[base] Fix `FT_Open_Face`'s handling of user-supplied streams.

This was already true (though undocumented) most of the time, but
not if `FT_NEW` inside `FT_Stream_New` failed or if the
`FT_OPEN_XXX` flags were bad.

Normally, `FT_Open_Face` calls `FT_Stream_New`, which returns the
user-supplied stream unchanged, and in case of any subsequent error
in `FT_Open_Face`, the stream is closed via `FT_Stream_Free`.

Up to now, however, `FT_Stream_New` allocates a new stream even if
it is already given one by the user.  If this allocation fails, the
user-supplied stream is not returned to `FT_Open_Face` and never
closed.  Moreover, the user cannot detect this situation: all they
see is that `FT_Open_Face` returns `FT_Err_Out_Of_Memory`, but that
can also happen after a different allocation fails within the main
body of `FT_Open_Face`, when the user's stream has already been
closed by `FT_Open_Face`.  It is plausible that the user stream's
`close` method frees memory allocated for the stream object itself,
so the user cannot defensively free it upon `FT_Open_Face` failure
lest it ends up doubly freed.  All in all, this ends up leaking the
memory/resources used by user's stream.

Furthermore, `FT_Stream_New` simply returns an error if the
`FT_OPEN_XXX` flags are unsupported, which can mean either an
invalid combination of flags or a perfectly innocent
`FT_OPEN_STREAM` on a FreeType build that lacks stream support.
With this patch, the user-supplied stream is closed even in these
cases, so the user can be sure that if `FT_Open_Face` failed, the
stream is definitely closed.

* src/base/ftobjs.c (FT_Stream_New): Don't allocate a buffer
unnecessarily.
Move error-handling code to make the control flow more obvious.
Close user-supplied stream if the flags are unsupported.
`FT_Stream_Open` always sets `pathname.pointer`, so remove the
redundant (re)assignment.  None of the `FT_Stream_Open...` functions
uses `stream->memory`, so keep just one assignment at the end,
shared among all possible control flow paths.
('Unsupported flags' that may need a stream closure can be either an
invalid combination of multiple `FT_OPEN_XXX` mode flags or a clean
`FT_OPEN_STREAM` flag on a FreeType build that lacks stream
support.)

1 files changed, 4 insertions, 0 deletions

diff --git a/include/freetype/freetype.h b/include/freetype/freetype.h
index 598abd8c9..566f56d7b 100644
--- a/include/freetype/freetype.h
+++ b/include/freetype/freetype.h
@@ -2301,6 +2301,10 @@ FT_BEGIN_HEADER
    *   See the discussion of reference counters in the description of
    *   @FT_Reference_Face.
    *
+   *   If `FT_OPEN_STREAM` is set in `args->flags`, the stream in
+   *   `args->stream` is automatically closed before this function returns
+   *   any error (including `FT_Err_Invalid_Argument`).
+   *
    * @example:
    *   To loop over all faces, use code similar to the following snippet
    *   (omitting the error handling).