address concerns from PR

importer/importer_test.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
+	mrand "math/rand"
 	"os"
 	"testing"
 
@@ -307,6 +308,51 @@ func TestSeekToAlmostBegin(t *testing.T) {
 	}
 }
 
+func TestSeekingStress(t *testing.T) {
+	nbytes := int64(1024 * 1024)
+	should := make([]byte, nbytes)
+	u.NewTimeSeededRand().Read(should)
+
+	read := bytes.NewReader(should)
+	dnp := getDagservAndPinner(t)
+	nd, err := BuildDagFromReader(read, dnp.ds, dnp.mp, &chunk.SizeSplitter{1000})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	rs, err := uio.NewDagReader(context.TODO(), nd, dnp.ds)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	testbuf := make([]byte, nbytes)
+	for i := 0; i < 50; i++ {
+		offset := mrand.Intn(int(nbytes))
+		l := int(nbytes) - offset
+		n, err := rs.Seek(int64(offset), os.SEEK_SET)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if n != int64(offset) {
+			t.Fatal("Seek failed to move to correct position")
+		}
+
+		nread, err := rs.Read(testbuf[:l])
+		if err != nil {
+			t.Fatal(err)
+		}
+		if nread != l {
+			t.Fatal("Failed to read enough bytes")
+		}
+
+		err = arrComp(testbuf[:l], should[offset:offset+l])
+		if err != nil {
+			t.Fatal(err)
+		}
+	}
+
+}
+
 func TestSeekingConsistency(t *testing.T) {
 	nbytes := int64(128 * 1024)
 	should := make([]byte, nbytes)

merkledag/merkledag.go

@@ -177,6 +177,8 @@ func (ds *dagService) GetDAG(ctx context.Context, root *Node) []NodeGetter {
 	return ds.GetNodes(ctx, keys)
 }
 
+// GetNodes returns an array of 'NodeGetter' promises, with each corresponding
+// to the key with the same index as the passed in keys
 func (ds *dagService) GetNodes(ctx context.Context, keys []u.Key) []NodeGetter {
 	promises := make([]NodeGetter, len(keys))
 	sendChans := make([]chan<- *Node, len(keys))

unixfs/io/dagmodifier_test.go

@@ -39,7 +39,7 @@ func getNode(t *testing.T, dserv mdag.DAGService, size int64) ([]byte, *mdag.Nod
 		t.Fatal(err)
 	}
 
-	dr, err := NewDagReader(context.TODO(), node, dserv)
+	dr, err := NewDagReader(context.Background(), node, dserv)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -76,7 +76,7 @@ func testModWrite(t *testing.T, beg, size uint64, orig []byte, dm *DagModifier)
 		t.Fatal(err)
 	}
 
-	rd, err := NewDagReader(context.TODO(), nd, dm.dagserv)
+	rd, err := NewDagReader(context.Background(), nd, dm.dagserv)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -174,7 +174,7 @@ func TestMultiWrite(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	read, err := NewDagReader(context.TODO(), nd, dserv)
+	read, err := NewDagReader(context.Background(), nd, dserv)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -216,7 +216,7 @@ func TestMultiWriteCoal(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	read, err := NewDagReader(context.TODO(), nd, dserv)
+	read, err := NewDagReader(context.Background(), nd, dserv)
 	if err != nil {
 		t.Fatal(err)
 	}

unixfs/io/dagreader.go

@@ -18,19 +18,31 @@ var ErrIsDir = errors.New("this dag node is a directory")
 
 // DagReader provides a way to easily read the data contained in a dag.
 type DagReader struct {
-	serv         mdag.DAGService
-	node         *mdag.Node
-	pbdata       *ftpb.Data
-	buf          ReadSeekCloser
-	promises     []mdag.NodeGetter
+	serv mdag.DAGService
+
+	// the node being read
+	node *mdag.Node
+
+	// cached protobuf structure from node.Data
+	pbdata *ftpb.Data
+
+	// the current data buffer to be read from
+	// will either be a bytes.Reader or a child DagReader
+	buf ReadSeekCloser
+
+	// NodeGetters for each of 'nodes' child links
+	promises []mdag.NodeGetter
+
+	// the index of the child link currently being read from
 	linkPosition int
-	offset       int64
+
+	// current offset for the read head within the 'file'
+	offset int64
 
 	// Our context
 	ctx context.Context
 
-	// Context for children
-	fctx   context.Context
+	// context cancel for children
 	cancel func()
 }
 
@@ -145,6 +157,8 @@ func (dr *DagReader) Close() error {
 	return nil
 }
 
+// Seek implements io.Seeker, and will seek to a given offset in the file
+// interface matches standard unix seek
 func (dr *DagReader) Seek(offset int64, whence int) (int64, error) {
 	switch whence {
 	case os.SEEK_SET:
@@ -152,18 +166,26 @@ func (dr *DagReader) Seek(offset int64, whence int) (int64, error) {
 			return -1, errors.New("Invalid offset")
 		}
 
+		// Grab cached protobuf object (solely to make code look cleaner)
 		pb := dr.pbdata
+
+		// left represents the number of bytes remaining to seek to (from beginning)
 		left := offset
 		if int64(len(pb.Data)) > offset {
+			// Close current buf to close potential child dagreader
 			dr.buf.Close()
 			dr.buf = NewRSNCFromBytes(pb.GetData()[offset:])
+
+			// start reading links from the beginning
 			dr.linkPosition = 0
 			dr.offset = offset
 			return offset, nil
 		} else {
+			// skip past root block data
 			left -= int64(len(pb.Data))
 		}
 
+		// iterate through links and find where we need to be
 		for i := 0; i < len(pb.Blocksizes); i++ {
 			if pb.Blocksizes[i] > uint64(left) {
 				dr.linkPosition = i
@@ -173,15 +195,19 @@ func (dr *DagReader) Seek(offset int64, whence int) (int64, error) {
 			}
 		}
 
+		// start sub-block request
 		err := dr.precalcNextBuf()
 		if err != nil {
 			return 0, err
 		}
 
+		// set proper offset within child readseeker
 		n, err := dr.buf.Seek(left, os.SEEK_SET)
 		if err != nil {
 			return -1, err
 		}
+
+		// sanity
 		left -= n
 		if left != 0 {
 			return -1, errors.New("failed to seek properly")
@@ -201,6 +227,7 @@ func (dr *DagReader) Seek(offset int64, whence int) (int64, error) {
 	return 0, nil
 }
 
+// readSeekNopCloser wraps a bytes.Reader to implement ReadSeekCloser
 type readSeekNopCloser struct {
 	*bytes.Reader
 }