Add `bitcoin-io` -> `std` bridge

This adds a reverse of the previous commit however it does not add
convenience methods since user should generally prefer the macro
instead. I had a clever idea to add a convenience conversion trait but
that is blocked by Rust stabilizing overlapping *marker* trait impls.

io/src/bridge.rs

@@ -127,3 +127,130 @@ impl<T: std::io::Write> std::io::Write for FromStd<T> {
         self.0.write_all(buf)
     }
 }
+
+/// A bridging wrapper providing the std traits for types that already implement our traits.
+#[repr(transparent)]
+pub struct ToStd<T>(T);
+
+impl<T> ToStd<T> {
+    /// Wraps an IO type.
+    #[inline]
+    pub const fn new(inner: T) -> Self { Self(inner) }
+
+    /// Returns the wrapped value.
+    #[inline]
+    pub fn into_inner(self) -> T {
+        self.0
+    }
+
+    /// Returns a reference to the wrapped value.
+    #[inline]
+    pub fn inner(&self) -> &T {
+        &self.0
+    }
+
+    /// Returns a mutable reference to the wrapped value.
+    #[inline]
+    pub fn inner_mut(&mut self) -> &mut T {
+        &mut self.0
+    }
+
+    /// Wraps a mutable reference to IO type.
+    #[inline]
+    pub fn new_mut(inner: &mut T) -> &mut Self {
+        // SAFETY: the type is repr(transparent) and the lifetimes match
+        unsafe { &mut *(inner as *mut _ as *mut Self) }
+    }
+
+    /// Wraps a boxed IO type.
+    #[cfg(feature = "alloc")]
+    #[inline]
+    pub fn new_boxed(inner: Box<T>) -> Box<Self> {
+        // SAFETY: the type is repr(transparent) and the pointer is created from Box
+        unsafe { Box::from_raw(Box::into_raw(inner) as *mut Self) }
+    }
+}
+
+impl<T: super::Read> std::io::Read for ToStd<T> {
+    #[inline]
+    fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
+        self.0.read(buf).map_err(Into::into)
+    }
+
+    #[inline]
+    fn read_exact(&mut self, buf: &mut [u8]) -> std::io::Result<()> {
+        self.0.read_exact(buf).map_err(Into::into)
+    }
+}
+
+impl<T: super::BufRead> std::io::BufRead for ToStd<T> {
+    #[inline]
+    fn fill_buf(&mut self) -> std::io::Result<&[u8]> {
+        self.0.fill_buf().map_err(Into::into)
+    }
+
+    #[inline]
+    fn consume(&mut self, amount: usize) {
+        self.0.consume(amount)
+    }
+}
+
+impl<T: super::Write> std::io::Write for ToStd<T> {
+    #[inline]
+    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
+        self.0.write(buf).map_err(Into::into)
+    }
+
+    #[inline]
+    fn flush(&mut self) -> std::io::Result<()> {
+        self.0.flush().map_err(Into::into)
+    }
+
+    #[inline]
+    fn write_all(&mut self, buf: &[u8]) -> std::io::Result<()> {
+        self.0.write_all(buf).map_err(Into::into)
+    }
+}
+
+// We also impl our traits so that mixing the calls is not annoying.
+
+impl<T: super::Read> super::Read for ToStd<T> {
+    #[inline]
+    fn read(&mut self, buf: &mut [u8]) -> super::Result<usize> {
+        self.0.read(buf)
+    }
+
+    #[inline]
+    fn read_exact(&mut self, buf: &mut [u8]) -> super::Result<()> {
+        self.0.read_exact(buf)
+    }
+}
+
+impl<T: super::BufRead> super::BufRead for ToStd<T> {
+    #[inline]
+    fn fill_buf(&mut self) -> super::Result<&[u8]> {
+        self.0.fill_buf()
+    }
+
+    #[inline]
+    fn consume(&mut self, amount: usize) {
+        self.0.consume(amount)
+    }
+}
+
+impl<T: super::Write> super::Write for ToStd<T> {
+    #[inline]
+    fn write(&mut self, buf: &[u8]) -> super::Result<usize> {
+        self.0.write(buf)
+    }
+
+    #[inline]
+    fn flush(&mut self) -> super::Result<()> {
+        self.0.flush()
+    }
+
+    #[inline]
+    fn write_all(&mut self, buf: &[u8]) -> super::Result<()> {
+        self.0.write_all(buf)
+    }
+}

io/src/lib.rs

@@ -27,7 +27,7 @@ mod macros;
 mod bridge;
 
 #[cfg(feature = "std")]
-pub use bridge::FromStd;
+pub use bridge::{FromStd, ToStd};
 
 #[cfg(all(not(feature = "std"), feature = "alloc"))]
 use alloc::vec::Vec;