WASI: Implement fd_sync

Sources/SystemExtras/FileOperations.swift

@@ -576,6 +576,28 @@ extension FileDescriptor {
     return .success(DirectoryStream(rawValue: dirp))
     #endif
   }
+
+  public func sync() throws {
+    return try _sync().get()
+  }
+
+  internal func _sync() -> Result<Void, Errno> {
+    #if os(Windows)
+    let handle = HANDLE(bitPattern: _get_osfhandle(self.rawValue))
+    return nothingOrErrno(retryOnInterrupt: false) {
+      let ok = FlushFileBuffers(handle)
+      return ok ? 0 : -1
+    }
+    #else
+    nothingOrErrno(retryOnInterrupt: false) {
+      #if SYSTEM_PACKAGE_DARWIN
+      system_fcntl(self.rawValue, F_FULLFSYNC)
+      #else
+      system_fsync(self.rawValue)
+      #endif
+    }
+    #endif
+  }
 }
 
 #if os(Windows)

Sources/SystemExtras/Syscalls.swift

@@ -47,6 +47,11 @@ internal func system_fcntl(_ fd: Int32, _ cmd: Int32) -> CInt {
   return fcntl(fd, cmd)
 }
 
+// fsync
+internal func system_fsync(_ fd: Int32) -> CInt {
+  return fsync(fd)
+}
+
 #endif
 
 #if os(Linux)

Sources/WASI/FileSystem.swift

@@ -24,6 +24,7 @@ protocol WASIFile: WASIEntry {
     func fdStat() throws -> WASIAbi.FdStat
     func setFdStatFlags(_ flags: WASIAbi.Fdflags) throws
     func setFilestatSize(_ size: WASIAbi.FileSize) throws
+    func sync() throws
 
     func tell() throws -> WASIAbi.FileSize
     func seek(offset: WASIAbi.FileDelta, whence: WASIAbi.Whence) throws -> WASIAbi.FileSize

Sources/WASI/Platform/File.swift

@@ -24,6 +24,12 @@ extension FdWASIFile {
         )
     }
 
+    func sync() throws {
+        try WASIAbi.Errno.translatingPlatformErrno {
+            try fd.sync()
+        }
+    }
+
     @inlinable
     func write<Buffer: Sequence>(vectored buffer: Buffer) throws -> WASIAbi.Size where Buffer.Element == WASIAbi.IOVec {
         guard accessMode.contains(.write) else {

Sources/WASI/WASI.swift

@@ -1695,7 +1695,10 @@ public class WASIBridgeToHost: WASI {
     }
 
     func fd_sync(fd: WASIAbi.Fd) throws {
-        throw WASIAbi.Errno.ENOTSUP
+        guard case let .file(fileEntry) = fdTable[fd] else {
+            throw WASIAbi.Errno.EBADF
+        }
+        return try fileEntry.sync()
     }
 
     func fd_tell(fd: WASIAbi.Fd) throws -> WASIAbi.FileSize {