sprinters: bugfix when NULL passed for a string.

The string function in a sprinter may be called with a NULL string
pointer (eg if a header is absent). This causes a segfault. We fix
this by checking for a null pointer in the string functions and update
the sprinter documentation.

At the moment some output when format=text is done directly rather than
via an sprinter: in that case a null pointer is passed to printf or
similar and a "(null)" appears in the output. That behaviour is not
changed in this patch.

1 files changed, 3 insertions, 1 deletions

diff --git a/sprinter.h b/sprinter.h
index 5f431757..912a5262 100644
--- a/sprinter.h
+++ b/sprinter.h
@@ -27,7 +27,9 @@ typedef struct sprinter {
      * a list or map, followed or preceded by separators).  For string
      * and string_len, the char * must be UTF-8 encoded.  string_len
      * allows non-terminated strings and strings with embedded NULs
-     * (though the handling of the latter is format-dependent).
+     * (though the handling of the latter is format-dependent). For
+     * string (but not string_len) the string pointer passed may be
+     * NULL.
      */
     void (*string) (struct sprinter *, const char *);
     void (*string_len) (struct sprinter *, const char *, size_t);