chore: Last-Modifiedヘッダーをリクエストから取り出せるようにする

packages/toy-blog/src/service/rest.rs

@@ -3,6 +3,7 @@ mod cors;
 pub(in crate::service) mod repository;
 mod auth;
 mod exposed_representation_format;
+mod header;
 
 use std::fs::File;
 use std::io::stdin;

packages/toy-blog/src/service/rest/header.rs

@@ -0,0 +1,98 @@
+use std::error::Error;
+use std::future::Ready;
+use std::str::FromStr;
+use actix_web::{FromRequest, HttpRequest};
+use actix_web::dev::Payload;
+use actix_web::http::header::{HeaderValue, ToStrError};
+use chrono::{DateTime, FixedOffset, ParseError, TimeZone};
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+pub enum LastModifiedParseError {
+    #[error("given value does not fit in ASCII: {0}")]
+    NotInAscii(#[from] ToStrError),
+    #[error("chrono reports parse failure: {0}")]
+    Chrono(#[from] ParseError)
+}
+
+#[derive(Eq, PartialEq, Debug)]
+pub struct LastModified(pub DateTime<FixedOffset>);
+
+impl FromStr for LastModified {
+    type Err = ParseError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let x = chrono::NaiveDateTime::parse_from_str(s, "%a, %d %b %Y %H:%M:%S GMT")?;
+        Ok(Self(FixedOffset::east_opt(0).unwrap().from_utc_datetime(&x)))
+    }
+}
+
+impl TryFrom<&HeaderValue> for LastModified {
+    type Error = LastModifiedParseError;
+
+    fn try_from(value: &HeaderValue) -> Result<Self, Self::Error> {
+        Ok(value.to_str()?.parse()?)
+    }
+}
+
+impl FromRequest for LastModified {
+    type Error = LastModifiedExtractionError;
+    type Future = Ready<Result<LastModified, Self::Error>>;
+
+    fn from_request(req: &HttpRequest, _: &mut Payload) -> Self::Future {
+        let w = req.headers().get("Last-Modified")
+            .ok_or(LastModifiedExtractionError::NotFound);
+        let w = match w {
+            Ok(t) => t,
+            Err(e) => return std::future::ready(Err(e)),
+        };
+
+        let r = Self::try_from(w);
+        let r = match r {
+            Ok(t) => t,
+            Err(e) => return std::future::ready(Err(LastModifiedExtractionError::from(e))),
+        };
+
+        std::future::ready(Ok(r))
+    }
+}
+
+#[derive(Error, Debug)]
+pub enum LastModifiedExtractionError {
+    #[error("request does not have Last-Modified header")]
+    NotFound,
+    #[error("header value is malformed: {0}")]
+    ParseFailure(#[from] LastModifiedParseError),
+}
+
+impl actix_web::ResponseError for LastModifiedExtractionError {}
+
+#[cfg(test)]
+mod tests {
+    use std::str::FromStr;
+    use chrono::{FixedOffset, NaiveDate, NaiveDateTime, NaiveTime, TimeZone};
+    use crate::service::rest::header::LastModified;
+
+    #[test]
+    fn rfc_7232_example() {
+        let parsed = LastModified::from_str("Tue, 15 Nov 1994 12:45:26 GMT").expect("failed to parse");
+        let expected = FixedOffset::east_opt(0).expect("timezone").from_utc_datetime(
+            &NaiveDateTime::new(
+                NaiveDate::from_ymd_opt(1994, 11, 15).expect("naive date"),
+                NaiveTime::from_hms_opt(12, 45, 26).expect("naive time")
+            )
+        );
+
+        assert_eq!(parsed.0, expected);
+    }
+    #[test]
+    #[should_panic]
+    fn xy() {
+        let _ = LastModified::from_str("Tue, 15 Nov 1994 12:45:26 GMT1").expect("failed to parse");
+    }
+    #[test]
+    #[should_panic]
+    fn xyz() {
+        let _ = LastModified::from_str("Tue").expect("failed to parse");
+    }
+}