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uvwasi

This project does not currently provide the comprehensive file system security properties provided by some WASI runtimes. Full support for secure file system sandboxing may or may not be implemented in future. In the mean time, do not rely on it to run untrusted code.

uvwasi implements the WASI system call API, so that WebAssembly runtimes can easily implement WASI calls. Under the hood, uvwasi leverages libuv where possible for maximum portability.

                              |
WebAssembly code              |      WebAssembly application code
                              |                 |
                              |                 v
                              | WASI syscalls (inserted by compiler toolchain)
                              |                 |
------------------------------+                 |
                              |                 v
WebAssembly runtime (Node.js) |    uvwasi (implementation of WASI)
                              |                 |
                              |                 v
                              |               libuv
                              |                 |
                              |                 v
                              |        platform-specific calls
                              |

(Hence uvwasi isn't for making C-programs-that-use-libuv-APIs execute on WASI runtimes. That would either be a new platform added by libuv, or done through POSIX emulation by the Emscripten or wasi-sdk toolchains.)

Building Locally

To build with CMake:

$ mkdir -p out/cmake ; cd out/cmake   # create build directory
$ cmake ../.. -DBUILD_TESTING=ON      # generate project with test
$ cmake --build .                     # build
$ ctest -C Debug --output-on-failure  # run tests

Example Usage

#include <stdlib.h>
#include <assert.h>
#include "uv.h"
#include "uvwasi.h"

int main(void) {
  uvwasi_t uvwasi;
  uvwasi_options_t init_options;
  uvwasi_errno_t err;

  /* Setup the initialization options. */
  init_options.in = 0;
  init_options.out = 1;
  init_options.err = 2;
  init_options.fd_table_size = 3;
  init_options.argc = 3;
  init_options.argv = calloc(3, sizeof(char*));
  init_options.argv[0] = "--foo=bar";
  init_options.argv[1] = "-baz";
  init_options.argv[2] = "100";
  init_options.envp = NULL;
  init_options.preopenc = 1;
  init_options.preopens = calloc(1, sizeof(uvwasi_preopen_t));
  init_options.preopens[0].mapped_path = "/var";
  init_options.preopens[0].real_path = ".";
  init_options.allocator = NULL;

  /* Initialize the sandbox. */
  err = uvwasi_init(&uvwasi, &init_options);
  assert(err == UVWASI_ESUCCESS);

  /* TODO(cjihrig): Show an example system call or two. */

  /* Clean up resources. */
  uvwasi_destroy(&uvwasi);
  return 0;
}

API

The WASI API is versioned. This documentation is based on the WASI preview 1 snapshot. uvwasi implements the WASI system call API with the following additions/modifications:

  • Each system call takes an additional uvwasi_t* as its first argument. The uvwasi_t is the sandbox under which system calls are issued. Each uvwasi_t can have different command line arguments, environment variables, preopened directories, file descriptor mappings, etc. This allows one controlling process to host multiple WASI applications simultaneously.
  • Each system call returns a uvwasi_errno_t. This appears to be expected of WASI system calls, but it is not explicitly part of the official API docs. This detail is explicitly documented here.
  • Additional functions and data types are provided for interacting with WASI sandboxes and the uvwasi library. These APIs are documented in the Unofficial APIs section below.

Unofficial APIs

This section contains data types and functions for working with uvwasi. They are not part of the official WASI API, but are used to embed uvwasi.

UVWASI_VERSION_MAJOR

The major release version of the uvwasi library. uvwasi follows semantic versioning. Changes to this value represent breaking changes in the public API.

UVWASI_VERSION_MINOR

The minor release version of the uvwasi library. uvwasi follows semantic versioning. Changes to this value represent feature additions in the public API.

UVWASI_VERSION_PATCH

The patch release version of the uvwasi library. uvwasi follows semantic versioning. Changes to this value represent bug fixes in the public API.

UVWASI_VERSION_HEX

The major, minor, and patch versions of the uvwasi library encoded as a single integer value.

UVWASI_VERSION_STRING

The major, minor, and patch versions of the uvwasi library encoded as a version string.

UVWASI_VERSION_WASI

The version of the WASI API targeted by uvwasi.

uvwasi_t

An individual WASI sandbox instance.

typedef struct uvwasi_s {
  struct uvwasi_fd_table_t fds;
  uvwasi_size_t argc;
  char** argv;
  char* argv_buf;
  uvwasi_size_t argv_buf_size;
  uvwasi_size_t envc;
  char** env;
  char* env_buf;
  uvwasi_size_t env_buf_size;
} uvwasi_t;

uvwasi_preopen_t

A data structure used to map a directory path within a WASI sandbox to a directory path on the WASI host platform.

typedef struct uvwasi_preopen_s {
  char* mapped_path;
  char* real_path;
} uvwasi_preopen_t;

uvwasi_options_t

A data structure used to pass configuration options to uvwasi_init().

typedef struct uvwasi_options_s {
  uvwasi_size_t fd_table_size;
  uvwasi_size_t preopenc;
  uvwasi_preopen_t* preopens;
  uvwasi_size_t argc;
  char** argv;
  char** envp;
  uvwasi_fd_t in;
  uvwasi_fd_t out;
  uvwasi_fd_t err;
  const uvwasi_mem_t* allocator;
} uvwasi_options_t;

uvwasi_init()

Initializes a sandbox represented by a uvwasi_t using the options represented by a uvwasi_options_t.

