Provide direct access to the underlying buffer (#91)
This allows zero-copy access to the linear memory.
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@ -48,7 +48,7 @@ impl ::std::ops::Deref for MemoryRef {
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///
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/// [`LINEAR_MEMORY_PAGE_SIZE`]: constant.LINEAR_MEMORY_PAGE_SIZE.html
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pub struct MemoryInstance {
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/// Memofy limits.
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/// Memory limits.
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limits: ResizableLimits,
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/// Linear memory buffer.
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buffer: RefCell<Vec<u8>>,
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@ -315,7 +315,7 @@ impl MemoryInstance {
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Ok(())
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}
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/// Fill memory region with a specified value.
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/// Fill the memory region with the specified value.
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///
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/// Semantically equivalent to `memset`.
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///
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@ -330,7 +330,7 @@ impl MemoryInstance {
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Ok(())
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}
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/// Fill specified memory region with zeroes.
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/// Fill the specified memory region with zeroes.
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///
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/// # Errors
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///
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@ -338,6 +338,35 @@ impl MemoryInstance {
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pub fn zero(&self, offset: usize, len: usize) -> Result<(), Error> {
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self.clear(offset, 0, len)
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}
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/// Provides direct access to the underlying memory buffer.
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///
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/// # Panics
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///
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/// Any call that requires write access to memory (such as [`set`], [`clear`], etc) made within
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/// the closure will panic. Proceed with caution.
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///
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/// [`set`]: #method.get
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/// [`clear`]: #method.set
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pub fn with_direct_access<R, F: FnOnce(&[u8]) -> R>(&self, f: F) -> R {
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let buf = self.buffer.borrow();
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f(&*buf)
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}
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/// Provides direct mutable access to the underlying memory buffer.
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///
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/// # Panics
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///
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/// Any calls that requires either read or write access to memory (such as [`get`], [`set`], [`copy`], etc) made
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/// within the closure will panic. Proceed with caution.
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///
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/// [`get`]: #method.get
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/// [`set`]: #method.set
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/// [`copy`]: #method.copy
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pub fn with_direct_access_mut<R, F: FnOnce(&mut [u8]) -> R>(&self, f: F) -> R {
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let mut buf = self.buffer.borrow_mut();
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f(&mut *buf)
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}
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}
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pub fn validate_memory(initial: Pages, maximum: Option<Pages>) -> Result<(), String> {
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@ -484,4 +513,27 @@ mod tests {
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assert_eq!(data, [17, 129]);
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}
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#[test]
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fn zero_copy() {
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let mem = MemoryInstance::alloc(Pages(1), None).unwrap();
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mem.with_direct_access_mut(|buf| {
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assert_eq!(buf.len(), 65536);
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buf[..10].copy_from_slice(&[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
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});
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mem.with_direct_access(|buf| {
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assert_eq!(buf.len(), 65536);
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assert_eq!(&buf[..10], &[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]);
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});
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}
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#[should_panic]
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#[test]
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fn zero_copy_panics_on_nested_access() {
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let mem = MemoryInstance::alloc(Pages(1), None).unwrap();
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let mem_inner = mem.clone();
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mem.with_direct_access(move |_| {
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let _ = mem_inner.set(0, &[11, 12, 13]);
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});
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}
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}
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