mprintf: Fix processing of width and prec args

Prior to this change a width arg could be erroneously output, and also
width and precision args could not be used together without crashing.

"%0*d%s", 2, 9, "foo"

Before: "092"
After: "09foo"

"%*.*s", 5, 2, "foo"

Before: crash
After: "   fo"

Test 557 is updated to verify this and more

1 files changed, 49 insertions, 0 deletions

diff --git a/tests/libtest/lib557.c b/tests/libtest/lib557.c
index 2e724897e..5bdb8abe0 100644
--- a/tests/libtest/lib557.c
+++ b/tests/libtest/lib557.c
@@ -1374,6 +1374,53 @@ static int test_curl_off_t_formatting(void)
   return failed;
 }
 
+static int string_check(char *buf, const char *buf2)
+{
+  if(strcmp(buf, buf2)) {
+    /* they shouldn't differ */
+    printf("sprintf failed:\nwe '%s'\nsystem: '%s'\n",
+           buf, buf2);
+    return 1;
+  }
+  return 0;
+}
+
+/*
+ * The output strings in this test need to have been verified with a system
+ * sprintf() before used here.
+ */
+static int test_string_formatting(void)
+{
+  int errors = 0;
+  char buf[256];
+  curl_msnprintf(buf, sizeof(buf), "%0*d%s", 2, 9, "foo");
+  errors += string_check(buf, "09foo");
+
+  curl_msnprintf(buf, sizeof(buf), "%*.*s", 5, 2, "foo");
+  errors += string_check(buf, "   fo");
+
+  curl_msnprintf(buf, sizeof(buf), "%*.*s", 2, 5, "foo");
+  errors += string_check(buf, "foo");
+
+  curl_msnprintf(buf, sizeof(buf), "%*.*s", 0, 10, "foo");
+  errors += string_check(buf, "foo");
+
+  curl_msnprintf(buf, sizeof(buf), "%-10s", "foo");
+  errors += string_check(buf, "foo       ");
+
+  curl_msnprintf(buf, sizeof(buf), "%10s", "foo");
+  errors += string_check(buf, "       foo");
+
+  curl_msnprintf(buf, sizeof(buf), "%*.*s", -10, -10, "foo");
+  errors += string_check(buf, "foo       ");
+
+  if(!errors)
+    printf("All curl_mprintf() strings tests OK!\n");
+  else
+    printf("Some curl_mprintf() string tests Failed!\n");
+
+  return errors;
+}
 
 int test(char *URL)
 {
@@ -1394,6 +1441,8 @@ int test(char *URL)
 
   errors += test_curl_off_t_formatting();
 
+  errors += test_string_formatting();
+
   if(errors)
     return TEST_ERR_MAJOR_BAD;
   else