From 246b8d8553b6880146d6c489a28cf4bacea8a199 Mon Sep 17 00:00:00 2001
From: Rainer Gerhards <rgerhards@adiscon.com>
Date: Fri, 30 Dec 2022 17:13:17 +0100
Subject: [PATCH] core bugfix: template system may generate invalid json
 
When
- a list template
- is created with option.jsonf="on"
- and the last list element is a property with onEmpty="skip"
- and that property is actually empty
invalid JSON is generated.
 
The JSON string in this case ends with ", " instead of "}\n". This
patch fixes the issue.
 
closes https://github.com/rsyslog/rsyslog/issues/5050
---
 
Conflict:NA
Reference:https://github.com/rsyslog/rsyslog/commit/246b8d8553b6880146d6c489a28cf4bacea8a199
---
 template.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)
 
diff --git a/template.c b/template.c
index 21d8b8d..18bcda7 100644
--- a/template.c
+++ b/template.c
@@ -163,6 +163,7 @@ tplToString(struct template *__restrict__ const pTpl,
 	unsigned short bMustBeFreed = 0;
 	uchar *pVal;
 	rs_size_t iLenVal = 0;
+	int need_comma = 0;
 
 	if(pTpl->pStrgen != NULL) {
 		CHKiRet(pTpl->pStrgen(pMsg, iparam));
@@ -230,15 +231,24 @@ tplToString(struct template *__restrict__ const pTpl,
 			if(iBuf + iLenVal + extra_space >= iparam->lenBuf) /* we reserve one char for the final \0! */
 				CHKiRet(ExtendBuf(iparam, iBuf + iLenVal + 1));
 
+			if(need_comma) {
+				memcpy(iparam->param + iBuf, ", ", 2);
+				iBuf += 2;
+			}
 			memcpy(iparam->param + iBuf, pVal, iLenVal);
 			iBuf += iLenVal;
 			if(pTpl->optFormatEscape == JSONF) {
-				memcpy(iparam->param + iBuf,
-					(pTpe->pNext == NULL) ? "}\n" : ", ", 2);
-				iBuf += 2;
+				need_comma = 1;
 			}
 		}
 
+		if((pTpl->optFormatEscape == JSONF) && (pTpe->pNext == NULL)) {
+			/* space was reserved while processing field above
+			   (via extra_space in ExtendBuf() new size formula. */
+			memcpy(iparam->param + iBuf, "}\n", 2);
+			iBuf += 2;
+		}
+
 		if(bMustBeFreed) {
 			free(pVal);
 			bMustBeFreed = 0;
-- 
2.27.0