[Fix] WASM

client/src/lib.rs

@@ -4,6 +4,20 @@ use mtp_codec::{CommunicationValue, DataTypeId, DataValue, PROTOCOL_VERSION, Ver
 use mtp_common::CommunicationError;
 use mtp_transport::{Policy, Receiver, Sender};
 
+#[cfg(feature = "crypto")]
+fn unexpected_response_type_error(
+    context: &str,
+    expected_type: mtp_codec::CommunicationTypeId,
+    response: &CommunicationValue,
+) -> CommunicationError {
+    CommunicationError::AuthenticationFailed(format!(
+        "unexpected response type during {context}: expected {:?}, got {:?}; parsed {}",
+        expected_type,
+        response.get_type(),
+        response
+    ))
+}
+
 pub struct ClientConfig {
     pub url: String,
     pub server_cert: Option<Vec<u8>>,
@@ -124,6 +138,15 @@ impl MTPClient {
         // 2. Receive host response (single message)
         let response = receiver.receive().await?;
 
+        let expected_type = mtp_codec::CommunicationTypeId(16); // IdentificationResponse
+        if response.get_type() != expected_type {
+            return Err(unexpected_response_type_error(
+                "auth_connect",
+                expected_type,
+                &response,
+            ));
+        }
+
         let connected = response.get_data(DataTypeId(11));
         match connected {
             DataValue::BoolTrue => {}
@@ -264,6 +287,15 @@ impl MTPClient {
         // 2. Receive host response (single message)
         let response = receiver.receive().await?;
 
+        let expected_type = mtp_codec::CommunicationTypeId(18); // RegisterResponse
+        if response.get_type() != expected_type {
+            return Err(unexpected_response_type_error(
+                "auth_register",
+                expected_type,
+                &response,
+            ));
+        }
+
         let connected = response.get_data(DataTypeId(11));
         match connected {
             DataValue::BoolTrue => {}

example-usage/client/src/main.rs

@@ -2,13 +2,29 @@ mod auth;
 mod messages;
 
 use std::fs;
+use std::path::Path;
 
 use mtp::client::ClientConfig;
 use mtp::crypto::{KemPublicKey, PublicKeyBundle, SignaturePqPublicKey, SignaturePublicKey};
 
+fn dev_cert_path() -> String {
+    std::env::var("MTP_DEV_CERT").unwrap_or_else(|_| {
+        if Path::new("example-usage/dev-cert/cert.pem").exists() {
+            "example-usage/dev-cert/cert.pem".to_string()
+        } else {
+            "dev-cert/cert.pem".to_string()
+        }
+    })
+}
+
 #[tokio::main]
 async fn main() -> Result<(), Box<dyn std::error::Error>> {
-    let cert_pem = fs::read("server.pem").expect("Missing server.pem: run server first");
+    let cert_path = dev_cert_path();
+    let cert_pem = fs::read(&cert_path).unwrap_or_else(|e| {
+        panic!(
+            "Missing TLS certificate at {cert_path}: enter the Nix shell first or run the server to generate it: {e}"
+        )
+    });
     let host_public_key = PublicKeyBundle::new(
         KemPublicKey::new(
             fs::read("host_enc_kem_pk.bin")

example-usage/client/src/messages.rs

@@ -13,8 +13,8 @@ fn derive_demo_key() -> [u8; 32] {
 
 pub fn build_demo_message(client_id: u64, keyring: &Keyring) -> CommunicationValue {
     let cipher = ChaCha20Poly1305::new(derive_demo_key());
-    let signer = Ed25519Signer::new(&keyring.sig_cl_secret_key)
+    let signer =
-        .expect("Ed25519 signer from keyring");
+        Ed25519Signer::new(&keyring.sig_cl_secret_key).expect("Ed25519 signer from keyring");
 
     let inner_enc = DataValue::Container(vec![
         (DataTypeId(1), DataValue::Str("secret inner data".into())),
@@ -31,7 +31,10 @@ pub fn build_demo_message(client_id: u64, keyring: &Keyring) -> CommunicationVal
     dv_sig.sign_container(SigAlgorithm::ED25519, &signer);
 
     let inner_sec = DataValue::Container(vec![
-        (DataTypeId(1), DataValue::Str("signed+encrypted payload".into())),
+        (
+            DataTypeId(1),
+            DataValue::Str("signed+encrypted payload".into()),
+        ),
         (DataTypeId(2), DataValue::UnsignedNumber(7)),
     ]);
     let mut dv_sec = inner_sec;
@@ -42,13 +45,22 @@ pub fn build_demo_message(client_id: u64, keyring: &Keyring) -> CommunicationVal
         .unwrap()
         .as_secs();
 
