Begin sketching out a new high-level fs API.

This is a very preliminary sketch of #83. It doesn't even compile yet,
but it shows a possible high-level structure of such an API.

Cargo.toml

@@ -18,6 +18,7 @@ rand = "0.6"
 cfg-if = "0.1.9"
 log = "0.4"
 filetime = "0.2.7"
+lazy_static = "1.4.0"
 
 [target.'cfg(unix)'.dependencies]
 nix = "0.15"

src/fs/ctx.rs

@@ -0,0 +1,7 @@
+use crate::WasiCtx;
+
+lazy_static! {
+    // TODO: Should we allow the context to be passed alternate arguments?
+    pub(crate) static ref CONTEXT: WasiCtx =
+        WasiCtx::new(std::env::args()).expect("initializing WASI state");
+}

src/fs/dir.rs

@@ -0,0 +1,66 @@
+use crate::fs::{ctx, error::wasi_errno_to_io_error, File};
+use crate::{host, hostcalls};
+use std::os::unix::ffi::OsStrExt;
+use std::{io, path::Path};
+
+/// A reference to an open directory on the filesystem.
+pub struct Dir {
+    fd: host::__wasi_fd_t,
+}
+
+impl Dir {
+    /// Constructs a new instance of Self from the given raw WASI file descriptor.
+    pub unsafe fn from_raw_wasi_fd(fd: host::__wasi_fd_t) -> Self {
+        Self { fd }
+    }
+
+    /// Attempts to open a file in read-only mode.
+    fn open_file<P: AsRef<Path>>(&mut self, path: P) -> io::Result<File> {
+        let path = path.as_ref();
+        let mut fd = 0;
+        wasi_errno_to_io_error(hostcalls::path_open(
+            &mut ctx::CONTEXT,
+            self.fd,
+            host::__WASI_LOOKUP_SYMLINK_FOLLOW,
+            path.as_os_str().as_bytes(),
+            path.as_os_str().len(),
+            0,
+            !0,
+            !0,
+            0,
+            &mut fd,
+        ))?;
+
+        Ok(File::from_raw_wasi_fd(fd))
+    }
+
+    /// Attempts to open a directory.
+    fn open_dir<P: AsRef<Path>>(&mut self, path: P) -> io::Result<Self> {
+        let path = path.as_ref();
+        let mut fd = 0;
+        wasi_errno_to_io_error(hostcalls::path_open(
+            &mut ctx::CONTEXT,
+            self.fd,
+            host::__WASI_LOOKUP_SYMLINK_FOLLOW,
+            path.as_os_str().as_bytes(),
+            host::__WASI_O_DIRECTORY,
+            !0,
+            !0,
+            0,
+            &mut fd,
+        ))?;
+
+        Ok(Self::from_raw_wasi_fd(fd))
+    }
+}
+
+impl Drop for Dir {
+    fn drop(&mut self) {
+        // Note that errors are ignored when closing a file descriptor. The
+        // reason for this is that if an error occurs we don't actually know if
+        // the file descriptor was closed or not, and if we retried (for
+        // something like EINTR), we might close another valid file descriptor
+        // opened after we closed ours.
+        let _ = hostcalls::fd_close(&mut ctx::CONTEXT, self.fd);
+    }
+}

