imapclient, imapserver: make capabilities case-insensitive

Author: emersion

imapclient/capability.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 
 	"github.com/emersion/go-imap/v2"
+	"github.com/emersion/go-imap/v2/internal"
 	"github.com/emersion/go-imap/v2/internal/imapwire"
 )
 
@@ -45,11 +46,11 @@ func readCapabilities(dec *imapwire.Decoder) (imap.CapSet, error) {
 		for dec.SP() {
 		}
 
-		var name string
-		if !dec.ExpectAtom(&name) {
-			return caps, fmt.Errorf("in capability-data: %v", dec.Err())
+		cap, err := internal.ExpectCap(dec)
+		if err != nil {
+			return caps, fmt.Errorf("in capability-data: %w", err)
 		}
-		caps[imap.Cap(name)] = struct{}{}
+		caps[cap] = struct{}{}
 	}
 	return caps, nil
 }

imapserver/enable.go

@@ -2,17 +2,18 @@ package imapserver
 
 import (
 	"github.com/emersion/go-imap/v2"
+	"github.com/emersion/go-imap/v2/internal"
 	"github.com/emersion/go-imap/v2/internal/imapwire"
 )
 
 func (c *Conn) handleEnable(dec *imapwire.Decoder) error {
 	var requested []imap.Cap
 	for dec.SP() {
-		var c string
-		if !dec.ExpectAtom(&c) {
-			return dec.Err()
+		cap, err := internal.ExpectCap(dec)
+		if err != nil {
+			return err
 		}
-		requested = append(requested, imap.Cap(c))
+		requested = append(requested, cap)
 	}
 	if !dec.ExpectCRLF() {
 		return dec.Err()

internal/internal.go

@@ -69,6 +69,14 @@ func ExpectFlagList(dec *imapwire.Decoder) ([]imap.Flag, error) {
 	return flags, err
 }
 
+func ExpectCap(dec *imapwire.Decoder) (imap.Cap, error) {
+	var name string
+	if !dec.ExpectAtom(&name) {
+		return "", dec.Err()
+	}
+	return canonicalCap(name), nil
+}
+
 func ExpectFlag(dec *imapwire.Decoder) (imap.Flag, error) {
 	isSystem := dec.Special('\\')
 	if isSystem && dec.Special('*') {
@@ -168,3 +176,13 @@ func canonicalMailboxAttr(s string) imap.MailboxAttr {
 	}
 	return imap.MailboxAttr(s)
 }
+
+func canonicalCap(s string) imap.Cap {
+	// Only two caps are not fully uppercase
+	for _, cap := range []imap.Cap{imap.CapIMAP4rev1, imap.CapIMAP4rev2} {
+		if strings.EqualFold(s, string(cap)) {
+			return cap
+		}
+	}
+	return imap.Cap(strings.ToUpper(s))
+}