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imapserver: add SupportedCaps #703

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9452482
imapserver: add SupportedCaps
emersion Oct 30, 2025
4dbfef3
wip
emersion Oct 30, 2025
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6 changes: 3 additions & 3 deletions cmd/imapmemserver/main.go
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Original file line number Diff line number Diff line change
Expand Up @@ -114,9 +114,9 @@ func main() {
NewSession: func(conn *imapserver.Conn) (imapserver.Session, *imapserver.GreetingData, error) {
return memServer.NewSession(), nil, nil
},
Caps: imap.CapSet{
imap.CapIMAP4rev1: {},
imap.CapIMAP4rev2: {},
Caps: &imapserver.SupportedCaps{
IMAP4rev1: true,
IMAP4rev2: true,
},
TLSConfig: tlsConfig,
InsecureAuth: insecureAuth,
Expand Down
6 changes: 3 additions & 3 deletions imapclient/client_test.go
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Expand Up @@ -99,9 +99,9 @@ func newMemClientServerPair(t *testing.T) (net.Conn, io.Closer) {
Certificates: []tls.Certificate{cert},
},
InsecureAuth: true,
Caps: imap.CapSet{
imap.CapIMAP4rev1: {},
imap.CapIMAP4rev2: {},
Caps: &imapserver.SupportedCaps{
IMAP4rev1: true,
IMAP4rev2: true,
},
})

Expand Down
50 changes: 25 additions & 25 deletions imapserver/capability.go
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Original file line number Diff line number Diff line change
Expand Up @@ -31,15 +31,15 @@ func (c *Conn) availableCaps() []imap.Cap {
available := c.server.options.caps()

var caps []imap.Cap
addAvailableCaps(&caps, available, []imap.Cap{
imap.CapIMAP4rev2,
imap.CapIMAP4rev1,
addAvailableCaps(&caps, map[imap.Cap]bool{
imap.CapIMAP4rev2: available.IMAP4rev1,
imap.CapIMAP4rev1: available.IMAP4rev2,
})
if len(caps) == 0 {
panic("imapserver: must support at least IMAP4rev1 or IMAP4rev2")
}

if available.Has(imap.CapIMAP4rev1) {
if available.IMAP4rev1 {
caps = append(caps, []imap.Cap{
imap.CapSASLIR,
imap.CapLiteralMinus,
Expand All @@ -60,7 +60,7 @@ func (c *Conn) availableCaps() []imap.Cap {
caps = append(caps, imap.CapLoginDisabled)
}
if c.state == imap.ConnStateAuthenticated || c.state == imap.ConnStateSelected {
if available.Has(imap.CapIMAP4rev1) {
if available.IMAP4rev1 {
// IMAP4rev1-specific capabilities that don't require backend
// support and are not applicable to IMAP4rev2
caps = append(caps, []imap.Cap{
Expand All @@ -72,42 +72,42 @@ func (c *Conn) availableCaps() []imap.Cap {

// IMAP4rev1-specific capabilities which require backend support
// and are not applicable to IMAP4rev2
addAvailableCaps(&caps, available, []imap.Cap{
imap.CapNamespace,
imap.CapUIDPlus,
imap.CapESearch,
imap.CapSearchRes,
imap.CapListExtended,
imap.CapListStatus,
imap.CapMove,
imap.CapStatusSize,
imap.CapBinary,
imap.CapChildren,
addAvailableCaps(&caps, map[imap.Cap]bool{
imap.CapNamespace: available.Namespace,
imap.CapUIDPlus: available.UIDPlus,
imap.CapESearch: available.ESearch,
//imap.CapSearchRes: available.SearchRes,
imap.CapListExtended: available.ListExtended,
imap.CapListStatus: available.ListStatus,
imap.CapMove: available.Move,
imap.CapStatusSize: available.StatusSize,
//imap.CapBinary: available.Binary,
//imap.CapChildren: available.Children,
})
}