src/fs/error.rs

@@ -0,0 +1,173 @@
+use crate::host;
+use std::io;
+
+pub(crate) fn wasi_errno_to_io_error(errno: host::__wasi_errno_t) -> io::Result<()> {
+    #[cfg(unix)]
+    let raw_os_error = match errno {
+        host::__WASI_ESUCCESS => return Ok(()),
+        host::__WASI_EINVAL => libc::EINVAL,
+        host::__WASI_EPIPE => libc::EPIPE,
+        host::__WASI_ENOTCONN => libc::ENOTCONN,
+        host::__WASI_E2BIG => libc::E2BIG,
+        host::__WASI_EACCES => libc::EACCES,
+        host::__WASI_EADDRINUSE => libc::EADDRINUSE,
+        host::__WASI_EADDRNOTAVAIL => libc::EADDRNOTAVAIL,
+        host::__WASI_EAFNOSUPPORT => libc::EAFNOSUPPORT,
+        host::__WASI_EAGAIN => libc::EAGAIN,
+        host::__WASI_EALREADY => libc::EALREADY,
+        host::__WASI_EBADF => libc::EBADF,
+        host::__WASI_EBADMSG => libc::EBADMSG,
+        host::__WASI_EBUSY => libc::EBUSY,
+        host::__WASI_ECANCELED => libc::ECANCELED,
+        host::__WASI_ECHILD => libc::ECHILD,
+        host::__WASI_ECONNABORTED => libc::ECONNABORTED,
+        host::__WASI_ECONNREFUSED => libc::ECONNREFUSED,
+        host::__WASI_ECONNRESET => libc::ECONNRESET,
+        host::__WASI_EDEADLK => libc::EDEADLK,
+        host::__WASI_EDESTADDRREQ => libc::EDESTADDRREQ,
+        host::__WASI_EDOM => libc::EDOM,
+        host::__WASI_EDQUOT => libc::EDQUOT,
+        host::__WASI_EEXIST => libc::EEXIST,
+        host::__WASI_EFAULT => libc::EFAULT,
+        host::__WASI_EFBIG => libc::EFBIG,
+        host::__WASI_EHOSTUNREACH => libc::EHOSTUNREACH,
+        host::__WASI_EIDRM => libc::EIDRM,
+        host::__WASI_EILSEQ => libc::EILSEQ,
+        host::__WASI_EINPROGRESS => libc::EINPROGRESS,
+        host::__WASI_EINTR => libc::EINTR,
+        host::__WASI_EISCONN => libc::EISCONN,
+        host::__WASI_EISDIR => libc::EISDIR,
+        host::__WASI_ELOOP => libc::ELOOP,
+        host::__WASI_EMFILE => libc::EMFILE,
+        host::__WASI_EMLINK => libc::EMLINK,
+        host::__WASI_EMSGSIZE => libc::EMSGSIZE,
+        host::__WASI_EMULTIHOP => libc::EMULTIHOP,
+        host::__WASI_ENAMETOOLONG => libc::ENAMETOOLONG,
+        host::__WASI_ENETDOWN => libc::ENETDOWN,
+        host::__WASI_ENETRESET => libc::ENETRESET,
+        host::__WASI_ENETUNREACH => libc::ENETUNREACH,
+        host::__WASI_ENFILE => libc::ENFILE,
+        host::__WASI_ENOBUFS => libc::ENOBUFS,
+        host::__WASI_ENODEV => libc::ENODEV,
+        host::__WASI_ENOENT => libc::ENOENT,
+        host::__WASI_ENOEXEC => libc::ENOEXEC,
+        host::__WASI_ENOLCK => libc::ENOLCK,
+        host::__WASI_ENOLINK => libc::ENOLINK,
+        host::__WASI_ENOMEM => libc::ENOMEM,
+        host::__WASI_ENOMSG => libc::ENOMSG,
+        host::__WASI_ENOPROTOOPT => libc::ENOPROTOOPT,
+        host::__WASI_ENOSPC => libc::ENOSPC,
+        host::__WASI_ENOSYS => libc::ENOSYS,
+        host::__WASI_ENOTDIR => libc::ENOTDIR,
+        host::__WASI_ENOTEMPTY => libc::ENOTEMPTY,
+        host::__WASI_ENOTRECOVERABLE => libc::ENOTRECOVERABLE,
+        host::__WASI_ENOTSOCK => libc::ENOTSOCK,
+        host::__WASI_ENOTSUP => libc::ENOTSUP,
+        host::__WASI_ENOTTY => libc::ENOTTY,
+        host::__WASI_ENXIO => libc::ENXIO,
+        host::__WASI_EOVERFLOW => libc::EOVERFLOW,
+        host::__WASI_EOWNERDEAD => libc::EOWNERDEAD,
+        host::__WASI_EPROTO => libc::EPROTO,
+        host::__WASI_EPROTONOSUPPORT => libc::EPROTONOSUPPORT,
+        host::__WASI_EPROTOTYPE => libc::EPROTOTYPE,
+        host::__WASI_ERANGE => libc::ERANGE,
+        host::__WASI_EROFS => libc::EROFS,
+        host::__WASI_ESPIPE => libc::ESPIPE,
+        host::__WASI_ESRCH => libc::ESRCH,
+        host::__WASI_ESTALE => libc::ESTALE,
+        host::__WASI_ETIMEDOUT => libc::ETIMEDOUT,
+        host::__WASI_ETXTBSY => libc::ETXTBSY,
+        host::__WASI_EXDEV => libc::EXDEV,
+        #[cfg(target_os = "wasi")]
+        host::__WASI_ENOTCAPABLE => libc::ENOTCAPABLE,
