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No longer open files in append mode, as this caused bugs when used with pwrite #82

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Merged
merged 1 commit into from
Jul 13, 2025
Merged

No longer open files in append mode, as this caused bugs when used with pwrite #82

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24 changes: 2 additions & 22 deletions pywasm/wasi.py
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Original file line number Diff line number Diff line change
@@ -1,5 +1,4 @@
import dataclasses
import fcntl
import os
import pywasm.core
import random
Expand Down Expand Up @@ -393,7 +392,6 @@ class Preview1:
@dataclasses.dataclass
class File:
host_fd: int
host_flag: int
host_name: str
host_status: int
pipe: typing.Optional[typing.BinaryIO]
Expand All @@ -413,7 +411,6 @@ 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,
Expand All @@ -427,7 +424,6 @@ 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,
Expand All @@ -441,7 +437,6 @@ 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,
Expand All @@ -458,7 +453,6 @@ 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=0,
host_name=v,
host_status=self.FILE_STATUS_OPENED,
pipe=None,
Expand Down Expand Up @@ -655,17 +649,12 @@ 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_APPEND
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]:
Expand Down Expand Up @@ -807,13 +796,6 @@ def fd_pwrite(self, m: pywasm.core.Machine, args: typing.List[int]) -> typing.Li
elem = mems.get(elem_ptr, elem_len)
iovs_ptr += 8
data.extend(elem)
if file.wasm_flag & self.FDFLAGS_APPEND:
# 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.
mems.put_u32(args[4], len(data))
return [self.ERRNO_SUCCESS]
size = os.pwrite(file.host_fd, data, args[3])
mems.put_u32(args[4], size)
return [self.ERRNO_SUCCESS]
Expand Down Expand Up @@ -886,7 +868,6 @@ 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
Expand Down Expand Up @@ -967,6 +948,8 @@ 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),
Expand Down Expand Up @@ -1182,8 +1165,6 @@ 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)
Expand Down Expand Up @@ -1226,7 +1207,6 @@ 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,
Expand Down
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