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 cap_rand::RngCore;
8use cap_std::ambient_authority;
9use std::future::Future;
10use std::mem;
11use std::net::SocketAddr;
12use std::path::Path;
13use std::pin::Pin;
14use tokio::io::{stderr, stdin, stdout};
15use wasmtime::Result;
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 then this asynchronous
151    /// operation is quickly turned back into a synchronous operation with a
152    /// `block_on` in Rust. This switching back-and-forth between a blocking a
153    /// non-blocking context can have overhead, and this option exists to help
154    /// alleviate this overhead.
155    ///
156    /// This option indicates that for WASI functions that are blocking from the
157    /// perspective of WebAssembly it's ok to block the native thread as well.
158    /// This means that this back-and-forth between async and sync won't happen
159    /// and instead blocking operations are performed on-thread (such as opening
160    /// a file). This can improve the performance of WASI operations when async
161    /// support is disabled.
162    pub fn allow_blocking_current_thread(&mut self, enable: bool) -> &mut Self {
163        self.filesystem.allow_blocking_current_thread = enable;
164        self
165    }
166
167    /// Appends multiple environment variables at once for this builder.
168    ///
169    /// All environment variables are appended to the list of environment
170    /// variables that this builder will configure.
171    ///
172    /// At this time environment variables are not deduplicated and if the same
173    /// key is set twice then the guest will see two entries for the same key.
174    ///
175    /// # Examples
176    ///
177    /// ```
178    /// use wasmtime_wasi::WasiCtxBuilder;
179    ///
180    /// let mut wasi = WasiCtxBuilder::new();
181    /// wasi.envs(&[
182    ///     ("FOO", "bar"),
183    ///     ("HOME", "/somewhere"),
184    /// ]);
185    /// ```
186    pub fn envs(&mut self, env: &[(impl AsRef<str>, impl AsRef<str>)]) -> &mut Self {
187        self.cli.environment.extend(
188            env.iter()
189                .map(|(k, v)| (k.as_ref().to_owned(), v.as_ref().to_owned())),
190        );
191        self
192    }
193
194    /// Appends a single environment variable for this builder.
195    ///
196    /// At this time environment variables are not deduplicated and if the same
197    /// key is set twice then the guest will see two entries for the same key.
198    ///
199    /// # Examples
200    ///
201    /// ```
202    /// use wasmtime_wasi::WasiCtxBuilder;
203    ///
204    /// let mut wasi = WasiCtxBuilder::new();
205    /// wasi.env("FOO", "bar");
206    /// ```
207    pub fn env(&mut self, k: impl AsRef<str>, v: impl AsRef<str>) -> &mut Self {
208        self.cli
209            .environment
210            .push((k.as_ref().to_owned(), v.as_ref().to_owned()));
211        self
212    }
213
214    /// Configures all environment variables to be inherited from the calling
215    /// process into this configuration.
216    ///
217    /// This will use [`envs`](WasiCtxBuilder::envs) to append all host-defined
218    /// environment variables.
219    pub fn inherit_env(&mut self) -> &mut Self {
220        self.cli.environment.extend(std::env::vars());
221        self
222    }
223
224    /// Appends a list of arguments to the argument array to pass to wasm.
225    pub fn args(&mut self, args: &[impl AsRef<str>]) -> &mut Self {
226        self.cli
227            .arguments
228            .extend(args.iter().map(|a| a.as_ref().to_owned()));
229        self
230    }
231
232    /// Appends a single argument to get passed to wasm.
233    pub fn arg(&mut self, arg: impl AsRef<str>) -> &mut Self {
234        self.cli.arguments.push(arg.as_ref().to_owned());
235        self
236    }
237
238    /// Appends all host process arguments to the list of arguments to get
239    /// passed to wasm.
240    pub fn inherit_args(&mut self) -> &mut Self {
241        self.cli.arguments.extend(std::env::args());
242        self
243    }
244
245    /// Configures a "preopened directory" to be available to WebAssembly.
246    ///
247    /// By default WebAssembly does not have access to the filesystem because
248    /// there are no preopened directories. All filesystem operations, such as
249    /// opening a file, are done through a preexisting handle. This means that
250    /// to provide WebAssembly access to a directory it must be configured
251    /// through this API.
