A virtual jailed shell environment for Go apps backed by an io/fs#FS.
fix(s3fs): support opening directories
WASI guests (e.g. python.wasm via wazero) call OpenFile(".", O_RDONLY)
during fd_prestat_get to enumerate preopens, then ask IsDir() on the
result. s3fs would issue a GetObject with an empty key, fail, and
surface as EIO -- crashing python at _start.
Add an s3DirFile pseudo-handle for directory paths and route OpenFile
through it: short-circuit "" / "." to skip the S3 call entirely, and
on NoSuchKey/NotFound probe with ListObjectsV2 so directory prefixes
return s3DirFile while real misses get fs.ErrNotExist (ENOENT).
Assisted-by: Claude Opus 4.7 via Claude Code
Signed-off-by: Xe Iaso <me@xeiaso.net>
+82
-1
+40
-1
internal/s3fs/basic.go
+40
-1
internal/s3fs/basic.go
···
59
59
60
60
switch flag & SupportedOFlags {
61
61
case O_RDONLY:
62
-
return newS3ReadFile(fs3.client, fs3.bucket, p)
62
+
// The bucket root is always a directory; short-circuit so WASI
63
+
// preopens (which OpenFile(".", O_RDONLY)) don't issue an S3 call.
64
+
key := strings.TrimPrefix(fs3.cleanPath(filename), "/")
65
+
if key == "" || key == "." {
66
+
return newS3DirFile(p), nil
67
+
}
68
+
69
+
f, err := newS3ReadFile(fs3.client, fs3.bucket, p)
70
+
if err == nil {
71
+
return f, nil
72
+
}
73
+
74
+
// If the object simply doesn't exist, the path may still be a
75
+
// directory prefix in S3. Probe for that before giving up.
76
+
var apiErr smithy.APIError
77
+
if !errors.As(err, &apiErr) {
78
+
return nil, err
79
+
}
80
+
switch apiErr.ErrorCode() {
81
+
case "NoSuchKey", "NotFound":
82
+
default:
83
+
return nil, err
84
+
}
85
+
86
+
ctx := context.TODO()
87
+
prefix := key + "/"
88
+
maxKeys := int32(1)
89
+
list, lerr := fs3.client.ListObjectsV2(ctx, &s3.ListObjectsV2Input{
90
+
Bucket: &fs3.bucket,
91
+
Prefix: &prefix,
92
+
Delimiter: &fs3.separator,
93
+
MaxKeys: &maxKeys,
94
+
})
95
+
if lerr != nil {
96
+
return nil, lerr
97
+
}
98
+
if len(list.Contents) > 0 || len(list.CommonPrefixes) > 0 {
99
+
return newS3DirFile(p), nil
100
+
}
101
+
return nil, &os.PathError{Op: "open", Path: filename, Err: fs.ErrNotExist}
63
102
64
103
case O_WRONLY:
65
104
return newS3WriteFile(fs3.client, fs3.bucket, p)
+42
internal/s3fs/file.go
+42
internal/s3fs/file.go
···
8
8
"io/fs"
9
9
"io/ioutil"
10
10
"os"
11
+
"syscall"
11
12
12
13
"github.com/aws/aws-sdk-go-v2/service/s3"
13
14
"go.uber.org/atomic"
···
353
354
func (f *s3MultipartUploadFile) Truncate(size int64) error {
354
355
return ErrTruncateNotSupported
355
356
}
357
+
358
+
// s3DirFile is a billy.File handle for a directory in S3. S3 has no real
359
+
// directories, but WASI guests (via wazero) open the preopen root by calling
360
+
// OpenFile(".", O_RDONLY) and then asking IsDir() — so we return a pseudo-file
361
+
// that reports as a directory and rejects byte I/O with EISDIR.
362
+
type s3DirFile struct {
363
+
name string
364
+
closed bool
365
+
}
366
+
367
+
func newS3DirFile(name string) *s3DirFile {
368
+
return &s3DirFile{name: name}
369
+
}
370
+
371
+
// Name returns the name of the file as presented to Open.
372
+
func (f *s3DirFile) Name() string {
373
+
return f.name
374
+
}
375
+
376
+
func (f *s3DirFile) eisdir(op string) error {
377
+
return &os.PathError{Op: op, Path: f.name, Err: syscall.EISDIR}
378
+
}
379
+
380
+
func (f *s3DirFile) Read(p []byte) (int, error) { return 0, f.eisdir("read") }
381
+
func (f *s3DirFile) ReadAt(p []byte, off int64) (int, error) { return 0, f.eisdir("read") }
382
+
func (f *s3DirFile) Write(p []byte) (int, error) { return 0, f.eisdir("write") }
383
+
func (f *s3DirFile) Seek(offset int64, whence int) (int64, error) {
384
+
return 0, f.eisdir("seek")
385
+
}
386
+
func (f *s3DirFile) Truncate(size int64) error { return f.eisdir("truncate") }
387
+
388
+
func (f *s3DirFile) Close() error {
389
+
if f.closed {
390
+
return ErrFileClosed
391
+
}
392
+
f.closed = true
393
+
return nil
394
+
}
395
+
396
+
func (f *s3DirFile) Lock() error { return ErrLockNotSupported }
397
+
func (f *s3DirFile) Unlock() error { return ErrLockNotSupported }