wasmtime_wasi/
ctx.rs

1use crate::cli::{StdinStream, StdoutStream, WasiCliCtx};
2use crate::clocks::{HostMonotonicClock, HostWallClock, WasiClocksCtx};
3use crate::filesystem::{Dir, WasiFilesystemCtx};
4use crate::random::WasiRandomCtx;
5use crate::sockets::{SocketAddrCheck, SocketAddrUse, WasiSocketsCtx};
6use crate::{DirPerms, FilePerms, OpenMode};
7use anyhow::Result;
8use cap_rand::RngCore;
9use cap_std::ambient_authority;
10use std::future::Future;
11use std::mem;
12use std::net::SocketAddr;
13use std::path::Path;
14use std::pin::Pin;
15use tokio::io::{stderr, stdin, stdout};
16
17/// Builder-style structure used to create a [`WasiCtx`].
18///
19/// This type is used to create a [`WasiCtx`] that is considered per-[`Store`]
20/// state. The [`build`][WasiCtxBuilder::build] method is used to finish the
21/// building process and produce a finalized [`WasiCtx`].
22///
23/// # Examples
24///
25/// ```
26/// use wasmtime_wasi::WasiCtx;
27///
28/// let mut wasi = WasiCtx::builder();
29/// wasi.arg("./foo.wasm");
30/// wasi.arg("--help");
31/// wasi.env("FOO", "bar");
32///
33/// let wasi: WasiCtx = wasi.build();
34/// ```
35///
36/// [`Store`]: wasmtime::Store
37#[derive(Default)]
38pub struct WasiCtxBuilder {
39    cli: WasiCliCtx,
40    clocks: WasiClocksCtx,
41    filesystem: WasiFilesystemCtx,
42    random: WasiRandomCtx,
43    sockets: WasiSocketsCtx,
44    built: bool,
45}
46
47impl WasiCtxBuilder {
48    /// Creates a builder for a new context with default parameters set.
49    ///
50    /// The current defaults are:
51    ///
52    /// * stdin is closed
53    /// * stdout and stderr eat all input and it doesn't go anywhere
54    /// * no env vars
55    /// * no arguments
56    /// * no preopens
57    /// * clocks use the host implementation of wall/monotonic clocks
58    /// * RNGs are all initialized with random state and suitable generator
59    ///   quality to satisfy the requirements of WASI APIs.
60    /// * TCP/UDP are allowed but all addresses are denied by default.
61    /// * `wasi:sockets/ip-name-lookup` is denied by default.
62    ///
63    /// These defaults can all be updated via the various builder configuration
64    /// methods below.
65    pub fn new() -> Self {
66        Self::default()
67    }
68
69    /// Provides a custom implementation of stdin to use.
70    ///
71    /// By default stdin is closed but an example of using the host's native
72    /// stdin looks like:
73    ///
74    /// ```
75    /// use wasmtime_wasi::WasiCtx;
76    /// use wasmtime_wasi::cli::stdin;
77    ///
78    /// let mut wasi = WasiCtx::builder();
79    /// wasi.stdin(stdin());
80    /// ```
81    ///
82    /// Note that inheriting the process's stdin can also be done through
83    /// [`inherit_stdin`](WasiCtxBuilder::inherit_stdin).
84    pub fn stdin(&mut self, stdin: impl StdinStream + 'static) -> &mut Self {
85        self.cli.stdin = Box::new(stdin);
86        self
87    }
88
89    /// Same as [`stdin`](WasiCtxBuilder::stdin), but for stdout.
90    pub fn stdout(&mut self, stdout: impl StdoutStream + 'static) -> &mut Self {
91        self.cli.stdout = Box::new(stdout);
92        self
93    }
94
95    /// Same as [`stdin`](WasiCtxBuilder::stdin), but for stderr.
96    pub fn stderr(&mut self, stderr: impl StdoutStream + 'static) -> &mut Self {
97        self.cli.stderr = Box::new(stderr);
98        self
99    }
100
101    /// Configures this context's stdin stream to read the host process's
102    /// stdin.
103    ///
104    /// Note that concurrent reads of stdin can produce surprising results so
105    /// when using this it's typically best to have a single wasm instance in
106    /// the process using this.
107    pub fn inherit_stdin(&mut self) -> &mut Self {
108        self.stdin(stdin())
109    }
110
111    /// Configures this context's stdout stream to write to the host process's
112    /// stdout.
