Allow to disable clocks in WasiCtx (#6007)

Takes the approach described in #6004, but also creates a wrapper for the monotonic time that encapsulates the `creation_time` field as well, since they logically belong and are always used together.

This makes it easier to configure `WasiCtx` with custom clocks as well as disable them for security or determinism reasons.

Closes #6004.

crates/wasi-common/cap-std-sync/src/clocks.rs

@@ -35,13 +35,7 @@ impl WasiMonotonicClock for MonotonicClock {
 }
 
 pub fn clocks_ctx() -> WasiClocks {
-    let system = Box::new(SystemClock::new(ambient_authority()));
-    let monotonic = cap_std::time::MonotonicClock::new(ambient_authority());
-    let creation_time = monotonic.now();
-    let monotonic = Box::new(MonotonicClock(monotonic));
-    WasiClocks {
-        system,
-        monotonic,
-        creation_time,
-    }
+    WasiClocks::new()
+        .with_system(SystemClock::new(ambient_authority()))
+        .with_monotonic(MonotonicClock::new(ambient_authority()))
 }

crates/wasi-common/src/clocks.rs

@@ -1,3 +1,4 @@
+use crate::{Error, ErrorExt};
 use cap_std::time::{Duration, Instant, SystemTime};
 
 pub enum SystemTimeSpec {
@@ -15,8 +16,52 @@ pub trait WasiMonotonicClock: Send + Sync {
     fn now(&self, precision: Duration) -> Instant;
 }
 
-pub struct WasiClocks {
-    pub system: Box<dyn WasiSystemClock>,
-    pub monotonic: Box<dyn WasiMonotonicClock>,
+pub struct WasiMonotonicOffsetClock {
     pub creation_time: cap_std::time::Instant,
+    pub abs_clock: Box<dyn WasiMonotonicClock>,
+}
+
+impl WasiMonotonicOffsetClock {
+    pub fn new(clock: impl 'static + WasiMonotonicClock) -> Self {
+        Self {
+            creation_time: clock.now(clock.resolution()),
+            abs_clock: Box::new(clock),
+        }
+    }
+}
+
+pub struct WasiClocks {
+    pub system: Option<Box<dyn WasiSystemClock>>,
+    pub monotonic: Option<WasiMonotonicOffsetClock>,
+}
+
+impl WasiClocks {
+    pub fn new() -> Self {
+        Self {
+            system: None,
+            monotonic: None,
+        }
+    }
+
+    pub fn with_system(mut self, clock: impl 'static + WasiSystemClock) -> Self {
+        self.system = Some(Box::new(clock));
+        self
+    }
+
+    pub fn with_monotonic(mut self, clock: impl 'static + WasiMonotonicClock) -> Self {
+        self.monotonic = Some(WasiMonotonicOffsetClock::new(clock));
+        self
+    }
+
+    pub fn system(&self) -> Result<&dyn WasiSystemClock, Error> {
+        self.system
+            .as_deref()
+            .ok_or_else(|| Error::badf().context("system clock is not supported"))
+    }
+
+    pub fn monotonic(&self) -> Result<&WasiMonotonicOffsetClock, Error> {
+        self.monotonic
+            .as_ref()
+            .ok_or_else(|| Error::badf().context("monotonic clock is not supported"))
+    }
 }

