Add more documentation and error handling

chunker/chunker.go

@@ -43,12 +43,17 @@ type Chunk struct {
 
 // A chunker takes a stream of bytes and emits average size chunks.
 type Chunker interface {
+	// Next returns the next chunk of data. If an error occurs while reading,
+	// the error is returned. The state of the current chunk is undefined. When
+	// the last chunk has been returned, all subsequent calls yield a nil chunk
+	// and an io.EOF error.
 	Next() (*Chunk, error)
 }
 
 // A chunker internally holds everything needed to split content.
 type chunker struct {
-	rd io.Reader
+	rd     io.Reader
+	closed bool
 
 	window []byte
 	wpos   int
@@ -141,13 +146,25 @@ func (c *chunker) Next() (*Chunk, error) {
 				err = nil
 			}
 
-			if err != nil {
+			// io.ReadFull only returns io.EOF when no bytes could be read. If
+			// this is the case and we're in this branch, there are no more
+			// bytes to buffer, so this was the last chunk. If a different
+			// error has occurred, return that error and abandon the current
+			// chunk.
+			if err == io.EOF && !c.closed {
+				c.closed = true
+
+				// return current chunk
 				return &Chunk{
 					Start:  c.start,
 					Length: c.count,
 					Cut:    c.digest,
 					Data:   c.data,
-				}, err
+				}, nil
+			}
+
+			if err != nil {
+				return nil, err
 			}
 
 			c.bpos = 0

chunker/chunker_test.go

@@ -50,14 +50,8 @@ func test_with_data(t *testing.T, chunker chunker.Chunker, chunks []chunk) {
 	for i, chunk := range chunks {
 		c, err := chunker.Next()
 
-		if i < len(chunks)-1 {
+		if err != nil {
-			if err != nil {
+			t.Fatalf("Error returned with chunk %d: %v", i, err)
-				t.Fatalf("Error returned with chunk %d: %v", i, err)
-			}
-		} else {
-			if err != io.EOF {
-				t.Fatalf("EOF not returned with chunk %d", i)
-			}
 		}
 
 		if c == nil {
@@ -76,6 +70,16 @@ func test_with_data(t *testing.T, chunker chunker.Chunker, chunks []chunk) {
 			}
 		}
 	}
+
+	c, err := chunker.Next()
+
+	if c != nil {
+		t.Fatal("additional non-nil chunk returned")
+	}
+
+	if err != io.EOF {
+		t.Fatal("wrong error returned after last chunk")
+	}
 }
 
 func get_random(seed, count int) []byte {
@@ -117,15 +121,15 @@ func BenchmarkChunker(b *testing.B) {
 		for {
 			_, err := ch.Next()
 
-			chunks++
-
-			if err != nil && err != io.EOF {
-				b.Fatalf("Unexpected error occurred: %v", err)
-			}
-
 			if err == io.EOF {
 				break
 			}
+
+			if err != nil {
+				b.Fatalf("Unexpected error occurred: %v", err)
+			}
+
+			chunks++
 		}
 	}