1 files changed, 181 insertions, 0 deletions
diff --git a/third_party/rust/wasmparser/src/readers.rs b/third_party/rust/wasmparser/src/readers.rs
new file mode 100644
index 0000000000..017a80df59
--- /dev/null
+++ b/third_party/rust/wasmparser/src/readers.rs
@@ -0,0 +1,181 @@
+/* Copyright 2018 Mozilla Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+use crate::{BinaryReaderError, Result};
+use std::ops::Range;
+
+mod component;
+mod core;
+
+pub use self::component::*;
+pub use self::core::*;
+
+/// A trait implemented by section readers.
+pub trait SectionReader {
+    /// The item returned by the reader.
+    type Item;
+
+    /// Reads an item from the section.
+    fn read(&mut self) -> Result<Self::Item>;
+
+    /// Determines if the reader is at end-of-section.
+    fn eof(&self) -> bool;
+
+    /// Gets the original position of the reader.
+    fn original_position(&self) -> usize;
+
+    /// Gets the range of the reader.
+    fn range(&self) -> Range<usize>;
+
+    /// Ensures the reader is at the end of the section.
+    ///
+    /// This methods returns an error if there is more data in the section
+    /// than what is described by the section's header.
+    fn ensure_end(&self) -> Result<()> {
+        if self.eof() {
+            return Ok(());
+        }
+        Err(BinaryReaderError::new(
+            "section size mismatch: unexpected data at the end of the section",
+            self.original_position(),
+        ))
+    }
+}
+
+/// Implemented by sections with a limited number of items.
+pub trait SectionWithLimitedItems: SectionReader {
+    /// Gets the count of the items in the section.
+    fn get_count(&self) -> u32;
+
+    /// Returns an iterator over the items within this section where the offset
+    /// in the original section is provided with the item.
+    fn into_iter_with_offsets(self) -> IntoIterWithOffsets<Self>
+    where
+        Self: Sized,
+    {
+        IntoIterWithOffsets {
+            iter: SectionIteratorLimited::new(self),
+        }
+    }
+}
+
+/// An iterator over items in a section.
+pub struct SectionIterator<R>
+where
+    R: SectionReader,
+{
+    reader: R,
+    err: bool,
+}
+
+impl<R> SectionIterator<R>
+where
+    R: SectionReader,
+{
+    /// Constructs a new `SectionIterator` for the given section reader.
+    pub fn new(reader: R) -> SectionIterator<R> {
+        SectionIterator { reader, err: false }
+    }
+}
+
+impl<R> Iterator for SectionIterator<R>
+where
+    R: SectionReader,
+{
+    type Item = Result<R::Item>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.err || self.reader.eof() {
+            return None;
+        }
+        let result = self.reader.read();
+        self.err = result.is_err();
+        Some(result)
+    }
+}
+
+/// An iterator over a limited section iterator.
+pub struct SectionIteratorLimited<R> {
+    reader: R,
+    left: u32,
+    end: bool,
+}
+
+impl<R> SectionIteratorLimited<R>
+where
+    R: SectionWithLimitedItems,
+{
+    /// Constructs a new `SectionIteratorLimited` for the given limited section reader.
+    pub fn new(reader: R) -> SectionIteratorLimited<R> {
+        let left = reader.get_count();
+        SectionIteratorLimited {
+            reader,
+            left,
+            end: false,
+        }
+    }
+}
+
+impl<R> Iterator for SectionIteratorLimited<R>
+where
+    R: SectionWithLimitedItems,
+{
+    type Item = Result<R::Item>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.end {
+            return None;
+        }
+        if self.left == 0 {
+            return match self.reader.ensure_end() {
+                Ok(()) => None,
+                Err(err) => {
+                    self.end = true;
+                    Some(Err(err))
+                }
+            };
+        }
+        let result = self.reader.read();
+        self.end = result.is_err();
+        self.left -= 1;
+        Some(result)
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let count = self.reader.get_count() as usize;
+        (count, Some(count))
+    }
+}
+
+/// An iterator over a limited section iterator.
+pub struct IntoIterWithOffsets<R> {
+    iter: SectionIteratorLimited<R>,
+}
+
+impl<R> Iterator for IntoIterWithOffsets<R>
+where
+    R: SectionWithLimitedItems,
+{
+    type Item = Result<(usize, R::Item)>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let pos = self.iter.reader.original_position();
+        Some(self.iter.next()?.map(|item| (pos, item)))
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}