Implement S3-HDFS gateway (#7440)

- [x] Support bucket and regular object operations
- [x] Supports Select API on HDFS
- [x] Implement multipart API support
- [x] Completion of ListObjects support

cmd/tree-walk-pool.go

@@ -43,25 +43,25 @@ var errWalkAbort = errors.New("treeWalk abort")
 
 // treeWalk - represents the go routine that does the file tree walk.
 type treeWalk struct {
-	resultCh   chan treeWalkResult
+	resultCh   chan TreeWalkResult
 	endWalkCh  chan struct{}   // To signal when treeWalk go-routine should end.
 	endTimerCh chan<- struct{} // To signal when timer go-routine should end.
 }
 
-// treeWalkPool - pool of treeWalk go routines.
+// TreeWalkPool - pool of treeWalk go routines.
 // A treeWalk is added to the pool by Set() and removed either by
 // doing a Release() or if the concerned timer goes off.
 // treeWalkPool's purpose is to maintain active treeWalk go-routines in a map so that
 // it can be looked up across related list calls.
-type treeWalkPool struct {
+type TreeWalkPool struct {
 	pool    map[listParams][]treeWalk
 	timeOut time.Duration
 	lock    *sync.Mutex
 }
 
-// newTreeWalkPool - initialize new tree walk pool.
-func newTreeWalkPool(timeout time.Duration) *treeWalkPool {
-	tPool := &treeWalkPool{
+// NewTreeWalkPool - initialize new tree walk pool.
+func NewTreeWalkPool(timeout time.Duration) *TreeWalkPool {
+	tPool := &TreeWalkPool{
 		pool:    make(map[listParams][]treeWalk),
 		timeOut: timeout,
 		lock:    &sync.Mutex{},
@@ -70,10 +70,10 @@ func newTreeWalkPool(timeout time.Duration) *treeWalkPool {
 }
 
 // Release - selects a treeWalk from the pool based on the input
-// listParams, removes it from the pool, and returns the treeWalkResult
+// listParams, removes it from the pool, and returns the TreeWalkResult
 // channel.
 // Returns nil if listParams does not have an asccociated treeWalk.
-func (t treeWalkPool) Release(params listParams) (resultCh chan treeWalkResult, endWalkCh chan struct{}) {
+func (t TreeWalkPool) Release(params listParams) (resultCh chan TreeWalkResult, endWalkCh chan struct{}) {
 	t.lock.Lock()
 	defer t.lock.Unlock()
 	walks, ok := t.pool[params] // Pick the valid walks.
@@ -103,7 +103,7 @@ func (t treeWalkPool) Release(params listParams) (resultCh chan treeWalkResult,
 // 2) Relase() signals the timer go-routine to end on endTimerCh.
 //    During listing the timer should not timeout and end the treeWalk go-routine, hence the
 //    timer go-routine should be ended.
-func (t treeWalkPool) Set(params listParams, resultCh chan treeWalkResult, endWalkCh chan struct{}) {
+func (t TreeWalkPool) Set(params listParams, resultCh chan TreeWalkResult, endWalkCh chan struct{}) {
 	t.lock.Lock()
 	defer t.lock.Unlock()