[trac703] Merge branch 'master' into trac703

... master being updated shortly after the last merge.
Conflicts:
	src/lib/asiodns/io_fetch.cc
	src/lib/asiodns/io_fetch.h

configure.ac

@@ -644,6 +644,8 @@ AC_CONFIG_FILES([Makefile
                  src/lib/Makefile
                  src/lib/asiolink/Makefile
                  src/lib/asiolink/tests/Makefile
+                 src/lib/asiodns/Makefile
+                 src/lib/asiodns/tests/Makefile
                  src/lib/bench/Makefile
                  src/lib/bench/example/Makefile
                  src/lib/bench/tests/Makefile

src/bin/auth/Makefile.am

@@ -49,6 +49,7 @@ b10_auth_LDADD += $(top_builddir)/src/lib/dns/libdns++.la
 b10_auth_LDADD += $(top_builddir)/src/lib/config/libcfgclient.la
 b10_auth_LDADD += $(top_builddir)/src/lib/cc/libcc.la
 b10_auth_LDADD += $(top_builddir)/src/lib/exceptions/libexceptions.la
+b10_auth_LDADD += $(top_builddir)/src/lib/asiodns/libasiodns.la
 b10_auth_LDADD += $(top_builddir)/src/lib/asiolink/libasiolink.la
 b10_auth_LDADD += $(top_builddir)/src/lib/nsas/libnsas.la
 b10_auth_LDADD += $(top_builddir)/src/lib/xfr/libxfr.la

src/bin/auth/auth_srv.cc

@@ -68,7 +68,8 @@ using namespace isc::dns::rdata;
 using namespace isc::data;
 using namespace isc::config;
 using namespace isc::xfr;
-using namespace asiolink;
+using namespace isc::asiolink;
+using namespace isc::asiodns;
 using namespace isc::server_common::portconfig;
 
 class AuthSrvImpl {
@@ -766,6 +767,6 @@ AuthSrv::setListenAddresses(const AddressList& addresses) {
 }
 
 void
-AuthSrv::setDNSService(asiolink::DNSService& dnss) {
+AuthSrv::setDNSService(isc::asiodns::DNSService& dnss) {
     dnss_ = &dnss;
 }

src/bin/auth/auth_srv.h

@@ -26,11 +26,11 @@
 #include <dns/message.h>
 #include <dns/buffer.h>
 
+#include <asiodns/dns_server.h>
+#include <asiodns/dns_lookup.h>
+#include <asiodns/dns_answer.h>
 #include <asiolink/io_message.h>
 #include <asiolink/io_service.h>
-#include <asiolink/dns_server.h>
-#include <asiolink/dns_lookup.h>
-#include <asiolink/dns_answer.h>
 #include <asiolink/simple_callback.h>
 
 #include <asiolink/asiolink.h>
@@ -116,10 +116,10 @@ public:
     /// \param server Pointer to the \c DNSServer
     ///
     /// \throw isc::Unexpected Protocol type of \a message is unexpected
-    void processMessage(const asiolink::IOMessage& io_message,
+    void processMessage(const isc::asiolink::IOMessage& io_message,
                         isc::dns::MessagePtr message,
                         isc::dns::OutputBufferPtr buffer,
-                        asiolink::DNSServer* server);
+                        isc::asiodns::DNSServer* server);
 
     /// \brief Set verbose flag
     ///
@@ -202,16 +202,16 @@ public:
     void setConfigSession(isc::config::ModuleCCSession* config_session);
 
     /// \brief Return this object's ASIO IO Service queue
-    asiolink::IOService& getIOService();
+    isc::asiolink::IOService& getIOService();
 
     /// \brief Return pointer to the DNS Lookup callback function
-    asiolink::DNSLookup* getDNSLookupProvider() const { return (dns_lookup_); }
+    isc::asiodns::DNSLookup* getDNSLookupProvider() const { return (dns_lookup_); }
 
     /// \brief Return pointer to the DNS Answer callback function
-    asiolink::DNSAnswer* getDNSAnswerProvider() const { return (dns_answer_); }
+    isc::asiodns::DNSAnswer* getDNSAnswerProvider() const { return (dns_answer_); }
 