Inputs:

  • __wasi_t uvwasi

    The sandbox to initialize.

  • __wasi_options_t options

    Configuration options used when initializing the sandbox.

Outputs:

  • None

Returns:

uvwasi_destroy()

Cleans up resources related to a WASI sandbox. This function notably does not return an error code.

Inputs:

  • __wasi_t uvwasi

    The sandbox to clean up.

Outputs:

  • None

Returns:

  • None

System Calls

This section has been adapted from the official WASI API documentation.

uvwasi_args_get()

Read command-line argument data.

The sizes of the buffers should match that returned by uvwasi_args_sizes_get().

Inputs:

  • char **argv

    A pointer to a buffer to write the argument pointers.

  • char *argv_buf

    A pointer to a buffer to write the argument string data.

uvwasi_args_sizes_get()

Return command-line argument data sizes.

Outputs:

  • __wasi_size_t *argc

    The number of arguments.

  • __wasi_size_t *argv_buf_size

    The size of the argument string data.

uvwasi_clock_res_get()

Return the resolution of a clock.

Implementations are required to provide a non-zero value for supported clocks. For unsupported clocks, return UVWASI_EINVAL.

Note: This is similar to clock_getres in POSIX.

Inputs:

Outputs:

uvwasi_clock_time_get()

Return the time value of a clock.

Note: This is similar to clock_gettime in POSIX.

Inputs:

  • __wasi_clockid_t clock_id

    The clock for which to return the time.

  • __wasi_timestamp_t precision

    The maximum lag (exclusive) that the returned time value may have, compared to its actual value.

Outputs:

uvwasi_environ_get()

Read environment variable data.

The sizes of the buffers should match that returned by uvwasi_environ_sizes_get().

Inputs:

  • char **environ

    A pointer to a buffer to write the environment variable pointers.

  • char *environ_buf

    A pointer to a buffer to write the environment variable string data.

uvwasi_environ_sizes_get()

Return command-line argument data sizes.

Outputs:

  • __wasi_size_t *environ_count

    The number of environment variables.

  • __wasi_size_t *environ_buf_size

    The size of the environment variable string data.

uvwasi_fd_advise()

Provide file advisory information on a file descriptor.

Note: This is similar to posix_fadvise in POSIX.

Inputs:

uvwasi_fd_allocate()

Force the allocation of space in a file.

Note: This is similar to posix_fallocate in POSIX.

Inputs:

uvwasi_fd_close()

Close a file descriptor.

Note: This is similar to close in POSIX.

Inputs:

uvwasi_fd_datasync()

Synchronize the data of a file to disk.

Note: This is similar to fdatasync in POSIX.

Inputs:

  • __wasi_fd_t fd

    The file descriptor of the file to synchronize to disk.

uvwasi_fd_fdstat_get()

Get the attributes of a file descriptor.

Note: This returns similar flags to fsync(fd, F_GETFL) in POSIX, as well as additional fields.

Inputs:

  • __wasi_fd_t fd

    The file descriptor to inspect.

  • __wasi_fdstat_t *buf

    The buffer where the file descriptor's attributes are stored.

uvwasi_fd_fdstat_set_flags()

Adjust the flags associated with a file descriptor.

Note: This is similar to fcntl(fd, F_SETFL, flags) in POSIX.

Inputs:

uvwasi_fd_fdstat_set_rights()

Adjust the rights associated with a file descriptor.

This can only be used to remove rights, and returns UVWASI_ENOTCAPABLE if called in a way that would attempt to add rights.

Inputs:

uvwasi_fd_filestat_get()

Return the attributes of an open file.

Inputs:

uvwasi_fd_filestat_set_size()

Adjust the size of an open file. If this increases the file's size, the extra bytes are filled with zeros.

Note: This is similar to ftruncate in POSIX.

Inputs:

uvwasi_fd_filestat_set_times()

Adjust the timestamps of an open file or directory.

Note: This is similar to futimens in POSIX.

Inputs:

uvwasi_fd_pread()

Read from a file descriptor, without using and updating the file descriptor's offset.

Note: This is similar to preadv in POSIX.

Inputs:

  • __wasi_fd_t fd

    The file descriptor from which to read data.

  • const __wasi_iovec_t *iovs and __wasi_size_t iovs_len

    List of scatter/gather vectors in which to store data.

  • __wasi_filesize_t offset

    The offset within the file at which to read.

Outputs:

  • __wasi_size_t nread

    The number of bytes read.

uvwasi_fd_prestat_get()

Return a description of the given preopened file descriptor.

Inputs:

  • __wasi_fd_t fd

    The file descriptor about which to retrieve information.

  • __wasi_prestat_t *buf

    The buffer where the description is stored.

uvwasi_fd_prestat_dir_name()

Return a description of the given preopened file descriptor.

