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src/extensions/extension_data/max_fragment_length.rs

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+use crate::{
+    ProtocolError,
+    buffer::CryptoBuffer,
+    parse_buffer::{ParseBuffer, ParseError},
+};
+
+/// Maximum plaintext fragment length
+///
+/// RFC 6066, Section 4.  Maximum Fragment Length Negotiation
+/// Without this extension, TLS specifies a fixed maximum plaintext
+/// fragment length of 2^14 bytes.  It may be desirable for constrained
+/// clients to negotiate a smaller maximum fragment length due to memory
+/// limitations or bandwidth limitations.
+#[derive(Debug, Copy, Clone, PartialEq)]
+#[cfg_attr(feature = "defmt", derive(defmt::Format))]
+pub enum MaxFragmentLength {
+    /// 512 bytes
+    Bits9 = 1,
+    /// 1024 bytes
+    Bits10 = 2,
+    /// 2048 bytes
+    Bits11 = 3,
+    /// 4096 bytes
+    Bits12 = 4,
+}
+
+impl MaxFragmentLength {
+    pub fn parse(buf: &mut ParseBuffer) -> Result<Self, ParseError> {
+        match buf.read_u8()? {
+            1 => Ok(Self::Bits9),
+            2 => Ok(Self::Bits10),
+            3 => Ok(Self::Bits11),
+            4 => Ok(Self::Bits12),
+            other => {
+                warn!("Read unknown MaxFragmentLength: {}", other);
+                Err(ParseError::InvalidData)
+            }
+        }
+    }
+
+    pub fn encode(&self, buf: &mut CryptoBuffer) -> Result<(), ProtocolError> {
+        buf.push(*self as u8).map_err(|_| ProtocolError::EncodeError)
+    }
+}