From 52961f71c8e585dbe91bf8f5a561e9b26218504b Mon Sep 17 00:00:00 2001
From: Yoshua Wuyts <yoshuawuyts@gmail.com>
Date: Mon, 2 Nov 2020 01:00:19 +0100
Subject: [PATCH] Add `other::Expect` header

---
 src/other/expect.rs | 110 ++++++++++++++++++++++++++++++++++++++++++++
 src/other/mod.rs    |   2 +
 2 files changed, 112 insertions(+)
 create mode 100644 src/other/expect.rs

diff --git a/src/other/expect.rs b/src/other/expect.rs
new file mode 100644
index 00000000..5e8fd307
--- /dev/null
+++ b/src/other/expect.rs
@@ -0,0 +1,110 @@
+use crate::ensure_eq_status;
+use crate::headers::{HeaderName, HeaderValue, Headers, ToHeaderValues, EXPECT};
+
+use std::fmt::Debug;
+use std::option;
+
+/// HTTP `Expect` header
+///
+/// [MDN Documentation](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Expect)
+///
+/// # Specifications
+///
+/// - [RFC 7231, section 5.1.1: Expect](https://tools.ietf.org/html/rfc7231#section-5.1.1)
+///
+/// # Examples
+///
+/// ```
+/// # fn main() -> http_types::Result<()> {
+/// #
+/// use http_types::Response;
+/// use http_types::other::Expect;
+///
+/// let expect = Expect::new();
+///
+/// let mut res = Response::new(200);
+/// expect.apply(&mut res);
+///
+/// let expect = Expect::from_headers(res)?.unwrap();
+/// assert_eq!(expect, Expect::new());
+/// #
+/// # Ok(()) }
+/// ```
+#[derive(Debug, Ord, PartialOrd, Eq, PartialEq)]
+pub struct Expect {
+    _priv: (),
+}
+
+impl Expect {
+    /// Create a new instance of `Expect`.
+    pub fn new() -> Self {
+        Self { _priv: () }
+    }
+
+    /// Create an instance of `Expect` from a `Headers` instance.
+    pub fn from_headers(headers: impl AsRef<Headers>) -> crate::Result<Option<Self>> {
+        let headers = match headers.as_ref().get(EXPECT) {
+            Some(headers) => headers,
+            None => return Ok(None),
+        };
+
+        // If we successfully parsed the header then there's always at least one
+        // entry. We want the last entry.
+        let header = headers.iter().last().unwrap();
+        ensure_eq_status!(header, "100-continue", 400, "malformed `Expect` header");
+
+        Ok(Some(Self { _priv: () }))
+    }
+
+    /// Insert a `HeaderName` + `HeaderValue` pair into a `Headers` instance.
+    pub fn apply(&self, mut headers: impl AsMut<Headers>) {
+        headers.as_mut().insert(EXPECT, self.value());
+    }
+
+    /// Get the `HeaderName`.
+    pub fn name(&self) -> HeaderName {
+        EXPECT
+    }
+
+    /// Get the `HeaderValue`.
+    pub fn value(&self) -> HeaderValue {
+        let value = "100-continue";
+        // SAFETY: the internal string is validated to be ASCII.
+        unsafe { HeaderValue::from_bytes_unchecked(value.into()) }
+    }
+}
+
+impl ToHeaderValues for Expect {
+    type Iter = option::IntoIter<HeaderValue>;
+    fn to_header_values(&self) -> crate::Result<Self::Iter> {
+        // A HeaderValue will always convert into itself.
+        Ok(self.value().to_header_values().unwrap())
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use crate::headers::Headers;
+
+    #[test]
+    fn smoke() -> crate::Result<()> {
+        let expect = Expect::new();
+
+        let mut headers = Headers::new();
+        expect.apply(&mut headers);
+
+        let expect = Expect::from_headers(headers)?.unwrap();
+        assert_eq!(expect, Expect::new());
+        Ok(())
+    }
+
+    #[test]
+    fn bad_request_on_parse_error() -> crate::Result<()> {
+        let mut headers = Headers::new();
+        headers.insert(EXPECT, "<nori ate the tag. yum.>");
+        let err = Expect::from_headers(headers).unwrap_err();
+        assert_eq!(err.status(), 400);
+        Ok(())
+    }
+}
diff --git a/src/other/mod.rs b/src/other/mod.rs
index f78a49f7..81b66daf 100644
--- a/src/other/mod.rs
+++ b/src/other/mod.rs
@@ -1,5 +1,7 @@
 //! Miscellaneous HTTP headers.
 
 mod date;
+mod expect;
 
 pub use date::Date;
+pub use expect::Expect;