// Capabilities which require backend support and apply to both
// IMAP4rev1 and IMAP4rev2
addAvailableCaps(&caps, available, []imap.Cap{
imap.CapSpecialUse,
imap.CapCreateSpecialUse,
imap.CapLiteralPlus,
imap.CapUnauthenticate,
addAvailableCaps(&caps, map[imap.Cap]bool{
imap.CapSpecialUse: available.SpecialUse,
imap.CapCreateSpecialUse: available.CreateSpecialUse,
imap.CapLiteralPlus: available.LiteralPlus,
imap.CapUnauthenticate: available.Unauthenticate,
})

if appendLimitSession, ok := c.session.(SessionAppendLimit); ok {
limit := appendLimitSession.AppendLimit()
caps = append(caps, imap.Cap(fmt.Sprintf("APPENDLIMIT=%d", limit)))
} else {
addAvailableCaps(&caps, available, []imap.Cap{imap.CapAppendLimit})
addAvailableCaps(&caps, map[imap.Cap]bool{imap.CapAppendLimit: available.AppendLimit})
}
}
return caps
}

func addAvailableCaps(caps *[]imap.Cap, available imap.CapSet, l []imap.Cap) {
for _, c := range l {
if available.Has(c) {
func addAvailableCaps(caps *[]imap.Cap, available map[imap.Cap]bool) {
for c, ok := range available {
if ok {
*caps = append(*caps, c)
}
}
Expand Down
6 changes: 3 additions & 3 deletions imapserver/conn.go
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Original file line number Diff line number Diff line change
Expand Up @@ -140,7 +140,7 @@ func (c *Conn) serve() {
}
}()

caps := c.server.options.caps()
caps := c.server.options.caps().set()
if _, ok := c.session.(SessionIMAP4rev2); !ok && caps.Has(imap.CapIMAP4rev2) {
panic("imapserver: server advertises IMAP4rev2 but session doesn't support it")
}
Expand Down Expand Up @@ -401,7 +401,7 @@ func (c *Conn) checkBufferedLiteral(size int64, nonSync bool) error {
}

func (c *Conn) acceptLiteral(size int64, nonSync bool) error {
if nonSync && size > 4096 && !c.server.options.caps().Has(imap.CapLiteralPlus) {
if nonSync && size > 4096 && !c.server.options.caps().set().Has(imap.CapLiteralPlus) {
return &imap.Error{
Type: imap.StatusResponseTypeBad,
Text: "Non-synchronizing literals are limited to 4096 bytes",
Expand Down Expand Up @@ -595,7 +595,7 @@ func (w *UpdateWriter) WriteNumMessages(n uint32) error {

// WriteNumRecent writes an RECENT response (not used in IMAP4rev2, will be ignored).
func (w *UpdateWriter) WriteNumRecent(n uint32) error {
if w.conn.enabled.Has(imap.CapIMAP4rev2) || !w.conn.server.options.caps().Has(imap.CapIMAP4rev1) {
if w.conn.enabled.Has(imap.CapIMAP4rev2) || !w.conn.server.options.caps().set().Has(imap.CapIMAP4rev1) {
return nil
}
return w.conn.writeObsoleteRecent(n)
Expand Down
2 changes: 1 addition & 1 deletion imapserver/select.go
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Original file line number Diff line number Diff line change
Expand Up @@ -41,7 +41,7 @@ func (c *Conn) handleSelect(tag string, dec *imapwire.Decoder, readOnly bool) er
if err := c.writeExists(data.NumMessages); err != nil {
return err
}
if !c.enabled.Has(imap.CapIMAP4rev2) && c.server.options.caps().Has(imap.CapIMAP4rev1) {
if !c.enabled.Has(imap.CapIMAP4rev2) && c.server.options.caps().set().Has(imap.CapIMAP4rev1) {
if err := c.writeObsoleteRecent(data.NumRecent); err != nil {
return err
}
Expand Down
77 changes: 62 additions & 15 deletions imapserver/server.go
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Expand Up @@ -21,6 +21,64 @@ type Logger interface {
Printf(format string, args ...interface{})
}

// SupportedCaps describes capabilities supported by the server.
type SupportedCaps struct {
// IMAP protocol version
IMAP4rev1 bool // RFC 3501
IMAP4rev2 bool // RFC 9051