     /// \brief Return pointer to the Checkin callback function
-    asiolink::SimpleCallback* getCheckinProvider() const { return (checkin_); }
+    isc::asiolink::SimpleCallback* getCheckinProvider() const { return (checkin_); }
 
     /// \brief Set or update the size (number of slots) of hot spot cache.
     ///
@@ -372,15 +372,15 @@ public:
         const;
 
     /// \brief Assign an ASIO DNS Service queue to this Auth object
-    void setDNSService(asiolink::DNSService& dnss);
+    void setDNSService(isc::asiodns::DNSService& dnss);
 
 
 private:
     AuthSrvImpl* impl_;
-    asiolink::SimpleCallback* checkin_;
-    asiolink::DNSLookup* dns_lookup_;
-    asiolink::DNSAnswer* dns_answer_;
-    asiolink::DNSService* dnss_;
+    isc::asiolink::SimpleCallback* checkin_;
+    isc::asiodns::DNSLookup* dns_lookup_;
+    isc::asiodns::DNSAnswer* dns_answer_;
+    isc::asiodns::DNSService* dnss_;
 };
 
 #endif // __AUTH_SRV_H

src/bin/auth/benchmarks/Makefile.am

@@ -22,6 +22,7 @@ query_bench_LDADD += $(top_builddir)/src/lib/cc/libcc.la
 query_bench_LDADD += $(top_builddir)/src/lib/xfr/libxfr.la
 query_bench_LDADD += $(top_builddir)/src/lib/log/liblog.la
 query_bench_LDADD += $(top_builddir)/src/lib/nsas/libnsas.la
+query_bench_LDADD += $(top_builddir)/src/lib/asiodns/libasiodns.la
 query_bench_LDADD += $(top_builddir)/src/lib/asiolink/libasiolink.la
 query_bench_LDADD += $(top_builddir)/src/lib/server_common/libserver_common.la
 query_bench_LDADD += $(SQLITE_LIBS)

src/bin/auth/benchmarks/query_bench.cc

@@ -36,6 +36,7 @@
 #include <auth/auth_config.h>
 #include <auth/query.h>
 
+#include <asiodns/asiodns.h>
 #include <asiolink/asiolink.h>
 
 using namespace std;
@@ -45,7 +46,8 @@ using namespace isc::auth;
 using namespace isc::dns;
 using namespace isc::xfr;
 using namespace isc::bench;
-using namespace asiolink;
+using namespace isc::asiodns;
+using namespace isc::asiolink;
 
 namespace {
 // Commonly used constant:

src/bin/auth/main.cc

@@ -43,6 +43,7 @@
 #include <auth/command.h>
 #include <auth/change_user.h>
 #include <auth/auth_srv.h>
+#include <asiodns/asiodns.h>
 #include <asiolink/asiolink.h>
 #include <log/dummylog.h>
 
@@ -52,7 +53,8 @@ using namespace isc::cc;
 using namespace isc::config;
 using namespace isc::dns;
 using namespace isc::xfr;
-using namespace asiolink;
+using namespace isc::asiolink;
+using namespace isc::asiodns;
 
 namespace {
 

src/bin/auth/tests/Makefile.am

@@ -45,6 +45,7 @@ run_unittests_LDADD += $(SQLITE_LIBS)
 run_unittests_LDADD += $(top_builddir)/src/lib/testutils/libtestutils.la
 run_unittests_LDADD +=  $(top_builddir)/src/lib/datasrc/libdatasrc.la
 run_unittests_LDADD +=  $(top_builddir)/src/lib/dns/libdns++.la
+run_unittests_LDADD += $(top_builddir)/src/lib/asiodns/libasiodns.la
 run_unittests_LDADD += $(top_builddir)/src/lib/asiolink/libasiolink.la
 run_unittests_LDADD += $(top_builddir)/src/lib/config/libcfgclient.la
 run_unittests_LDADD += $(top_builddir)/src/lib/cc/libcc.la

