The handler function has this signature.

Sample handler:
```go
    handler :=  func(ctx context.Context, payload []byte, in <-chan []byte, out chan<- []byte) *RemoteErr {
        fmt.Println("Got request with initial payload", p, "from", GetCaller(ctx context.Context))
        fmt.Println("Subroute:", GetSubroute(ctx))
        for {
            select {

// errLessData - returned when less data available than what was requested.
var errLessData = StorageErr("less data available than what was requested")

// errMoreData = returned when more data was sent by the caller than what it was supposed to.
var errMoreData = StorageErr("more data was sent than what was advertised")

// indicates readDirFn to return without further applying the fn()

	// Use buffered channel to take care of burst sends or slow w.Write()
	mergeCh := make(chan []byte, globalAPIConfig.getRequestsPoolCapacity()*len(globalEndpoints.Hostnames()))
	localCh := make(chan event.Event, globalAPIConfig.getRequestsPoolCapacity())

	// Convert local messages to JSON and send to mergeCh
	go func() {

func readMultipleFiles(ctx context.Context, disks []StorageAPI, req ReadMultipleReq, readQuorum int) ([]ReadMultipleResp, error) {
	resps := make([]chan ReadMultipleResp, len(disks))
	for i := range resps {
		resps[i] = make(chan ReadMultipleResp, len(req.Files))
	}
	g := errgroup.WithNErrs(len(disks))
	// Read files in parallel across disks.
	for index := range disks {
		index := index

	globalBucketObjectLockSys = &BucketObjectLockSys{}
	globalBucketVersioningSys = &BucketVersioningSys{}
	es := newExpiryState(context.Background(), objAPI, 0)
	workers := []chan expiryOp{make(chan expiryOp)}
	es.workers.Store(&workers)
	globalExpiryState = es
	var wg sync.WaitGroup
	wg.Add(1)
	expired := make([]ObjectToDelete, 0, 5)
	go func() {
		defer wg.Done()

	return d.disk.GetDiskID()
}

func (d *naughtyDisk) SetDiskID(id string) {
	d.disk.SetDiskID(id)
}

func (d *naughtyDisk) NSScanner(ctx context.Context, cache dataUsageCache, updates chan<- dataUsageEntry, scanMode madmin.HealScanMode, weSleep func() bool) (info dataUsageCache, err error) {
	if err := d.calcError(); err != nil {
		return info, err
	}

	setIndex, poolIndex int
	queued              time.Time
	scanMode            madmin.HealScanMode
}

// mrfState sncapsulates all the information
// related to the global background MRF.
type mrfState struct {
	opCh chan partialOperation
}

// Add a partial S3 operation (put/delete) when one or more disks are offline.
func (m *mrfState) addPartialOp(op partialOperation) {
	if m == nil {
		return
	}

	select {

			Optional:    true,
			Type:        "number",
		},
		config.HelpKV{
			Key:         apiStaleUploadsExpiry,
			Description: `set to expire stale multipart uploads older than this values` + defaultHelpPostfix(apiStaleUploadsExpiry),
			Optional:    true,
			Type:        "duration",
		},
		config.HelpKV{
			Key:         apiStaleUploadsCleanupInterval,

		Encoding: "console",
	}
	cfg.Endpoints = etcdEndpoints
	cfg.CoreDNSPath = env.Get(EnvEtcdCoreDNSPath, kvs.Get(CoreDNSPath))
	// Default path prefix for all keys on etcd, other than CoreDNSPath.
	cfg.PathPrefix = env.Get(EnvEtcdPathPrefix, kvs.Get(PathPrefix))
	if etcdSecure {
		cfg.TLS = &tls.Config{
			RootCAs: rootCAs,
		}
		// This is only to support client side certificate authentication

Date:   Sat Jun 15 11:27:17 2019 -0700

    [security] Match ${aws:username} exactly instead of prefix match (#7791)

    This PR fixes a security issue where an IAM user based
    on his policy is granted more privileges than restricted
    by the users IAM policy.

    This is due to an issue of prefix based Matcher() function
    which was incorrectly matching prefix based on resource
    prefixes instead of exact match.
```