Inputs:

  • __wasi_fd_t fd

    The file descriptor about which to retrieve information.

  • const char *path and __wasi_size_t path_len

    A buffer into which to write the preopened directory name.

uvwasi_fd_pwrite()

Write to a file descriptor, without using and updating the file descriptor's offset.

Note: This is similar to pwritev in POSIX.

Inputs:

  • __wasi_fd_t fd

    The file descriptor to which to write data.

  • const __wasi_ciovec_t *iovs and __wasi_size_t iovs_len

    List of scatter/gather vectors from which to retrieve data.

  • __wasi_filesize_t offset

    The offset within the file at which to write.

Outputs:

  • __wasi_size_t nwritten

    The number of bytes written.

uvwasi_fd_read()

Read from a file descriptor.

Note: This is similar to readv in POSIX.

Inputs:

  • __wasi_fd_t fd

    The file descriptor from which to read data.

  • const __wasi_iovec_t *iovs and __wasi_size_t iovs_len

    List of scatter/gather vectors to which to store data.

Outputs:

  • __wasi_size_t nread

    The number of bytes read.

uvwasi_fd_readdir()

Read directory entries from a directory.

When successful, the contents of the output buffer consist of a sequence of directory entries. Each directory entry consists of a uvwasi_dirent_t object, followed by uvwasi_dirent_t::d_namlen bytes holding the name of the directory entry.

This function fills the output buffer as much as possible, potentially truncating the last directory entry. This allows the caller to grow its read buffer size in case it's too small to fit a single large directory entry, or skip the oversized directory entry.

Inputs:

  • __wasi_fd_t fd

    The directory from which to read the directory entries.

  • void *buf and __wasi_size_t buf_len

    The buffer where directory entries are stored.

  • __wasi_dircookie_t cookie

    The location within the directory to start reading.

Outputs:

  • __wasi_size_t bufused

    The number of bytes stored in the read buffer. If less than the size of the read buffer, the end of the directory has been reached.

uvwasi_fd_renumber()

Atomically replace a file descriptor by renumbering another file descriptor.

Due to the strong focus on thread safety, this environment does not provide a mechanism to duplicate or renumber a file descriptor to an arbitrary number, like dup2(). This would be prone to race conditions, as an actual file descriptor with the same number could be allocated by a different thread at the same time.

This function provides a way to atomically renumber file descriptors, which would disappear if dup2() were to be removed entirely.

Inputs:

uvwasi_fd_seek()

Move the offset of a file descriptor.

Note: This is similar to lseek in POSIX.

Inputs:

Outputs:

  • __wasi_filesize_t newoffset

    The new offset of the file descriptor, relative to the start of the file.

uvwasi_fd_sync()

Synchronize the data and metadata of a file to disk.

Note: This is similar to fsync in POSIX.

Inputs:

  • __wasi_fd_t fd

    The file descriptor of the file containing the data and metadata to synchronize to disk.

uvwasi_fd_tell()

Return the current offset of a file descriptor.

Note: This is similar to lseek(fd, 0, SEEK_CUR) in POSIX.

Inputs:

Outputs:

  • __wasi_filesize_t offset

    The current offset of the file descriptor, relative to the start of the file.

uvwasi_fd_write()

Write to a file descriptor.

Note: This is similar to writev in POSIX.

Inputs:

  • __wasi_fd_t fd

    The file descriptor to which to write data.

  • const __wasi_ciovec_t *iovs and __wasi_size_t iovs_len

    List of scatter/gather vectors from which to retrieve data.

Outputs:

  • __wasi_size_t nwritten

    The number of bytes written.

uvwasi_path_create_directory()

Create a directory.

Note: This is similar to mkdirat in POSIX.

Inputs:

  • __wasi_fd_t fd

    The working directory at which the resolution of the path starts.

  • const char *path and __wasi_size_t path_len

    The path at which to create the directory.

uvwasi_path_filestat_get()

Return the attributes of a file or directory.

Note: This is similar to stat in POSIX.

Inputs:

  • __wasi_fd_t fd

    The working directory at which the resolution of the path starts.

  • __wasi_lookupflags_t flags

    Flags determining the method of how the path is resolved.

  • const char *path and __wasi_size_t path_len

    The path of the file or directory to inspect.

  • __wasi_filestat_t *buf

    The buffer where the file's attributes are stored.

uvwasi_path_filestat_set_times()

Adjust the timestamps of a file or directory.

Note: This is similar to utimensat in POSIX.

Inputs:

  • __wasi_fd_t fd

    The working directory at which the resolution of the path starts.

  • __wasi_lookupflags_t flags

    Flags determining the method of how the path is resolved.

  • const char *path and __wasi_size_t path_len

    The path of the file or directory to operate on.

  • __wasi_timestamp_t st_atim

    The desired values of the data access timestamp.

  • __wasi_timestamp_t st_mtim

    The desired values of the data modification timestamp.

  • __wasi_fstflags_t fst_flags

    A bitmask indicating which timestamps to adjust.

uvwasi_path_link()

Create a hard link.

Note: This is similar to linkat in POSIX.

Inputs:

  • __wasi_fd_t old_fd

    The working directory at which the resolution of the old path starts.