src/bin/auth/tests/auth_srv_unittest.cc

@@ -44,7 +44,8 @@ using namespace isc::dns;
 using namespace isc::dns::rdata;
 using namespace isc::data;
 using namespace isc::xfr;
-using namespace asiolink;
+using namespace isc::asiodns;
+using namespace isc::asiolink;
 using namespace isc::testutils;
 using namespace isc::server_common::portconfig;
 using isc::UnitTestUtil;

src/bin/auth/tests/command_unittest.cc

@@ -99,7 +99,7 @@ AuthConmmandTest::stopServer() {
 }
 
 TEST_F(AuthConmmandTest, shutdown) {
-    asiolink::IntervalTimer itimer(server.getIOService());
+    isc::asiolink::IntervalTimer itimer(server.getIOService());
     itimer.setup(boost::bind(&AuthConmmandTest::stopServer, this), 1);
     server.getIOService().run();
     EXPECT_EQ(0, rcode);

src/bin/auth/tests/config_unittest.cc

@@ -35,7 +35,8 @@
 using namespace isc::dns;
 using namespace isc::data;
 using namespace isc::datasrc;
-using namespace asiolink;
+using namespace isc::asiodns;
+using namespace isc::asiolink;
 
 namespace {
 class AuthConfigTest : public ::testing::Test {

src/bin/resolver/Makefile.am

@@ -4,6 +4,8 @@ AM_CPPFLAGS = -I$(top_srcdir)/src/lib -I$(top_builddir)/src/lib
 AM_CPPFLAGS += -I$(top_srcdir)/src/bin -I$(top_builddir)/src/bin
 AM_CPPFLAGS += -I$(top_srcdir)/src/lib/dns -I$(top_builddir)/src/lib/dns
 AM_CPPFLAGS += -I$(top_srcdir)/src/lib/cc -I$(top_builddir)/src/lib/cc
+AM_CPPFLAGS += -I$(top_srcdir)/src/lib/asiodns
+AM_CPPFLAGS += -I$(top_builddir)/src/lib/asiodns
 AM_CPPFLAGS += -I$(top_srcdir)/src/lib/asiolink
 AM_CPPFLAGS += -I$(top_builddir)/src/lib/asiolink
 AM_CPPFLAGS += $(BOOST_INCLUDES)
@@ -45,6 +47,7 @@ b10_resolver_LDADD =  $(top_builddir)/src/lib/dns/libdns++.la
 b10_resolver_LDADD += $(top_builddir)/src/lib/config/libcfgclient.la
 b10_resolver_LDADD += $(top_builddir)/src/lib/cc/libcc.la
 b10_resolver_LDADD += $(top_builddir)/src/lib/exceptions/libexceptions.la
+b10_resolver_LDADD += $(top_builddir)/src/lib/asiodns/libasiodns.la
 b10_resolver_LDADD += $(top_builddir)/src/lib/asiolink/libasiolink.la
 b10_resolver_LDADD += $(top_builddir)/src/lib/xfr/libxfr.la
 b10_resolver_LDADD += $(top_builddir)/src/lib/log/liblog.la

src/bin/resolver/main.cc

@@ -27,6 +27,7 @@
 
 #include <boost/foreach.hpp>
 
+#include <asiodns/asiodns.h>
 #include <asiolink/asiolink.h>
 
 #include <exceptions/exceptions.h>
@@ -58,7 +59,8 @@ using namespace isc::cc;
 using namespace isc::config;
 using namespace isc::data;
 using isc::log::dlog;
-using namespace asiolink;
+using namespace isc::asiodns;
+using namespace isc::asiolink;
 
 namespace {
 

src/bin/resolver/resolver.cc

@@ -20,6 +20,7 @@
 #include <vector>
 #include <cassert>
 
+#include <asiodns/asiodns.h>
 #include <asiolink/asiolink.h>
 
 #include <boost/foreach.hpp>
@@ -54,7 +55,8 @@ using namespace isc::dns;
 using namespace isc::data;
 using namespace isc::config;
 using isc::log::dlog;
-using namespace asiolink;
+using namespace isc::asiodns;
+using namespace isc::asiolink;
 using namespace isc::server_common::portconfig;
 
