implement the guess charset parser

src/multipass/guess_charset.rs

@@ -0,0 +1,51 @@
+use std::borrow::Cow;
+use chardetng::EncodingDetector;
+use encoding_rs::Encoding;
+
+use crate::multipass::segment::Segment;
+
+#[derive(Debug, PartialEq)]
+pub struct GuessCharset<'a> {
+    pub header: Cow<'a, str>,
+    pub encoding: &'static Encoding,
+    pub malformed: bool,
+    pub body: &'a [u8],
+}
+
+const IS_LAST_BUFFER: bool = true;
+const ALLOW_UTF8: bool = true;
+const NO_TLD: Option<&[u8]> = None;
+
+impl<'a> From<Segment<'a>> for GuessCharset<'a> {
+    fn from(seg: Segment<'a>) -> Self {
+        // Create detector
+        let mut detector = EncodingDetector::new();
+        detector.feed(&seg.header, IS_LAST_BUFFER);
+
+        // Get encoding
+        let enc: &Encoding = detector.guess(NO_TLD, ALLOW_UTF8);
+        let (header, encoding, malformed) = enc.decode(&seg.header);
+
+        GuessCharset { header, encoding, malformed, body: seg.body }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_charset() {
+        assert_eq!(
+            GuessCharset::from(Segment {
+                body: b"Hello world!", 
+                header: b"From: hello@world.com\r\nDate: 12 Mar 1997 07:33:25 Z\r\n",
+            }),
+            GuessCharset {
+                header: Cow::Borrowed("From: hello@world.com\r\nDate: 12 Mar 1997 07:33:25 Z\r\n"),
+                encoding: encoding_rs::UTF_8,
+                malformed: false,
+                body: b"Hello world!",
+            });
+    }
+}

src/multipass/mod.rs

@@ -1 +1,2 @@
 pub mod segment;
+pub mod guess_charset;