252    ///
253    /// WASI will also prevent access outside of files provided here. For
254    /// example `..` can't be used to traverse up from the `host_path` provided here
255    /// to the containing directory.
256    ///
257    /// * `host_path` - a path to a directory on the host to open and make
258    ///   accessible to WebAssembly. Note that the name of this directory in the
259    ///   guest is configured with `guest_path` below.
260    /// * `guest_path` - the name of the preopened directory from WebAssembly's
261    ///   perspective. Note that this does not need to match the host's name for
262    ///   the directory.
263    /// * `dir_perms` - this is the permissions that wasm will have to operate on
264    ///   `guest_path`. This can be used, for example, to provide readonly access to a
265    ///   directory.
266    /// * `file_perms` - similar to `dir_perms` but corresponds to the maximum set
267    ///   of permissions that can be used for any file in this directory.
268    ///
269    /// # Errors
270    ///
271    /// This method will return an error if `host_path` cannot be opened.
272    ///
273    /// # Examples
274    ///
275    /// ```
276    /// use wasmtime_wasi::WasiCtxBuilder;
277    /// use wasmtime_wasi::{DirPerms, FilePerms};
278    ///
279    /// # fn main() {}
280    /// # fn foo() -> wasmtime::Result<()> {
281    /// let mut wasi = WasiCtxBuilder::new();
282    ///
283    /// // Make `./host-directory` available in the guest as `.`
284    /// wasi.preopened_dir("./host-directory", ".", DirPerms::all(), FilePerms::all());
285    ///
286    /// // Make `./readonly` available in the guest as `./ro`
287    /// wasi.preopened_dir("./readonly", "./ro", DirPerms::READ, FilePerms::READ);
288    /// # Ok(())
289    /// # }
290    /// ```
291    pub fn preopened_dir(
292        &mut self,
293        host_path: impl AsRef<Path>,
294        guest_path: impl AsRef<str>,
295        dir_perms: DirPerms,
296        file_perms: FilePerms,
297    ) -> Result<&mut Self> {
298        let dir = cap_std::fs::Dir::open_ambient_dir(host_path.as_ref(), ambient_authority())?;
299        let mut open_mode = OpenMode::empty();
300        if dir_perms.contains(DirPerms::READ) {
301            open_mode |= OpenMode::READ;
302        }
303        if dir_perms.contains(DirPerms::MUTATE) {
304            open_mode |= OpenMode::WRITE;
305        }
306        self.filesystem.preopens.push((
307            Dir::new(
308                dir,
309                dir_perms,
310                file_perms,
311                open_mode,
312                self.filesystem.allow_blocking_current_thread,
313            ),
314            guest_path.as_ref().to_owned(),
315        ));
316        Ok(self)
317    }
318
319    /// Set the generator for the `wasi:random/random` number generator to the
320    /// custom generator specified.
321    ///
322    /// Note that contexts have a default RNG configured which is a suitable
323    /// generator for WASI and is configured with a random seed per-context.
324    ///
325    /// Guest code may rely on this random number generator to produce fresh
326    /// unpredictable random data in order to maintain its security invariants,
327    /// and ideally should use the insecure random API otherwise, so using any
328    /// prerecorded or otherwise predictable data may compromise security.
329    pub fn secure_random(&mut self, random: impl RngCore + Send + 'static) -> &mut Self {
330        self.random.random = Box::new(random);
331        self
332    }
333
334    /// Configures the generator for `wasi:random/insecure`.
335    ///
336    /// The `insecure_random` generator provided will be used for all randomness
337    /// requested by the `wasi:random/insecure` interface.
338    pub fn insecure_random(&mut self, insecure_random: impl RngCore + Send + 'static) -> &mut Self {
339        self.random.insecure_random = Box::new(insecure_random);
340        self
341    }
342
343    /// Configures the seed to be returned from `wasi:random/insecure-seed` to
344    /// the specified custom value.
345    ///
346    /// By default this number is randomly generated when a builder is created.