  • __wasi_lookupflags_t old_flags

    Flags determining the method of how the path is resolved.

  • const char *old_path and __wasi_size_t old_path_len

    The source path from which to link.

  • __wasi_fd_t new_fd

    The working directory at which the resolution of the new path starts.

  • const char *new_path and __wasi_size_t new_path_len

    The destination path at which to create the hard link.

uvwasi_path_open()

Open a file or directory.

The returned file descriptor is not guaranteed to be the lowest-numbered file descriptor not currently open; it is randomized to prevent applications from depending on making assumptions about indexes, since this is error-prone in multi-threaded contexts. The returned file descriptor is guaranteed to be less than 231.

Note: This is similar to openat in POSIX.

Inputs:

  • __wasi_fd_t dirfd

    The working directory at which the resolution of the path starts.

  • __wasi_lookupflags_t dirflags

    Flags determining the method of how the path is resolved.

  • const char *path and __wasi_size_t path_len

    The relative path of the file or directory to open, relative to the dirfd directory.

  • __wasi_oflags_t o_flags

    The method by which to open the file.

  • __wasi_rights_t fs_rights_base and __wasi_rights_t fs_rights_inheriting

    The initial rights of the newly created file descriptor. The implementation is allowed to return a file descriptor with fewer rights than specified, if and only if those rights do not apply to the type of file being opened.

    The base rights are rights that will apply to operations using the file descriptor itself, while the inheriting rights are rights that apply to file descriptors derived from it.

  • __wasi_fdflags_t fs_flags

    The initial flags of the file descriptor.

Outputs:

  • __wasi_fd_t fd

    The file descriptor of the file that has been opened.

uvwasi_path_readlink()

Read the contents of a symbolic link.

Note: This is similar to readlinkat in POSIX.

Inputs:

  • __wasi_fd_t fd

    The working directory at which the resolution of the path starts.

  • const char *path and __wasi_size_t path_len

    The path of the symbolic link from which to read.

  • char *buf and __wasi_size_t buf_len

    The buffer to which to write the contents of the symbolic link.

Outputs:

  • __wasi_size_t bufused

    The number of bytes placed in the buffer.

uvwasi_path_remove_directory()

Remove a directory.

Return UVWASI_ENOTEMPTY if the directory is not empty.

Note: This is similar to unlinkat(fd, path, AT_REMOVEDIR) in POSIX.

Inputs:

  • __wasi_fd_t fd

    The working directory at which the resolution of the path starts.

  • const char *path and __wasi_size_t path_len

    The path to a directory to remove.

uvwasi_path_rename()

Rename a file or directory.

Note: This is similar to renameat in POSIX.

Inputs:

  • __wasi_fd_t old_fd

    The working directory at which the resolution of the old path starts.

  • const char *old_path and __wasi_size_t old_path_len

    The source path of the file or directory to rename.

  • __wasi_fd_t new_fd

    The working directory at which the resolution of the new path starts.

  • const char *new_path and __wasi_size_t new_path_len

    The destination path to which to rename the file or directory.

uvwasi_path_symlink()

Create a symbolic link.

Note: This is similar to symlinkat in POSIX.

Inputs:

  • const char *old_path and __wasi_size_t old_path_len

    The contents of the symbolic link.

  • __wasi_fd_t fd

    The working directory at which the resolution of the path starts.

  • const char *new_path and __wasi_size_t new_path_len

    The destination path at which to create the symbolic link.

uvwasi_path_unlink_file()

Unlink a file.

Return UVWASI_EISDIR if the path refers to a directory.

Note: This is similar to unlinkat(fd, path, 0) in POSIX.

Inputs:

  • __wasi_fd_t fd

    The working directory at which the resolution of the path starts.

  • const char *path and __wasi_size_t path_len

    The path to a file to unlink.

uvwasi_poll_oneoff()

Concurrently poll for the occurrence of a set of events.

Inputs:

  • const __wasi_subscription_t *in

    The events to which to subscribe.

  • __wasi_event_t *out

    The events that have occurred.

  • __wasi_size_t nsubscriptions

    Both the number of subscriptions and events.

Outputs:

  • __wasi_size_t nevents

    The number of events stored.

uvwasi_proc_exit()

Terminate the process normally. An exit code of 0 indicates successful termination of the program. The meanings of other values is dependent on the environment.

Note: This is similar to _Exit in POSIX.

Inputs:

Does not return.

uvwasi_proc_raise()

Send a signal to the process of the calling thread.

Note: This is similar to raise in POSIX.

Inputs:

uvwasi_random_get()

Write high-quality random data into a buffer.

This function blocks when the implementation is unable to immediately provide sufficient high-quality random data.

This function may execute slowly, so when large mounts of random data are required, it's advisable to use this function to seed a pseudo-random number generator, rather than to provide the random data directly.

Inputs:

  • void *buf and __wasi_size_t buf_len

    The buffer to fill with random data.

uvwasi_sched_yield()

Temporarily yield execution of the calling thread.

Note: This is similar to sched_yield in POSIX.

uvwasi_sock_recv()

Receive a message from a socket.

