Add tests for snprintf

- Added in each tests program to be sure they are run (putting them in a test
  suite/function specific to the platform layer would cause them to be skipped
when PLATFORM_C is not defined).
- Platforms have already moved from a standard to a broken snprintf in the
  past [1], so make sure to catch that if it ever happens again.

[1]: http://sourceforge.net/p/mingw-w64/mailman/message/31241434/

programs/test/selftest.c

@@ -60,12 +60,41 @@
 #else
 #include <stdio.h>
 #define mbedtls_printf     printf
+#define mbedtls_snprintf   snprintf
 #endif
 
 #if defined(MBEDTLS_MEMORY_BUFFER_ALLOC_C)
 #include "mbedtls/memory_buffer_alloc.h"
 #endif
 
+static int test_snprintf( size_t n, const char ref_buf[10], int ref_ret )
+{
+    int ret;
+    char buf[10] = "xxxxxxxxx";
+
+    ret = mbedtls_snprintf( buf, n, "%s", "123" );
+    if( ret < 0 || (size_t) ret >= n )
+        ret = -1;
+
+    if( memcmp( ref_buf, buf, sizeof buf ) != 0 ||
+        ref_ret != ret )
+    {
+        return( 1 );
+    }
+
+    return( 0 );
+}
+
+static int run_test_snprintf( void )
+{
+    return( test_snprintf( 0, "xxxxxxxxx",  -1 ) != 0 ||
+            test_snprintf( 1, "\0xxxxxxxx", -1 ) != 0 ||
+            test_snprintf( 2, "1\0xxxxxxx", -1 ) != 0 ||
+            test_snprintf( 3, "12\0xxxxxx", -1 ) != 0 ||
+            test_snprintf( 4, "123\0xxxxx",  3 ) != 0 ||
+            test_snprintf( 5, "123\0xxxxx",  3 ) != 0 );
+}
+
 int main( int argc, char *argv[] )
 {
     int ret = 0, v;
@@ -86,6 +115,15 @@ int main( int argc, char *argv[] )
         return( 1 );
     }
 
+    /*
+     * Make sure we have a snprintf that correctly zero-terminates
+     */
+    if( run_test_snprintf() != 0 )
+    {
+        mbedtls_printf( "the snprintf implementation is broken\n" );
+        return( 0 );
+    }
+
     if( argc == 2 && strcmp( argv[1], "-quiet" ) == 0 )
         v = 0;
     else

tests/suites/main_test.function

@@ -4,11 +4,13 @@
 #include "mbedtls/platform.h"
 #else
 #include <stdio.h>
+#include <stdlib.h>
 #define mbedtls_exit       exit
 #define mbedtls_free       free
-#define mbedtls_calloc    calloc
+#define mbedtls_calloc     calloc
 #define mbedtls_fprintf    fprintf
 #define mbedtls_printf     printf
+#define mbedtls_snprintf   snprintf
 #endif
 
 #if defined(MBEDTLS_MEMORY_BUFFER_ALLOC_C)
@@ -209,6 +211,34 @@ int parse_arguments( char *buf, size_t len, char *params[50] )
     return( cnt );
 }
 
+static int test_snprintf( size_t n, const char ref_buf[10], int ref_ret )
+{
+    int ret;
+    char buf[10] = "xxxxxxxxx";
+
+    ret = mbedtls_snprintf( buf, n, "%s", "123" );
+    if( ret < 0 || (size_t) ret >= n )
+        ret = -1;
+
+    if( memcmp( ref_buf, buf, sizeof buf ) != 0 ||
+        ref_ret != ret )
+    {
+        return( 1 );
+    }
+
+    return( 0 );
+}
+
+static int run_test_snprintf( void )
+{
+    return( test_snprintf( 0, "xxxxxxxxx",  -1 ) != 0 ||
+            test_snprintf( 1, "\0xxxxxxxx", -1 ) != 0 ||
+            test_snprintf( 2, "1\0xxxxxxx", -1 ) != 0 ||
+            test_snprintf( 3, "12\0xxxxxx", -1 ) != 0 ||
+            test_snprintf( 4, "123\0xxxxx",  3 ) != 0 ||
+            test_snprintf( 5, "123\0xxxxx",  3 ) != 0 );
+}
+
 int main()
 {
     int ret, i, cnt, total_errors = 0, total_tests = 0, total_skipped = 0;
@@ -236,6 +266,15 @@ int main()
         return( 1 );
     }
 
+    /*
+     * Make sure we have a snprintf that correctly zero-terminates
+     */
+    if( run_test_snprintf() != 0 )
+    {
+        mbedtls_fprintf( stderr, "the snprintf implementation is broken\n" );
+        return( 0 );
+    }
+
     file = fopen( filename, "r" );
     if( file == NULL )
     {