From 5b4485a90d4efda42017615fa5df2ac400a81ef6 Mon Sep 17 00:00:00 2001
From: "Enrico Weigelt, metux IT consult" <info@metux.net>
Date: Wed, 24 Jul 2024 16:39:49 +0200
Subject: [PATCH] (cleanup/xext-xres) Xext: xres: ProcXResQueryClientIds()
 collect reply in one stack buffer

In order to allow simplifying the reply send path, collect the reply
fragments into one buffer, instead of arbitrary number of WriteToClient()
calls. This also makes it much easier for potentially new purely packet-based
transports which (eg. binder) that would need their own stream parsing logic.

This xres function is an exceptionally hard case, since payload is constructed
step by step, and it's size only known when finished. The current way of the
fragment handling still has lots of room for improvement (eg. using very small
number of allocations), but leaving this for later exercise.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
---
 Xext/xres.c | 37 +++++++++++++++++++------------------
 1 file changed, 19 insertions(+), 18 deletions(-)

diff --git a/Xext/xres.c b/Xext/xres.c
index c2616e2bb..d3973cc9f 100644
--- a/Xext/xres.c
+++ b/Xext/xres.c
@@ -111,21 +111,6 @@ AddFragment(struct xorg_list *frags, int bytes)
     }
 }
 
-/** @brief Sends all fragments in the list to the client. Does not
-           free anything.
-
-    @param client The client to send the fragments to
-    @param frags The head of the list of fragments
-*/
-static void
-WriteFragmentsToClient(ClientPtr client, struct xorg_list *frags)
-{
-    FragmentList *it;
-    xorg_list_for_each_entry(it, frags, l) {
-        WriteToClient(client, it->bytes, (char*) it + sizeof(*it));
-    }
-}
-
 /** @brief Frees a list of fragments. Does not free() root node.
 
     @param frags The head of the list of fragments
@@ -583,7 +568,14 @@ ProcXResQueryClientIds (ClientPtr client)
     rc = ConstructClientIds(client, stuff->numSpecs, specs, &ctx);
 
     if (rc == Success) {
-        assert((ctx.resultBytes & 3) == 0);
+        char buf[ctx.resultBytes];
+        char *walk = buf;
+
+        FragmentList *it;
+        xorg_list_for_each_entry(it, &ctx.response, l) {
+            memcpy(walk, FRAGMENT_DATA(it), it->bytes);
+            walk += it->bytes;
+        }
 
         xXResQueryClientIdsReply rep = {
             .type = X_Reply,
@@ -599,7 +591,7 @@ ProcXResQueryClientIds (ClientPtr client)
         }
 
         WriteToClient(client, sizeof(rep), &rep);
-        WriteFragmentsToClient(client, &ctx.response);
+        WriteToClient(client, sizeof(buf), buf);
     }
 
     DestroyConstructClientIdCtx(&ctx);
@@ -975,8 +967,17 @@ ProcXResQueryResourceBytes (ClientPtr client)
             SwapXResQueryResourceBytes(&ctx.response);
         }
 
+        char buf[ctx.resultBytes];
+        {
+            char *walk = buf;
+            FragmentList *it;
+            xorg_list_for_each_entry(it, &ctx.response, l) {
+                memcpy(walk, FRAGMENT_DATA(it), it->bytes);
+                walk += it->bytes;
+            }
+        }
         WriteToClient(client, sizeof(rep), &rep);
-        WriteFragmentsToClient(client, &ctx.response);
+        WriteToClient(client, sizeof(buf), buf);
     }
 
     DestroyConstructResourceBytesCtx(&ctx);