blob: document, clean up ChanPeeker

Change-Id: I7c721f1e3fb81011cf2911be8889dcb9abc66dd5

pkg/blob/chanpeek.go

@@ -16,15 +16,18 @@ limitations under the License.
 
 package blob
 
-// TODO: use Generics if/when available
+// ChanPeeker wraps a channel receiving SizedRefs and adds a 1 element
+// buffer on it, with Peek and Take methods.
 type ChanPeeker struct {
 	Ch <-chan SizedRef
 
-	// A channel should either have a peek value or be closed:
+	// Invariant after a call to Peek: either peekok or closed.
-	peek   *SizedRef
 	closed bool
+	peekok bool // whether peek is valid
+	peek   SizedRef
 }
 
+// MustPeek returns the next SizedRef or panics if none is available.
 func (cp *ChanPeeker) MustPeek() SizedRef {
 	sr, ok := cp.Peek()
 	if !ok {
@@ -33,27 +36,31 @@ func (cp *ChanPeeker) MustPeek() SizedRef {
 	return sr
 }
 
+// Peek returns the next SizedRef and whether one was available.
 func (cp *ChanPeeker) Peek() (sr SizedRef, ok bool) {
 	if cp.closed {
 		return
 	}
-	if cp.peek != nil {
+	if cp.peekok {
-		return *cp.peek, true
+		return cp.peek, true
 	}
 	v, ok := <-cp.Ch
 	if !ok {
 		cp.closed = true
 		return
 	}
-	cp.peek = &v
+	cp.peek = v
-	return *cp.peek, true
+	cp.peekok = true
+	return cp.peek, true
 }
 
+// Closed reports true if no more SizedRef values are available.
 func (cp *ChanPeeker) Closed() bool {
 	cp.Peek()
 	return cp.closed
 }
 
+// MustTake returns the next SizedRef, else panics if none is available.
 func (cp *ChanPeeker) MustTake() SizedRef {
 	sr, ok := cp.Take()
 	if !ok {
@@ -62,15 +69,17 @@ func (cp *ChanPeeker) MustTake() SizedRef {
 	return sr
 }
 
+// Take returns the next SizedRef and whether one was available for the taking.
 func (cp *ChanPeeker) Take() (sr SizedRef, ok bool) {
 	v, ok := cp.Peek()
 	if !ok {
 		return
 	}
-	cp.peek = nil
+	cp.peekok = false
 	return v, true
 }
 
+// ConsumeAll drains the channel of all items.
 func (cp *ChanPeeker) ConsumeAll() {
 	for !cp.Closed() {
 		cp.Take()