347    pub fn insecure_random_seed(&mut self, insecure_random_seed: u128) -> &mut Self {
348        self.random.insecure_random_seed = insecure_random_seed;
349        self
350    }
351
352    /// Configures the maximum len accepted by
353    /// `wasi:random/random.get-random-bytes` and
354    /// `wasi:random/insecure.get-insecure-random-bytes`. Calls with a len
355    /// larger than this limit will trap.
356    ///
357    /// Limited to 64M by default. This limit protects the host implementation
358    /// from memory exhaustion from untrusted guest input. A limit of `u64::MAX`
359    /// is equivalent to no limit, but note that this enables a guest to also
360    /// force the host to attempt an allocation of that size.
361    pub fn max_random_size(&mut self, max_size: u64) -> &mut Self {
362        self.random.max_size = max_size;
363        self
364    }
365
366    /// Configures `wasi:clocks/wall-clock` to use the `clock` specified.
367    ///
368    /// By default the host's wall clock is used.
369    pub fn wall_clock(&mut self, clock: impl HostWallClock + 'static) -> &mut Self {
370        self.clocks.wall_clock = Box::new(clock);
371        self
372    }
373
374    /// Configures `wasi:clocks/monotonic-clock` to use the `clock` specified.
375    ///
376    /// By default the host's monotonic clock is used.
377    pub fn monotonic_clock(&mut self, clock: impl HostMonotonicClock + 'static) -> &mut Self {
378        self.clocks.monotonic_clock = Box::new(clock);
379        self
380    }
381
382    /// Allow all network addresses accessible to the host.
383    ///
384    /// This method will inherit all network addresses meaning that any address
385    /// can be bound by the guest or connected to by the guest using any
386    /// protocol.
387    ///
388    /// See also [`WasiCtxBuilder::socket_addr_check`].
389    pub fn inherit_network(&mut self) -> &mut Self {
390        self.socket_addr_check(|_, _| Box::pin(async { true }))
391    }
392
393    /// A check that will be called for each socket address that is used.
394    ///
395    /// Returning `true` will permit socket connections to the `SocketAddr`,
396    /// while returning `false` will reject the connection.
397    pub fn socket_addr_check<F>(&mut self, check: F) -> &mut Self
398    where
399        F: Fn(SocketAddr, SocketAddrUse) -> Pin<Box<dyn Future<Output = bool> + Send + Sync>>
400            + Send
401            + Sync
402            + 'static,
403    {
404        self.sockets.socket_addr_check = SocketAddrCheck::new(check);
405        self
406    }
407
408    /// Allow usage of `wasi:sockets/ip-name-lookup`
409    ///
410    /// By default this is disabled.
411    pub fn allow_ip_name_lookup(&mut self, enable: bool) -> &mut Self {
412        self.sockets.allowed_network_uses.ip_name_lookup = enable;
413        self
414    }
415
416    /// Allow usage of UDP.
417    ///
418    /// This is enabled by default, but can be disabled if UDP should be blanket
419    /// disabled.
420    pub fn allow_udp(&mut self, enable: bool) -> &mut Self {
421        self.sockets.allowed_network_uses.udp = enable;
422        self
423    }
424
425    /// Allow usage of TCP
426    ///
427    /// This is enabled by default, but can be disabled if TCP should be blanket
428    /// disabled.
429    pub fn allow_tcp(&mut self, enable: bool) -> &mut Self {
430        self.sockets.allowed_network_uses.tcp = enable;
431        self
432    }
433
434    /// Uses the configured context so far to construct the final [`WasiCtx`].
435    ///
436    /// Note that each `WasiCtxBuilder` can only be used to "build" once, and
437    /// calling this method twice will panic.
438    ///
439    /// # Panics
440    ///
441    /// Panics if this method is called twice. Each [`WasiCtxBuilder`] can be
442    /// used to create only a single [`WasiCtx`]. Repeated usage of this method
443    /// is not allowed and should use a second builder instead.
444    pub fn build(&mut self) -> WasiCtx {
445        assert!(!self.built);
446
447        let Self {
448            cli,
449            clocks,
450            filesystem,
451            random,
452            sockets,
453            built: _,
454        } = mem::replace(self, Self::new());
455        self.built = true;
456
457        WasiCtx {
458            cli,
459            clocks,
460            filesystem,
461            random,
462            sockets,
463        }
464    }
465    /// Builds a WASIp1 context instead of a [`WasiCtx`].
