Adds test delegating to iotest against a wasi fs.Fs implementation (#553)

* Adds test delegating to iotest against a wasi fs.Fs implementation

Signed-off-by: Anuraag Agrawal <anuraaga@gmail.com>

* Use MapFS instead of DirFS

Signed-off-by: Anuraag Agrawal <anuraaga@gmail.com>

internal/integration_test/fs/fs_test.go

@@ -0,0 +1,198 @@
+package fs
+
+import (
+	"context"
+	_ "embed"
+	"fmt"
+	"io"
+	"io/fs"
+	"testing"
+	"testing/fstest"
+	"testing/iotest"
+
+	"github.com/tetratelabs/wazero"
+	"github.com/tetratelabs/wazero/api"
+	"github.com/tetratelabs/wazero/internal/testing/require"
+	"github.com/tetratelabs/wazero/wasi"
+)
+
+var testCtx = context.Background()
+
+//go:embed testdata/animals.txt
+var animals []byte
+
+// wasiFs is an implementation of fs.Fs calling into wasi. Not thread-safe because we use
+// fixed Memory offsets for transferring data with wasm.
+type wasiFs struct {
+	t *testing.T
+
+	wasm   wazero.Runtime
+	memory api.Memory
+
+	workdirFd uint32
+
+	pathOpen api.Function
+	fdClose  api.Function
+	fdRead   api.Function
+	fdSeek   api.Function
+}
+
+func (fs *wasiFs) Open(name string) (fs.File, error) {
+	pathBytes := []byte(name)
+	// Pick anywhere in memory to write the path to.
+	pathPtr := uint32(0)
+	ok := fs.memory.Write(testCtx, pathPtr, pathBytes)
+	require.True(fs.t, ok)
+	resultOpenedFd := pathPtr + uint32(len(pathBytes))
+
+	fd := fs.workdirFd
+	dirflags := uint32(0) // arbitrary dirflags
+	pathLen := len(pathBytes)
+	oflags := uint32(0) // arbitrary oflags
+	// rights are ignored per https://github.com/WebAssembly/WASI/issues/469#issuecomment-1045251844
+	fsRightsBase, fsRightsInheriting := uint64(1), uint64(2)
+	fdflags := uint32(0) // arbitrary fdflags
+	res, err := fs.pathOpen.Call(
+		testCtx,
+		uint64(fd), uint64(dirflags), uint64(pathPtr), uint64(pathLen), uint64(oflags),
+		fsRightsBase, fsRightsInheriting, uint64(fdflags), uint64(resultOpenedFd))
+	require.NoError(fs.t, err)
+	require.Equal(fs.t, uint64(wasi.ErrnoSuccess), res[0])
+
+	resFd, ok := fs.memory.ReadUint32Le(testCtx, resultOpenedFd)
+	require.True(fs.t, ok)
+
+	return &wasiFile{fd: resFd, fs: fs}, nil
+}
+
+// wasiFile implements io.Reader and io.Seeker using wasi functions. It does not
+// implement io.ReaderAt because there is no wasi function for directly reading
+// from an offset.
+type wasiFile struct {
+	fd uint32
+	fs *wasiFs
+}
+
+func (f *wasiFile) Stat() (fs.FileInfo, error) {
+	// We currently don't implement wasi's fd_stat but also don't use this method from this test.
+	panic("unused")
+}
+
+func (f *wasiFile) Read(bytes []byte) (int, error) {
+	// Pick anywhere in memory for wasm to write resultSize too. We do this first since it's fixed length
+	// while iovs is variable.
+	resultSizeOff := uint32(0)
+	// Next place iovs
+	iovsOff := uint32(4)
+	// We do not directly write to hardware, there is no need for more than one iovec
+	iovsCount := uint32(1)
+	// iov starts at iovsOff + 8 because we first write four bytes for the offset itself, and
+	// four bytes for the length of the iov.
+	iovOff := iovsOff + uint32(8)
+	ok := f.fs.memory.WriteUint32Le(testCtx, iovsOff, iovOff)
+	require.True(f.fs.t, ok)
+	// Next write the length.
+	ok = f.fs.memory.WriteUint32Le(testCtx, iovsOff+uint32(4), uint32(len(bytes)))
+	require.True(f.fs.t, ok)
+
+	res, err := f.fs.fdRead.Call(testCtx, uint64(f.fd), uint64(iovsOff), uint64(iovsCount), uint64(resultSizeOff))
+	require.NoError(f.fs.t, err)
+
