Eph. memory catches invalid target (hi.s. delete)

If hist == nil and mysql database Delete msgid function returns
ErrDBIsNil, we know that the target does not match any channel or user.
Return invalid target error to operator (see #2020)

irc/errors.go

@@ -54,6 +54,7 @@ var (
  errConfusableIdentifier = errors.New("This identifier is confusable with one already in use")
  errInsufficientPrivs = errors.New("Insufficient privileges")
  errInvalidUsername = errors.New("Invalid username")
+ errInvalidTarget = errors.New("Invalid target")
  errFeatureDisabled = errors.New(`That feature is disabled`)
  errBanned = errors.New("IP or nickmask banned")
  errInvalidParams = utils.ErrInvalidParams

irc/mysql/history.go

@@ -24,6 +24,7 @@ import (
 
 var (
  ErrDisallowed = errors.New("disallowed")
+ ErrDBIsNil = errors.New("db == nil")
 )
 
 const (
@@ -726,7 +727,7 @@ func (mysql *MySQL) AddDirectMessage(sender, senderAccount, recipient, recipient
 // note that accountName is the unfolded name
 func (mysql *MySQL) DeleteMsgid(msgid, accountName string) (err error) {
  if mysql.db == nil {
- return nil
+ return ErrDBIsNil
  }
 
  ctx, cancel := context.WithTimeout(context.Background(), mysql.getTimeout())

irc/server.go

@@ -6,6 +6,7 @@
 package irc
 
 import (
+ "errors"
  "fmt"
  "net"
  "net/http"
@@ -1074,6 +1075,15 @@ func (server *Server) DeleteMessage(target, msgid, accountName string) (err erro
 
  if hist == nil {
  err = server.historyDB.DeleteMsgid(msgid, accountName)
+ if err != nil && errors.Is(err, mysql.ErrDBIsNil) {
+ /*
+ hist == nil, and db == nil. We know that the
+ target was not either a current channel or
+ client, and persistent storage is not used.
+ So this is an invalid target. (see #2020)
+ */
+ return errInvalidTarget
+ }
  } else {
  count := hist.Delete(func(item *history.Item) bool {
  return item.Message.Msgid == msgid && (accountName == "*" || item.AccountName == accountName)