BUG/MEDIUM: stconn: Disable 0-copy forwarding for filters altering the payload

It is especially a problem with Lua filters, but it is important to disable
the 0-copy forwarding if a filter alters the payload, or at least to be able
to disable it. While the filter is registered on the data filtering, it is
not an issue (and it is the common case) because, there is now way to
fast-forward data at all. But it may be an issue if a filter decides to
alter the payload and to unregister from data filtering. In that case, the
0-copy forwarding can be re-enabled in a hardly precdictable state.

To fix the issue, a SC flags was added to do so. The HTTP compression filter
set it and lua filters too if the body length is changed (via
HTTPMessage.set_body_len()).

Note that it is an issue because of a bad design about the HTX. Many info
about the message are stored in the HTX structure itself. It must be
refactored to move several info to the stream-endpoint descriptor. This
should ease modifications at the stream level, from filter or a TCP/HTTP
rules.

This should be backported as far as 3.0. If necessary, it may be backported
on lower versions, as far as 2.6. In that case, it must be reviewed and
adapted.

Author: capflam

include/haproxy/stconn-t.h

@@ -206,6 +206,7 @@ enum sc_flags {
 
 	SC_FL_EOS           = 0x00040000,  /* End of stream was reached (from down side to up side) */
 	SC_FL_HAVE_BUFF     = 0x00080000,  /* A buffer is ready, flag will be cleared once allocated */
+	SC_FL_NO_FASTFWD    = 0x00100000,  /* disable data fast-forwarding */
 };
 
 /* This function is used to report flags in debugging tools. Please reflect

src/flt_http_comp.c

@@ -515,6 +515,7 @@ set_compression_header(struct comp_state *st, struct stream *s, struct http_msg
 			goto error;
 	}
 
+	chn_prod(msg->chn)->flags |= SC_FL_NO_FASTFWD;
 	return 1;
 
   error:

src/hlua.c

@@ -7262,6 +7262,7 @@ __LJMP static int hlua_http_msg_set_body_len(lua_State *L)
 	}
 
   success:
+	chn_prod(msg->chn)->flags |= SC_FL_NO_FASTFWD;
 	lua_pushboolean(L, 1);
 	return 1;
 

src/stconn.c

@@ -604,6 +604,7 @@ static inline int sc_cond_forward_shut(struct stconn *sc)
 static inline int sc_is_fastfwd_supported(struct stconn *sc)
 {
 	return (!(global.tune.no_zero_copy_fwd & NO_ZERO_COPY_FWD) &&
+		!(sc->flags & SC_FL_NO_FASTFWD) &&
 		sc_ep_test(sc, SE_FL_MAY_FASTFWD_PROD) &&
 		sc_ep_test(sc_opposite(sc), SE_FL_MAY_FASTFWD_CONS) &&
 		sc_ic(sc)->to_forward);