From f6fd6ee777e14c2e75debf673ae26bfeb3861f65 Mon Sep 17 00:00:00 2001
From: Nick Craig-Wood <nick@craig-wood.com>
Date: Fri, 6 May 2022 14:03:01 +0100
Subject: [PATCH] fs: fix FixRangeOption make SeekOptions into absolute
 RangeOptions

Cloudflare R2 doesn't support range options like `Range: bytes=21-`.

This patch makes FixRangeOption turn a SeekOption into an absolute
RangeOption like this `Range: bytes=21-25` to interoperate with R2.

See: #5642
---
 fs/open_options.go      | 11 ++++++++---
 fs/open_options_test.go | 14 ++++++++++++++
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/fs/open_options.go b/fs/open_options.go
index 268024b17..38a391fb9 100644
--- a/fs/open_options.go
+++ b/fs/open_options.go
@@ -138,6 +138,9 @@ func (o *RangeOption) Decode(size int64) (offset, limit int64) {
 // absolute fetch using the size passed in and makes sure the range does
 // not exceed filesize. Some remotes (e.g. Onedrive, Box) don't support
 // range requests which index from the end.
+//
+// It also adjusts any SeekOption~s, turning them into absolute
+// RangeOption~s instead.
 func FixRangeOption(options []OpenOption, size int64) {
 	if size == 0 {
 		// if size 0 then remove RangeOption~s
@@ -150,9 +153,9 @@ func FixRangeOption(options []OpenOption, size int64) {
 		}
 		return
 	}
-	for i := range options {
-		option := options[i]
-		if x, ok := option.(*RangeOption); ok {
+	for i, option := range options {
+		switch x := option.(type) {
+		case *RangeOption:
 			// If start is < 0 then fetch from the end
 			if x.Start < 0 {
 				x = &RangeOption{Start: size - x.End, End: -1}
@@ -163,6 +166,8 @@ func FixRangeOption(options []OpenOption, size int64) {
 				x = &RangeOption{Start: x.Start, End: size - 1}
 				options[i] = x
 			}
+		case *SeekOption:
+			options[i] = &RangeOption{Start: x.Offset, End: size - 1}
 		}
 	}
 }
diff --git a/fs/open_options_test.go b/fs/open_options_test.go
index 6327a8c9e..fefd1f906 100644
--- a/fs/open_options_test.go
+++ b/fs/open_options_test.go
@@ -207,6 +207,20 @@ func TestFixRangeOptions(t *testing.T) {
 			},
 			size: 100,
 		},
+		{
+			name: "SeekOption",
+			in: []OpenOption{
+				&HTTPOption{Key: "a", Value: "1"},
+				&SeekOption{Offset: 10},
+				&HTTPOption{Key: "b", Value: "2"},
+			},
+			want: []OpenOption{
+				&HTTPOption{Key: "a", Value: "1"},
+				&RangeOption{Start: 10, End: 99},
+				&HTTPOption{Key: "b", Value: "2"},
+			},
+			size: 100,
+		},
 	} {
 		FixRangeOption(test.in, test.size)
 		assert.Equal(t, test.want, test.in, test.name)