[Cleanup] Packet validator ensure DCP open only called once

The packet validator won't accept a DCP open to be called
on a connection already set up as a DCP connection so the
engine don't need to do the same check.

Change-Id: Iaa2ee94805ef8acb7b315e19818512e10312b4f1
Reviewed-on: http://review.couchbase.org/c/kv_engine/+/140962
Tested-by: Build Bot <[email protected]>
Reviewed-by: Jim Walker <[email protected]>
Reviewed-by: Paolo Cocchi <[email protected]>

Author: trondn

engines/ep/src/ep_engine.cc

@@ -6147,17 +6147,8 @@ ENGINE_ERROR_CODE EventuallyPersistentEngine::dcpOpen(
         uint32_t flags,
         std::string_view stream_name,
         std::string_view value) {
-    (void) opaque;
-    (void) seqno;
     std::string connName{stream_name};
-
-    auto* handler = getConnHandler(cookie);
-    if (handler) {
-        EP_LOG_WARN(
-                "Cannot open DCP connection as another connection exists on "
-                "the same socket");
-        return ENGINE_DISCONNECT;
-    }
+    ConnHandler* handler = nullptr;
 
     if (flags & (cb::mcbp::request::DcpOpenPayload::Producer |
                  cb::mcbp::request::DcpOpenPayload::Notifier)) {

tests/testapp/testapp_dcp.cc

@@ -162,3 +162,18 @@ TEST_P(DcpTest, MB35928_DcpCantReauthenticate) {
                 << "SASL AUTH should fail";
     }
 }
+
+TEST_P(DcpTest, CantDcpOpenTwice) {
+    auto& conn = getAdminConnection();
+    conn.selectBucket("default");
+    auto rsp = conn.execute(BinprotDcpOpenCommand{
+            "ewb_internal:1", cb::mcbp::request::DcpOpenPayload::Producer});
+    ASSERT_TRUE(rsp.isSuccess());
+
+    rsp = conn.execute(BinprotDcpOpenCommand{
+            "ewb_internal:1", cb::mcbp::request::DcpOpenPayload::Producer});
+    ASSERT_FALSE(rsp.isSuccess());
+    auto json = nlohmann::json::parse(rsp.getDataString());
+    EXPECT_EQ("The connection is already opened as a DCP connection",
+              json["error"]["context"]);
+}