Preserve caller context across DNS lookups (#496)

For now, the context is restored when communicating with _individual_
callers waiting for their DNS lookup results. Eventually, we might also
support establishing a multi-caller context during DNS answer parsing,
before individual callers are notified. That feature would most likely
require making idns_query refcount-based (a serious change). Or we could
realize that maintaining a very basic query ID-based context is enough.

diff --git a/src/dns_internal.cc b/src/dns_internal.cc
index 10fcb486a313157914a26a8cc7f38c70ce769a51..30502dc210ed2894022a06d61dbef60df604cc9b 100644 (file)
--- a/src/dns_internal.cc
+++ b/src/dns_internal.cc
@@ -9,6 +9,7 @@
 /* DEBUG: section 78    DNS lookups; interacts with dns/rfc1035.cc */
 
 #include "squid.h"
+#include "base/CodeContext.h"
 #include "base/InstanceId.h"
 #include "base/RunnersRegistry.h"
 #include "comm.h"
@@ -103,7 +104,9 @@ class idns_query
     CBDATA_CLASS(idns_query);
 
 public:
-    idns_query() {
+    idns_query():
+        codeContext(CodeContext::Current())
+    {
         callback = nullptr;
         memset(&query, 0, sizeof(query));
         *buf = 0;
@@ -141,8 +144,11 @@ public:
     struct timeval sent_t;
     struct timeval queue_t;
     dlink_node lru;
+
     IDNSCB *callback;
     void *callback_data = nullptr;
+    CodeContext::Pointer codeContext; ///< requestor's context
+
     int attempt = 0;
     int rcode = 0;
     idns_query *queue = nullptr;
@@ -1104,6 +1110,7 @@ idnsCallbackNewCallerWithOldAnswers(IDNSCB *callback, void *cbdata, const idns_q
     for (auto query = master; query; query = query->slave) {
         if (query->pending)
             continue; // no answer yet
+        // no CallBack(CodeContext...) -- we always run in requestor's context
         if (!idnsCallbackOneWithAnswer(callback, cbdata, *query, lastAnswer))
             break; // the caller disappeared
     }
@@ -1116,8 +1123,10 @@ idnsCallbackAllCallersWithNewAnswer(const idns_query * const answered, const boo
     const auto master = answered->master ? answered->master : answered;
     // iterate all queued lookup callers
     for (auto looker = master; looker; looker = looker->queue) {
-        (void)idnsCallbackOneWithAnswer(looker->callback, looker->callback_data,
-                                        *answered, lastAnswer);
+        CallBack(looker->codeContext, [&] {
+            (void)idnsCallbackOneWithAnswer(looker->callback, looker->callback_data,
+            *answered, lastAnswer);
+        });
     }
 }