 class ResolverImpl {
@@ -295,7 +297,7 @@ public:
             edns_response->setUDPSize(Message::DEFAULT_MAX_EDNS0_UDPSIZE);
             answer_message->setEDNS(edns_response);
         }
-        
+
         if (io_message.getSocket().getProtocol() == IPPROTO_UDP) {
             if (edns) {
                 renderer.setLengthLimit(edns->getUDPSize());
@@ -345,7 +347,7 @@ Resolver::~Resolver() {
 }
 
 void
-Resolver::setDNSService(asiolink::DNSService& dnss) {
+Resolver::setDNSService(isc::asiodns::DNSService& dnss) {
     dnss_ = &dnss;
 }
 

src/bin/resolver/resolver.h

@@ -24,12 +24,12 @@
 #include <dns/message.h>
 #include <dns/buffer.h>
 
+#include <asiodns/dns_server.h>
+#include <asiodns/dns_service.h>
+#include <asiodns/dns_lookup.h>
+#include <asiodns/dns_answer.h>
 #include <asiolink/io_message.h>
 #include <asiolink/io_service.h>
-#include <asiolink/dns_server.h>
-#include <asiolink/dns_service.h>
-#include <asiolink/dns_lookup.h>
-#include <asiolink/dns_answer.h>
 #include <asiolink/simple_callback.h>
 
 #include <nsas/nameserver_address_store.h>
@@ -82,11 +82,11 @@ public:
     /// shall return to the client
     /// \param buffer Pointer to an \c OutputBuffer for the resposne
     /// \param server Pointer to the \c DNSServer
-    void processMessage(const asiolink::IOMessage& io_message,
+    void processMessage(const isc::asiolink::IOMessage& io_message,
                         isc::dns::MessagePtr query_message,
                         isc::dns::MessagePtr answer_message,
                         isc::dns::OutputBufferPtr buffer,
-                        asiolink::DNSServer* server);
+                        isc::asiodns::DNSServer* server);
 
     /// \brief Set and get the config session
     isc::config::ModuleCCSession* getConfigSession() const;
@@ -96,16 +96,16 @@ public:
     isc::data::ConstElementPtr updateConfig(isc::data::ConstElementPtr config);
 
     /// \brief Assign an ASIO IO Service queue to this Resolver object
-    void setDNSService(asiolink::DNSService& dnss);
-    
+    void setDNSService(isc::asiodns::DNSService& dnss);
+
     /// \brief Assign a NameserverAddressStore to this Resolver object
     void setNameserverAddressStore(isc::nsas::NameserverAddressStore &nsas);
-    
+
     /// \brief Assign a cache to this Resolver object
     void setCache(isc::cache::ResolverCache& cache);
 
     /// \brief Return this object's ASIO IO Service queue
-    asiolink::DNSService& getDNSService() const { return (*dnss_); }
+    isc::asiodns::DNSService& getDNSService() const { return (*dnss_); }
 
     /// \brief Returns this object's NSAS
     isc::nsas::NameserverAddressStore& getNameserverAddressStore() const {
@@ -116,15 +116,15 @@ public:
     isc::cache::ResolverCache& getResolverCache() const {
         return *cache_;
     };
-    
+
     /// \brief Return pointer to the DNS Lookup callback function
-    asiolink::DNSLookup* getDNSLookupProvider() { return (dns_lookup_); }
+    isc::asiodns::DNSLookup* getDNSLookupProvider() { return (dns_lookup_); }
 
     /// \brief Return pointer to the DNS Answer callback function
-    asiolink::DNSAnswer* getDNSAnswerProvider() { return (dns_answer_); }
+    isc::asiodns::DNSAnswer* getDNSAnswerProvider() { return (dns_answer_); }
 
     /// \brief Return pointer to the Checkin callback function
-    asiolink::SimpleCallback* getCheckinProvider() { return (checkin_); }
+    isc::asiolink::SimpleCallback* getCheckinProvider() { return (checkin_); }
 
