Squid-2.2.STABLE2: Don't give ICP HIT on non-200 objects
  There is a common false hit condition with objects with a HTTP status
  other than 200 (HTTP_OK). These will cause false hits if a client sends
  a If-Modified-Since request. This patch makes a minor change to the
  on-disk store, and may or may not be fully compatible with future Squid
  releases. Don't use this patch unless you are prepared to clean your
  cache on next upgrade.

Index: squid/src/icp_v2.c
diff -u squid/src/icp_v2.c:1.1.1.23 squid/src/icp_v2.c:1.1.1.23.8.1
--- squid/src/icp_v2.c:1.1.1.23	Sun Feb 14 23:30:01 1999
+++ squid/src/icp_v2.c	Tue May 11 04:43:31 1999
@@ -173,6 +173,8 @@
 	return 0;
     if (Config.onoff.icp_hit_stale)
 	return 1;
+    if (EBIT_TEST(e->flags, ENTRY_NOT_HTTP_OK))
+	return 0;
     if (refreshCheckICP(e, request))
 	return 0;
     return 1;
Index: squid/src/store_swapout.c
diff -u squid/src/store_swapout.c:1.1.1.14 squid/src/store_swapout.c:1.1.1.14.8.1
--- squid/src/store_swapout.c:1.1.1.14	Sun Feb 14 23:30:10 1999
+++ squid/src/store_swapout.c	Tue May 11 04:43:31 1999
@@ -58,6 +58,9 @@
     ctrlp->swapfilename = xstrdup(storeSwapFullPath(e->swap_file_number, NULL));
     ctrlp->e = e;
     ctrlp->oldswapstatus = e->swap_status;
+    if (e->mem_obj->reply && e->mem_obj->reply->sline.status != HTTP_OK) {
+	EBIT_SET(e->flags, ENTRY_NOT_HTTP_OK);
+    }
     e->swap_status = SWAPOUT_OPENING;
     e->mem_obj->swapout.ctrl = ctrlp;
     store_open_disk_fd++;
Index: squid/src/enums.h
diff -u squid/src/enums.h:1.1.1.31.8.1 squid/src/enums.h:1.1.1.31.8.2
--- squid/src/enums.h:1.1.1.31.8.1	Wed May  5 11:33:50 1999
+++ squid/src/enums.h	Tue May 11 04:43:59 1999
@@ -449,7 +449,8 @@
     ENTRY_NEGCACHED,
     ENTRY_VALIDATED,
     ENTRY_BAD_LENGTH,
-    ENTRY_ABORTED
+    ENTRY_ABORTED,
+    ENTRY_NOT_HTTP_OK
 };
 
 typedef enum {