113    ///
114    /// Note that unlike [`inherit_stdin`](WasiCtxBuilder::inherit_stdin)
115    /// multiple instances printing to stdout works well.
116    pub fn inherit_stdout(&mut self) -> &mut Self {
117        self.stdout(stdout())
118    }
119
120    /// Configures this context's stderr stream to write to the host process's
121    /// stderr.
122    ///
123    /// Note that unlike [`inherit_stdin`](WasiCtxBuilder::inherit_stdin)
124    /// multiple instances printing to stderr works well.
125    pub fn inherit_stderr(&mut self) -> &mut Self {
126        self.stderr(stderr())
127    }
128
129    /// Configures all of stdin, stdout, and stderr to be inherited from the
130    /// host process.
131    ///
132    /// See [`inherit_stdin`](WasiCtxBuilder::inherit_stdin) for some rationale
133    /// on why this should only be done in situations of
134    /// one-instance-per-process.
135    pub fn inherit_stdio(&mut self) -> &mut Self {
136        self.inherit_stdin().inherit_stdout().inherit_stderr()
137    }
138
139    /// Configures whether or not blocking operations made through this
140    /// `WasiCtx` are allowed to block the current thread.
141    ///
142    /// WASI is currently implemented on top of the Rust
143    /// [Tokio](https://tokio.rs/) library. While most WASI APIs are
144    /// non-blocking some are instead blocking from the perspective of
145    /// WebAssembly. For example opening a file is a blocking operation with
146    /// respect to WebAssembly but it's implemented as an asynchronous operation
147    /// on the host. This is currently done with Tokio's
148    /// [`spawn_blocking`](https://docs.rs/tokio/latest/tokio/task/fn.spawn_blocking.html).
149    ///
150    /// When WebAssembly is used in a synchronous context, for example when
151    /// [`Config::async_support`] is disabled, then this asynchronous operation
152    /// is quickly turned back into a synchronous operation with a `block_on` in
153    /// Rust. This switching back-and-forth between a blocking a non-blocking
154    /// context can have overhead, and this option exists to help alleviate this
155    /// overhead.
156    ///
157    /// This option indicates that for WASI functions that are blocking from the
158    /// perspective of WebAssembly it's ok to block the native thread as well.
159    /// This means that this back-and-forth between async and sync won't happen
160    /// and instead blocking operations are performed on-thread (such as opening
161    /// a file). This can improve the performance of WASI operations when async
162    /// support is disabled.
163    ///
164    /// [`Config::async_support`]: https://docs.rs/wasmtime/latest/wasmtime/struct.Config.html#method.async_support
165    pub fn allow_blocking_current_thread(&mut self, enable: bool) -> &mut Self {
166        self.filesystem.allow_blocking_current_thread = enable;
167        self
168    }
169
170    /// Appends multiple environment variables at once for this builder.
171    ///
172    /// All environment variables are appended to the list of environment
173    /// variables that this builder will configure.
174    ///
175    /// At this time environment variables are not deduplicated and if the same
176    /// key is set twice then the guest will see two entries for the same key.
177    ///
178    /// # Examples
179    ///
180    /// ```
181    /// use wasmtime_wasi::WasiCtxBuilder;
182    ///
183    /// let mut wasi = WasiCtxBuilder::new();
184    /// wasi.envs(&[
185    ///     ("FOO", "bar"),
186    ///     ("HOME", "/somewhere"),
187    /// ]);
188    /// ```
189    pub fn envs(&mut self, env: &[(impl AsRef<str>, impl AsRef<str>)]) -> &mut Self {
190        self.cli.environment.extend(
191            env.iter()
192                .map(|(k, v)| (k.as_ref().to_owned(), v.as_ref().to_owned())),
193        );
194        self
195    }
196
197    /// Appends a single environment variable for this builder.
198    ///
199    /// At this time environment variables are not deduplicated and if the same
200    /// key is set twice then the guest will see two entries for the same key.
201    ///
202    /// # Examples
203    ///
204    /// ```
205    /// use wasmtime_wasi::WasiCtxBuilder;
206    ///
207    /// let mut wasi = WasiCtxBuilder::new();
208    /// wasi.env("FOO", "bar");
209    /// ```
210    pub fn env(&mut self, k: impl AsRef<str>, v: impl AsRef<str>) -> &mut Self {
211        self.cli
212            .environment
213            .push((k.as_ref().to_owned(), v.as_ref().to_owned()));
214        self
215    }
216
217    /// Configures all environment variables to be inherited from the calling
218    /// process into this configuration.
