implement randomness

crates/wasi-c2/TEST_FAILURES

@@ -1,6 +1,4 @@
 
-wasi_tests::big_random_buf
-    - no randomness yet
 wasi_tests::clock_time_get
     - no clocks yet
 wasi_tests::dangling_symlink

crates/wasi-c2/src/ctx.rs

@@ -1,5 +1,6 @@
 use crate::dir::{DirCaps, DirEntry, WasiDir};
 use crate::file::{FileCaps, FileEntry, WasiFile};
+use crate::random::WasiRandom;
 use crate::string_array::{StringArray, StringArrayError};
 use crate::table::Table;
 use crate::Error;
@@ -10,6 +11,7 @@ use std::rc::Rc;
 pub struct WasiCtx {
     pub(crate) args: StringArray,
     pub(crate) env: StringArray,
+    pub(crate) random: Box<dyn WasiRandom>,
     table: Rc<RefCell<Table>>,
 }
 
@@ -22,6 +24,7 @@ impl WasiCtx {
         WasiCtx {
             args: StringArray::new(),
             env: StringArray::new(),
+            random: Box::new(crate::random::GetRandom),
             table: Rc::new(RefCell::new(Table::new())),
         }
     }
@@ -110,4 +113,9 @@ impl WasiCtxBuilder {
         )))?;
         Ok(self)
     }
+
+    pub fn random(&mut self, random: Box<dyn WasiRandom>) -> &mut Self {
+        self.0.random = random;
+        self
+    }
 }

crates/wasi-c2/src/lib.rs

@@ -4,6 +4,7 @@ mod ctx;
 mod dir;
 mod error;
 mod file;
+pub mod random;
 pub mod snapshots;
 pub mod stdio;
 mod string_array;

crates/wasi-c2/src/random.rs

@@ -0,0 +1,37 @@
+use crate::Error;
+use std::cell::RefCell;
+
+pub trait WasiRandom {
+    fn get(&self, buf: &mut [u8]) -> Result<(), Error>;
+}
+
+pub struct GetRandom;
+
+impl WasiRandom for GetRandom {
+    fn get(&self, buf: &mut [u8]) -> Result<(), Error> {
+        getrandom::getrandom(buf)?;
+        Ok(())
+    }
+}
+
+pub struct Deterministic {
+    sequence: RefCell<std::iter::Cycle<std::vec::IntoIter<u8>>>,
+}
+
+impl Deterministic {
+    pub fn new(bytes: Vec<u8>) -> Self {
+        Deterministic {
+            sequence: RefCell::new(bytes.into_iter().cycle()),
+        }
+    }
+}
+
+impl WasiRandom for Deterministic {
+    fn get(&self, buf: &mut [u8]) -> Result<(), Error> {
+        let mut s = self.sequence.borrow_mut();
+        for b in buf.iter_mut() {
+            *b = s.next().expect("infinite sequence");
+        }
+        Ok(())
+    }
+}

crates/wasi-c2/src/snapshots/preview_1.rs

@@ -6,7 +6,7 @@ use fs_set_times::SystemTimeSpec;
 use std::cell::{Ref, RefMut};
 use std::convert::{TryFrom, TryInto};
 use std::io::{IoSlice, IoSliceMut};
-use std::ops::Deref;
+use std::ops::{Deref, DerefMut};
 use tracing::debug;
 use wiggle::GuestPtr;
 
@@ -801,7 +801,9 @@ impl<'a> wasi_snapshot_preview1::WasiSnapshotPreview1 for WasiCtx {
     }
 
     fn random_get(&self, buf: &GuestPtr<u8>, buf_len: types::Size) -> Result<(), Error> {
-        unimplemented!()
+        let mut buf = buf.as_array(buf_len).as_slice_mut()?;
+        self.random.get(buf.deref_mut())?;
+        Ok(())
     }
 
     fn sock_recv(