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From Joe Orton <jor...@redhat.com>
Subject Re: cvs commit: httpd-2.0/modules/filters mod_deflate.c
Date Mon, 19 Jul 2004 15:41:52 GMT
On Mon, Jul 19, 2004 at 03:47:45PM +0100, Nick Kew wrote:
> On Mon, 19 Jul 2004, Joe Orton wrote:
> 
> > On Sat, Jul 17, 2004 at 03:22:35PM -0000, niq@apache.org wrote:
> > > niq         2004/07/17 08:22:35
> > >
> > >   Modified:    modules/filters mod_deflate.c
> > >   Log:
> > >   Fix previous patch to deal correctly with multiple empty brigades before
> > >   we know if there's any content, and not re-process the headers.
> >
> > Is there no simpler fix for this e.g. first thing the filter does is "if
> > (APR_BRIGADE_EMPTY(bb)) return APR_SUCCESS;".  And to avoid the
> 
> Yes, that should work (but leaves us to reprocess the whole thing next
> time round).  Is that better or worse?  Or come to think of it, we can
> both return APR_SUCCESS and set a flag.

Why set a flag at all - if asked to filter nothing what interesting
state has changed since the last invocation?

> > re-process issue just ap_remove_output_filter(f) if finding an EOS-only
> > brigade?
> 
> Do you recollect the discussion around when that patch went in?
> I don't in full, but I had a nagging recollection of someone having
> proposed a simpler solution but found it didn't work.  Just enough
> to persuade me to preserve the loop-over-buckets test.

Nothing like that was posted to the list, at least.  Patch below is
still sufficient to fix the proxy+304 case; does it work for you too?

--- mod_deflate.c	18 Jul 2004 01:18:58 -0000	1.56
+++ mod_deflate.c	19 Jul 2004 15:29:02 -0000
@@ -247,7 +247,6 @@
     apr_bucket_brigade *bb, *proc_bb;
 } deflate_ctx;
 
-static void* const deflate_yes = (void*)"YES";
 static apr_status_t deflate_out_filter(ap_filter_t *f,
                                        apr_bucket_brigade *bb)
 {
@@ -255,14 +254,14 @@
     request_rec *r = f->r;
     deflate_ctx *ctx = f->ctx;
     int zRC;
-    char* buf;
-    int eos_only = 1;
-    apr_bucket *bkt;
-    char *token;
-    const char *encoding = NULL;
     deflate_filter_config *c = ap_get_module_config(r->server->module_config,
                                                     &deflate_module);
 
+    /* Do nothing if asked to filter nothing. */
+    if (APR_BRIGADE_EMPTY(bb)) {
+        return APR_SUCCESS;
+    }
+
     /* If we don't have a context, we need to ensure that it is okay to send
      * the deflated content.  If we have a context, that means we've done
      * this before and we liked it.
@@ -270,6 +269,8 @@
      * we're in better shape.
      */
     if (!ctx) {
+        char *buf, *token;
+        const char *encoding;
 
         /* only work on main request/no subrequests */
         if (r->main) {
@@ -349,7 +350,13 @@
          */
         apr_table_setn(r->headers_out, "Vary", "Accept-Encoding");
 
-
+        /* Deflating a zero-length response would make it longer; the
+         * proxy may pass through an empty response for a 304 too. */
+        if (APR_BUCKET_IS_EOS(APR_BRIGADE_FIRST(bb))) {
+            ap_remove_output_filter(f);
+            return ap_pass_brigade(f->next, bb);
+        }
+            
         /* force-gzip will just force it out regardless if the browser
          * can actually do anything with it.
          */
@@ -383,41 +390,6 @@
                 return ap_pass_brigade(f->next, bb);
             }
         }
-
-        /* don't deflate responses with zero length e.g. proxied 304's but
-         * we do set the header on eos_only at this point for headers_filter
-         *
-         * if we get eos_only and come round again, we want to avoid redoing
-         * what we've already done, so set f->ctx to a flag here
-         */
-        f->ctx = ctx = deflate_yes;
-    }
-    if (ctx == deflate_yes) {
-        /* deal with the pathological case of lots of empty brigades and
-         * no knowledge of whether content will follow
-         */
-        for (bkt = APR_BRIGADE_FIRST(bb);
-             bkt != APR_BRIGADE_SENTINEL(bb);
-             bkt = APR_BUCKET_NEXT(bkt))
-        {
-            if (!APR_BUCKET_IS_EOS(bkt)) {
-                 eos_only = 0;                 
-                 break;
-            }
-        }
-        if (eos_only) {
-            if (!encoding || !strcasecmp(encoding, "identity")) {
-                apr_table_set(r->headers_out, "Content-Encoding", "gzip");
-            }
-            else {
-                apr_table_merge(r->headers_out, "Content-Encoding", "gzip");
-            }
-            apr_table_unset(r->headers_out, "Content-Length");
-            return ap_pass_brigade(f->next, bb);
-        }
-    }
-    if (!ctx || (ctx==deflate_yes)) {
-
         /* We're cool with filtering this. */
         ctx = f->ctx = apr_pcalloc(r->pool, sizeof(*ctx));
         ctx->bb = apr_brigade_create(r->pool, f->c->bucket_alloc);


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