-    CommunicationValue::new(CommunicationType::Ping)
+    let msg = CommunicationValue::new(CommunicationType::Ping)
-        .add_typed_default(DataType::Description, DataValue::Str("MTP Data Type Demo".into()))
+        .add_typed_default(
-        .add_typed_default(DataType::Timestamp, DataValue::UnsignedNumber(timestamp as u128))
+            DataType::Description,
+            DataValue::Str("MTP Data Type Demo".into()),
+        )
+        .add_typed_default(
+            DataType::Timestamp,
+            DataValue::UnsignedNumber(timestamp as u128),
+        )
         .add_typed_default(DataType::Data, DataValue::Str("Hello, MTP!".into()))
         .add_typed_default(DataType::Flags, DataValue::BoolTrue)
         .add_typed_default(DataType::Value, DataValue::Float(2, 12345))
-        .add_typed_default(DataType::BinaryData, DataValue::Bytes(vec![0xDE, 0xAD, 0xBE, 0xEF, 0x42]))
+        .add_typed_default(
+            DataType::BinaryData,
+            DataValue::Bytes(vec![0xDE, 0xAD, 0xBE, 0xEF, 0x42]),
+        )
         .add_typed_default(
             DataType::Items,
             DataValue::Array(vec![
@@ -60,7 +72,8 @@ pub fn build_demo_message(client_id: u64, keyring: &Keyring) -> CommunicationVal
         .add_typed_default(DataType::EncryptedPayload, dv_enc)
         .add_typed_default(DataType::SignedPayload, dv_sig)
         .add_typed_default(DataType::SecurePayload, dv_sec)
-        .with_sender(client_id)
+        .with_sender(client_id);
+    msg
 }
 
 pub async fn send_and_receive(
@@ -72,7 +85,9 @@ pub async fn send_and_receive(
     conn.sender.send(&msg).await?;
 
     match conn.receiver.receive().await {
-        Ok(resp) => println!("Received: {resp}"),
+        Ok(resp) => {
+            println!("Received: {resp}");
+        }
         Err(e) => eprintln!("Receive error: {e}"),
     }
 

example-usage/server/src/clients.rs

@@ -8,14 +8,18 @@ pub fn load_client_db(
     path: &str,
 ) -> Result<(Arc<Mutex<HashMap<u64, PublicKeyBundle>>>, Arc<Mutex<u64>>), Box<dyn std::error::Error>>
 {
-    let clients: Arc<Mutex<HashMap<u64, PublicKeyBundle>>> =
+    let clients_map = match fs::read_to_string(path) {
-        Arc::new(Mutex::new(if let Ok(data) = fs::read_to_string(path) {
+        Ok(data) => match serde_json::from_str(&data) {
-            serde_json::from_str(&data).unwrap_or_default()
+            Ok(clients) => clients,
-        } else {
+            Err(e) => {
-            HashMap::new()
+                eprintln!("Failed to parse {path}; starting with empty client database: {e}");
-        }));
+                HashMap::new()
-    let next_id = Arc::new(Mutex::new(
+            }
-        clients.lock().unwrap().keys().max().unwrap_or(&999) + 1,
+        },
-    ));
+        Err(_) => HashMap::new(),
+    };
+    let clients: Arc<Mutex<HashMap<u64, PublicKeyBundle>>> = Arc::new(Mutex::new(clients_map));
+    let next_value = clients.lock().unwrap().keys().max().unwrap_or(&999) + 1;
+    let next_id = Arc::new(Mutex::new(next_value));
     Ok((clients, next_id))
 }

example-usage/server/src/handlers.rs

@@ -1,5 +1,7 @@
 use mtp::codec::{CommunicationType, CommunicationValue, DataType, DataTypeId, DataValue, TypeMap};
-use mtp::crypto::{ChaCha20Poly1305, CryptoError, SignatureScheme, SignaturePublicKey, verify_ed25519};
+use mtp::crypto::{
+    ChaCha20Poly1305, CryptoError, SignaturePublicKey, SignatureScheme, verify_ed25519,
+};
 
 struct Ed25519Verifier(SignaturePublicKey);
 
@@ -71,6 +73,7 @@ pub fn process_and_respond(
                 enc_status = format!("EncryptedPayload decrypted OK ({} entries)", entries.len());
             }
         } else {
+            eprintln!("  EncryptedPayload decryption failed");
             enc_status = String::from("EncryptedPayload: decryption FAILED");
         }
     }
@@ -83,13 +86,14 @@ pub fn process_and_respond(
             if dv.verify_into_container(&verifier).is_some() {
                 if let Some(entries) = dv.as_container() {
                     println!("  Verified SignedPayload: {:?}", entries);
-                    sig_status =
+                    sig_status = format!("SignedPayload verified OK ({} entries)", entries.len());
-                        format!("SignedPayload verified OK ({} entries)", entries.len());
                 }
             } else {
+                eprintln!("  SignedPayload verification failed");
                 sig_status = String::from("SignedPayload: verification FAILED");
             }
         } else {
+            eprintln!("  SignedPayload cannot be verified; no client public key available");
             sig_status = String::from("SignedPayload: no client public key available");
         }
     }
@@ -99,7 +103,9 @@ pub fn process_and_respond(
         if let Some(pk_bundle) = client_pk {
             let verifier = Ed25519Verifier(pk_bundle.sig_cl_public_key.clone());
             let mut dv = secure.clone();
-            if dv.decrypt_signed_encrypted_container(&cipher, b"demo-aad").is_some()
+            if dv
+                .decrypt_signed_encrypted_container(&cipher, b"demo-aad")
+                .is_some()
                 && dv.verify_into_container(&verifier).is_some()
             {
                 if let Some(entries) = dv.as_container() {
@@ -110,9 +116,11 @@ pub fn process_and_respond(
                     );
                 }
             } else {
+                eprintln!("  SecurePayload decryption/verification failed");
                 secure_status = String::from("SecurePayload: decryption/verification FAILED");
             }
         } else {
+            eprintln!("  SecurePayload cannot be verified; no client public key available");
             secure_status = String::from("SecurePayload: no client public key available");
         }
     }

example-usage/server/src/keys.rs

@@ -1,9 +1,11 @@
 use std::fs;
 
-use mtp::crypto::{Ed25519Signer, Keyring, MlDsaSigner};
 use mtp::crypto::kem::HybridKem;
+use mtp::crypto::{Ed25519Signer, Keyring, MlDsaSigner};
 
-pub fn load_or_generate_host_keys(path: &str) -> Result<(u64, Keyring), Box<dyn std::error::Error>> {
+pub fn load_or_generate_host_keys(
+    path: &str,
+) -> Result<(u64, Keyring), Box<dyn std::error::Error>> {
     if let Ok(data) = fs::read_to_string(path) {
         let json: serde_json::Value = serde_json::from_str(&data)?;
         let hid = json["host_id"].as_u64().unwrap_or(1);
@@ -29,10 +31,7 @@ pub fn load_or_generate_host_keys(path: &str) -> Result<(u64, Keyring), Box<dyn
 pub fn export_host_public_keys(host_keyring: &Keyring) -> Result<(), Box<dyn std::error::Error>> {
     let public_key_bundle_hex = hex::encode(host_keyring.public_key_bundle().as_bytes());
 
-    fs::write(
+    fs::write("host_public_key_bundle.hex", &public_key_bundle_hex)?;
-        "host_public_key_bundle.hex",
-        &public_key_bundle_hex,
-    )?;
     fs::create_dir_all("web-client/public")?;
     fs::write(
         "web-client/public/host_public_key_bundle.hex",

example-usage/server/src/main.rs

@@ -40,7 +40,13 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
 
     let clients_for_get = clients.clone();
     let get_existing_user = Box::new(move |id: u64| -> Option<mtp::crypto::PublicKeyBundle> {
-        clients_for_get.lock().unwrap().get(&id).cloned()
+        let result = clients_for_get.lock().unwrap().get(&id).cloned();
+        if result.is_some() {
+            println!("Auth lookup: client ID {id} found");
+        } else {
+            eprintln!("Auth lookup: unknown client ID {id}");
+        }
+        result
     });
 
     let clients_for_register = clients.clone();
@@ -52,7 +58,13 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
         let id = *nid;
         *nid += 1;
         db.insert(id, bundle);
-        std::fs::write(&clients_path, serde_json::to_string_pretty(&*db).unwrap()).ok();
+        match serde_json::to_string_pretty(&*db) {
+            Ok(json) => match std::fs::write(&clients_path, json) {
+                Ok(()) => {}
+                Err(e) => eprintln!("Failed to persist client database to {clients_path}: {e}"),
+            },
+            Err(e) => eprintln!("Failed to serialize client database after registering {id}: {e}"),
+        }
         println!("Registered new client with ID: {}", id);
         id
     });

example-usage/web-client/src/main.ts

@@ -6,6 +6,7 @@ import init, {
   ed25519_generate,
   keyring_from_ed25519,
   build_demo_message,
+  format_frame,
 } from "mtp-wasm";
 
 const STATUS = document.getElementById("status")!;
@@ -57,7 +58,9 @@ function hexToBytes(value: string): Uint8Array {
 }
 
 function saveKeys() {
-  if (!keyringBytes) return;
+  if (!keyringBytes) {
+    return;
+  }
 
   let hostPublicKey: number[] | undefined;
   try {
@@ -106,7 +109,7 @@ async function loadHostPublicKey() {
 
     HOST_PUBLIC_KEY.value = hostPublicKey;
     saveKeys();
-    log("Loaded host public key bundle from public file.");
+    log(`Loaded host public key bundle (${hostPublicKey.length / 2} bytes).`);
   } catch {
     // Manual paste still works when the server has not exported the file yet.
   }
@@ -138,11 +141,11 @@ function createClient(): WasmClient {
     (state: number) =>
       log(`[state] ${ConnectionState[state] ?? state}`, "state"),
     (data: Uint8Array) => {
-      const decoder = new TextDecoder();
+      try {
-      log(
+        log(`Received: ${format_frame(data)}`, "received");
-        `[message] ${data.length} bytes: ${decoder.decode(data)}`,
+      } catch (e) {
-        "received",
+        log(`[message parse error] ${e}`, "error");
-      );
+      }
     },
     (err: any) => log(`[error] ${err}`, "error"),
   );
@@ -181,7 +184,8 @@ async function connect() {
   await loadDevCertHash();
 
   const client = createClient();
-  const config = new ConnectionConfig(SERVER_URL.value.trim());
+  const serverUrl = SERVER_URL.value.trim();
+  const config = new ConnectionConfig(serverUrl);
   if (devCertHash) {
     log(`Pinning WebTransport certificate hash: sha-256:${devCertHash}`);
     config.server_certificate_hashes = [`sha-256:${devCertHash}`];
@@ -210,6 +214,7 @@ async function connect() {
 
     log("\nSending demo message...");
     const frame = build_demo_message(activeClientId, keyringBytes);
+    log(`Sending: ${format_frame(frame)}`, "state");
     await client.send(frame);
     log(`Sent ${frame.length} bytes`);
 
@@ -236,6 +241,10 @@ GENERATE_KEYPAIR.addEventListener("click", () => {
 CONNECT.addEventListener("click", () => {
   connect().catch((e) => {
     log(`Fatal error: ${e}`, "error");
+    log(
+      `[fatal context] clientId=${clientId?.toString() ?? "unregistered"}, server=${SERVER_URL.value.trim()}, hostPkChars=${HOST_PUBLIC_KEY.value.replace(/[^0-9a-fA-F]/g, "").length}, keyringBytes=${keyringBytes?.length ?? 0}, certHash=${devCertHash || "none"}`,
+      "error",
+    );
     console.error(e);
   });
 });

flake.nix

@@ -7,18 +7,16 @@
     flake-utils.url = "github:numtide/flake-utils";
   };
 
