Fix deserialization of unknown extensions

OpenSSH 8.9 ssh client started sending EXTENSION commands. Unfortunately
ssh-agent.rs didn't deserialize them correctly and even though these
extensions were optional the agent didn't work.

This patch adjusts the deserialization of extension contents to properly
capture all bytes and includes a test code observed in the wild.

Fixes #30.

src/proto/de.rs

@@ -49,8 +49,10 @@ pub fn from_bytes<'a, T: Deserialize<'a>>(bytes: &[u8]) -> ProtoResult<T> {
 impl<'de, 'a, R: io::Read> de::Deserializer<'de> for &'a mut Deserializer<R> {
     type Error = ProtoError;
 
-    fn deserialize_any<V: Visitor<'de>>(self, _visitor: V) -> ProtoResult<V::Value> {
-        unimplemented!()
+    fn deserialize_any<V: Visitor<'de>>(self, visitor: V) -> ProtoResult<V::Value> {
+        let mut bytes = vec![];
+        self.reader.read_to_end(&mut bytes)?;
+        visitor.visit_byte_buf(bytes)
     }
 
     fn deserialize_bool<V: Visitor<'de>>(self, visitor: V) -> ProtoResult<V::Value> {

src/proto/message.rs

@@ -1,4 +1,5 @@
 use serde::{Deserialize, Serialize};
+use serde::de::{Deserializer, Visitor};
 
 use super::private_key::PrivateKey;
 
@@ -52,8 +53,42 @@ pub struct AddSmartcardKeyConstrained {
 
 #[derive(Clone, PartialEq, Debug, Serialize, Deserialize)]
 pub struct Extension {
-    extension_type: String,
-    extension_contents: Vec<u8>
+    pub extension_type: String,
+    pub extension_contents: ExtensionContents,
+}
+
+#[derive(Debug, PartialEq, Clone)]
+pub struct ExtensionContents(pub Vec<u8>);
+
+impl Serialize for ExtensionContents {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::Serializer {
+        serializer.serialize_bytes(&self.0)
+    }
+}
+
+impl<'de> Deserialize<'de> for ExtensionContents {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        struct ContentsVisitor;
+
+        impl<'de> Visitor<'de> for ContentsVisitor {
+            type Value = ExtensionContents;
+
+            fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
+                formatter.write_str("raw bytes buffer")
+            }
+
+            fn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<Self::Value, E> {
+                Ok(ExtensionContents(v))
+            }
+        }
+
+        deserializer.deserialize_any(ContentsVisitor)
+    }
 }
 
 pub type Passphrase = String;

src/proto/tests/mod.rs

@@ -1,7 +1,7 @@
 use super::{to_bytes, from_bytes, Blob};
 use super::public_key::*;
 use super::private_key::*;
-use super::message::{Message, SignRequest, Identity};
+use super::message::{Message, SignRequest, Identity, Extension};
 use super::signature::Signature;
 
 #[test]
@@ -163,3 +163,10 @@ fn raw_protocol_test() {
 
     assert_eq!(response_bytes.as_slice(), &include_bytes!("id_ans_response.bin")[..]);
 }
+
+#[test]
+fn test_extension() {
+    let extension_bytes: &[u8] = &[0, 0, 0, 24, 115, 101, 115, 115, 105, 111, 110, 45, 98, 105, 110, 100, 64, 111, 112, 101, 110, 115, 115, 104, 46, 99, 111, 109, 0, 0, 0, 51, 0, 0, 0, 11, 115, 115, 104, 45, 101, 100, 50, 53, 53, 49, 57, 0, 0, 0, 32, 177, 185, 198, 92, 165, 45, 127, 95, 202, 195, 226, 63, 6, 115, 10, 104, 18, 137, 172, 240, 153, 154, 174, 74, 83, 7, 1, 204, 14, 177, 153, 40, 0, 0, 0, 32, 175, 96, 42, 133, 218, 171, 58, 220, 97, 78, 155, 114, 20, 67, 90, 133, 24, 185, 156, 71, 128, 163, 234, 195, 202, 15, 160, 177, 130, 229, 114, 164, 0, 0, 0, 83, 0, 0, 0, 11, 115, 115, 104, 45, 101, 100, 50, 53, 53, 49, 57, 0, 0, 0, 64, 4, 235, 93, 135, 144, 110, 220, 24, 17, 150, 40, 11, 143, 37, 207, 58, 215, 159, 23, 233, 95, 218, 115, 22, 205, 101, 55, 159, 146, 42, 121, 190, 229, 82, 75, 174, 143, 199, 121, 141, 52, 155, 73, 215, 119, 220, 104, 241, 116, 83, 96, 129, 184, 12, 93, 93, 33, 243, 171, 236, 201, 123, 17, 1, 0];
+    let extension: Extension = from_bytes(&extension_bytes).unwrap();
+    assert_eq!(extension.extension_type, "session-bind@openssh.com");
+}