Decouple FileStore from *os.File for object-store backends

The FileStore interface returned concrete *os.File from Open/Create/
OpenFile, which no non-filesystem backend (e.g. S3/R2) can produce, and
many file-library hot paths bypassed the interface entirely with direct
os.* / filepath.Walk calls.

Widen the interface to return io.ReadCloser / io.WriteCloser and add
ReadDir, ReadLink, and Walk so directory traversal no longer escapes the
abstraction. Route every file-library call site (fork writers, upload/
download handlers, GetFileNameList, CalcTotalSize/CalcItemCount, the set-
file-info folder rename) through the injected FileStore, and add a
WithFileStore option. OSFileStore keeps byte-identical behavior.

DownloadHandler now nil-guards the optional resource-fork reader instead
of relying on *os.File's nil-receiver tolerance, so a backend returning an
untyped-nil reader does not panic.

1 files changed, 4 insertions, 4 deletions

diff --git a/hotline/file_wrapper.go b/hotline/file_wrapper.go
index de3cbe4..4aeaf25 100644
--- a/hotline/file_wrapper.go
+++ b/hotline/file_wrapper.go
@@ -103,7 +103,7 @@ func (f *File) infoForkName() string {
 }
 
 func (f *File) rsrcForkWriter() (io.WriteCloser, error) {
-	file, err := os.OpenFile(f.rsrcPath, os.O_CREATE|os.O_WRONLY, 0644)
+	file, err := f.fs.OpenFile(f.rsrcPath, os.O_CREATE|os.O_WRONLY, 0644)
 	if err != nil {
 		return nil, err
 	}
@@ -112,7 +112,7 @@ func (f *File) rsrcForkWriter() (io.WriteCloser, error) {
 }
 
 func (f *File) InfoForkWriter() (io.WriteCloser, error) {
-	file, err := os.OpenFile(f.infoPath, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
+	file, err := f.fs.OpenFile(f.infoPath, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
 	if err != nil {
 		return nil, err
 	}
@@ -121,7 +121,7 @@ func (f *File) InfoForkWriter() (io.WriteCloser, error) {
 }
 
 func (f *File) incFileWriter() (io.WriteCloser, error) {
-	file, err := os.OpenFile(f.incompletePath, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0644)
+	file, err := f.fs.OpenFile(f.incompletePath, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0644)
 	if err != nil {
 		return nil, err
 	}
@@ -137,7 +137,7 @@ func (f *File) dataForkReader() (io.Reader, error) {
 	return f.fs.Open(f.incompletePath)
 }
 
-func (f *File) rsrcForkFile() (*os.File, error) {
+func (f *File) rsrcForkFile() (io.ReadCloser, error) {
 	return f.fs.Open(f.rsrcPath)
 }