-  outputs =
+  outputs = {
-    {
+    self,
-      self,
+    nixpkgs,
-      nixpkgs,
+    rust-overlay,
-      rust-overlay,
+    flake-utils,
-      flake-utils,
+  }:
-    }:
     flake-utils.lib.eachDefaultSystem (
-      system:
+      system: let
-      let
+        overlays = [rust-overlay.overlays.default];
-        overlays = [ rust-overlay.overlays.default ];
+        pkgs = import nixpkgs {inherit system overlays;};
-        pkgs = import nixpkgs { inherit system overlays; };
 
         rustToolchain = pkgs.rust-bin.stable.latest.default.override {
           extensions = [
@@ -26,68 +24,80 @@
             "clippy"
             "rustfmt"
           ];
-          targets = [ "wasm32-unknown-unknown" ];
+          targets = ["wasm32-unknown-unknown"];
         };
-      in
+      in {
-      {
+        devShells = {
-        devShells.default = pkgs.mkShell {
+          default = pkgs.mkShell {
-          name = "mtp-dev";
+            name = "mtp-dev";
 
-          buildInputs = with pkgs; [
+            buildInputs = with pkgs; [
-            rustToolchain
+              rustToolchain
-            wasm-pack
+              wasm-pack
-            pkg-config
+              pkg-config
-            openssl
+              openssl
-          ];
+            ];
 
-          MTP_TYPE_MAPS = "${toString ./example-usage/type-maps.yaml}";
+            MTP_TYPE_MAPS = "${toString ./example-usage/type-maps.yaml}";
 
-          shellHook = ''
+            shellHook = ''
-            cert_dir="$PWD/example-usage/dev-cert"
+              repo_root="$(git rev-parse --show-toplevel 2>/dev/null || pwd)"
-            public_dir="$PWD/example-usage/web-client/public"
+              cert_dir="$repo_root/example-usage/dev-cert"
-            cert_key="$cert_dir/key.pem"
+              public_dir="$repo_root/example-usage/web-client/public"
-            cert_pem="$cert_dir/cert.pem"
+              cert_key="$cert_dir/key.pem"
-            cert_hash="$cert_dir/sha256.txt"
+              cert_pem="$cert_dir/cert.pem"
+              cert_hash="$cert_dir/sha256.txt"
 
-            mkdir -p "$cert_dir"
+              mkdir -p "$cert_dir"
-            mkdir -p "$public_dir"
+              mkdir -p "$public_dir"
 
-            if [ ! -f "$cert_key" ] || [ ! -f "$cert_pem" ]; then
+              if [ ! -f "$cert_key" ] || [ ! -f "$cert_pem" ]; then
-              openssl ecparam -name prime256v1 -genkey -noout -out "$cert_key"
+                openssl ecparam -name prime256v1 -genkey -noout -out "$cert_key"
-              openssl req -new -x509 \
+                openssl req -new -x509 \
-                -sha256 \
+                  -sha256 \
-                -key "$cert_key" \
+                  -key "$cert_key" \
-                -out "$cert_pem" \
+                  -out "$cert_pem" \
-                -days 13 \
+                  -days 13 \
-                -subj "/CN=localhost" \
+                  -subj "/CN=localhost" \
-                -addext "subjectAltName=DNS:localhost,IP:127.0.0.1" \
+                  -addext "subjectAltName=DNS:localhost,IP:127.0.0.1" \
-                -addext "basicConstraints=critical,CA:FALSE" \
+                  -addext "basicConstraints=critical,CA:FALSE" \
-                -addext "keyUsage=critical,digitalSignature" \
+                  -addext "keyUsage=critical,digitalSignature" \
-                -addext "extendedKeyUsage=serverAuth"
+                  -addext "extendedKeyUsage=serverAuth"
-              cert_status="generated"
+                cert_status="generated"
-            else
+              else
-              cert_status="cached"
+                cert_status="cached"
-            fi
+              fi
 
-            openssl x509 -in "$cert_pem" -outform der \
+              openssl x509 -in "$cert_pem" -outform der \
-              | openssl dgst -sha256 -binary \
+                | openssl dgst -sha256 -binary \
-              | od -An -tx1 -v \
+                | od -An -tx1 -v \
-              | tr -d ' \n' > "$cert_hash"
+                | tr -d ' \n' > "$cert_hash"
-            cp "$cert_hash" "$public_dir/mtp_dev_cert_hash.txt"
+              cp "$cert_hash" "$public_dir/mtp_dev_cert_hash.txt"
 
