HTTP Compliance: add appropriate Warnings if serving a stale hit.

Per RFC 2616, we MUST add "110 Response is stale" Warning if serving a
stale reply for any reason, including configured overrides. We MUST add
"111 Revalidation failed" Warning if serving a stale reply because an
attempt to revalidate the response failed, due to an inability to reach
the server.

The patch adds a new stale_if_hit request flag, which is set in
refreshCheckHTTP() when entry freshness is calculated. refreshCheckHTTP()
is now called in offline mode, to set stale_if_hit properly. We check for
the offline mode before returning from refreshCheckHTTP() to preserve the
original logic.

refreshCheckHTTP() is no longer called for internal requests, to avoid
setting of stale_if_hit flag. It did not do anything important for
internal requests anyway.

Co-Advisor test cases:
    test_case/rfc2616/noSrv-hit-stale-max-age-req
    test_case/rfc2616/ccReqDirMsg-max-stale-warning

=== modified file 'src/HttpHeader.cc'
--- src/HttpHeader.cc	2010-09-10 21:12:54 +0000
+++ src/HttpHeader.cc	2010-09-21 16:17:28 +0000
@@ -1195,6 +1195,14 @@
     mb.clean();
 }
 
+void
+HttpHeader::putWarning(const int code, const char *const text)
+{
+    char buf[512];
+    snprintf(buf, sizeof(buf), "%i %s \"%s\"", code, visible_appname_string, text);
+    putStr(HDR_WARNING, buf);
+}
+
 /* add extension header (these fields are not parsed/analyzed/joined, etc.) */
 void
 HttpHeader::putExt(const char *name, const char *value)

=== modified file 'src/HttpHeader.h'
--- src/HttpHeader.h	2010-08-25 00:14:25 +0000
+++ src/HttpHeader.h	2010-09-19 04:37:31 +0000
@@ -238,6 +238,7 @@
     void putContRange(const HttpHdrContRange * cr);
     void putRange(const HttpHdrRange * range);
     void putSc(HttpHdrSc *sc);
+    void putWarning(const int code, const char *const text); ///< add a Warning header
     void putExt(const char *name, const char *value);
     int getInt(http_hdr_type id) const;
     int64_t getInt64(http_hdr_type id) const;

=== modified file 'src/client_side_reply.cc'
--- src/client_side_reply.cc	2010-09-19 04:32:46 +0000
+++ src/client_side_reply.cc	2010-09-21 16:21:01 +0000
@@ -518,7 +518,7 @@
        ) {
         http->logType = LOG_TCP_NEGATIVE_HIT;
         sendMoreData(result);
-    } else if (!Config.onoff.offline && refreshCheckHTTP(e, r) && !http->flags.internal) {
+    } else if (!http->flags.internal && refreshCheckHTTP(e, r)) {
         debugs(88, 5, "clientCacheHit: in refreshCheck() block");
         /*
          * We hold a stale copy; it needs to be validated
@@ -1309,6 +1309,13 @@
         }
     }
 
+    // add Warnings required by RFC 2616 if serving a stale hit
+    if (http->request->flags.stale_if_hit && logTypeIsATcpHit(http->logType)) {
+        hdr->putWarning(110, "Response is stale");
+        if (http->request->flags.need_validation)
+            hdr->putWarning(111, "Revalidation failed");
+    }
+
     /* Filter unproxyable authentication types */
 
     if (http->logType != LOG_TCP_DENIED &&

=== modified file 'src/refresh.cc'
--- src/refresh.cc	2010-09-19 04:33:46 +0000
+++ src/refresh.cc	2010-09-21 16:16:31 +0000
@@ -434,6 +434,20 @@
     return 1;
 }
 
+/// whether reply is stale if it is a hit
+static bool
+refreshIsStaleIfHit(const int reason)
+{
+    switch (reason) {
+    case FRESH_MIN_RULE:
+    case FRESH_LMFACTOR_RULE:
+    case FRESH_EXPIRES:
+        return false;
+    default:
+        return true;
+    }
+}
+
 /* refreshCheck... functions below are protocol-specific wrappers around
  * refreshCheck() function above */
 
@@ -443,7 +457,8 @@
     int reason = refreshCheck(entry, request, 0);
     refreshCounts[rcHTTP].total++;
     refreshCounts[rcHTTP].status[reason]++;
-    return (reason < 200) ? 0 : 1;
+    request->flags.stale_if_hit = refreshIsStaleIfHit(reason);
+    return (Config.onoff.offline || reason < 200) ? 0 : 1;
 }
 
 int

=== modified file 'src/structs.h'
--- src/structs.h	2010-09-19 04:32:46 +0000
+++ src/structs.h	2010-09-19 04:37:31 +0000
@@ -1008,7 +1008,7 @@
 
 
 struct request_flags {
-    request_flags(): range(0),nocache(0),ims(0),auth(0),cachable(0),hierarchical(0),loopdetect(0),proxy_keepalive(0),proxying(0),refresh(0),redirected(0),need_validation(0),fail_on_validation_err(0),accelerated(0),ignore_cc(0),intercepted(0),spoof_client_ip(0),internal(0),internalclient(0),must_keepalive(0),chunked_reply(0),stream_error(0),destinationIPLookedUp_(0) {
+    request_flags(): range(0),nocache(0),ims(0),auth(0),cachable(0),hierarchical(0),loopdetect(0),proxy_keepalive(0),proxying(0),refresh(0),redirected(0),need_validation(0),fail_on_validation_err(0),stale_if_hit(0),accelerated(0),ignore_cc(0),intercepted(0),spoof_client_ip(0),internal(0),internalclient(0),must_keepalive(0),chunked_reply(0),stream_error(0),destinationIPLookedUp_(0) {
 #if USE_HTTP_VIOLATIONS
         nocache_hack = 0;
 #endif
@@ -1031,6 +1031,7 @@
     unsigned int redirected:1;
     unsigned int need_validation:1;
     unsigned int fail_on_validation_err:1; ///< whether we should fail if validation fails
+    unsigned int stale_if_hit:1; ///< reply is stale if it is a hit
 #if USE_HTTP_VIOLATIONS
     unsigned int nocache_hack:1;	/* for changing/ignoring no-cache requests */
 #endif