// Capabilities which are part of IMAP4rev2 and need to be explicitly
// enabled by IMAP4rev1-only servers
Namespace bool // RFC 2342
UIDPlus bool // RFC 4315
ESearch bool // RFC 4731
SearchRes bool // RFC 5182
ListExtended bool // RFC 5258
ListStatus bool // RFC 5819
Move bool // RFC 6851
StatusSize bool // RFC 8438
Binary bool // RFC 3516
Children bool // RFC 3348

// Capabilities which need to be explicitly enabled on both IMAP4rev1 and
// IMAP4rev2 servers
SpecialUse bool // RFC 6154
CreateSpecialUse bool // RFC 6154
LiteralPlus bool // RFC 7888
Unauthenticate bool // RFC 8437
AppendLimit bool // RFC 7889
}

func (caps *SupportedCaps) set() imap.CapSet {
m := map[imap.Cap]bool{
imap.CapIMAP4rev1: caps.IMAP4rev1,
imap.CapIMAP4rev2: caps.IMAP4rev2,
imap.CapNamespace: caps.Namespace,
imap.CapUIDPlus: caps.UIDPlus,
imap.CapESearch: caps.ESearch,
imap.CapSearchRes: caps.SearchRes,
imap.CapListExtended: caps.ListExtended,
imap.CapListStatus: caps.ListStatus,
imap.CapMove: caps.Move,
imap.CapStatusSize: caps.StatusSize,
imap.CapBinary: caps.Binary,
imap.CapChildren: caps.Children,
imap.CapSpecialUse: caps.SpecialUse,
imap.CapCreateSpecialUse: caps.CreateSpecialUse,
imap.CapLiteralPlus: caps.LiteralPlus,
imap.CapUnauthenticate: caps.Unauthenticate,
imap.CapAppendLimit: caps.AppendLimit,
}

set := make(imap.CapSet, len(m))
for name, ok := range m {
if ok {
set[name] = struct{}{}
}
}
return set
}

// Options contains server options.
//
// The only required field is NewSession.
Expand All @@ -29,18 +87,7 @@ type Options struct {
NewSession func(*Conn) (Session, *GreetingData, error)
// Supported capabilities. If nil, only IMAP4rev1 is advertised. This set
// must contain at least IMAP4rev1 or IMAP4rev2.
//
// The following capabilities are part of IMAP4rev2 and need to be
// explicitly enabled by IMAP4rev1-only servers:
//
// - NAMESPACE
// - UIDPLUS
// - ESEARCH
// - LIST-EXTENDED
// - LIST-STATUS
// - MOVE
// - STATUS=SIZE
Caps imap.CapSet
Caps *SupportedCaps
// Logger is a logger to print error messages. If nil, log.Default is used.
Logger Logger
// TLSConfig is a TLS configuration for STARTTLS. If nil, STARTTLS is
Expand Down Expand Up @@ -68,11 +115,11 @@ func (options *Options) wrapReadWriter(rw io.ReadWriter) io.ReadWriter {
}
}

func (options *Options) caps() imap.CapSet {
func (options *Options) caps() *SupportedCaps {
if options.Caps != nil {
return options.Caps
}
return imap.CapSet{imap.CapIMAP4rev1: {}}
return &SupportedCaps{IMAP4rev1: true}
}

// Server is an IMAP server.
Expand All @@ -89,7 +136,7 @@ type Server struct {

// New creates a new server.
func New(options *Options) *Server {
if caps := options.caps(); !caps.Has(imap.CapIMAP4rev2) && !caps.Has(imap.CapIMAP4rev1) {
if caps := options.caps().set(); !caps.Has(imap.CapIMAP4rev2) && !caps.Has(imap.CapIMAP4rev1) {
panic("imapserver: at least IMAP4rev1 must be supported")
}
return &Server{
Expand Down
2 changes: 1 addition & 1 deletion imapserver/status.go
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Original file line number Diff line number Diff line change
Expand Up @@ -29,7 +29,7 @@ func (c *Conn) handleStatus(dec *imapwire.Decoder) error {
return dec.Err()
}

if options.NumRecent && !c.server.options.caps().Has(imap.CapIMAP4rev1) {
if options.NumRecent && !c.server.options.caps().set().Has(imap.CapIMAP4rev1) {
return &imap.Error{
Type: imap.StatusResponseTypeBad,
Text: "Unknown STATUS data item",
Expand Down