     /**
      * \brief Tell the Resolver that is has already been configured
@@ -238,10 +238,10 @@ public:
 
 private:
     ResolverImpl* impl_;
-    asiolink::DNSService* dnss_;
-    asiolink::SimpleCallback* checkin_;
-    asiolink::DNSLookup* dns_lookup_;
-    asiolink::DNSAnswer* dns_answer_;
+    isc::asiodns::DNSService* dnss_;
+    isc::asiolink::SimpleCallback* checkin_;
+    isc::asiodns::DNSLookup* dns_lookup_;
+    isc::asiodns::DNSAnswer* dns_answer_;
     isc::nsas::NameserverAddressStore* nsas_;
     isc::cache::ResolverCache* cache_;
     // This value is initally false, and will be set to true
@@ -252,6 +252,6 @@ private:
 
 #endif // __RESOLVER_H
 
-// Local Variables: 
+// Local Variables:
 // mode: c++
-// End: 
+// End:

src/bin/resolver/response_scrubber.cc

@@ -26,7 +26,7 @@ using namespace std;
 // Compare addresses etc.
 
 ResponseScrubber::Category ResponseScrubber::addressCheck(
-    const asiolink::IOEndpoint& to, const asiolink::IOEndpoint& from)
+    const isc::asiolink::IOEndpoint& to, const isc::asiolink::IOEndpoint& from)
 {
     if (from.getProtocol() == to.getProtocol()) {
         if (from.getAddress() == to.getAddress()) {

src/bin/resolver/response_scrubber.h

@@ -282,8 +282,8 @@ public:
     ///
     /// \return SUCCESS if the two endpoints match, otherwise an error status
     /// indicating what was incorrect.
-    static Category addressCheck(const asiolink::IOEndpoint& to,
-        const asiolink::IOEndpoint& from);
+    static Category addressCheck(const isc::asiolink::IOEndpoint& to,
+        const isc::asiolink::IOEndpoint& from);
 
     /// \brief Check QID
     ///

src/bin/resolver/tests/Makefile.am

@@ -31,6 +31,7 @@ run_unittests_LDADD += $(SQLITE_LIBS)
 run_unittests_LDADD += $(top_builddir)/src/lib/testutils/libtestutils.la
 run_unittests_LDADD += $(top_builddir)/src/lib/datasrc/libdatasrc.la
 run_unittests_LDADD += $(top_builddir)/src/lib/dns/libdns++.la
+run_unittests_LDADD += $(top_builddir)/src/lib/asiodns/libasiodns.la
 run_unittests_LDADD += $(top_builddir)/src/lib/asiolink/libasiolink.la
 run_unittests_LDADD += $(top_builddir)/src/lib/config/libcfgclient.la
 run_unittests_LDADD += $(top_builddir)/src/lib/cc/libcc.la

src/bin/resolver/tests/resolver_config_unittest.cc

@@ -20,6 +20,7 @@
 
 #include <cc/data.h>
 
+#include <asiodns/asiodns.h>
 #include <asiolink/asiolink.h>
 
 #include <resolver/resolver.h>
@@ -31,7 +32,8 @@
 using namespace std;
 using namespace isc::data;
 using namespace isc::testutils;
-using namespace asiolink;
+using namespace isc::asiodns;
+using namespace isc::asiolink;
 using isc::UnitTestUtil;
 
 namespace {

src/bin/resolver/tests/response_scrubber_unittest.cc

@@ -41,6 +41,7 @@
 // Class for endpoint checks.  The family of the endpoint is set in the
 // constructor; the address family by the string provided for the address.
 
