implement Response api

src/response/success/default.rs

@@ -0,0 +1,65 @@
+use anyhow::{bail, Result};
+
+pub const CODE: &[u8] = b"20";
+
+/// [Success](https://geminiprotocol.net/docs/protocol-specification.gmi#success)
+pub struct Default {
+    pub mime: String,
+}
+
+impl Default {
+    /// Build `Self` from UTF-8 header bytes
+    /// * expected buffer includes leading status code, message, CRLF
+    pub fn from_bytes(buffer: &[u8]) -> Result<Self> {
+        // calculate length once
+        let len = buffer.len();
+        // validate headers for this response type
+        if !(3..=1024).contains(&len) {
+            bail!("Unexpected header length")
+        }
+        if buffer
+            .get(..2)
+            .is_none_or(|c| c[0] != CODE[0] || c[1] != CODE[1])
+        {
+            bail!("Invalid status code")
+        }
+        // collect data bytes
+        let mut m = Vec::with_capacity(len);
+        for b in buffer[3..].iter() {
+            if *b == b'\r' {
+                continue;
+            }
+            if *b == b'\n' {
+                break;
+            }
+            m.push(*b)
+        }
+
+        Ok(Self {
+            mime: if m.is_empty() {
+                bail!("Content type required")
+            } else {
+                String::from_utf8(m)?
+            },
+        })
+    }
+
+    /// Convert `Self` into UTF-8 bytes presentation
+    pub fn into_bytes(self) -> Vec<u8> {
+        let mut bytes = Vec::with_capacity(self.mime.len() + 5);
+        bytes.extend(CODE);
+        bytes.push(b' ');
+        bytes.extend(self.mime.into_bytes());
+        bytes.extend([b'\r', b'\n']);
+        bytes
+    }
+}
+
+#[test]
+fn test() {
+    let request = format!("20 text/gemini\r\n");
+    let source = Default::from_bytes(request.as_bytes()).unwrap();
+
+    assert_eq!(source.mime, "text/gemini".to_string());
+    assert_eq!(source.into_bytes(), request.as_bytes());
+}