+        #[cfg(not(target_os = "wasi"))]
+        host::__WASI_ENOTCAPABLE => libc::EIO,
+    };
+
+    #[cfg(windows)]
+    use winapi::shared::winerror::*;
+
+    #[cfg(windows)]
+    let raw_os_error = match errno {
+        host::__WASI_ESUCCESS => return Ok(()),
+        host::__WASI_EINVAL => WSAEINVAL,
+        host::__WASI_EPIPE => ERROR_BROKEN_PIPE,
+        host::__WASI_ENOTCONN => WSAENOTCONN,
+        host::__WASI_EACCES => ERROR_ACCESS_DENIED,
+        host::__WASI_EADDRINUSE => WSAEADDRINUSE,
+        host::__WASI_EADDRNOTAVAIL => WSAEADDRNOTAVAIL,
+        host::__WASI_EAGAIN => WSAEWOULDBLOCK,
+        host::__WASI_ECONNABORTED => WSAECONNABORTED,
+        host::__WASI_ECONNREFUSED => WSAECONNREFUSED,
+        host::__WASI_ECONNRESET => WSAECONNRESET,
+        host::__WASI_EEXIST => ERROR_ALREADY_EXISTS,
+        host::__WASI_ENOENT => ERROR_FILE_NOT_FOUND,
+        host::__WASI_ETIMEDOUT => WSAETIMEDOUT,
+        host::__WASI_E2BIG => WSAE2BIG,
+        host::__WASI_EAFNOSUPPORT => WSAEAFNOSUPPORT,
+        host::__WASI_EALREADY => WSAEALREADY,
+        host::__WASI_EBADF => WSAEBADF,
+        host::__WASI_EBADMSG => WSAEBADMSG,
+        host::__WASI_EBUSY => WSAEBUSY,
+        host::__WASI_ECANCELED => WSAECANCELED,
+        host::__WASI_ECHILD => WSAECHILD,
+        host::__WASI_EDEADLK => WSAEDEADLK,
+        host::__WASI_EDESTADDRREQ => WSAEDESTADDRREQ,
+        host::__WASI_EDOM => WSAEDOM,
+        host::__WASI_EDQUOT => WSAEDQUOT,
+        host::__WASI_EFAULT => WSAEFAULT,
+        host::__WASI_EFBIG => WSAEFBIG,
+        host::__WASI_EHOSTUNREACH => WSAEHOSTUNREACH,
+        host::__WASI_EIDRM => WSAEIDRM,
+        host::__WASI_EILSEQ => WSAEILSEQ,
+        host::__WASI_EINPROGRESS => WSAEINPROGRESS,
+        host::__WASI_EINTR => WSAEINTR,
+        host::__WASI_EISCONN => WSAEISCONN,
+        host::__WASI_EISDIR => WSAEISDIR,
+        host::__WASI_ELOOP => WSAELOOP,
+        host::__WASI_EMFILE => WSAEMFILE,
+        host::__WASI_EMLINK => WSAEMLINK,
+        host::__WASI_EMSGSIZE => WSAEMSGSIZE,
+        host::__WASI_EMULTIHOP => WSAEMULTIHOP,
+        host::__WASI_ENAMETOOLONG => WSAENAMETOOLONG,
+        host::__WASI_ENETDOWN => WSAENETDOWN,
+        host::__WASI_ENETRESET => WSAENETRESET,
+        host::__WASI_ENETUNREACH => WSAENETUNREACH,
+        host::__WASI_ENFILE => WSAENFILE,
+        host::__WASI_ENOBUFS => WSAENOBUFS,
+        host::__WASI_ENODEV => WSAENODEV,
+        host::__WASI_ENOEXEC => WSAENOEXEC,
+        host::__WASI_ENOLCK => WSAENOLCK,
+        host::__WASI_ENOLINK => WSAENOLINK,
+        host::__WASI_ENOMEM => WSAENOMEM,
+        host::__WASI_ENOMSG => WSAENOMSG,
+        host::__WASI_ENOPROTOOPT => WSAENOPROTOOPT,
+        host::__WASI_ENOSPC => WSAENOSPC,
+        host::__WASI_ENOSYS => WSAENOSYS,
+        host::__WASI_ENOTDIR => WSAENOTDIR,
+        host::__WASI_ENOTEMPTY => WSAENOTEMPTY,
+        host::__WASI_ENOTRECOVERABLE => WSAENOTRECOVERABLE,
+        host::__WASI_ENOTSOCK => WSAENOTSOCK,
+        host::__WASI_ENOTSUP => WSAENOTSUP,
+        host::__WASI_ENOTTY => WSAENOTTY,
+        host::__WASI_ENXIO => WSAENXIO,
+        host::__WASI_EOVERFLOW => WSAEOVERFLOW,
+        host::__WASI_EOWNERDEAD => WSAEOWNERDEAD,
+        host::__WASI_EPROTO => WSAEPROTO,
+        host::__WASI_EPROTONOSUPPORT => WSAEPROTONOSUPPORT,
+        host::__WASI_EPROTOTYPE => WSAEPROTOTYPE,
+        host::__WASI_ERANGE => WSAERANGE,
+        host::__WASI_EROFS => WSAEROFS,
+        host::__WASI_ESPIPE => WSAESPIPE,
+        host::__WASI_ESRCH => WSAESRCH,
+        host::__WASI_ESTALE => WSAESTALE,
+        host::__WASI_ETXTBSY => WSAETXTBSY,
+        host::__WASI_EXDEV => WSAEXDEV,
+        #[cfg(target_os = "wasi")]
+        host::__WASI_ENOTCAPABLE => WSAENOTCAPABLE,
+        #[cfg(not(target_os = "wasi"))]
+        host::__WASI_ENOTCAPABLE => WSAEIO,
+    };
+
+    Err(io::Error::from_raw_os_error(raw_os_error))
+}

