From e2fcf5f92c2405f30dac3e083d0aafcc98596983 Mon Sep 17 00:00:00 2001
From: Sergey Lyubka <valenok@gmail.com>
Date: Mon, 30 May 2022 18:40:44 +0100
Subject: [PATCH] Fix #1565 - mg_snprintf %.*s with zero len printing

---
 mongoose.c       | 5 +++--
 src/str.c        | 5 +++--
 test/unit_test.c | 1 +
 3 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/mongoose.c b/mongoose.c
index 0e249e4c..dfff4278 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -4918,7 +4918,7 @@ size_t mg_vsnprintf(char *buf, size_t len, const char *fmt, va_list ap) {
   size_t i = 0, n = 0;
   while (fmt[i] != '\0') {
     if (fmt[i] == '%') {
-      size_t j, k, x = 0, is_long = 0, w = 0 /* width */, pr = 0 /* prec */;
+      size_t j, k, x = 0, is_long = 0, w = 0 /* width */, pr = ~0U /* prec */;
       char pad = ' ', minus = 0, c = fmt[++i];
       if (c == '#') x++, c = fmt[++i];
       if (c == '-') minus++, c = fmt[++i];
@@ -4930,6 +4930,7 @@ size_t mg_vsnprintf(char *buf, size_t len, const char *fmt, va_list ap) {
           pr = (size_t) va_arg(ap, int);
           c = fmt[++i];
         } else {
+          pr = 0;
           while (is_digit(c)) pr *= 10, pr += (size_t) (c - '0'), c = fmt[++i];
         }
       }
@@ -4968,7 +4969,7 @@ size_t mg_vsnprintf(char *buf, size_t len, const char *fmt, va_list ap) {
         n++;
       } else if (c == 's') {
         char *p = va_arg(ap, char *);
-        if (pr == 0) pr = p == NULL ? 0 : strlen(p);
+        if (pr == ~0U) pr = p == NULL ? 0 : strlen(p);
         for (j = 0; !minus && pr < w && j + pr < w; j++)
           n += mg_copys(buf, len, n, &pad, 1);
         n += mg_copys(buf, len, n, p, pr);
diff --git a/src/str.c b/src/str.c
index cb5693bf..b6fb5b04 100644
--- a/src/str.c
+++ b/src/str.c
@@ -286,7 +286,7 @@ size_t mg_vsnprintf(char *buf, size_t len, const char *fmt, va_list ap) {
   size_t i = 0, n = 0;
   while (fmt[i] != '\0') {
     if (fmt[i] == '%') {
-      size_t j, k, x = 0, is_long = 0, w = 0 /* width */, pr = 0 /* prec */;
+      size_t j, k, x = 0, is_long = 0, w = 0 /* width */, pr = ~0U /* prec */;
       char pad = ' ', minus = 0, c = fmt[++i];
       if (c == '#') x++, c = fmt[++i];
       if (c == '-') minus++, c = fmt[++i];
@@ -298,6 +298,7 @@ size_t mg_vsnprintf(char *buf, size_t len, const char *fmt, va_list ap) {
           pr = (size_t) va_arg(ap, int);
           c = fmt[++i];
         } else {
+          pr = 0;
           while (is_digit(c)) pr *= 10, pr += (size_t) (c - '0'), c = fmt[++i];
         }
       }
@@ -336,7 +337,7 @@ size_t mg_vsnprintf(char *buf, size_t len, const char *fmt, va_list ap) {
         n++;
       } else if (c == 's') {
         char *p = va_arg(ap, char *);
-        if (pr == 0) pr = p == NULL ? 0 : strlen(p);
+        if (pr == ~0U) pr = p == NULL ? 0 : strlen(p);
         for (j = 0; !minus && pr < w && j + pr < w; j++)
           n += mg_copys(buf, len, n, &pad, 1);
         n += mg_copys(buf, len, n, p, pr);
diff --git a/test/unit_test.c b/test/unit_test.c
index fa64b4f8..8ad5b1c5 100644
--- a/test/unit_test.c
+++ b/test/unit_test.c
@@ -1329,6 +1329,7 @@ static void test_str(void) {
   ASSERT(sn("%d", 0));
   ASSERT(sn("%d", 1));
   ASSERT(sn("%d", -1));
+  ASSERT(sn("%.*s", 0, "ab"));
   ASSERT(sn("%.*s", 1, "ab"));
   ASSERT(sn("%.1s", "ab"));
   ASSERT(sn("%.99s", "a"));