GODRIVER-3054 LB init handshake should always be hello

Author: prestonvasquez

mongo/integration/handshake_test.go

@@ -215,12 +215,9 @@ func TestLoadBalancedConnectionHandshake(t *testing.T) {
 		messages := mt.GetProxiedMessages()
 		handshakeMessage := messages[:1][0]
 
-		hello := handshake.LegacyHello
-		if os.Getenv("REQUIRE_API_VERSION") == "true" {
-			hello = "hello"
-		}
-
-		assert.Equal(mt, hello, handshakeMessage.CommandName)
+		// Per the specifications, if loadBalanced=true, drivers MUST use the hello
+		// command for the initial handshake and use the OP_MSG protocol.
+		assert.Equal(mt, "hello", handshakeMessage.CommandName)
 		assert.Equal(mt, wiremessage.OpMsg, handshakeMessage.Sent.OpCode)
 	})
 

testdata/load-balancers/sdam-error-handling.json

@@ -279,7 +279,8 @@
               },
               "data": {
                 "failCommands": [
-                  "isMaster"
+                  "isMaster",
+                  "hello"
                 ],
                 "closeConnection": true,
                 "appName": "lbSDAMErrorTestClient"

testdata/load-balancers/sdam-error-handling.yml

@@ -153,7 +153,7 @@ tests:
             configureFailPoint: failCommand
             mode: { times: 1 }
             data:
-              failCommands: [isMaster]
+              failCommands: [isMaster, hello]
               closeConnection: true
               appName: *singleClientAppName
       - name: insertOne

x/mongo/driver/operation/hello.go

@@ -530,7 +530,7 @@ func (h *Hello) handshakeCommand(dst []byte, desc description.SelectedServer) ([
 func (h *Hello) command(dst []byte, desc description.SelectedServer) ([]byte, error) {
 	// Use "hello" if topology is LoadBalanced, API version is declared or server
 	// has responded with "helloOk". Otherwise, use legacy hello.
-	if desc.Kind == description.LoadBalanced || h.serverAPI != nil || desc.Server.HelloOK {
+	if h.loadBalanced || h.serverAPI != nil || desc.Server.HelloOK {
 		dst = bsoncore.AppendInt32Element(dst, "hello", 1)
 	} else {
 		dst = bsoncore.AppendInt32Element(dst, handshake.LegacyHello, 1)