Use linux style pwrite

Author: mohanson

example/wasi_httpbin.py

@@ -1,3 +1,4 @@
+import os
 import pywasm
 import socket
 
@@ -16,6 +17,7 @@
 wasi = pywasm.wasi.Preview1(['wasi_httpbin.wasm'], {}, {})
 wasi.fd.append(pywasm.wasi.Preview1.File(
     host_fd=client_socket.fileno(),
+    host_flag=os.O_RDWR,
     host_name=client_socket.getsockname(),
     host_status=pywasm.wasi.Preview1.FILE_STATUS_OPENED,
     pipe=None,

pywasm/wasi.py

@@ -1,4 +1,5 @@
 import dataclasses
+import fcntl
 import os
 import platform
 import pywasm.core
@@ -395,6 +396,7 @@ class Preview1:
     @dataclasses.dataclass
     class File:
         host_fd: int
+        host_flag: int
         host_name: str
         host_status: int
         pipe: typing.Optional[typing.BinaryIO]
@@ -414,6 +416,7 @@ def __init__(self, args: typing.List[str], dirs: typing.Dict[str, str], envs: ty
         self.fd: typing.List[Preview1.File] = []
         self.fd.append(self.File(
             host_fd=sys.stdin.fileno(),
+            host_flag=0,
             host_name=sys.stdin.name,
             host_status=self.FILE_STATUS_OPENED,
             pipe=None,
@@ -427,6 +430,7 @@ def __init__(self, args: typing.List[str], dirs: typing.Dict[str, str], envs: ty
         ))
         self.fd.append(self.File(
             host_fd=sys.stdout.fileno(),
+            host_flag=0,
             host_name=sys.stdout.name,
             host_status=self.FILE_STATUS_OPENED,
             pipe=None,
@@ -440,6 +444,7 @@ def __init__(self, args: typing.List[str], dirs: typing.Dict[str, str], envs: ty
         ))
         self.fd.append(self.File(
             host_fd=sys.stderr.fileno(),
+            host_flag=0,
             host_name=sys.stderr.name,
             host_status=self.FILE_STATUS_OPENED,
             pipe=None,
@@ -456,6 +461,7 @@ def __init__(self, args: typing.List[str], dirs: typing.Dict[str, str], envs: ty
             v = os.path.abspath(os.path.normpath(v))
             self.fd.append(self.File(
                 host_fd=os.open(v, os.O_RDONLY | os.O_DIRECTORY),
+                host_flag=os.O_RDONLY | os.O_DIRECTORY,
                 host_name=v,
                 host_status=self.FILE_STATUS_OPENED,
                 pipe=None,
@@ -652,12 +658,17 @@ def fd_fdstat_set_flags(self, _: pywasm.core.Machine, args: typing.List[int]) ->
         if file.wasm_flag ^ args[1] | fyes != fyes:
             # Only support changing the NONBLOCK or APPEND flags.
             return [self.ERRNO_INVAL]
+        file.host_flag &= ~os.O_APPEND
+        file.host_flag &= ~os.O_NONBLOCK
         file.wasm_flag &= ~self.FDFLAGS_APPEND
         file.wasm_flag &= ~self.FDFLAGS_NONBLOCK
         if args[1] & self.FDFLAGS_APPEND:
+            file.host_flag |= os.O_APPEND
             file.wasm_flag |= self.FDFLAGS_APPEND
         if args[1] & self.FDFLAGS_NONBLOCK:
+            file.host_flag |= os.O_NONBLOCK
             file.wasm_flag |= self.FDFLAGS_NONBLOCK
+        fcntl.fcntl(file.host_fd, fcntl.F_SETFL, file.host_flag)
         return [self.ERRNO_SUCCESS]
 
     def fd_fdstat_set_rights(self, _: pywasm.core.Machine, args: typing.List[int]) -> typing.List[int]:
@@ -871,6 +882,7 @@ def fd_renumber(self, _: pywasm.core.Machine, args: typing.List[int]) -> typing.
         if dest.wasm_type != self.FILETYPE_CHARACTER_DEVICE:
             os.close(dest.host_fd)
         dest.host_fd = stem.host_fd
+        dest.host_flag = stem.host_flag
         dest.host_name = stem.host_name
         dest.host_status = stem.host_status
         dest.pipe = stem.pipe
@@ -951,8 +963,6 @@ def fd_write(self, m: pywasm.core.Machine, args: typing.List[int]) -> typing.Lis
             elem = mems.get(elem_ptr, elem_len)
             iovs_ptr += 8
             data.extend(elem)
-        if file.wasm_flag & self.FDFLAGS_APPEND:
-            os.lseek(file.host_fd, 0, os.SEEK_END)
         size = [
             lambda: os.write(file.host_fd, data),
             lambda: file.pipe.write(data),
@@ -1171,6 +1181,8 @@ def path_open(self, m: pywasm.core.Machine, args: typing.List[int]) -> typing.Li
             flag |= os.O_WRONLY
         if args[5] & self.RIGHTS_FD_READ + self.RIGHTS_FD_WRITE == self.RIGHTS_FD_READ + self.RIGHTS_FD_WRITE:
             flag |= os.O_RDWR
+        if args[7] & self.FDFLAGS_APPEND:
+            flag |= os.O_APPEND
         wasm_fd = len(self.fd)
         try:
             host_fd = os.open(name, flag, 0o644, dir_fd=self.fd[args[0]].host_fd)
@@ -1217,6 +1229,7 @@ def path_open(self, m: pywasm.core.Machine, args: typing.List[int]) -> typing.Li
             rights_root &= ~void
         self.fd.append(Preview1.File(
             host_fd=host_fd,
+            host_flag=flag,
             host_name=host_name,
             host_status=self.FILE_STATUS_OPENED,
             pipe=None,

test/wasi.py

@@ -34,6 +34,13 @@ def cd(dst: str) -> typing.Generator[None, typing.Any, None]:
 case.extend(sorted(glob.glob('res/wasi-testsuite/tests/c/testsuite/*.wasm')))
 case.extend(sorted(glob.glob('res/wasi-testsuite/tests/rust/testsuite/*.wasm')))
 skip = [
+    # POSIX requires that opening a file with the O_APPEND flag should have no affect on the location at which pwrite()
+    # writes data. However, on Linux, if a file is opened with O_APPEND, pwrite() appends data to the end of the file,
+    # regardless of the value of offset.
+    #
+    # See https://linux.die.net/man/2/pwrite.
+    # See https://github.com/WebAssembly/wasi-testsuite/issues/111
+    'res/wasi-testsuite/tests/c/testsuite/pwrite-with-append.wasm'
 ]
 for wasm_path in case:
     if wasm_path in skip: