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Only create relative symlinks in WasiFileSystem
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Creating absolute symlinks is broken in WASI. This also works
better for preopens.
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@squarejesse
squarejesse committed Aug 1, 2023
1 parent 094fd45 commit b900105
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Showing 2 changed files with 56 additions and 47 deletions.
31 changes: 16 additions & 15 deletions okio-testing-support/src/commonMain/kotlin/okio/AbstractFileSystemTest.kt
View file
Original file line number Diff line number Diff line change
Expand Up @@ -607,7 +607,6 @@ abstract class AbstractFileSystemTest(
@Test
fun listRecursivelyFollowsSymlinks() {
if (!supportsSymlink()) return
if (isWasiFileSystem) return // Symlinks to absolute paths are broken on WASI.

val baseA = base / "a"
val baseAA = baseA / "a"
Expand Down Expand Up @@ -639,7 +638,6 @@ abstract class AbstractFileSystemTest(
@Test
fun listRecursivelyOnSymlink() {
if (!supportsSymlink()) return
if (isWasiFileSystem) return // Symlinks to absolute paths are broken on WASI.

val baseA = base / "a"
val baseAA = baseA / "a"
Expand Down Expand Up @@ -673,7 +671,6 @@ abstract class AbstractFileSystemTest(
@Test
fun listRecursiveOnSymlinkWithSpecialCharacterNamedFiles() {
if (!supportsSymlink()) return
if (isWasiFileSystem) return // Symlinks to absolute paths are broken on WASI.

val baseA = base / "ä"
val baseASuperSaiyan = baseA / "超サイヤ人"
Expand All @@ -691,7 +688,6 @@ abstract class AbstractFileSystemTest(
@Test
fun listRecursivelyOnSymlinkCycleThrows() {
if (!supportsSymlink()) return
if (isWasiFileSystem) return // Symlinks to absolute paths are broken on WASI.

val baseA = base / "a"
val baseAB = baseA / "b"
Expand Down Expand Up @@ -2311,7 +2307,14 @@ abstract class AbstractFileSystemTest(
val maxTime = clock.now()

val sourceMetadata = fileSystem.metadata(source)
assertEquals(target, sourceMetadata.symlinkTarget)
// Okio's WasiFileSystem only creates relative symlinks.
assertEquals(
when {
isWasiFileSystem -> target.relativeTo(source.parent!!)
else -> target
},
sourceMetadata.symlinkTarget,
)
assertInRange(sourceMetadata.createdAt, minTime, maxTime)
}

Expand Down Expand Up @@ -2359,7 +2362,6 @@ abstract class AbstractFileSystemTest(
@Test
fun openSymlinkSource() {
if (!supportsSymlink()) return
if (isWasiFileSystem) return // Symlinks to absolute paths are broken on WASI.

val target = base / "symlink-target"
val source = base / "symlink-source"
Expand All @@ -2373,7 +2375,6 @@ abstract class AbstractFileSystemTest(
fun openSymlinkSink() {
if (!supportsSymlink()) return
if (isJimFileSystem()) return
if (isWasiFileSystem) return // Symlinks to absolute paths are broken on WASI.

val target = base / "symlink-target"
val source = base / "symlink-source"
Expand All @@ -2387,7 +2388,6 @@ abstract class AbstractFileSystemTest(
@Test
fun openFileWithDirectorySymlink() {
if (!supportsSymlink()) return
if (isWasiFileSystem) return // Symlinks to absolute paths are broken on WASI.

val baseA = base / "a"
val baseAA = base / "a" / "a"
Expand All @@ -2403,7 +2403,6 @@ abstract class AbstractFileSystemTest(
@Test
fun openSymlinkFileHandle() {
if (!supportsSymlink()) return
if (isWasiFileSystem) return // Symlinks to absolute paths are broken on WASI.

val target = base / "symlink-target"
val source = base / "symlink-source"
Expand All @@ -2418,7 +2417,6 @@ abstract class AbstractFileSystemTest(
@Test
fun listSymlinkDirectory() {
if (!supportsSymlink()) return
if (isWasiFileSystem) return // Symlinks to absolute paths are broken on WASI.

val baseA = base / "a"
val baseAA = base / "a" / "a"
Expand All @@ -2436,7 +2434,6 @@ abstract class AbstractFileSystemTest(
@Test
fun symlinkFileLastAccessedAt() {
if (!supportsSymlink()) return
if (isWasiFileSystem) return // Symlinks to absolute paths are broken on WASI.

val target = base / "symlink-target"
val source = base / "symlink-source"
Expand All @@ -2452,7 +2449,6 @@ abstract class AbstractFileSystemTest(
@Test
fun symlinkDirectoryLastAccessedAt() {
if (!supportsSymlink()) return
if (isWasiFileSystem) return // Symlinks to absolute paths are broken on WASI.