466    ///
467    /// This method is the same as [`build`](WasiCtxBuilder::build) but it
468    /// creates a [`WasiP1Ctx`] instead. This is intended for use with the
469    /// [`p1`] module of this crate
470    ///
471    /// [`WasiP1Ctx`]: crate::p1::WasiP1Ctx
472    /// [`p1`]: crate::p1
473    ///
474    /// # Panics
475    ///
476    /// Panics if this method is called twice. Each [`WasiCtxBuilder`] can be
477    /// used to create only a single [`WasiCtx`] or [`WasiP1Ctx`]. Repeated
478    /// usage of this method is not allowed and should use a second builder
479    /// instead.
480    #[cfg(feature = "p1")]
481    pub fn build_p1(&mut self) -> crate::p1::WasiP1Ctx {
482        let wasi = self.build();
483        crate::p1::WasiP1Ctx::new(wasi)
484    }
485}
486
487/// Per-[`Store`] state which holds state necessary to implement WASI from this
488/// crate.
489///
490/// This structure is created through [`WasiCtxBuilder`] and is stored within
491/// the `T` of [`Store<T>`][`Store`]. Access to the structure is provided
492/// through the [`WasiView`](crate::WasiView) trait as an implementation on `T`.
493///
494/// Note that this structure itself does not have any accessors, it's here for
495/// internal use within the `wasmtime-wasi` crate's implementation of
496/// bindgen-generated traits.
497///
498/// [`Store`]: wasmtime::Store
499///
500/// # Example
501///
502/// ```
503/// use wasmtime_wasi::{ResourceTable, WasiCtx, WasiCtxView, WasiView, WasiCtxBuilder};
504///
505/// struct MyState {
506///     ctx: WasiCtx,
507///     table: ResourceTable,
508/// }
509///
510/// impl WasiView for MyState {
511///     fn ctx(&mut self) -> WasiCtxView<'_> {
512///         WasiCtxView { ctx: &mut self.ctx, table: &mut self.table }
513///     }
514/// }
515///
516/// impl MyState {
517///     fn new() -> MyState {
518///         let mut wasi = WasiCtxBuilder::new();
519///         wasi.arg("./foo.wasm");
520///         wasi.arg("--help");
521///         wasi.env("FOO", "bar");
522///
523///         MyState {
524///             ctx: wasi.build(),
525///             table: ResourceTable::new(),
526///         }
527///     }
528/// }
529/// ```
530#[derive(Default)]
531pub struct WasiCtx {
532    pub(crate) cli: WasiCliCtx,
533    pub(crate) clocks: WasiClocksCtx,
534    pub(crate) filesystem: WasiFilesystemCtx,
535    pub(crate) random: WasiRandomCtx,
536    pub(crate) sockets: WasiSocketsCtx,
537}
538
539impl WasiCtx {
540    /// Convenience function for calling [`WasiCtxBuilder::new`].
541    pub fn builder() -> WasiCtxBuilder {
542        WasiCtxBuilder::new()
543    }
544
545    /// Returns access to the underlying [`WasiRandomCtx`].
546    pub fn random(&mut self) -> &mut WasiRandomCtx {
547        &mut self.random
548    }
549
550    /// Returns access to the underlying [`WasiClocksCtx`].
551    pub fn clocks(&mut self) -> &mut WasiClocksCtx {
552        &mut self.clocks
553    }
554
555    /// Returns access to the underlying [`WasiFilesystemCtx`].
556    pub fn filesystem(&mut self) -> &mut WasiFilesystemCtx {
557        &mut self.filesystem
558    }
559
560    /// Returns access to the underlying [`WasiCliCtx`].
561    pub fn cli(&mut self) -> &mut WasiCliCtx {
562        &mut self.cli
563    }
564
565    /// Returns access to the underlying [`WasiSocketsCtx`].
566    pub fn sockets(&mut self) -> &mut WasiSocketsCtx {
567        &mut self.sockets
568    }
569}
wasmtime_wasi/ctx.rs

wasmtime_wasi/
ctx.rs