+namespace isc {
 namespace asiolink {
 
 class GenericEndpoint : public IOEndpoint {
@@ -73,13 +74,14 @@ private:
     short       protocol_;      // Protocol of the endpoint
     };
 }
+}
 
 using namespace asio::ip;
 using namespace isc::dns;
 using namespace rdata;
 using namespace isc::dns::rdata::generic;
 using namespace isc::dns::rdata::in;
-using namespace asiolink;
+using namespace isc::asiolink;
 
 // Test class
 

src/lib/Makefile.am

 SUBDIRS = exceptions dns cc config util python xfr bench log asiolink \
-          nsas cache resolve testutils datasrc server_common
+          asiodns nsas cache resolve testutils datasrc server_common

src/lib/asiodns/Makefile.am

+SUBDIRS = . tests
+
+AM_CPPFLAGS = -I$(top_srcdir)/src/lib -I$(top_builddir)/src/lib
+AM_CPPFLAGS += $(BOOST_INCLUDES)
+AM_CPPFLAGS += -I$(top_srcdir)/src/lib/dns -I$(top_builddir)/src/lib/dns
+AM_CPPFLAGS += -I$(top_srcdir)/src/lib/asiolink -I$(top_builddir)/src/lib/asiolink
+
+AM_CXXFLAGS = $(B10_CXXFLAGS)
+
+CLEANFILES = *.gcno *.gcda
+
+lib_LTLIBRARIES = libasiodns.la
+libasiodns_la_SOURCES = dns_answer.h
+libasiodns_la_SOURCES += asiodef.cc asiodef.h
+libasiodns_la_SOURCES += dns_lookup.h
+libasiodns_la_SOURCES += dns_server.h
+libasiodns_la_SOURCES += dns_service.cc dns_service.h
+libasiodns_la_SOURCES += tcp_server.cc tcp_server.h
+libasiodns_la_SOURCES += udp_server.cc udp_server.h
+libasiodns_la_SOURCES += io_fetch.cc io_fetch.h
+libasiodns_la_SOURCES += qid_gen.cc qid_gen.h
+
+EXTRA_DIST = asiodef.msg
+
+# Note: the ordering matters: -Wno-... must follow -Wextra (defined in
+# B10_CXXFLAGS)
+libasiodns_la_CXXFLAGS = $(AM_CXXFLAGS)
+if USE_CLANGPP
+# Same for clang++, but we need to turn off -Werror completely.
+libasiodns_la_CXXFLAGS += -Wno-error
+endif
+libasiodns_la_CPPFLAGS = $(AM_CPPFLAGS)
+libasiodns_la_LIBADD = $(top_builddir)/src/lib/log/liblog.la