val baseA = base / "a"
val baseAA = base / "a" / "a"
Expand Down Expand Up @@ -2483,7 +2479,6 @@ abstract class AbstractFileSystemTest(
@Test
fun moveSymlinkDoesntMoveTargetFile() {
if (!supportsSymlink()) return
if (isWasiFileSystem) return // Symlinks to absolute paths are broken on WASI.

val target = base / "symlink-target"
val source1 = base / "symlink-source-1"
Expand All @@ -2493,7 +2488,14 @@ abstract class AbstractFileSystemTest(
fileSystem.atomicMove(source1, source2)
assertEquals("I am the target file", target.readUtf8())
assertEquals("I am the target file", source2.readUtf8())
assertEquals(target, fileSystem.metadata(source2).symlinkTarget)
// Okio's WasiFileSystem only creates relative symlinks.
assertEquals(
when {
isWasiFileSystem -> target.relativeTo(source1.parent!!)
else -> target
},
fileSystem.metadata(source2).symlinkTarget,
)
}

@Test
Expand Down Expand Up @@ -2525,7 +2527,6 @@ abstract class AbstractFileSystemTest(
@Test
fun followingRecursiveSymlinksIsOkay() {
if (!supportsSymlink()) return
if (isWasiFileSystem) return // Symlinks to absolute paths are broken on WASI.

val pathA = base / "symlink-a"
val pathB = base / "symlink-b"
Expand Down
72 changes: 40 additions & 32 deletions okio-wasifilesystem/src/wasmMain/kotlin/okio/WasiFileSystem.kt
View file
Original file line number Diff line number Diff line change
Expand Up @@ -62,15 +62,13 @@ import okio.internal.write
* [WASI]: https://wasi.dev/
*/
object WasiFileSystem : FileSystem() {
private val pathToPreopen: Map<Path, Int> = run {
private val preopens: List<Preopen> = buildList {
// File descriptor of the first preopen in the `WASI` instance's configured `preopens` property.
// This is 3 by default, assuming `stdin` is 0, `stdout` is 1, and `stderr` is 2. Other preopens
// are assigned sequentially starting at this value.
val firstPreopen = 3

withScopedMemoryAllocator { allocator ->
val map = mutableMapOf<Path, Int>()

val bufSize = 2048
val bufPointer = allocator.allocate(bufSize)

Expand All @@ -86,16 +84,13 @@ object WasiFileSystem : FileSystem() {
val dirNameErrno = fd_prestat_dir_name(fd, bufPointer.address.toInt(), size + 1)
if (dirNameErrno != 0) throw ErrnoException(dirNameErrno.toShort())
val dirName = bufPointer.readString(size)
map[dirName.toPath()] = fd
val dirNamePath = dirName.toPath()
add(Preopen(dirNamePath.segmentsBytes, fd))
}

return@run map
}
}

private val pathSegmentsToPreopen: Map<List<ByteString>, Int> =
pathToPreopen.mapKeys { (key, _) -> key.segmentsBytes }
private val relativePathPreopen: Int = pathToPreopen.values.firstOrNull()
private val relativePathPreopen: Preopen = preopens.firstOrNull()
?: throw IllegalStateException("no preopens")

override fun canonicalize(path: Path): Path {
Expand Down Expand Up @@ -142,10 +137,11 @@ object WasiFileSystem : FileSystem() {
override fun metadataOrNull(path: Path): FileMetadata? {
withScopedMemoryAllocator { allocator ->
val returnPointer = allocator.allocate(64)
val preopen = preopenForPath(path) ?: return null
val (pathAddress, pathSize) = allocator.write(path.toString())

val errno = path_filestat_get(
fd = preopenFd(path) ?: return null,
fd = preopen.fd,
flags = 0,
path = pathAddress.address.toInt(),
pathSize = pathSize,
Expand Down Expand Up @@ -176,7 +172,7 @@ object WasiFileSystem : FileSystem() {
val bufPointer = allocator.allocate(bufLen)
val readlinkReturnPointer = allocator.allocate(4) // `size` is u32, 4 bytes.
val readlinkErrno = path_readlink(
fd = preopenFd(path) ?: return null,
fd = preopen.fd,
path = pathAddress.address.toInt(),
pathSize = pathSize,
buf = bufPointer.address.toInt(),
Expand Down Expand Up @@ -360,7 +356,7 @@ object WasiFileSystem : FileSystem() {
val (pathAddress, pathSize) = allocator.write(dir.toString())

val errno = path_create_directory(
fd = preopenFd(dir) ?: throw FileNotFoundException("no preopen: $dir"),
fd = preopenForPath(dir)?.fd ?: throw FileNotFoundException("no preopen: $dir"),
path = pathAddress.address.toInt(),
pathSize = pathSize,
)
Expand All @@ -379,10 +375,10 @@ object WasiFileSystem : FileSystem() {
val (targetPathAddress, targetPathSize) = allocator.write(target.toString())