219    ///
220    /// This will use [`envs`](WasiCtxBuilder::envs) to append all host-defined
221    /// environment variables.
222    pub fn inherit_env(&mut self) -> &mut Self {
223        self.envs(&std::env::vars().collect::<Vec<(String, String)>>())
224    }
225
226    /// Appends a list of arguments to the argument array to pass to wasm.
227    pub fn args(&mut self, args: &[impl AsRef<str>]) -> &mut Self {
228        self.cli
229            .arguments
230            .extend(args.iter().map(|a| a.as_ref().to_owned()));
231        self
232    }
233
234    /// Appends a single argument to get passed to wasm.
235    pub fn arg(&mut self, arg: impl AsRef<str>) -> &mut Self {
236        self.cli.arguments.push(arg.as_ref().to_owned());
237        self
238    }
239
240    /// Appends all host process arguments to the list of arguments to get
241    /// passed to wasm.
242    pub fn inherit_args(&mut self) -> &mut Self {
243        self.args(&std::env::args().collect::<Vec<String>>())
244    }
245
246    /// Configures a "preopened directory" to be available to WebAssembly.
247    ///
248    /// By default WebAssembly does not have access to the filesystem because
249    /// there are no preopened directories. All filesystem operations, such as
250    /// opening a file, are done through a preexisting handle. This means that
251    /// to provide WebAssembly access to a directory it must be configured
252    /// through this API.
253    ///
254    /// WASI will also prevent access outside of files provided here. For
255    /// example `..` can't be used to traverse up from the `host_path` provided here
256    /// to the containing directory.
257    ///
258    /// * `host_path` - a path to a directory on the host to open and make
259    ///   accessible to WebAssembly. Note that the name of this directory in the
260    ///   guest is configured with `guest_path` below.
261    /// * `guest_path` - the name of the preopened directory from WebAssembly's
262    ///   perspective. Note that this does not need to match the host's name for
263    ///   the directory.
264    /// * `dir_perms` - this is the permissions that wasm will have to operate on
265    ///   `guest_path`. This can be used, for example, to provide readonly access to a
266    ///   directory.
267    /// * `file_perms` - similar to `dir_perms` but corresponds to the maximum set
268    ///   of permissions that can be used for any file in this directory.
269    ///
270    /// # Errors
271    ///
272    /// This method will return an error if `host_path` cannot be opened.
273    ///
274    /// # Examples
275    ///
276    /// ```
277    /// use wasmtime_wasi::WasiCtxBuilder;
278    /// use wasmtime_wasi::{DirPerms, FilePerms};
279    ///
280    /// # fn main() {}
281    /// # fn foo() -> wasmtime::Result<()> {
282    /// let mut wasi = WasiCtxBuilder::new();
283    ///
284    /// // Make `./host-directory` available in the guest as `.`
285    /// wasi.preopened_dir("./host-directory", ".", DirPerms::all(), FilePerms::all());
286    ///
287    /// // Make `./readonly` available in the guest as `./ro`
288    /// wasi.preopened_dir("./readonly", "./ro", DirPerms::READ, FilePerms::READ);
289    /// # Ok(())
290    /// # }
291    /// ```
292    pub fn preopened_dir(
293        &mut self,
294        host_path: impl AsRef<Path>,
295        guest_path: impl AsRef<str>,
296        dir_perms: DirPerms,
297        file_perms: FilePerms,
298    ) -> Result<&mut Self> {
299        let dir = cap_std::fs::Dir::open_ambient_dir(host_path.as_ref(), ambient_authority())?;
300        let mut open_mode = OpenMode::empty();
301        if dir_perms.contains(DirPerms::READ) {
302            open_mode |= OpenMode::READ;
303        }
304        if dir_perms.contains(DirPerms::MUTATE) {
305            open_mode |= OpenMode::WRITE;
306        }
307        self.filesystem.preopens.push((
308            Dir::new(
309                dir,
310                dir_perms,
311                file_perms,
312                open_mode,
313                self.filesystem.allow_blocking_current_thread,
314            ),
315            guest_path.as_ref().to_owned(),
316        ));
317        Ok(self)
318    }
319
320    /// Set the generator for the `wasi:random/random` number generator to the
321    /// custom generator specified.
322    ///
323    /// Note that contexts have a default RNG configured which is a suitable
324    /// generator for WASI and is configured with a random seed per-context.