crates/wasi-common/src/snapshots/preview_0.rs

@@ -959,25 +959,22 @@ impl wasi_unstable::WasiUnstable for WasiCtx {
             match sub.u {
                 types::SubscriptionU::Clock(clocksub) => match clocksub.id {
                     types::Clockid::Monotonic => {
-                        let clock = self.clocks.monotonic.deref();
+                        let clock = self.clocks.monotonic()?;
                         let precision = Duration::from_nanos(clocksub.precision);
                         let duration = Duration::from_nanos(clocksub.timeout);
-                        let deadline = if clocksub
+                        let start = if clocksub
                             .flags
                             .contains(types::Subclockflags::SUBSCRIPTION_CLOCK_ABSTIME)
                         {
-                            self.clocks
-                                .creation_time
-                                .checked_add(duration)
-                                .ok_or_else(|| Error::overflow().context("deadline"))?
+                            clock.creation_time
                         } else {
-                            clock
-                                .now(precision)
-                                .checked_add(duration)
-                                .ok_or_else(|| Error::overflow().context("deadline"))?
+                            clock.abs_clock.now(precision)
                         };
+                        let deadline = start
+                            .checked_add(duration)
+                            .ok_or_else(|| Error::overflow().context("deadline"))?;
                         poll.subscribe_monotonic_clock(
-                            clock,
+                            &*clock.abs_clock,
                             deadline,
                             precision,
                             sub.userdata.into(),

crates/wasi-common/src/snapshots/preview_1.rs

@@ -68,8 +68,8 @@ impl wasi_snapshot_preview1::WasiSnapshotPreview1 for WasiCtx {
 
     async fn clock_res_get(&mut self, id: types::Clockid) -> Result<types::Timestamp, Error> {
         let resolution = match id {
-            types::Clockid::Realtime => Ok(self.clocks.system.resolution()),
-            types::Clockid::Monotonic => Ok(self.clocks.monotonic.resolution()),
+            types::Clockid::Realtime => Ok(self.clocks.system()?.resolution()),
+            types::Clockid::Monotonic => Ok(self.clocks.monotonic()?.abs_clock.resolution()),
             types::Clockid::ProcessCputimeId | types::Clockid::ThreadCputimeId => {
                 Err(Error::badf().context("process and thread clocks are not supported"))
             }
@@ -85,7 +85,7 @@ impl wasi_snapshot_preview1::WasiSnapshotPreview1 for WasiCtx {
         let precision = Duration::from_nanos(precision);
         match id {
             types::Clockid::Realtime => {
-                let now = self.clocks.system.now(precision).into_std();
+                let now = self.clocks.system()?.now(precision).into_std();
                 let d = now
                     .duration_since(std::time::SystemTime::UNIX_EPOCH)
                     .map_err(|_| {
@@ -94,8 +94,9 @@ impl wasi_snapshot_preview1::WasiSnapshotPreview1 for WasiCtx {
                 Ok(d.as_nanos().try_into()?)
             }
             types::Clockid::Monotonic => {
-                let now = self.clocks.monotonic.now(precision);
-                let d = now.duration_since(self.clocks.creation_time);
+                let clock = self.clocks.monotonic()?;
+                let now = clock.abs_clock.now(precision);
+                let d = now.duration_since(clock.creation_time);
                 Ok(d.as_nanos().try_into()?)
             }
             types::Clockid::ProcessCputimeId | types::Clockid::ThreadCputimeId => {
@@ -909,25 +910,22 @@ impl wasi_snapshot_preview1::WasiSnapshotPreview1 for WasiCtx {
             match sub.u {
                 types::SubscriptionU::Clock(clocksub) => match clocksub.id {
                     types::Clockid::Monotonic => {
-                        let clock = self.clocks.monotonic.deref();
+                        let clock = self.clocks.monotonic()?;
                         let precision = Duration::from_nanos(clocksub.precision);
                         let duration = Duration::from_nanos(clocksub.timeout);
-                        let deadline = if clocksub
+                        let start = if clocksub
                             .flags
                             .contains(types::Subclockflags::SUBSCRIPTION_CLOCK_ABSTIME)
                         {
-                            self.clocks
-                                .creation_time
-                                .checked_add(duration)
-                                .ok_or_else(|| Error::overflow().context("deadline"))?
+                            clock.creation_time
                         } else {
-                            clock
-                                .now(precision)
-                                .checked_add(duration)
-                                .ok_or_else(|| Error::overflow().context("deadline"))?
+                            clock.abs_clock.now(precision)
                         };
+                        let deadline = start
+                            .checked_add(duration)
+                            .ok_or_else(|| Error::overflow().context("deadline"))?;
                         poll.subscribe_monotonic_clock(
-                            clock,
+                            &*clock.abs_clock,
                             deadline,
                             precision,
                             sub.userdata.into(),
@@ -939,7 +937,7 @@ impl wasi_snapshot_preview1::WasiSnapshotPreview1 for WasiCtx {
                         // on threads waiting in these functions. MONOTONIC should always have
                         // resolution at least as good as REALTIME, so we can translate a
                         // non-absolute `REALTIME` request into a `MONOTONIC` request.
-                        let clock = self.clocks.monotonic.deref();
+                        let clock = self.clocks.monotonic()?;
                         let precision = Duration::from_nanos(clocksub.precision);
                         let duration = Duration::from_nanos(clocksub.timeout);
                         let deadline = if clocksub
@@ -949,12 +947,13 @@ impl wasi_snapshot_preview1::WasiSnapshotPreview1 for WasiCtx {
                             return Err(Error::not_supported());
                         } else {
                             clock
+                                .abs_clock
                                 .now(precision)
                                 .checked_add(duration)
                                 .ok_or_else(|| Error::overflow().context("deadline"))?
                         };
                         poll.subscribe_monotonic_clock(
-                            clock,
+                            &*clock.abs_clock,
                             deadline,
                             precision,
                             sub.userdata.into(),

