New function ERR_error_string_n.

doc/crypto/ERR_error_string.pod

@@ -9,6 +9,7 @@ ERR_error_string - obtain human-readable error message
  #include <openssl/err.h>
 
  char *ERR_error_string(unsigned long e, char *buf);
+ char *ERR_error_string_n(unsigned long e, char *buf, size_t len);
 
  const char *ERR_lib_error_string(unsigned long e);
  const char *ERR_func_error_string(unsigned long e);
@@ -17,9 +18,13 @@ ERR_error_string - obtain human-readable error message
 =head1 DESCRIPTION
 
 ERR_error_string() generates a human-readable string representing the
-error code B<e>, and places it at B<buf>. B<buf> must be at least 120
-bytes long. If B<buf> is B<NULL>, the error string is placed in a
+error code I<e>, and places it at I<buf>. I<buf> must be at least 120
+bytes long. If I<buf> is B<NULL>, the error string is placed in a
 static buffer.
+ERR_error_string_n() is a variant of ERR_error_string() that writes
+at most I<len> characters (including the terminating 0)
+and truncates the resulting string if necessary.
+For ERR_error_string_n(), I<buf> may not be B<NULL>.
 
 The string will have the following format:
 
@@ -45,7 +50,7 @@ all error codes currently in the queue.
 =head1 RETURN VALUES
 
 ERR_error_string() returns a pointer to a static buffer containing the
-string if B<buf == NULL>, B<buf> otherwise.
+string if I<buf> B<== NULL>, I<buf> otherwise.
 
 ERR_lib_error_string(), ERR_func_error_string() and
 ERR_reason_error_string() return the strings, and B<NULL> if
@@ -61,5 +66,6 @@ L<ERR_print_errors(3)|ERR_print_errors(3)>
 =head1 HISTORY
 
 ERR_error_string() is available in all versions of SSLeay and OpenSSL.
+ERR_error_string_n() was added in OpenSSL 0.9.6.
 
 =cut