msnprintf: return number of printed characters excluding null byte

... even when the output is "capped" by the maximum length argument.

Clarified in the docs.

Closes #7361

3 files changed, 43 insertions, 10 deletions

diff --git a/tests/libtest/lib557.c b/tests/libtest/lib557.c
index 00fbca38c..b6b8bec1f 100644
--- a/tests/libtest/lib557.c
+++ b/tests/libtest/lib557.c
@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2021, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -1541,8 +1541,9 @@ static int test_weird_arguments(void)
   buf[0] = 0;
   rc = curl_msnprintf(buf, sizeof(buf), "%d, %.*1$d", 500, 1);
 
-  if(rc != 256) {
-    printf("curl_mprintf() returned %d and not 256!\n", rc);
+  if(rc != sizeof(buf) - 1) {
+    printf("curl_mprintf() returned %d and not %d!\n", rc,
+           sizeof(buf) - 1);
     errors++;
   }
 
@@ -1669,6 +1670,36 @@ static int test_float_formatting(void)
 }
 /* !checksrc! enable LONGLINE */
 
+static int test_return_codes(void)
+{
+  char buf[128];
+  int rc;
+
+  rc = curl_msnprintf(buf, 100, "%d", 9999);
+  if(rc != 4)
+    return 1;
+
+  rc = curl_msnprintf(buf, 100, "%d", 99999);
+  if(rc != 5)
+    return 1;
+
+  /* returns the length excluding the nul byte */
+  rc = curl_msnprintf(buf, 5, "%d", 99999);
+  if(rc != 4)
+    return 1;
+
+  /* returns the length excluding the nul byte */
+  rc = curl_msnprintf(buf, 5, "%s", "helloooooooo");
+  if(rc != 4)
+    return 1;
+
+  /* returns the length excluding the nul byte */
+  rc = curl_msnprintf(buf, 6, "%s", "helloooooooo");
+  if(rc != 5)
+    return 1;
+
+  return 0;
+}
 int test(char *URL)
 {
   int errors = 0;
@@ -1702,6 +1733,8 @@ int test(char *URL)
 
   errors += test_float_formatting();
 
+  errors += test_return_codes();
+
   if(errors)
     return TEST_ERR_MAJOR_BAD;
   else
diff --git a/tests/unit/unit1398.c b/tests/unit/unit1398.c
index 43e1f47a5..e73ce24b0 100644
--- a/tests/unit/unit1398.c
+++ b/tests/unit/unit1398.c
@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2021, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -64,27 +64,27 @@ fail_unless(!strcmp(output, "012"), "wrong output");
 
 /* negative width */
 rc = curl_msnprintf(output, 8, "%-8s", str);
-fail_unless(rc == 8, "return code should be 8");
+fail_unless(rc == 7, "return code should be 7");
 fail_unless(!strcmp(output, "bug    "), "wrong output");
 
 /* larger width that string length */
 rc = curl_msnprintf(output, 8, "%8s", str);
-fail_unless(rc == 8, "return code should be 8");
+fail_unless(rc == 7, "return code should be 7");
 fail_unless(!strcmp(output, "     bu"), "wrong output");
 
 /* output a number in a limited output */
 rc = curl_msnprintf(output, 4, "%d", 10240);
-fail_unless(rc == 4, "return code should be 4");
+fail_unless(rc == 3, "return code should be 3");
 fail_unless(!strcmp(output, "102"), "wrong output");
 
 /* padded strings */
 rc = curl_msnprintf(output, 16, "%8s%8s", str, str);
-fail_unless(rc == 16, "return code should be 16");
+fail_unless(rc == 15, "return code should be 15");
 fail_unless(!strcmp(output, "     bug     bu"), "wrong output");
 
 /* padded numbers */
 rc = curl_msnprintf(output, 16, "%8d%8d", 1234, 5678);
-fail_unless(rc == 16, "return code should be 16");
+fail_unless(rc == 15, "return code should be 15");
 fail_unless(!strcmp(output, "    1234    567"), "wrong output");
 
 UNITTEST_STOP
diff --git a/tests/unit/unit1652.c b/tests/unit/unit1652.c
index 26f11e483..56dad0c34 100644
--- a/tests/unit/unit1652.c
+++ b/tests/unit/unit1652.c
@@ -108,7 +108,7 @@ fail_unless(verify(result, "(nil)") == 0, "Passing NULL as string");
 
 /* A string just long enough to not be truncated */
 memset(input, '\0', sizeof(input));
-memset(input, 'A', 2048);
+memset(input, 'A', 2047);
 Curl_infof(data, "%s", input);
 fail_unless(strlen(result) == 2048, "No truncation of infof input");
 fail_unless(verify(result, input) == 0, "No truncation of infof input");