crates/wasi-common/tokio/tests/poll_oneoff.rs

@@ -38,14 +38,14 @@ async fn empty_file_readable() -> Result<(), Error> {
     let mut poll = Poll::new();
     poll.subscribe_read(&mut *f, Userdata::from(123));
     // Timeout bounds time in poll_oneoff
+    let monotonic = &*clocks.monotonic()?.abs_clock;
     poll.subscribe_monotonic_clock(
-        &*clocks.monotonic,
-        clocks
-            .monotonic
-            .now(clocks.monotonic.resolution())
+        monotonic,
+        monotonic
+            .now(monotonic.resolution())
             .checked_add(TIMEOUT)
             .unwrap(),
-        clocks.monotonic.resolution(),
+        monotonic.resolution(),
         Userdata::from(0),
     );
     poll_oneoff(&mut poll).await?;
@@ -81,14 +81,14 @@ async fn empty_file_writable() -> Result<(), Error> {
     let mut poll = Poll::new();
     poll.subscribe_write(&mut *writable_f, Userdata::from(123));
     // Timeout bounds time in poll_oneoff
+    let monotonic = &*clocks.monotonic()?.abs_clock;
     poll.subscribe_monotonic_clock(
-        &*clocks.monotonic,
-        clocks
-            .monotonic
-            .now(clocks.monotonic.resolution())
+        monotonic,
+        monotonic
+            .now(monotonic.resolution())
             .checked_add(TIMEOUT)
             .unwrap(),
-        clocks.monotonic.resolution(),
+        monotonic.resolution(),
         Userdata::from(0),
     );
     poll_oneoff(&mut poll).await?;
@@ -110,9 +110,9 @@ async fn empty_file_writable() -> Result<(), Error> {
 async fn stdio_readable() -> Result<(), Error> {
     let clocks = clocks_ctx();
 
-    let deadline = clocks
-        .monotonic
-        .now(clocks.monotonic.resolution())
+    let monotonic = &*clocks.monotonic()?.abs_clock;
+    let deadline = monotonic
+        .now(monotonic.resolution())
         .checked_add(TIMEOUT)
         .unwrap();
 
@@ -133,10 +133,11 @@ async fn stdio_readable() -> Result<(), Error> {
             poll.subscribe_write(&mut **file, Userdata::from(*ix));
         }
         // Timeout bounds time in poll_oneoff
+        let monotonic = &*clocks.monotonic()?.abs_clock;
         poll.subscribe_monotonic_clock(
-            &*clocks.monotonic,
+            monotonic,
             deadline,
-            clocks.monotonic.resolution(),
+            monotonic.resolution(),
             Userdata::from(999),
         );
         poll_oneoff(&mut poll).await?;