add core::char::DecodeUtf8

1 files changed, 47 insertions, 0 deletions

diff --git a/src/libcore/char.rs b/src/libcore/char.rs
index d80b456181a..0e7f04c7758 100644
--- a/src/libcore/char.rs
+++ b/src/libcore/char.rs
@@ -676,3 +676,50 @@ impl Iterator for EncodeUtf16 {
         self.as_slice().iter().size_hint()
     }
 }
+
+
+/// An iterator over an iterator of bytes of the characters the bytes represent
+/// as UTF-8
+#[unstable(feature = "decode_utf8", issue = "33906")]
+#[derive(Clone, Debug)]
+pub struct DecodeUtf8<I: Iterator<Item = u8>>(::iter::Peekable<I>);
+
+/// Decodes an `Iterator` of bytes as UTF-8.
+#[unstable(feature = "decode_utf8", issue = "33906")]
+#[inline]
+pub fn decode_utf8<I: IntoIterator<Item = u8>>(i: I) -> DecodeUtf8<I::IntoIter> {
+    DecodeUtf8(i.into_iter().peekable())
+}
+
+/// `<DecodeUtf8 as Iterator>::next` returns this for an invalid input sequence.
+#[unstable(feature = "decode_utf8", issue = "33906")]
+#[derive(PartialEq, Debug)]
+pub struct InvalidSequence(());
+
+#[unstable(feature = "decode_utf8", issue = "33906")]
+impl<I: Iterator<Item = u8>> Iterator for DecodeUtf8<I> {
+    type Item = Result<char, InvalidSequence>;
+    #[inline]
+    fn next(&mut self) -> Option<Result<char, InvalidSequence>> {
+        self.0.next().map(|b| {
+            if b & 0x80 == 0 { Ok(b as char) } else {
+                let l = (!b).leading_zeros() as usize; // number of bytes in UTF-8 representation
+                if l < 2 || l > 6 { return Err(InvalidSequence(())) };
+                let mut x = (b as u32) & (0x7F >> l);
+                for _ in 0..l-1 {
+                    match self.0.peek() {
+                        Some(&b) if b & 0xC0 == 0x80 => {
+                            self.0.next();
+                            x = (x << 6) | (b as u32) & 0x3F;
+                        },
+                        _ => return Err(InvalidSequence(())),
+                    }
+                }
+                match from_u32(x) {
+                    Some(x) if l == x.len_utf8() => Ok(x),
+                    _ => Err(InvalidSequence(())),
+                }
+            }
+        })
+    }
+}