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.
---

This could really do with some tests (it is the second time this type of
bug has occurred). To be considered as a message by notmuch new a file
needs at least one of a From: Subject: or To: header. Thus we should
have three messages each of which just contains that single header (and
nothing else) and check that search and show work as expected. 



 sprinter-json.c |    2 ++
 sprinter-text.c |    2 ++
 sprinter.h      |    4 +++-
 3 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/sprinter-json.c b/sprinter-json.c
index c9b6835..0a07790 100644
--- a/sprinter-json.c
+++ b/sprinter-json.c
@@ -118,6 +118,8 @@ json_string_len (struct sprinter *sp, const char *val, size_t len)
 static void
 json_string (struct sprinter *sp, const char *val)
 {
+    if (val == NULL)
+	val = "";
     json_string_len (sp, val, strlen (val));
 }
 
diff --git a/sprinter-text.c b/sprinter-text.c
index dfa54b5..10343be 100644
--- a/sprinter-text.c
+++ b/sprinter-text.c
@@ -38,6 +38,8 @@ text_string_len (struct sprinter *sp, const char *val, size_t len)
 static void
 text_string (struct sprinter *sp, const char *val)
 {
+    if (val == NULL)
+	val = "";
     text_string_len (sp, val, strlen (val));
 }
 
diff --git a/sprinter.h b/sprinter.h
index 5f43175..912a526 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);
-- 
1.7.9.1


H