Move demuxArena to message.go, where it is used.

arena.go

@@ -185,24 +185,6 @@ var multiSegmentPool = sync.Pool{
 	},
 }
 
-// demuxArena slices b into a multi-segment arena.  It assumes that
-// len(data) >= hdr.totalSize().
-func demuxArena(hdr streamHeader, data []byte) (Arena, error) {
-	maxSeg := hdr.maxSegment()
-	if int64(maxSeg) > int64(maxInt-1) {
-		return nil, errors.New("number of segments overflows int")
-	}
-	segs := make([][]byte, int(maxSeg+1))
-	for i := range segs {
-		sz, err := hdr.segmentSize(SegmentID(i))
-		if err != nil {
-			return nil, err
-		}
-		segs[i], data = data[:sz:sz], data[sz:]
-	}
-	return MultiSegment(segs), nil
-}
-
 func (msa *MultiSegmentArena) NumSegments() int64 {
 	return int64(len(*msa))
 }

message.go

@@ -762,4 +762,22 @@ func hasCapacity(b []byte, sz Size) bool {
 	return sz <= Size(cap(b)-len(b))
 }
 
+// demuxArena slices b into a multi-segment arena.  It assumes that
+// len(data) >= hdr.totalSize().
+func demuxArena(hdr streamHeader, data []byte) (Arena, error) {
+	maxSeg := hdr.maxSegment()
+	if int64(maxSeg) > int64(maxInt-1) {
+		return nil, errors.New("number of segments overflows int")
+	}
+	segs := make([][]byte, int(maxSeg+1))
+	for i := range segs {
+		sz, err := hdr.segmentSize(SegmentID(i))
+		if err != nil {
+			return nil, err
+		}
+		segs[i], data = data[:sz:sz], data[sz:]
+	}
+	return MultiSegment(segs), nil
+}
+
 const maxInt = int(^uint(0) >> 1)