Note: This is similar to recv in POSIX, though it also supports reading the data into multiple buffers in the manner of readv.

Inputs:

  • __wasi_fd_t sock

    The socket on which to receive data.

  • const __wasi_iovec_t *ri_data and __wasi_size_t ri_data_len

    List of scatter/gather vectors to which to store data.

  • __wasi_riflags_t ri_flags

    Message flags.

Outputs:

uvwasi_sock_send()

Send a message on a socket.

Note: This is similar to send in POSIX, though it also supports writing the data from multiple buffers in the manner of writev.

Inputs:

  • __wasi_fd_t sock

    The socket on which to send data.

  • const __wasi_ciovec_t *si_data and __wasi_size_t si_data_len

    List of scatter/gather vectors to which to retrieve data

  • __wasi_siflags_t si_flags

    Message flags.

Outputs:

  • __wasi_size_t so_datalen

    Number of bytes transmitted.

uvwasi_sock_shutdown()

Shut down socket send and receive channels.

Note: This is similar to shutdown in POSIX.

Inputs:

Types

uvwasi_advice_t (uint8_t)

File or memory access pattern advisory information.

Used by uvwasi_fd_advise().

Possible values:

  • UVWASI_ADVICE_DONTNEED

    The application expects that it will not access the specified data in the near future.

  • UVWASI_ADVICE_NOREUSE

    The application expects to access the specified data once and then not reuse it thereafter.

  • UVWASI_ADVICE_NORMAL

    The application has no advice to give on its behavior with respect to the specified data.

  • UVWASI_ADVICE_RANDOM

    The application expects to access the specified data in a random order.

  • UVWASI_ADVICE_SEQUENTIAL

    The application expects to access the specified data sequentially from lower offsets to higher offsets.

  • UVWASI_ADVICE_WILLNEED

    The application expects to access the specified data in the near future.

uvwasi_ciovec_t (struct)

A region of memory for scatter/gather writes.

Used by uvwasi_fd_pwrite(), uvwasi_fd_write(), and uvwasi_sock_send().

Members:

  • const void *buf and __wasi_size_t buf_len

    The address and length of the buffer to be written.

uvwasi_clockid_t (uint32_t)

Identifiers for clocks.

Used by uvwasi_subscription_t, uvwasi_clock_res_get(), and uvwasi_clock_time_get().

Possible values:

  • UVWASI_CLOCK_MONOTONIC

    The store-wide monotonic clock, which is defined as a clock measuring real time, whose value cannot be adjusted and which cannot have negative clock jumps.

    The epoch of this clock is undefined. The absolute time value of this clock therefore has no meaning.

  • UVWASI_CLOCK_PROCESS_CPUTIME_ID

    The CPU-time clock associated with the current process.

  • UVWASI_CLOCK_REALTIME

    The clock measuring real time. Time value zero corresponds with 1970-01-01T00:00:00Z.

  • UVWASI_CLOCK_THREAD_CPUTIME_ID

    The CPU-time clock associated with the current thread.

uvwasi_device_t (uint64_t)

Identifier for a device containing a file system. Can be used in combination with uvwasi_inode_t to uniquely identify a file or directory in the filesystem.

Used by uvwasi_filestat_t.

uvwasi_dircookie_t (uint64_t)

A reference to the offset of a directory entry.

Used by uvwasi_dirent_t and uvwasi_fd_readdir().

Special values:

  • UVWASI_DIRCOOKIE_START

    Permanent reference to the first directory entry within a directory.

uvwasi_dirent_t (struct)

A directory entry.

Members:

  • __wasi_dircookie_t d_next

    The offset of the next directory entry stored in this directory.

  • __wasi_inode_t d_ino

    The serial number of the file referred to by this directory entry.

  • uint32_t d_namlen

    The length of the name of the directory entry.

  • __wasi_filetype_t d_type

    The type of the file referred to by this directory entry.

uvwasi_errno_t (uint16_t)

Error codes returned by functions.

Not all of these error codes are returned by the functions provided by this API; some are used in higher-level library layers, and others are provided merely for alignment with POSIX.

Used by uvwasi_event_t.

Possible values:

  • UVWASI_ESUCCESS

    No error occurred. System call completed successfully.

  • UVWASI_E2BIG

    Argument list too long.

  • UVWASI_EACCES

    Permission denied.

  • UVWASI_EADDRINUSE

    Address in use.

  • UVWASI_EADDRNOTAVAIL

    Address not available.

  • UVWASI_EAFNOSUPPORT

    Address family not supported.

  • UVWASI_EAGAIN

    Resource unavailable, or operation would block.

  • UVWASI_EALREADY

    Connection already in progress.

  • UVWASI_EBADF

    Bad file descriptor.

  • UVWASI_EBADMSG

    Bad message.

  • UVWASI_EBUSY

    Device or resource busy.

  • UVWASI_ECANCELED

    Operation canceled.

  • UVWASI_ECHILD

    No child processes.

  • UVWASI_ECONNABORTED

    Connection aborted.

  • UVWASI_ECONNREFUSED

    Connection refused.

  • UVWASI_ECONNRESET

    Connection reset.

