Support register listener filters.

[wangfakang]

Issues associated with this PR

Support register listener filters, such as original_dst listener filter.

Note Need to merge #1005 first .

Solutions

Execution phase

When a new connection is received, MOSN's OnAccept execution process is triggered. The listener filter will execute before the connection instance created. As follows

// ListenerEventListener
func (al *activeListener) OnAccept(rawc net.Conn, useOriginalDst bool, oriRemoteAddr net.Addr, ch chan types.Connection, buf []byte) {
	var rawf *os.File
    
	arc := newActiveRawConn(rawc, al) 

	arc.ContinueFilterChain(ctx, true)
}

func (arc *activeRawConn) ContinueFilterChain(ctx context.Context, success bool) {
        //execute listener filter handler
	for ; arc.acceptedFilterIndex < len(arc.acceptedFilters); arc.acceptedFilterIndex++ {
		filterStatus := arc.acceptedFilters[arc.acceptedFilterIndex].OnAccept(arc)   // running filter 
		if filterStatus == types.Stop {
			return
		}
	}
    // Create connection
    arc.activeListener.newConnection(ctx, arc.rawc)
}

Filter registration API

RegisterListener API is provided to RegisterListener filter instances. The listener filter instance only need to implement ListenerFilterChainFactory interface (such as realize OnAccept method) and ListenerFilterFactoryCreator type method for parse the filter configuration.

// ListenerFilterFactoryCreator creates a ListenerFilterChainFactory according to config
type ListenerFilterFactoryCreator func(config map[string]interface{}) (ListenerFilterChainFactory, error)

var creatorListenerFactory map[string]ListenerFilterFactoryCreator

func init() {
	creatorListenerFactory = make(map[string]ListenerFilterFactoryCreator)
}

// RegisterListener registers the filterType as ListenerFilterFactoryCreator
func RegisterListener(filterType string, creator ListenerFilterFactoryCreator) {
	creatorListenerFactory[filterType] = creator
}

// ListenerFilterChainFactory adds filter into ListenerFilterChainFactoryCallbacks
type ListenerFilterChainFactory interface {
	OnAccept(callbacks ListenerFilterChainFactoryCallbacks) FilterStatus
}

// CreateListenerFilterChainFactory creates a ListenerFilterChainFactory according to filterType
func CreateListenerFilterChainFactory(filterType string, config map[string]interface{}) (ListenerFilterChainFactory, error) {
	if cf, ok := creatorListenerFactory[filterType]; ok {
		lfcf, err := cf(config)
		if err != nil {
			return nil, fmt.Errorf("create listener filter chain factory failed: %v", err)
		}
		return lfcf, nil
	}
	return nil, fmt.Errorf("unsupported listener filter type: %v", filterType)
}

Configuration

Support for both static and XDS configuration, such as

"listener_filters": [
                {
                  "type": "orginal_dst",
                  "config": {
                   }
                }
           ]

UT result

Unit Test is needed if the code is changed, your unit test should cover boundary cases, corner cases, and some exceptional cases. And you need to show the UT result.

Benchmark

If your code involves the processing of every request, you should give the Benchmark Result.

Code Style

• Make sure Goimports has run
• Show Golint result

[codecov-io]

Codecov Report

Merging #1014 into master will increase coverage by 0.03%.
The diff coverage is 52.43%.

@@            Coverage Diff             @@
##           master    #1014      +/-   ##
==========================================
+ Coverage   56.59%   56.62%   +0.03%     
==========================================
  Files         238      238              
  Lines       22737    22786      +49     
==========================================
+ Hits        12868    12903      +35     
- Misses       8710     8722      +12     
- Partials     1159     1161       +2     

Impacted Files	Coverage Δ
pkg/config/v2/filter.go	50.00% <ø> (ø)
pkg/config/v2/server.go	91.30% <ø> (ø)
pkg/config/v2/upstream.go	70.83% <ø> (ø)
pkg/configmanager/parser.go	44.52% <0.00%> (-3.14%)	⬇️
pkg/mosn/starter.go	33.12% <0.00%> (ø)
pkg/server/server.go	0.00% <0.00%> (ø)
pkg/types/network.go	0.00% <ø> (ø)
pkg/upstream/cluster/host.go	54.92% <20.00%> (-6.98%)	⬇️
pkg/server/handler.go	41.17% <52.94%> (+0.64%)	⬆️
pkg/server/adapter.go	64.70% <66.66%> (ø)
... and 6 more

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