chore: checkpoint before Python removal

vendor/headers-core/src/lib.rs

@@ -0,0 +1,68 @@
+#![deny(missing_docs)]
+#![deny(missing_debug_implementations)]
+#![cfg_attr(test, deny(warnings))]
+#![doc(html_root_url = "https://docs.rs/headers-core/0.3.0")]
+
+//! # headers-core
+//!
+//! This is the core crate of the typed HTTP headers system, providing only
+//! the relevant traits. All actual header implementations are in other crates.
+
+extern crate http;
+
+pub use http::header::{self, HeaderName, HeaderValue};
+
+use std::error;
+use std::fmt::{self, Display, Formatter};
+
+/// A trait for any object that will represent a header field and value.
+///
+/// This trait represents the construction and identification of headers,
+/// and contains trait-object unsafe methods.
+pub trait Header {
+    /// The name of this header.
+    fn name() -> &'static HeaderName;
+
+    /// Decode this type from an iterator of `HeaderValue`s.
+    fn decode<'i, I>(values: &mut I) -> Result<Self, Error>
+    where
+        Self: Sized,
+        I: Iterator<Item = &'i HeaderValue>;
+
+    /// Encode this type to a `HeaderMap`.
+    ///
+    /// This function should be infallible. Any errors converting to a
+    /// `HeaderValue` should have been caught when parsing or constructing
+    /// this value.
+    fn encode<E: Extend<HeaderValue>>(&self, values: &mut E);
+}
+
+/// Errors trying to decode a header.
+#[derive(Debug)]
+pub struct Error {
+    kind: Kind,
+}
+
+#[derive(Debug)]
+enum Kind {
+    Invalid,
+}
+
+impl Error {
+    /// Create an 'invalid' Error.
+    pub fn invalid() -> Error {
+        Error {
+            kind: Kind::Invalid,
+        }
+    }
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        match &self.kind {
+            Kind::Invalid => f.write_str("invalid HTTP header"),
+        }
+    }
+}
+
+impl error::Error for Error {}