[type42] Track how much type42 ttf data is available.

Currently `T42_Open_Face` eagerly allocates 12 bytes for the ttf header
data which it expects `t42_parse_sfnts` to fill out from /sfnts data.
However, there is no guarantee that `t42_parse_sfnts` will actually be
called while parsing the type42 data as the /sfnts array may be missing
or very short. This is also confusing behavior as it means
`T42_Open_Face` is tightly coupled to the implementation of the very
distant `t42_parse_sfnts` code which requires at least 12 bytes to
already be reserved in `face->ttf_data`.

`t42_parse_sfnts` itself eagerly updates `face->ttf_size` to track how
much space is reserved for ttf data instead of traking how much data has
actually been written into `face->ttf_data`. It will also act strangely
in the presense of multiple /sfnts arrays.

* src/type42/t42objs.c (T42_Open_Face): ensure `ttf_data` is initialized
to NULL. Free `ttf_data` on error.

* src/type42/t42parse.c (t42_parse_sfnts): delay setting `ttf_size` and
set it to the actual number of bytes read. Ensure `ttf_data` is freed
if there are multiple /sfnts arrays or there are any errors.

1 files changed, 7 insertions, 9 deletions

diff --git a/src/type42/t42objs.c b/src/type42/t42objs.c
index c3e844a5b..4078777f2 100644
--- a/src/type42/t42objs.c
+++ b/src/type42/t42objs.c
@@ -44,15 +44,8 @@
 
     parser = &loader.parser;
 
-    /* To handle buggy fonts we don't use `FT_QALLOC` here. */
-    if ( FT_ALLOC( face->ttf_data, 12 ) )
-      goto Exit;
-
-    /* while parsing the font we always update `face->ttf_size' so that */
-    /* even in case of buggy data (which might lead to premature end of */
-    /* scanning without causing an error) the call to `FT_Open_Face' in */
-    /* `T42_Face_Init' passes the correct size                          */
-    face->ttf_size = 12;
+    face->ttf_data = NULL;
+    face->ttf_size = 0;
 
     error = t42_parser_init( parser,
                              face->root.stream,
@@ -153,6 +146,11 @@
 
   Exit:
     t42_loader_done( &loader );
+    if ( error )
+    {
+      FT_FREE(face->ttf_data);
+      face->ttf_size = 0;
+    }
     return error;
   }