mox!

smtpserver/authresults.go

@@ -0,0 +1,116 @@
+package smtpserver
+
+import (
+	"fmt"
+
+	"github.com/mjl-/mox/message"
+)
+
+// ../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.
+}
+
+// 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 := &message.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
+}