src/lib/asiodns/README

+The asiodns library is intended to provide an abstraction layer between
+BIND10 modules and asiolink library.
+
+These DNS server and client routines are written using the "stackless
+coroutine" pattern invented by Chris Kohlhoff and described at
+http://blog.think-async.com/2010/03/potted-guide-to-stackless-coroutines.html.
+This is intended to simplify development a bit, since it allows the
+routines to be written in a straightfowrard step-step-step fashion rather
+than as a complex chain of separate handler functions.
+
+Coroutine objects (i.e., UDPServer, TCPServer and IOFetch) are objects
+with reenterable operator() members.  When an instance of one of these
+classes is called as a function, it resumes at the position where it left
+off.  Thus, a UDPServer can issue an asynchronous I/O call and specify
+itself as the handler object; when the call completes, the UDPServer
+carries on at the same position.  As a result, the code can look as
+if it were using synchronous, not asynchronous, I/O, providing some of
+the benefit of threading but with minimal switching overhead.
+
+So, in simplified form, the behavior of a DNS Server is:
+
+  REENTER:
+    while true:
+      YIELD packet = read_packet
+      FORK
+      if not parent:
+        break
+
+    # This callback informs the caller that a packet has arrived, and
+    # gives it a chance to update configuration, etc
+    SimpleCallback(packet)
+    YIELD answer = DNSLookup(packet, this)
+    response = DNSAnswer(answer)
+    YIELD send(response)
+
+At each "YIELD" point, the coroutine initiates an asynchronous operation,
+then pauses and turns over control to some other task on the ASIO service
+queue.  When the operation completes, the coroutine resumes.
+
+DNSLookup, DNSAnswer and SimpleCallback define callback methods
+used by a DNS Server to communicate with the module that called it.
+They are abstract-only classes whose concrete implementations
+are supplied by the calling module.
+
+The DNSLookup callback always runs asynchronously.  Concrete
+implementations must be sure to call the server's "resume" method when
+it is finished.
+
+In an authoritative server, the DNSLookup implementation would examine
+the query, look up the answer, then call "resume".  (See the diagram
+in doc/auth_process.jpg.)
+
+In a recursive server, the DNSLookup impelemtation would initiate a
+DNSQuery, which in turn would be responsible for calling the server's
+"resume" method.  (See the diagram in doc/recursive_process.jpg.)
+
+A DNSQuery object is intended to handle resolution of a query over
+the network when the local authoritative data sources or cache are not
+sufficient.  The plan is that it will make use of subsidiary DNSFetch
+calls to get data from particular authoritative servers, and when it has
+gotten a complete answer, it calls "resume".
+
+In current form, however, DNSQuery is much simpler; it forwards queries
+to a single upstream resolver and passes the answers back to the client.
+It is constructed with the address of the forward server.  Queries are
+initiated with the question to ask the forward server, a buffer into
+which to write the answer, and a pointer to the coroutine to be resumed
+when the answer has arrived.  In simplified form, the DNSQuery routine is:
+
+  REENTER:
+    render the question into a wire-format query packet
+    YIELD send(query)
+    YIELD response = read_packet
+    server->resume
+
+Currently, DNSQuery is only implemented for UDP queries.  In future work
+it will be necessary to write code to fall back to TCP when circumstances
+require it.
+
+
+Upstream Fetches
+================
+Upstream fetches (queries by the resolver on behalf of a client) are made
+using a slightly-modified version of the pattern described above.
+
+Sockets
+-------
+First, it will be useful to understand the class hierarchy used in the
+fetch logic:
+
+        IOSocket
+           |
+      IOAsioSocket
+           |
+     +-----+-----+                
+     |           |
+UDPSocket    TCPSocket
+
+IOSocket is a wrapper class for a socket and is used by the authoritative
+server code.  It is an abstract base class, providing little more that the ability to hold the socket and to return the protocol in use.
+
+Built on this is IOAsioSocket, which adds the open, close, asyncSend and
+asyncReceive methods.  This is a template class, which takes as template
+argument the class of the object that will be used as the callback when the
+asynchronous operation completes. This object can be of any type, but must
+include an operator() method with the signature:
+
+   operator()(asio::error_code ec, size_t length)
+
+... the two arguments being the status of the completed I/O operation and
+the number of bytes transferred. (In the case of the open method, the second
+argument will be zero.)
+
+Finally, the TCPSocket and UDPSocket classes provide the body of the
+asynchronous operations.
+
+Fetch Sequence
+--------------
+The fetch is implemented by the IOFetch class, which takes as argument the
+protocol to use.  The sequence is:
+
+  REENTER:
+    render the question into a wire-format query packet
+    open()                           // Open socket and optionally connect
+    if (! synchronous) {
+        YIELD;
+    }
+    YIELD asyncSend(query)           // Send query 
+    do {
+        YIELD asyncReceive(response) // Read response
+    } while (! complete(response))
+    close()                          // Drop connection and close socket
+    server->resume
+
+The open() method opens a socket for use.  On TCP, it also makes a
+connection to the remote end.  So under UDP the operation will complete
+immediately, but under TCP it could take a long time.  One solution would be
+for the open operation to post an event to the I/O queue; then both cases
+could be regarded as being equivalent, with the completion being signalled
+by the posting of the completion event.  However UDP is the most common case
+and that would involve extra overhead.  So the open() returns a status
+indicating whether the operation completed asynchronously.  If it did, the
+code yields back to the coroutine; if not the yield is bypassed.
+
+The asynchronous send is straightforward, invoking the underlying ASIO
+function.  (Note that the address/port is supplied to both the open() and
+asyncSend() methods - it is used by the TCPSocket in open() and by the
+UDPSocket in asyncSend().)
+
+The asyncReceive() method issues an asynchronous read and waits for completion.
+The fetch object keeps track of the amount of data received so far and when
+the receive completes it calls a method on the socket to determine if the
+entire message has been received.  (This will always be the case for UDP.  On
+TCP though, the message is preceded by a co