src/fs/file.rs

@@ -0,0 +1,50 @@
+use crate::fs::{ctx, error::wasi_errno_to_io_error};
+use crate::{host, hostcalls};
+use std::io;
+
+/// A reference to an open file on the filesystem.
+pub struct File {
+    fd: host::__wasi_fd_t,
+}
+
+impl File {
+    /// Constructs a new instance of Self from the given raw WASI file descriptor.
+    pub unsafe fn from_raw_wasi_fd(fd: host::__wasi_fd_t) -> Self {
+        Self { fd }
+    }
+
+    // TODO: functions to implement: sync_all, sync_data, set_len, metadata
+}
+
+impl Drop for File {
+    fn drop(&mut self) {
+        // Note that errors are ignored when closing a file descriptor. The
+        // reason for this is that if an error occurs we don't actually know if
+        // the file descriptor was closed or not, and if we retried (for
+        // something like EINTR), we might close another valid file descriptor
+        // opened after we closed ours.
+        let _ = hostcalls::fd_close(&mut ctx::CONTEXT, self.fd);
+    }
+}
+
+impl io::Read for File {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        let iov = [host::__wasi_iovec_t {
+            buf: buf.as_mut_ptr() as *mut core::ffi::c_void,
+            buf_len: buf.len(),
+        }];
+        let mut nread = 0;
+
+        wasi_errno_to_io_error(hostcalls::fd_read(
+            &mut ctx::CONTEXT,
+            self.fd,
+            &iov,
+            1,
+            &mut nread,
+        ))?;
+
+        Ok(nread)
+    }
+}
+
+// TODO: traits to implement: Write, Seek, FileExt

src/fs/mod.rs

@@ -0,0 +1,9 @@
+mod ctx;
+mod dir;
+mod error;
+mod file;
+
+pub use dir::*;
+pub use file::*;
+
+// TODO: Implement more things from std::fs.

src/lib.rs

@@ -20,6 +20,9 @@
     )
 )]
 
+#[macro_use]
+extern crate lazy_static;
+
 mod ctx;
 mod error;
 mod fdentry;
@@ -29,6 +32,7 @@ mod sys;
 #[macro_use]
 mod macros;
 
+pub mod fs;
 pub mod host;
 pub mod hostcalls;
 pub mod memory;