  • UVWASI_EDEADLK

    Resource deadlock would occur.

  • UVWASI_EDESTADDRREQ

    Destination address required.

  • UVWASI_EDOM

    Mathematics argument out of domain of function.

  • UVWASI_EDQUOT

    Reserved.

  • UVWASI_EEXIST

    File exists.

  • UVWASI_EFAULT

    Bad address.

  • UVWASI_EFBIG

    File too large.

  • UVWASI_EHOSTUNREACH

    Host is unreachable.

  • UVWASI_EIDRM

    Identifier removed.

  • UVWASI_EILSEQ

    Illegal byte sequence.

  • UVWASI_EINPROGRESS

    Operation in progress.

  • UVWASI_EINTR

    Interrupted function.

  • UVWASI_EINVAL

    Invalid argument.

  • UVWASI_EIO

    I/O error.

  • UVWASI_EISCONN

    Socket is connected.

  • UVWASI_EISDIR

    Is a directory.

  • UVWASI_ELOOP

    Too many levels of symbolic links.

  • UVWASI_EMFILE

    File descriptor value too large.

  • UVWASI_EMLINK

    Too many links.

  • UVWASI_EMSGSIZE

    Message too large.

  • UVWASI_EMULTIHOP

    Reserved.

  • UVWASI_ENAMETOOLONG

    Filename too long.

  • UVWASI_ENETDOWN

    Network is down.

  • UVWASI_ENETRESET

    Connection aborted by network.

  • UVWASI_ENETUNREACH

    Network unreachable.

  • UVWASI_ENFILE

    Too many files open in system.

  • UVWASI_ENOBUFS

    No buffer space available.

  • UVWASI_ENODEV

    No such device.

  • UVWASI_ENOENT

    No such file or directory.

  • UVWASI_ENOEXEC

    Executable file format error.

  • UVWASI_ENOLCK

    No locks available.

  • UVWASI_ENOLINK

    Reserved.

  • UVWASI_ENOMEM

    Not enough space.

  • UVWASI_ENOMSG

    No message of the desired type.

  • UVWASI_ENOPROTOOPT

    Protocol not available.

  • UVWASI_ENOSPC

    No space left on device.

  • UVWASI_ENOSYS

    Function not supported.

  • UVWASI_ENOTCONN

    The socket is not connected.

  • UVWASI_ENOTDIR

    Not a directory or a symbolic link to a directory.

  • UVWASI_ENOTEMPTY

    Directory not empty.

  • UVWASI_ENOTRECOVERABLE

    State not recoverable.

  • UVWASI_ENOTSOCK

    Not a socket.

  • UVWASI_ENOTSUP

    Not supported, or operation not supported on socket.

  • UVWASI_ENOTTY

    Inappropriate I/O control operation.

  • UVWASI_ENXIO

    No such device or address.

  • UVWASI_EOVERFLOW

    Value too large to be stored in data type.

  • UVWASI_EOWNERDEAD

    Previous owner died.

  • UVWASI_EPERM

    Operation not permitted.

  • UVWASI_EPIPE

    Broken pipe.

  • UVWASI_EPROTO

    Protocol error.

  • UVWASI_EPROTONOSUPPORT

    Protocol not supported.

  • UVWASI_EPROTOTYPE

    Protocol wrong type for socket.

  • UVWASI_ERANGE

    Result too large.

  • UVWASI_EROFS

    Read-only file system.

  • UVWASI_ESPIPE

    Invalid seek.

  • UVWASI_ESRCH

    No such process.

  • UVWASI_ESTALE

    Reserved.

  • UVWASI_ETIMEDOUT

    Connection timed out.

  • UVWASI_ETXTBSY

    Text file busy.

  • UVWASI_EXDEV

    Cross-device link.

  • UVWASI_ENOTCAPABLE

    Extension: Capabilities insufficient.

uvwasi_event_t (struct)

An event that occurred.

Used by uvwasi_poll_oneoff().

Members:

uvwasi_eventrwflags_t (uint16_t bitfield)

The state of the file descriptor subscribed to with UVWASI_EVENTTYPE_FD_READ or UVWASI_EVENTTYPE_FD_WRITE.

Used by uvwasi_event_t.

Possible values:

  • UVWASI_EVENT_FD_READWRITE_HANGUP

    The peer of this socket has closed or disconnected.

uvwasi_eventtype_t (uint8_t)

Type of a subscription to an event or its occurrence.

Used by uvwasi_event_t and uvwasi_subscription_t.

Possible values:

uvwasi_exitcode_t (uint32_t)

Exit code generated by a process when exiting.

Used by uvwasi_proc_exit().

uvwasi_fd_t (uint32_t)

A file descriptor number.

Used by many functions in this API.

As in POSIX, three file descriptor numbers are provided to instances on startup -- 0, 1, and 2, (a.k.a. STDIN_FILENO, STDOUT_FILENO, and STDERR_FILENO).

Other than these, WASI implementations are not required to allocate new file descriptors in ascending order.

uvwasi_fdflags_t (uint16_t bitfield)

File descriptor flags.