325    ///
326    /// Guest code may rely on this random number generator to produce fresh
327    /// unpredictable random data in order to maintain its security invariants,
328    /// and ideally should use the insecure random API otherwise, so using any
329    /// prerecorded or otherwise predictable data may compromise security.
330    pub fn secure_random(&mut self, random: impl RngCore + Send + 'static) -> &mut Self {
331        self.random.random = Box::new(random);
332        self
333    }
334
335    /// Configures the generator for `wasi:random/insecure`.
336    ///
337    /// The `insecure_random` generator provided will be used for all randomness
338    /// requested by the `wasi:random/insecure` interface.
339    pub fn insecure_random(&mut self, insecure_random: impl RngCore + Send + 'static) -> &mut Self {
340        self.random.insecure_random = Box::new(insecure_random);
341        self
342    }
343
344    /// Configures the seed to be returned from `wasi:random/insecure-seed` to
345    /// the specified custom value.
346    ///
347    /// By default this number is randomly generated when a builder is created.
348    pub fn insecure_random_seed(&mut self, insecure_random_seed: u128) -> &mut Self {
349        self.random.insecure_random_seed = insecure_random_seed;
350        self
351    }
352
353    /// Configures `wasi:clocks/wall-clock` to use the `clock` specified.
354    ///
355    /// By default the host's wall clock is used.
356    pub fn wall_clock(&mut self, clock: impl HostWallClock + 'static) -> &mut Self {
357        self.clocks.wall_clock = Box::new(clock);
358        self
359    }
360
361    /// Configures `wasi:clocks/monotonic-clock` to use the `clock` specified.
362    ///
363    /// By default the host's monotonic clock is used.
364    pub fn monotonic_clock(&mut self, clock: impl HostMonotonicClock + 'static) -> &mut Self {
365        self.clocks.monotonic_clock = Box::new(clock);
366        self
367    }
368
369    /// Allow all network addresses accessible to the host.
370    ///
371    /// This method will inherit all network addresses meaning that any address
372    /// can be bound by the guest or connected to by the guest using any
373    /// protocol.
374    ///
375    /// See also [`WasiCtxBuilder::socket_addr_check`].
376    pub fn inherit_network(&mut self) -> &mut Self {
377        self.socket_addr_check(|_, _| Box::pin(async { true }))
378    }
379
380    /// A check that will be called for each socket address that is used.
381    ///
382    /// Returning `true` will permit socket connections to the `SocketAddr`,
383    /// while returning `false` will reject the connection.
384    pub fn socket_addr_check<F>(&mut self, check: F) -> &mut Self
385    where
386        F: Fn(SocketAddr, SocketAddrUse) -> Pin<Box<dyn Future<Output = bool> + Send + Sync>>
387            + Send
388            + Sync
389            + 'static,
390    {
391        self.sockets.socket_addr_check = SocketAddrCheck::new(check);
392        self
393    }
394
395    /// Allow usage of `wasi:sockets/ip-name-lookup`
396    ///
397    /// By default this is disabled.
398    pub fn allow_ip_name_lookup(&mut self, enable: bool) -> &mut Self {
399        self.sockets.allowed_network_uses.ip_name_lookup = enable;
400        self
401    }
402
403    /// Allow usage of UDP.
404    ///
405    /// This is enabled by default, but can be disabled if UDP should be blanket
406    /// disabled.
407    pub fn allow_udp(&mut self, enable: bool) -> &mut Self {
408        self.sockets.allowed_network_uses.udp = enable;
409        self
410    }
411
412    /// Allow usage of TCP
413    ///
414    /// This is enabled by default, but can be disabled if TCP should be blanket
415    /// disabled.
416    pub fn allow_tcp(&mut self, enable: bool) -> &mut Self {
417        self.sockets.allowed_network_uses.tcp = enable;
418        self
419    }
420
421    /// Uses the configured context so far to construct the final [`WasiCtx`].
422    ///
423    /// Note that each `WasiCtxBuilder` can only be used to "build" once, and
424    /// calling this method twice will panic.
425    ///
426    /// # Panics
427    ///
428    /// Panics if this method is called twice. Each [`WasiCtxBuilder`] can be
429    /// used to create only a single [`WasiCtx`]. Repeated usage of this method
430    /// is not allowed and should use a second builder instead.
