Combined patch for simscan-1.4.1 (https://github.com/qmail/simscan/releases) by Roberto Puzzanghera
More info at https://notes.sagredo.eu/en/qmail-notes-185/simscan-38.html
v. 20210728

This patch puts together:

* jms patch to improve the debugging of simscan on qmail-smtpd log
  https://notes.sagredo.eu/files/qmail/patches/simscan/jms/simscan-1.4.0-debug.patch
  more info here https://qmail.jms1.net/simscan/

* A bug fix by Bob Greco where a received message with multiple 'local' recipients executes spamc
  as null user and not as the user extracted from the first local recipient.
  https://notes.sagredo.eu/en/qmail-notes-185/simscan-38.html#comment844

* The "attachments-size-limit" patch by Roberto Puzzanghera
  https://notes.sagredo.eu/files/qmail/patches/simscan/simscan-1.4.1_attachments-size-limit.patch

  Simscan doesn't pass messages over 250k to spamassassin. This patch let the administrator set the
  attachments' size limit in bytes at compilation time configuring in this way

  autoreconf -f -i (this in needed as configure.ac was modified)
  configure --with-attachments-size-limit=250000 (default 250k, value must be a number)

  Furthermore, events where simscan is not activated are now logged at smtpd level (it was logged
  only when debug is active).

===================================================================================================

diff -ruN ../simscan-1.4.1_original/configure.ac simscan-1.4.1/configure.ac
--- ../simscan-1.4.1_original/configure.ac	2015-01-23 09:57:43.000000000 +0100
+++ simscan-1.4.1/configure.ac	2021-07-28 13:51:50.658779381 +0200
@@ -17,6 +17,23 @@
 fi
 
 #----------------------------------------------------------------------
+# AC_ARG_WITH (package, help-string, [action-if-given], [action-if-not-given])
+AC_ARG_WITH(attachments-size-limit,
+    [  --with-attachments-size-limit=250000   Attachments with size above the limit in bytes are not passed to spamassassin (default 250k).],
+    [
+       case $withval in
+           ''|*[0-9]*) AC_MSG_ERROR(attachments-size-limit is not a number) ;;
+           *) attachments_size_limit="$withval" ;;
+       esac
+    ],
+    attachments_size_limit=250000)
+
+if [[ "$withval" == "no" ]]; then
+    attachments_size_limit=2500000
+fi
+AC_DEFINE_UNQUOTED(ATTACHMENTS_SIZE_LIMIT,$attachments_size_limit,"")
+
+#----------------------------------------------------------------------
 AC_ARG_ENABLE(user, [  --enable-user=<user> Change the user for simscan.  Default: simscan.],
 	ENABLE_USER="$enableval",
 	[
@@ -870,10 +887,10 @@
 
   case $ENABLE_SPAM_AUTH_USER in
     0*|n*|N*)
-      echo "authenticated users scanned = OFF"
+      echo " authenticated users scanned = OFF"
       ;;
     *)
-      echo "authenticated users scanned = ON"
+      echo " authenticated users scanned = ON"
       ;;
   esac
 
@@ -929,4 +946,7 @@
     ;;
 esac
 
+echo " attachments with size above $attachments_size_limit bytes are not passed to spamassassin"
+
 echo ""
+	
diff -ruN ../simscan-1.4.1_original/simscan.c simscan-1.4.1/simscan.c
--- ../simscan-1.4.1_original/simscan.c	2015-01-23 09:57:43.000000000 +0100
+++ simscan-1.4.1/simscan.c	2021-07-28 13:51:50.660779363 +0200
@@ -102,6 +102,7 @@
 int str_rstr(register char *h,register char *n);
 char *replace(char *string, char *oldpiece, char *newpiece);
 int DebugFlag = 0;
+int DebugFiles = 0;
 
 /* --stdout is required for reading virus names */
 char *viri_args[] = { "clamdscan", "--stdout", message_name, NULL };
@@ -171,6 +172,7 @@
 int InClamHeaders;
 int check_clam();
 int is_clam(char *clambuf);
+void log_clam(char *clambuf);
 #endif
 
 /* Attachment scanning globals */
@@ -274,6 +276,11 @@
   if ( (tmpstr=getenv("SIMSCAN_DEBUG"))!=NULL ) {
     DebugFlag = atoi(tmpstr);
   }
+
+  /* Set the "leave temp files alone" flag */
+  if ( (tmpstr=getenv("SIMSCAN_DEBUG_FILES"))!=NULL ) {
+    DebugFiles = atoi(tmpstr);
+  }
   
 #ifdef ENABLE_ATTACH
   init_attach();
@@ -546,11 +553,11 @@
 #endif
 
 #ifdef ENABLE_SPAM
-if (msgsize >= 250000) {
-  if ( DebugFlag > 0 ) {
+if (msgsize >= ATTACHMENTS_SIZE_LIMIT) {
+//  if ( DebugFlag > 0 ) {
     fprintf(stderr, "simscan: big file (%lu bytes); skipping SpamAssassin\n",
       (unsigned long) msgsize);
-  }
+//  }
 } else {
   /* re-open the file read only */
   if ( (fd = open(message_name, O_RDONLY)) == -1 ) {
@@ -828,10 +835,12 @@
   }
 
   /* remove the working files */
-  if ( remove_files(workdir) == -1 ) {
-    exit_clean(EXIT_400);
+  if ( DebugFiles < 2 ) {
+    if ( remove_files(workdir) == -1 ) {
+      exit_clean(EXIT_400);
+    }
   }
-  
+
   /* pass qmail-queue's exit status on */
   _exit(WEXITSTATUS(qstat));
 
@@ -984,6 +993,7 @@
   InClamHeaders = 1;
   memset(buffer,0,sizeof(buffer));
   while((file_count=read(0,buffer,BUFFER_SIZE))>0) {
+    if ( DebugFlag > 2 ) log_clam(buffer) ;
     if ( InClamHeaders == 1 ) {
       is_clam(buffer);
     }
@@ -1010,6 +1020,35 @@
   return(-1);
 }
 
+void log_clam(char *clambuf)
+{
+	char *p ;
+	int needh = 1 ;
+
+	p = clambuf ;
+	while ( *p )
+	{
+		if ( *p != '\r' )
+		{
+			if ( needh )
+			{
+				fputs ( "simscan: clamdscan: " , stderr ) ;
+				needh = 0 ;
+			}
+
+			fputc ( *p , stderr ) ;
+
+			if ( *p == '\n' )
+				needh = 1 ;
+		}
+
+		p++ ;
+	}
+
+	if ( ! needh )
+		fputc ( '\n' , stderr ) ;
+}
+
 int is_clam(char *clambuf)
 {
  int i,j,k;
@@ -1315,7 +1354,7 @@
     spamc_args[i++] = "-u";
     spamc_args[i++] = spamuser;
 #ifdef ENABLE_SPAMC_USER
-  } else if ( MaxRcptTo==1 && i<MAX_SPAMC_ARGS-2 && strlen(spamuser) == 0) {
+  } else if ( MaxRcptTo>0 && i<MAX_SPAMC_ARGS-2 && strlen(spamuser) == 0) {
     spamc_args[i++] = "-u";
     spamc_args[i++] = RcptTo[0];
 #endif
@@ -1638,7 +1677,8 @@
  */
 void exit_clean( int error_code )
 {
-  remove_files(workdir);
+  if ( DebugFiles < 1 )
+    remove_files(workdir);
   if ( DebugFlag > 0 ) {
     fprintf(stderr, "simscan:[%d]: exit error code: %d\n", getppid(), error_code); 
   }