Used by uvwasi_fdstat_t, uvwasi_fd_fdstat_set_flags(), and uvwasi_path_open().

Possible values:

  • UVWASI_FDFLAG_APPEND

    Append mode: Data written to the file is always appended to the file's end.

  • UVWASI_FDFLAG_DSYNC

    Write according to synchronized I/O data integrity completion. Only the data stored in the file is synchronized.

  • UVWASI_FDFLAG_NONBLOCK

    Non-blocking mode.

  • UVWASI_FDFLAG_RSYNC

    Synchronized read I/O operations.

  • UVWASI_FDFLAG_SYNC

    Write according to synchronized I/O file integrity completion. In addition to synchronizing the data stored in the file, the implementation may also synchronously update the file's metadata.

uvwasi_fdstat_t (struct)

File descriptor attributes.

Used by uvwasi_fd_fdstat_get().

Members:

uvwasi_filedelta_t (int64_t)

Relative offset within a file.

Used by uvwasi_fd_seek().

uvwasi_filesize_t (uint64_t)

Non-negative file size or length of a region within a file.

Used by uvwasi_event_t, uvwasi_filestat_t, uvwasi_fd_pread(), uvwasi_fd_pwrite(), uvwasi_fd_seek(), uvwasi_path_tell(), uvwasi_fd_advise(), uvwasi_fd_allocate(), and uvwasi_fd_filestat_set_size().

uvwasi_filestat_t (struct)

File attributes.

Used by uvwasi_fd_filestat_get() and uvwasi_path_filestat_get().

Members:

uvwasi_filetype_t (uint8_t)

The type of a file descriptor or file.

Used by uvwasi_dirent_t, uvwasi_fdstat_t, and uvwasi_filestat_t.

Possible values:

  • UVWASI_FILETYPE_UNKNOWN

    The type of the file descriptor or file is unknown or is different from any of the other types specified.

  • UVWASI_FILETYPE_BLOCK_DEVICE

    The file descriptor or file refers to a block device inode.

  • UVWASI_FILETYPE_CHARACTER_DEVICE

    The file descriptor or file refers to a character device inode.

  • UVWASI_FILETYPE_DIRECTORY

    The file descriptor or file refers to a directory inode.

  • UVWASI_FILETYPE_REGULAR_FILE

    The file descriptor or file refers to a regular file inode.

  • UVWASI_FILETYPE_SOCKET_DGRAM

    The file descriptor or file refers to a datagram socket.

  • UVWASI_FILETYPE_SOCKET_STREAM

    The file descriptor or file refers to a byte-stream socket.

  • UVWASI_FILETYPE_SYMBOLIC_LINK

    The file refers to a symbolic link inode.

uvwasi_fstflags_t (uint16_t bitfield)

Which file time attributes to adjust.

Used by uvwasi_fd_filestat_set_times() and uvwasi_path_filestat_set_times().

Possible values:

uvwasi_inode_t (uint64_t)

File serial number that is unique within its file system.

Used by uvwasi_dirent_t and uvwasi_filestat_t.

uvwasi_iovec_t (struct)

A region of memory for scatter/gather reads.

Used by uvwasi_fd_pread(), uvwasi_fd_read(), and uvwasi_sock_recv().

Members:

  • void *buf and __wasi_size_t buf_len

    The address and length of the buffer to be filled.

uvwasi_linkcount_t (uint64_t)

Number of hard links to an inode.

Used by uvwasi_filestat_t.

uvwasi_lookupflags_t (uint32_t bitfield)

Flags determining the method of how paths are resolved.

Used by uvwasi_path_filestat_get(), uvwasi_path_filestat_set_times(), uvwasi_path_link(), and uvwasi_path_open().

Possible values:

  • UVWASI_LOOKUP_SYMLINK_FOLLOW

    As long as the resolved path corresponds to a symbolic link, it is expanded.

uvwasi_oflags_t (uint16_t bitfield)

Open flags used by uvwasi_path_open().

Used by uvwasi_path_open().

Possible values:

  • UVWASI_O_CREAT

    Create file if it does not exist.

  • UVWASI_O_DIRECTORY

    Fail if not a directory.

  • UVWASI_O_EXCL

    Fail if file already exists.

  • UVWASI_O_TRUNC

    Truncate file to size 0.

uvwasi_riflags_t (uint16_t bitfield)

Flags provided to uvwasi_sock_recv().

Used by uvwasi_sock_recv().

Possible values:

  • UVWASI_SOCK_RECV_PEEK

    Returns the message without removing it from the socket's receive queue.

  • UVWASI_SOCK_RECV_WAITALL

    On byte-stream sockets, block until the full amount of data can be returned.

uvwasi_rights_t (uint64_t bitfield)

File descriptor rights, determining which actions may be performed.

Used by uvwasi_fdstat_t, uvwasi_fd_fdstat_set_rights(), and uvwasi_path_open().

Possible values:

uvwasi_roflags_t (uint16_t bitfield)

Flags returned by uvwasi_sock_recv().

Used by uvwasi_sock_recv().