431    pub fn build(&mut self) -> WasiCtx {
432        assert!(!self.built);
433
434        let Self {
435            cli,
436            clocks,
437            filesystem,
438            random,
439            sockets,
440            built: _,
441        } = mem::replace(self, Self::new());
442        self.built = true;
443
444        WasiCtx {
445            cli,
446            clocks,
447            filesystem,
448            random,
449            sockets,
450        }
451    }
452    /// Builds a WASIp1 context instead of a [`WasiCtx`].
453    ///
454    /// This method is the same as [`build`](WasiCtxBuilder::build) but it
455    /// creates a [`WasiP1Ctx`] instead. This is intended for use with the
456    /// [`p1`] module of this crate
457    ///
458    /// [`WasiP1Ctx`]: crate::p1::WasiP1Ctx
459    /// [`p1`]: crate::p1
460    ///
461    /// # Panics
462    ///
463    /// Panics if this method is called twice. Each [`WasiCtxBuilder`] can be
464    /// used to create only a single [`WasiCtx`] or [`WasiP1Ctx`]. Repeated
465    /// usage of this method is not allowed and should use a second builder
466    /// instead.
467    #[cfg(feature = "p1")]
468    pub fn build_p1(&mut self) -> crate::p1::WasiP1Ctx {
469        let wasi = self.build();
470        crate::p1::WasiP1Ctx::new(wasi)
471    }
472}
473
474/// Per-[`Store`] state which holds state necessary to implement WASI from this
475/// crate.
476///
477/// This structure is created through [`WasiCtxBuilder`] and is stored within
478/// the `T` of [`Store<T>`][`Store`]. Access to the structure is provided
479/// through the [`WasiView`](crate::WasiView) trait as an implementation on `T`.
480///
481/// Note that this structure itself does not have any accessors, it's here for
482/// internal use within the `wasmtime-wasi` crate's implementation of
483/// bindgen-generated traits.
484///
485/// [`Store`]: wasmtime::Store
486///
487/// # Example
488///
489/// ```
490/// use wasmtime_wasi::{ResourceTable, WasiCtx, WasiCtxView, WasiView, WasiCtxBuilder};
491///
492/// struct MyState {
493///     ctx: WasiCtx,
494///     table: ResourceTable,
495/// }
496///
497/// impl WasiView for MyState {
498///     fn ctx(&mut self) -> WasiCtxView<'_> {
499///         WasiCtxView { ctx: &mut self.ctx, table: &mut self.table }
500///     }
501/// }
502///
503/// impl MyState {
504///     fn new() -> MyState {
505///         let mut wasi = WasiCtxBuilder::new();
506///         wasi.arg("./foo.wasm");
507///         wasi.arg("--help");
508///         wasi.env("FOO", "bar");
509///
510///         MyState {
511///             ctx: wasi.build(),
512///             table: ResourceTable::new(),
513///         }
514///     }
515/// }
516/// ```
517#[derive(Default)]
518pub struct WasiCtx {
519    pub(crate) cli: WasiCliCtx,
520    pub(crate) clocks: WasiClocksCtx,
521    pub(crate) filesystem: WasiFilesystemCtx,
522    pub(crate) random: WasiRandomCtx,
523    pub(crate) sockets: WasiSocketsCtx,
524}
525
526impl WasiCtx {
527    /// Convenience function for calling [`WasiCtxBuilder::new`].
528    pub fn builder() -> WasiCtxBuilder {
529        WasiCtxBuilder::new()
530    }
531
532    /// Returns access to the underlying [`WasiRandomCtx`].
533    pub fn random(&mut self) -> &mut WasiRandomCtx {
534        &mut self.random
535    }
536
537    /// Returns access to the underlying [`WasiClocksCtx`].
538    pub fn clocks(&mut self) -> &mut WasiClocksCtx {
539        &mut self.clocks
540    }
541
542    /// Returns access to the underlying [`WasiFilesystemCtx`].
543    pub fn filesystem(&mut self) -> &mut WasiFilesystemCtx {
544        &mut self.filesystem
545    }
546
547    /// Returns access to the underlying [`WasiCliCtx`].
548    pub fn cli(&mut self) -> &mut WasiCliCtx {
549        &mut self.cli
550    }
551
552    /// Returns access to the underlying [`WasiSocketsCtx`].
553    pub fn sockets(&mut self) -> &mut WasiSocketsCtx {
554        &mut self.sockets
555    }
556}
wasmtime_wasi/ctx.rs

wasmtime_wasi/
ctx.rs
