From 99f28195dbfad2572bdcffdda674ec1fed422143 Mon Sep 17 00:00:00 2001
From: Simon Ser <contact@emersion.fr>
Date: Fri, 7 Apr 2023 18:21:21 +0200
Subject: [PATCH] Add support for SEARCHRES

---
 imapserver/capability.go     |  2 +-
 internal/imapwire/decoder.go |  5 +++++
 internal/imapwire/encoder.go |  5 +++--
 search.go                    | 24 ++++++++++++++++++++++++
 seqset.go                    |  3 +++
 5 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/imapserver/capability.go b/imapserver/capability.go
index 9c303314..ffcd1d64 100644
--- a/imapserver/capability.go
+++ b/imapserver/capability.go
@@ -64,11 +64,11 @@ func (c *Conn) availableCaps() []imap.Cap {
 				imap.CapEnable,
 				imap.CapIdle,
 			}...)
-			// TODO: implement imap.CapSearchRes
 			addAvailableCaps(&caps, available, []imap.Cap{
 				imap.CapNamespace,
 				imap.CapUIDPlus,
 				imap.CapESearch,
+				imap.CapSearchRes,
 				imap.CapListExtended,
 				imap.CapListStatus,
 				imap.CapMove,
diff --git a/internal/imapwire/decoder.go b/internal/imapwire/decoder.go
index 80b6a911..363364fd 100644
--- a/internal/imapwire/decoder.go
+++ b/internal/imapwire/decoder.go
@@ -461,6 +461,11 @@ func (dec *Decoder) ExpectMailbox(ptr *string) bool {
 }
 
 func (dec *Decoder) ExpectSeqSet(ptr *imap.SeqSet) bool {
+	if dec.Special('$') {
+		*ptr = imap.SearchRes()
+		return true
+	}
+
 	var s string
 	if !dec.Expect(dec.Func(&s, isSeqSetChar), "sequence-set") {
 		return false
diff --git a/internal/imapwire/encoder.go b/internal/imapwire/encoder.go
index 399e4611..f7e00c44 100644
--- a/internal/imapwire/encoder.go
+++ b/internal/imapwire/encoder.go
@@ -159,11 +159,12 @@ func (enc *Encoder) Mailbox(name string) *Encoder {
 }
 
 func (enc *Encoder) SeqSet(seqSet imap.SeqSet) *Encoder {
-	if len(seqSet) == 0 {
+	s := seqSet.String()
+	if s == "" {
 		enc.setErr(fmt.Errorf("imapwire: cannot encode empty sequence set"))
 		return enc
 	}
-	return enc.writeString(seqSet.String())
+	return enc.writeString(s)
 }
 
 func (enc *Encoder) Flag(flag imap.Flag) *Encoder {
diff --git a/search.go b/search.go
index 425c700c..3af63d06 100644
--- a/search.go
+++ b/search.go
@@ -1,6 +1,7 @@
 package imap
 
 import (
+	"reflect"
 	"time"
 )
 
@@ -11,6 +12,8 @@ type SearchOptions struct {
 	ReturnMax   bool
 	ReturnAll   bool
 	ReturnCount bool
+	// Requires IMAP4rev2 or SEARCHRES
+	ReturnSave  bool
 }
 
 // SearchCriteria is a criteria for the SEARCH command.
@@ -116,3 +119,24 @@ func (data *SearchData) AllNums() []uint32 {
 	nums, _ := data.All.Nums()
 	return nums
 }
+
+// searchRes is a special empty SeqSet which can be used as a marker. It has
+// a non-zero cap so that its data pointer is non-nil and can be compared.
+var (
+	searchRes     = make(SeqSet, 0, 1)
+	searchResAddr = reflect.ValueOf(searchRes).Pointer()
+)
+
+// SearchRes returns a special marker which can be used instead of a SeqSet to
+// reference the last SEARCH result. On the wire, it's encoded as '$'.
+//
+// It requires IMAP4rev2 or the SEARCHRES extension.
+func SearchRes() SeqSet {
+	return searchRes
+}
+
+// IsSearchRes checks whether a sequence set is a reference to the last SEARCH
+// result. See SearchRes.
+func IsSearchRes(seqSet SeqSet) bool {
+	return reflect.ValueOf(seqSet).Pointer() == searchResAddr
+}
diff --git a/seqset.go b/seqset.go
index 3dcc3627..84fd5aba 100644
--- a/seqset.go
+++ b/seqset.go
@@ -214,6 +214,9 @@ func (s SeqSet) Nums() (nums []uint32, ok bool) {
 
 // String returns a sorted representation of all contained sequence values.
 func (s SeqSet) String() string {
+	if IsSearchRes(s) {
+		return "$"
+	}
 	if len(s) == 0 {
 		return ""
 	}