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 `wasi:clocks/wall-clock` to use the `clock` specified.
353    ///
354    /// By default the host's wall clock is used.
355    pub fn wall_clock(&mut self, clock: impl HostWallClock + 'static) -> &mut Self {
356        self.clocks.wall_clock = Box::new(clock);
357        self
358    }
359
360    /// Configures `wasi:clocks/monotonic-clock` to use the `clock` specified.
361    ///
362    /// By default the host's monotonic clock is used.
363    pub fn monotonic_clock(&mut self, clock: impl HostMonotonicClock + 'static) -> &mut Self {
364        self.clocks.monotonic_clock = Box::new(clock);
365        self
366    }
367
368    /// Allow all network addresses accessible to the host.
369    ///
370    /// This method will inherit all network addresses meaning that any address
371    /// can be bound by the guest or connected to by the guest using any
372    /// protocol.
373    ///
374    /// See also [`WasiCtxBuilder::socket_addr_check`].
375    pub fn inherit_network(&mut self) -> &mut Self {
376        self.socket_addr_check(|_, _| Box::pin(async { true }))
377    }
378
379    /// A check that will be called for each socket address that is used.
380    ///
381    /// Returning `true` will permit socket connections to the `SocketAddr`,
382    /// while returning `false` will reject the connection.
383    pub fn socket_addr_check<F>(&mut self, check: F) -> &mut Self
384    where
385        F: Fn(SocketAddr, SocketAddrUse) -> Pin<Box<dyn Future<Output = bool> + Send + Sync>>
386            + Send
387            + Sync
388            + 'static,
389    {
390        self.sockets.socket_addr_check = SocketAddrCheck::new(check);
391        self
392    }
393
394    /// Allow usage of `wasi:sockets/ip-name-lookup`
395    ///
396    /// By default this is disabled.
397    pub fn allow_ip_name_lookup(&mut self, enable: bool) -> &mut Self {
398        self.sockets.allowed_network_uses.ip_name_lookup = enable;
399        self
400    }
401
402    /// Allow usage of UDP.
403    ///
404    /// This is enabled by default, but can be disabled if UDP should be blanket
405    /// disabled.
406    pub fn allow_udp(&mut self, enable: bool) -> &mut Self {
407        self.sockets.allowed_network_uses.udp = enable;
408        self
409    }
410
411    /// Allow usage of TCP
412    ///
413    /// This is enabled by default, but can be disabled if TCP should be blanket
414    /// disabled.
415    pub fn allow_tcp(&mut self, enable: bool) -> &mut Self {
416        self.sockets.allowed_network_uses.tcp = enable;
417        self
418    }
419
420    /// Uses the configured context so far to construct the final [`WasiCtx`].
421    ///
422    /// Note that each `WasiCtxBuilder` can only be used to "build" once, and
423    /// calling this method twice will panic.
424    ///
425    /// # Panics
426    ///
427    /// Panics if this method is called twice. Each [`WasiCtxBuilder`] can be
428    /// used to create only a single [`WasiCtx`]. Repeated usage of this method
429    /// is not allowed and should use a second builder instead.
430    pub fn build(&mut self) -> WasiCtx {
431        assert!(!self.built);
432
433        let Self {
434            cli,
435            clocks,
436            filesystem,
437            random,
438            sockets,
439            built: _,
440        } = mem::replace(self, Self::new());
441        self.built = true;
442
443        WasiCtx {
444            cli,
445            clocks,
446            filesystem,
447            random,
448            sockets,
449        }
450    }
451    /// Builds a WASIp1 context instead of a [`WasiCtx`].
452    ///
453    /// This method is the same as [`build`](WasiCtxBuilder::build) but it
454    /// creates a [`WasiP1Ctx`] instead. This is intended for use with the
455    /// [`p1`] module of this crate
456    ///
457    /// [`WasiP1Ctx`]: crate::p1::WasiP1Ctx
458    /// [`p1`]: crate::p1
459    ///
460    /// # Panics
461    ///
462    /// Panics if this method is called twice. Each [`WasiCtxBuilder`] can be
463    /// used to create only a single [`WasiCtx`] or [`WasiP1Ctx`]. Repeated
464    /// usage of this method is not allowed and should use a second builder
465    /// instead.
466    #[cfg(feature = "p1")]
467    pub fn build_p1(&mut self) -> crate::p1::WasiP1Ctx {
468        let wasi = self.build();
469        crate::p1::WasiP1Ctx::new(wasi)
470    }
471}
472
473/// Per-[`Store`] state which holds state necessary to implement WASI from this
474/// crate.
475///
476/// This structure is created through [`WasiCtxBuilder`] and is stored within
477/// the `T` of [`Store<T>`][`Store`]. Access to the structure is provided
478/// through the [`WasiView`](crate::WasiView) trait as an implementation on `T`.
479///
480/// Note that this structure itself does not have any accessors, it's here for
481/// internal use within the `wasmtime-wasi` crate's implementation of
482/// bindgen-generated traits.
483///
484/// [`Store`]: wasmtime::Store
485///
486/// # Example
487///
488/// ```
489/// use wasmtime_wasi::{ResourceTable, WasiCtx, WasiCtxView, WasiView, WasiCtxBuilder};
490///
491/// struct MyState {
492///     ctx: WasiCtx,
493///     table: ResourceTable,
494/// }
495///
496/// impl WasiView for MyState {
497///     fn ctx(&mut self) -> WasiCtxView<'_> {
498///         WasiCtxView { ctx: &mut self.ctx, table: &mut self.table }
499///     }
500/// }
501///
502/// impl MyState {
503///     fn new() -> MyState {
504///         let mut wasi = WasiCtxBuilder::new();
505///         wasi.arg("./foo.wasm");
506///         wasi.arg("--help");
507///         wasi.env("FOO", "bar");
508///
509///         MyState {
510///             ctx: wasi.build(),
511///             table: ResourceTable::new(),
512///         }
513///     }
514/// }
515/// ```
516#[derive(Default)]
517pub struct WasiCtx {
518    pub(crate) cli: WasiCliCtx,
519    pub(crate) clocks: WasiClocksCtx,
520    pub(crate) filesystem: WasiFilesystemCtx,
521    pub(crate) random: WasiRandomCtx,
522    pub(crate) sockets: WasiSocketsCtx,
523}
524
525impl WasiCtx {
526    /// Convenience function for calling [`WasiCtxBuilder::new`].
527    pub fn builder() -> WasiCtxBuilder {
528        WasiCtxBuilder::new()
529    }
530
531    /// Returns access to the underlying [`WasiRandomCtx`].
532    pub fn random(&mut self) -> &mut WasiRandomCtx {
533        &mut self.random
534    }
535
536    /// Returns access to the underlying [`WasiClocksCtx`].
537    pub fn clocks(&mut self) -> &mut WasiClocksCtx {
538        &mut self.clocks
539    }
540
541    /// Returns access to the underlying [`WasiFilesystemCtx`].
542    pub fn filesystem(&mut self) -> &mut WasiFilesystemCtx {
543        &mut self.filesystem
544    }
545
546    /// Returns access to the underlying [`WasiCliCtx`].
547    pub fn cli(&mut self) -> &mut WasiCliCtx {
548        &mut self.cli
549    }
550
551    /// Returns access to the underlying [`WasiSocketsCtx`].
552    pub fn sockets(&mut self) -> &mut WasiSocketsCtx {
553        &mut self.sockets
554    }
555}
wasmtime_wasi/ctx.rs

wasmtime_wasi/
ctx.rs