Possible values:

  • UVWASI_SOCK_RECV_DATA_TRUNCATED

    Returned by uvwasi_sock_recv(): Message data has been truncated.

uvwasi_sdflags_t (uint8_t bitfield)

Which channels on a socket to shut down.

Used by uvwasi_sock_shutdown().

Possible values:

  • UVWASI_SHUT_RD

    Disables further receive operations.

  • UVWASI_SHUT_WR

    Disables further send operations.

uvwasi_siflags_t (uint16_t bitfield)

Flags provided to uvwasi_sock_send(). As there are currently no flags defined, it must be set to zero.

Used by uvwasi_sock_send().

uvwasi_signal_t (uint8_t)

Signal condition.

Used by uvwasi_proc_raise().

Possible values:

  • UVWASI_SIGABRT

    Process abort signal.

    Action: Terminates the process.

  • UVWASI_SIGALRM

    Alarm clock.

    Action: Terminates the process.

  • UVWASI_SIGBUS

    Access to an undefined portion of a memory object.

    Action: Terminates the process.

  • UVWASI_SIGCHLD

    Child process terminated, stopped, or continued.

    Action: Ignored.

  • UVWASI_SIGCONT

    Continue executing, if stopped.

    Action: Continues executing, if stopped.

  • UVWASI_SIGFPE

    Erroneous arithmetic operation.

    Action: Terminates the process.

  • UVWASI_SIGHUP

    Hangup.

    Action: Terminates the process.

  • UVWASI_SIGILL

    Illegal instruction.

    Action: Terminates the process.

  • UVWASI_SIGINT

    Terminate interrupt signal.

    Action: Terminates the process.

  • UVWASI_SIGKILL

    Kill.

    Action: Terminates the process.

  • UVWASI_SIGPIPE

    Write on a pipe with no one to read it.

    Action: Ignored.

  • UVWASI_SIGQUIT

    Terminal quit signal.

    Action: Terminates the process.

  • UVWASI_SIGSEGV

    Invalid memory reference.

    Action: Terminates the process.

  • UVWASI_SIGSTOP

    Stop executing.

    Action: Stops executing.

  • UVWASI_SIGSYS

    Bad system call.

    Action: Terminates the process.

  • UVWASI_SIGTERM

    Termination signal.

    Action: Terminates the process.

  • UVWASI_SIGTRAP

    Trace/breakpoint trap.

    Action: Terminates the process.

  • UVWASI_SIGTSTP

    Terminal stop signal.

    Action: Stops executing.

  • UVWASI_SIGTTIN

    Background process attempting read.

    Action: Stops executing.

  • UVWASI_SIGTTOU

    Background process attempting write.

    Action: Stops executing.

  • UVWASI_SIGURG

    High bandwidth data is available at a socket.

    Action: Ignored.

  • UVWASI_SIGUSR1

    User-defined signal 1.

    Action: Terminates the process.

  • UVWASI_SIGUSR2

    User-defined signal 2.

    Action: Terminates the process.

  • UVWASI_SIGVTALRM

    Virtual timer expired.

    Action: Terminates the process.

  • UVWASI_SIGXCPU

    CPU time limit exceeded.

    Action: Terminates the process.

  • UVWASI_SIGXFSZ

    File size limit exceeded.

    Action: Terminates the process.

uvwasi_subclockflags_t (uint16_t bitfield)

Flags determining how to interpret the timestamp provided in uvwasi_subscription_t::u.clock.timeout.

Used by uvwasi_subscription_t.

Possible values:

uvwasi_subscription_t (struct)

Subscription to an event.

Used by uvwasi_poll_oneoff().

Members:

uvwasi_timestamp_t (uint64_t)

Timestamp in nanoseconds.

Used by uvwasi_filestat_t, uvwasi_subscription_t, uvwasi_clock_res_get(), uvwasi_clock_time_get(), uvwasi_fd_filestat_set_times(), and uvwasi_path_filestat_set_times().

uvwasi_userdata_t (uint64_t)

User-provided value that may be attached to objects that is retained when extracted from the implementation.

Used by uvwasi_event_t and uvwasi_subscription_t.

uvwasi_whence_t (uint8_t)

The position relative to which to set the offset of the file descriptor.

Used by uvwasi_fd_seek().

Possible values:

  • UVWASI_WHENCE_CUR

    Seek relative to current position.

  • UVWASI_WHENCE_END

    Seek relative to end-of-file.

  • UVWASI_WHENCE_SET

    Seek relative to start-of-file.

Doing a release

To do a release complete the following steps:

Running fuzzers locally

We support fuzzing by way of ClusterFuzzLite, which is run automatically against pull requests. You can run these fuzzers locally with the OSS-Fuzz fuzzing infrastructure, using the following steps:

git clone https://github.com/google/oss-fuzz
git clone https://github.com/nodejs/uvwasi
cd uvwasi

# Build the fuzzers in .clusterfuzzlite
python3 ../oss-fuzz/infra/helper.py build_fuzzers --external $PWD

# Run the fuzzer for 10 seconds
python3 ../oss-fuzz/infra/helper.py run_fuzzer --external $PWD fuzz_normalize_path -- -max_total_time=10

About

WASI syscall API built atop libuv

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Sep 3, 2025
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