Added files.

imapserver/capability.go

@@ -0,0 +1,114 @@
+package imapserver
+
+import (
+	"fmt"
+
+	"github.com/emersion/go-imap/v2"
+	"github.com/emersion/go-imap/v2/internal/imapwire"
+)
+
+func (c *Conn) handleCapability(dec *imapwire.Decoder) error {
+	if !dec.ExpectCRLF() {
+		return dec.Err()
+	}
+
+	enc := newResponseEncoder(c)
+	defer enc.end()
+	enc.Atom("*").SP().Atom("CAPABILITY")
+	for _, c := range c.availableCaps() {
+		enc.SP().Atom(string(c))
+	}
+	return enc.CRLF()
+}
+
+// availableCaps returns the capabilities supported by the server.
+//
+// They depend on the connection state.
+//
+// Some extensions (e.g. SASL-IR, ENABLE) don't require backend support and
+// thus are always enabled.
+func (c *Conn) availableCaps() []imap.Cap {
+	available := c.server.options.caps()
+
+	var caps []imap.Cap
+	addAvailableCaps(&caps, available, []imap.Cap{
+		imap.CapIMAP4rev2,
+		imap.CapIMAP4rev1,
+	})
+	if len(caps) == 0 {
+		panic("imapserver: must support at least IMAP4rev1 or IMAP4rev2")
+	}
+
+	if available.Has(imap.CapIMAP4rev1) {
+		caps = append(caps, []imap.Cap{
+			imap.CapSASLIR,
+			imap.CapLiteralMinus,
+		}...)
+	}
+	if c.canStartTLS() {
+		caps = append(caps, imap.CapStartTLS)
+	}
+	if c.canAuth() {
+		mechs := []string{"PLAIN"}
+		if authSess, ok := c.session.(SessionSASL); ok {
+			mechs = authSess.AuthenticateMechanisms()
+		}
+		for _, mech := range mechs {
+			caps = append(caps, imap.Cap("AUTH="+mech))
+		}
+	} else if c.state == imap.ConnStateNotAuthenticated {
+		caps = append(caps, imap.CapLoginDisabled)
+	}
+	if c.state == imap.ConnStateAuthenticated || c.state == imap.ConnStateSelected {
+		if available.Has(imap.CapIMAP4rev1) {
+			// IMAP4rev1-specific capabilities that don't require backend
+			// support and are not applicable to IMAP4rev2
+			caps = append(caps, []imap.Cap{
+				imap.CapUnselect,
+				imap.CapEnable,
+				imap.CapIdle,
+				imap.CapUTF8Accept,
+			}...)
+
+			// 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,
+			})
+		}
+
+		// 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,
+		})
+
+		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})
+		}
+	}
+	return caps
+}
+
+func addAvailableCaps(caps *[]imap.Cap, available imap.CapSet, l []imap.Cap) {
+	for _, c := range l {
+		if available.Has(c) {
+			*caps = append(*caps, c)
+		}
+	}
+}