-            export MTP_DEV_CERT="$cert_pem"
+              export MTP_DEV_CERT="$cert_pem"
-            export MTP_DEV_KEY="$cert_key"
+              export MTP_DEV_KEY="$cert_key"
-            export MTP_DEV_CERT_HASH="$(cat "$cert_hash")"
+              export MTP_DEV_CERT_HASH="$(cat "$cert_hash")"
 
-            echo "MTP dev shell"
+              echo "MTP dev shell"
-            echo "  rustc  : $(rustc --version)"
+              echo "  rustc  : $(rustc --version)"
-            echo "  cargo  : $(cargo --version)"
+              echo "  cargo  : $(cargo --version)"
-            echo "  wasm-pack : $(wasm-pack --version 2>/dev/null || echo 'not found')"
+              echo "  wasm-pack : $(wasm-pack --version 2>/dev/null || echo 'not found')"
-            echo "  targets: $(rustc --print target-list | grep wasm32 | tr '\n' ' ')"
+              echo "  targets: $(rustc --print target-list | grep wasm32 | tr '\n' ' ')"
-            echo "  MTP_TYPE_MAPS = $MTP_TYPE_MAPS"
+              echo "  MTP_TYPE_MAPS = $MTP_TYPE_MAPS"
-            echo "  dev cert: $MTP_DEV_CERT ($cert_status)"
+              echo "  dev cert: $MTP_DEV_CERT ($cert_status)"
-            echo "  cert sha256: $MTP_DEV_CERT_HASH"
+              echo "  cert sha256: $MTP_DEV_CERT_HASH"
-          '';
+            '';
+          };
+          autoStart = pkgs.mkShell {
+            name = "autoStart";
+            buildInputs = with pkgs; [
+              mprocs
+            ];
+            shellHook = ''
+              nix develop --command bash -c "mprocs 'cd wasm && wasm-pack build --target web --out-dir pkg && cd ../example-usage/web-client && bun dev' 'cargo b && cd example-usage && cargo r --bin server'"
+              exit
+            '';
+          };
         };
 
         # Ad-hoc WASM build using wasm-pack

host/src/lib.rs

@@ -176,7 +176,9 @@ impl MTPHost {
             _ => vec![],
         };
 
-        let (assigned_id, client_bundle) = if msg.get_type() == mtp_codec::CommunicationTypeId(15) {
+        let (assigned_id, client_bundle, response_type) = if msg.get_type()
+            == mtp_codec::CommunicationTypeId(15)
+        {
             // LOGIN
             let cid = match msg.get_data(DataTypeId(6)) {
                 DataValue::UnsignedNumber(n) => *n as u64,
@@ -237,7 +239,11 @@ impl MTPHost {
             }
             /* ===== End Signature ===== */
 
-            (cid, bundle)
+            (
+                cid,
+                bundle,
+                mtp_codec::CommunicationType::IdentificationResponse,
+            )
         } else if msg.get_type() == mtp_codec::CommunicationTypeId(17) {
             // REGISTER
             let bundle = match msg.get_data(DataTypeId(9)) {
@@ -284,7 +290,11 @@ impl MTPHost {
             /* ===== End Signature ===== */
 
             let new_id = (self.config.complete_register)(bundle.clone());
-            (new_id, bundle)
+            (
+                new_id,
+                bundle,
+                mtp_codec::CommunicationType::RegisterResponse,
+            )
         } else {
             sender.close();
             return None;
@@ -304,16 +314,15 @@ impl MTPHost {
         /* ===== Signature ===== */
         let host_sig = host_signer.sign(&host_sig_payload).ok()?;
 
-        let mut response =
+        let mut response = CommunicationValue::new(response_type)
-            CommunicationValue::new(mtp_codec::CommunicationType::IdentificationResponse)
+            .add_typed_default(DataType::Connected, DataValue::BoolTrue)
-                .add_typed_default(DataType::Connected, DataValue::BoolTrue)
+            .add_typed_default(
-                .add_typed_default(
+                DataType::ClientNonce,
-                    DataType::ClientNonce,
+                DataValue::UnsignedNumber(client_nonce),
-                    DataValue::UnsignedNumber(client_nonce),
+            )
-                )
+            .add_typed_default(DataType::Timestamp, DataValue::UnsignedNumber(new_nonce))
-                .add_typed_default(DataType::Timestamp, DataValue::UnsignedNumber(new_nonce))
+            .add_typed_default(DataType::Signature, DataValue::Bytes(host_sig))
-                .add_typed_default(DataType::Signature, DataValue::Bytes(host_sig))
+            .add_typed_default(DataType::Id, DataValue::UnsignedNumber(assigned_id as u128));
-                .add_typed_default(DataType::Id, DataValue::UnsignedNumber(assigned_id as u128));
 
         if !self
             .config
@@ -335,6 +344,7 @@ impl MTPHost {
         /* ===== End Signature ===== */
 
         sender.send(&response).await.ok()?;
+        sender.finish_stream().await.ok()?;
 
