feat: improve auth & automatic padding

Cargo.toml

@@ -17,4 +17,5 @@ sha1 = "*"
 hmac = "*"
 tokio-util = { version = "*", features = ["full"] }
 futures-util = "0.3.26"
-sha2 = "*"
+sha2 = "*"
+rand = "0.8.5"

src/args.rs

@@ -61,6 +61,16 @@ pub struct Opt {
     /// the password to authenticate connections
     #[structopt(short = "p", long, parse(from_str = make_password))]
     pub password: Password,
+
+    /// The target length of early server data. Packets that exceed this
+    /// will be truncated.
+    #[structopt(long, default_value = "1385")]
+    pub mtu: u16,
+
+    /// The minimal length of server data. Packets that below this
+    /// will be padded.
+    #[structopt(long, default_value = "15")]
+    pub min_record_len: u16,
 }
 
 // #[derive(Debug)]

src/common.rs

@@ -2,6 +2,8 @@
 pub const REQUIRED_SESSION_ID_LEN: usize = 32;
 pub const RESTLS_HANDSHAKE_HMAC_LEN: usize = 16;
 pub const RESTLS_APPDATA_HMAC_LEN: usize = 8;
+pub const RESTLS_APPDATA_LEN_OFFSET: usize = 5 + RESTLS_APPDATA_HMAC_LEN;
+pub const RESTLS_APPDATA_OFFSET: usize = 5 + RESTLS_APPDATA_HMAC_LEN + 2;
 
 // record type
 pub const RECORD_HANDSHAKE: u8 = 0x16;
@@ -25,3 +27,8 @@ pub const HELLO_RETRY_RANDOM: [u8; 32] = [
     0xCF, 0x21, 0xAD, 0x74, 0xE5, 0x9A, 0x61, 0x11, 0xBE, 0x1D, 0x8C, 0x02, 0x1E, 0x65, 0xB8, 0x91,
     0xC2, 0xA2, 0x11, 0x16, 0x7A, 0xBB, 0x8C, 0x5E, 0x07, 0x9E, 0x09, 0xE2, 0xC8, 0xA8, 0x33, 0x9C,
 ];
+
+pub const TO_CLIENT_MAGIC: &'static [u8] = "server-to-client".as_bytes();
+pub const TO_SERVER_MAGIC: &'static [u8] = "client-to-server".as_bytes();
+
+pub const BUF_SIZE: usize = 0x2000;