val errno = path_rename(
fd = preopenFd(source) ?: throw FileNotFoundException("no preopen: $source"),
fd = preopenForPath(source)?.fd ?: throw FileNotFoundException("no preopen: $source"),
old_path = sourcePathAddress.address.toInt(),
old_pathSize = sourcePathSize,
new_fd = preopenFd(target) ?: throw FileNotFoundException("no preopen: $target"),
new_fd = preopenForPath(target)?.fd ?: throw FileNotFoundException("no preopen: $target"),
new_path = targetPathAddress.address.toInt(),
new_pathSize = targetPathSize,
)
Expand All @@ -397,10 +393,10 @@ object WasiFileSystem : FileSystem() {
override fun delete(path: Path, mustExist: Boolean) {
withScopedMemoryAllocator { allocator ->
val (pathAddress, pathSize) = allocator.write(path.toString())
val preopenFd = preopenFd(path) ?: throw FileNotFoundException("no preopen: $path")
val preopenFd = preopenForPath(path) ?: throw FileNotFoundException("no preopen: $path")

var errno = path_unlink_file(
fd = preopenFd,
fd = preopenFd.fd,
path = pathAddress.address.toInt(),
pathSize = pathSize,
)
Expand All @@ -415,7 +411,7 @@ object WasiFileSystem : FileSystem() {
Errno.isdir.ordinal,
-> {
errno = path_remove_directory(
fd = preopenFd,
fd = preopenFd.fd,
path = pathAddress.address.toInt(),
pathSize = pathSize,
)
Expand All @@ -427,13 +423,25 @@ object WasiFileSystem : FileSystem() {

override fun createSymlink(source: Path, target: Path) {
withScopedMemoryAllocator { allocator ->
val sourcePreopen = preopenForPath(source)
?: throw FileNotFoundException("no preopen: $source")

// Always create symlinks relative to their source. Absolute symlinks are trouble because the
// absolute paths used by WASI are different from the absolute paths on the host file system.
val sourceParent = source.parent
?: throw IOException("unexpected symlink source: $source")
val targetRelative = when {
target.isRelative -> target
else -> target.relativeTo(sourceParent)
}

val (sourcePathAddress, sourcePathSize) = allocator.write(source.toString())
val (targetPathAddress, targetPathSize) = allocator.write(target.toString())
val (targetPathAddress, targetPathSize) = allocator.write(targetRelative.toString())

val errno = path_symlink(
old_path = targetPathAddress.address.toInt(),
old_pathSize = targetPathSize,
fd = preopenFd(source) ?: throw FileNotFoundException("no preopen: $source"),
fd = sourcePreopen.fd,
new_path = sourcePathAddress.address.toInt(),
new_pathSize = sourcePathSize,
)
Expand All @@ -448,12 +456,12 @@ object WasiFileSystem : FileSystem() {
fdflags: fdflags = 0,
): fd {
withScopedMemoryAllocator { allocator ->
val preopenFd = preopenFd(path) ?: throw FileNotFoundException("no preopen: $path")
val preopenFd = preopenForPath(path) ?: throw FileNotFoundException("no preopen: $path")
val (pathAddress, pathSize) = allocator.write(path.toString())

val returnPointer: Pointer = allocator.allocate(4) // fd is u32.
val errno = path_open(
fd = preopenFd,
fd = preopenFd.fd,
dirflags = 0,
path = pathAddress.address.toInt(),
pathSize = pathSize,
Expand All @@ -472,27 +480,27 @@ object WasiFileSystem : FileSystem() {
}

/**
* Returns the file descriptor of the preopened path that is either an ancestor of [path], or that
* [path] is an ancestor of.
* Returns the preopen whose path is either an ancestor of [path], or whose path [path] is an
* ancestor of.
*
* If [path] is an ancestor of our preopen, then operating on the path will ultimately fail with a
* `notcapable` errno.
*/
private fun preopenFd(path: Path): fd? {
private fun preopenForPath(path: Path): Preopen? {
if (path.isRelative) return relativePathPreopen

val pathSegmentsBytes = path.segmentsBytes

preopens@
for ((candidate, fd) in pathSegmentsToPreopen) {
val commonSize = minOf(pathSegmentsBytes.size, candidate.size)
for (i in 0 until commonSize) {
if (pathSegmentsBytes[i] != candidate[i]) continue@preopens
}
return fd
return preopens.firstOrNull { preopen ->
val commonSize = minOf(pathSegmentsBytes.size, preopen.segmentsBytes.size)
preopen.segmentsBytes.subList(0, commonSize) == pathSegmentsBytes.subList(0, commonSize)
}
return null
}

override fun toString() = "okio.WasiFileSystem"

private class Preopen(
val segmentsBytes: List<ByteString>,
val fd: fd,
)
}

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