+	require.NotEqual(f.fs.t, uint64(wasi.ErrnoFault), res[0])
+
+	numRead, ok := f.fs.memory.ReadUint32Le(testCtx, resultSizeOff)
+	require.True(f.fs.t, ok)
+
+	if numRead == 0 {
+		if len(bytes) == 0 {
+			return 0, nil
+		}
+		if wasi.Errno(res[0]) == wasi.ErrnoSuccess {
+			return 0, io.EOF
+		} else {
+			return 0, fmt.Errorf("could not read from file")
+		}
+	}
+
+	buf, ok := f.fs.memory.Read(testCtx, iovOff, numRead)
+	require.True(f.fs.t, ok)
+	copy(bytes, buf)
+	return int(numRead), nil
+}
+
+func (f *wasiFile) Close() error {
+	res, err := f.fs.fdClose.Call(testCtx, uint64(f.fd))
+	require.NoError(f.fs.t, err)
+	require.NotEqual(f.fs.t, uint64(wasi.ErrnoFault), res[0])
+	return nil
+}
+
+func (f *wasiFile) Seek(offset int64, whence int) (int64, error) {
+	// Pick anywhere in memory for wasm to write the result newOffset to
+	resultNewoffsetOff := uint32(0)
+
+	res, err := f.fs.fdSeek.Call(testCtx, uint64(f.fd), uint64(offset), uint64(whence), uint64(resultNewoffsetOff))
+	require.NoError(f.fs.t, err)
+	require.NotEqual(f.fs.t, uint64(wasi.ErrnoFault), res[0])
+
+	newOffset, ok := f.fs.memory.ReadUint32Le(testCtx, resultNewoffsetOff)
+	require.True(f.fs.t, ok)
+
+	return int64(newOffset), nil
+}
+
+func TestReader(t *testing.T) {
+	r := wazero.NewRuntime()
+	defer r.Close(testCtx)
+
+	_, err := wasi.InstantiateSnapshotPreview1(testCtx, r)
+	require.NoError(t, err)
+
+	realFs := fstest.MapFS{"animals.txt": &fstest.MapFile{Data: animals}}
+	sys := wazero.NewModuleConfig().WithWorkDirFS(realFs)
+
+	// Create a module that just delegates to wasi functions.
+	compiled, err := r.CompileModule(testCtx, []byte(`(module
+  (import "wasi_snapshot_preview1" "path_open"
+    (func $wasi.path_open (param $fd i32) (param $dirflags i32) (param $path i32) (param $path_len i32) (param $oflags i32) (param $fs_rights_base i64) (param $fs_rights_inheriting i64) (param $fdflags i32) (param $result.opened_fd i32) (result (;errno;) i32)))
+  (import "wasi_snapshot_preview1" "fd_close"
+    (func $wasi.fd_close (param $fd i32) (result (;errno;) i32)))
+  (import "wasi_snapshot_preview1" "fd_read"
+    (func $wasi.fd_read (param $fd i32) (param $iovs i32) (param $iovs_len i32) (param $result.size i32) (result (;errno;) i32)))
+  (import "wasi_snapshot_preview1" "fd_seek"
+    (func $wasi.fd_seek (param $fd i32) (param $offset i64) (param $whence i32) (param $result.newoffset i32) (result (;errno;) i32)))
+  (memory 1 1)  ;; just an arbitrary size big enough for tests
+  (export "memory" (memory 0))
+  (export "path_open" (func $wasi.path_open))
+  (export "fd_close" (func $wasi.fd_close))
+  (export "fd_read" (func $wasi.fd_read))
+  (export "fd_seek" (func $wasi.fd_seek))
+)`), wazero.NewCompileConfig())
+	require.NoError(t, err)
+
+	mod, err := r.InstantiateModule(testCtx, compiled, sys)
+	require.NoError(t, err)
+
+	pathOpen := mod.ExportedFunction("path_open")
+	fdClose := mod.ExportedFunction("fd_close")
+	fdRead := mod.ExportedFunction("fd_read")
+	fdSeek := mod.ExportedFunction("fd_seek")
+
+	wasiFs := &wasiFs{
+		t:         t,
+		wasm:      r,
+		memory:    mod.Memory(),
+		workdirFd: uint32(3),
+		pathOpen:  pathOpen,
+		fdClose:   fdClose,
+		fdRead:    fdRead,
+		fdSeek:    fdSeek,
+	}
+
+	f, err := wasiFs.Open("animals.txt")
+	require.NoError(t, err)
+	defer f.Close()
+
+	err = iotest.TestReader(f, animals)
+	require.NoError(t, err)
+}

internal/integration_test/fs/testdata/animals.txt

@@ -0,0 +1,5 @@
+bear
+cat
+shark
+dinosaur
+human