From 3fbb77153b676c773dd12821cf46be1ed351f65f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C5=81ukasz=20Magiera?= <magik6k@gmail.com>
Date: Wed, 18 Oct 2017 22:25:36 +0200
Subject: [PATCH] gateway: custom seeker for files
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

License: MIT
Signed-off-by: Łukasz Magiera <magik6k@gmail.com>
---
 core/corehttp/gateway_handler.go | 24 ++++++++++++++++++++++++
 unixfs/io/pbdagreader.go         |  7 +++++++
 2 files changed, 31 insertions(+)

diff --git a/core/corehttp/gateway_handler.go b/core/corehttp/gateway_handler.go
index 336169404..0a7e657de 100644
--- a/core/corehttp/gateway_handler.go
+++ b/core/corehttp/gateway_handler.go
@@ -372,7 +372,31 @@ func (i *gatewayHandler) getOrHeadHandler(ctx context.Context, w http.ResponseWr
 	}
 }
 
+type sizeReadSeeker interface {
+  Size() uint64
+
+	io.ReadSeeker
+}
+
+type sizeSeeker struct {
+	sizeReadSeeker
+}
+
+func (s *sizeSeeker) Seek(offset int64, whence int) (int64, error) {
+	if whence == io.SeekEnd && offset == 0 {
+		return int64(s.Size()), nil
+	}
+
+	return s.sizeReadSeeker.Seek(offset, whence)
+}
+
 func (i *gatewayHandler) serverFile(w http.ResponseWriter, req *http.Request, name string, modtime time.Time, content io.ReadSeeker) {
+	if sp, ok := content.(sizeReadSeeker); ok {
+		content = &sizeSeeker{
+			sizeReadSeeker: sp,
+		}
+	}
+
 	http.ServeContent(w, req, name, modtime, content)
 	//TODO: check for errors in ServeContent.. somehow
 
diff --git a/unixfs/io/pbdagreader.go b/unixfs/io/pbdagreader.go
index 7ba63649f..dcd383460 100644
--- a/unixfs/io/pbdagreader.go
+++ b/unixfs/io/pbdagreader.go
@@ -188,6 +188,9 @@ func (dr *pbDagReader) Seek(offset int64, whence int) (int64, error) {
 		if offset < 0 {
 			return -1, errors.New("Invalid offset")
 		}
+		if offset == dr.offset {
+			return offset, nil
+		}
 
 		// Grab cached protobuf object (solely to make code look cleaner)
 		pb := dr.pbdata
@@ -239,6 +242,10 @@ func (dr *pbDagReader) Seek(offset int64, whence int) (int64, error) {
 		return offset, nil
 	case io.SeekCurrent:
 		// TODO: be smarter here
+		if offset == 0 {
+			return dr.offset, nil
+		}
+
 		noffset := dr.offset + offset
 		return dr.Seek(noffset, io.SeekStart)
 	case io.SeekEnd: