+
+	"github.com/mjl-/mox/mlog"
+)
+
+// TLSReceivedComment returns a comment about TLS of the connection for use in a Receive header.
+func TLSReceivedComment(log *mlog.Log, cs tls.ConnectionState) []string {
+	// todo future: we could use the "tls" clause for the Received header as specified in ../rfc/8314:496. however, the text implies it is only for submission, not regular smtp. and it cannot specify the tls version. for now, not worth the trouble.
+
+	// Comments from other mail servers:
+	// gmail.com: (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128)
+	// yahoo.com: (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256)
+	// proton.me: (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested)
+	// outlook.com: (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384)
+
+	var l []string
+	add := func(s string) {
+		l = append(l, s)
+	}
+
+	versions := map[uint16]string{
+		tls.VersionTLS10: "TLS1.0",
+		tls.VersionTLS11: "TLS1.1",
+		tls.VersionTLS12: "TLS1.2",
+		tls.VersionTLS13: "TLS1.3",
+	}
+
+	if version, ok := versions[cs.Version]; ok {
+		add(version)
+	} else {
+		log.Info("unknown tls version identifier", mlog.Field("version", cs.Version))
+		add(fmt.Sprintf("TLS identifier %x", cs.Version))
+	}
+
+	add(tls.CipherSuiteName(cs.CipherSuite))
+
+	// Make it a comment.
+	l[0] = "(" + l[0]
+	l[len(l)-1] = l[len(l)-1] + ")"
+
+	return l
+}