         // 3. Version negotiation
         let negotiated = self.registry.negotiate(&[client_version])?;

transport/src/connection.rs

@@ -61,7 +61,7 @@ enum ReceivedFrame {
 
 pub struct Sender {
     send_guard: Mutex<()>,
-    stream_guard: Mutex<Option<wtransport::SendStream>>,
+    stream_guard: Arc<Mutex<Option<wtransport::SendStream>>>,
     handle: Arc<ConnectionHandle>,
     connection: Connection,
     policy: Arc<Policy>,
@@ -71,7 +71,7 @@ impl Sender {
     pub fn new(connection: Connection, handle: Arc<ConnectionHandle>, policy: Arc<Policy>) -> Self {
         Self {
             send_guard: Mutex::new(()),
-            stream_guard: Mutex::new(None),
+            stream_guard: Arc::new(Mutex::new(None)),
             handle,
             connection,
             policy,
@@ -275,6 +275,18 @@ impl Sender {
         }
     }
 
+    pub async fn finish_stream(&self) -> Result<(), CommunicationError> {
+        let _send_lock = self.send_guard.lock().await;
+        let mut stream_opt = self.stream_guard.lock().await;
+        if let Some(mut stream) = stream_opt.take() {
+            timeout(self.policy.write_timeout, stream.finish())
+                .await
+                .map_err(|_| CommunicationError::StreamError)?
+                .map_err(|_| CommunicationError::StreamError)?;
+        }
+        Ok(())
+    }
+
     pub fn handle(&self) -> &Arc<ConnectionHandle> {
         &self.handle
     }
@@ -283,6 +295,7 @@ impl Sender {
         let connection = self.connection.clone();
         let handle = self.handle.clone();
         let policy = self.policy.clone();
+        let stream_guard = self.stream_guard.clone();
 
         tokio::spawn(async move {
             if connection.quic_connection().close_reason().is_some() || handle.is_closed() {
@@ -290,6 +303,14 @@ impl Sender {
                 return;
             }
 
+            if let Some(mut stream) = stream_guard.lock().await.take() {
+                match timeout(policy.write_timeout, stream.finish()).await {
+                    Ok(Ok(())) => {}
+                    Ok(Err(e)) => log::warn!("[Sender] persistent stream finish failed: {e}"),
+                    Err(_) => log::warn!("[Sender] persistent stream finish timed out"),
+                }
+            }
+
             let _ = Self::send_close_frame(&connection, &policy).await;
 
             handle.close(Some(CommunicationError::StreamClosed));

wasm/src/client.rs

@@ -3,9 +3,7 @@ use std::rc::Rc;
 
 use wasm_bindgen::prelude::*;
 
-use mtp_codec::{
+use mtp_codec::{CommunicationType, CommunicationValue, DataType, DataValue, PROTOCOL_VERSION};
-    CommunicationType, CommunicationValue, DataType, DataValue, PROTOCOL_VERSION,
-};
 use mtp_type_map::{CommunicationTypeId, DataTypeId};
 
 use mtp_crypto::SignatureScheme;
@@ -13,6 +11,31 @@ use mtp_crypto::SignatureScheme;
 use crate::error::js_error;
 use crate::transport::WasmTransport;
 
+fn raw_frame_preview(bytes: &[u8]) -> String {
+    let shown = bytes.len().min(256);
+    let mut preview = hex::encode(&bytes[..shown]);
+    if bytes.len() > shown {
+        preview.push_str("...");
+    }
+    format!("{} bytes, hex={preview}", bytes.len())
+}
+
+fn unexpected_response_type_error(
+    context: &str,
+    expected_type: CommunicationTypeId,
+    response_type: CommunicationTypeId,
+    response: &[u8],
+    parsed: &CommunicationValue,
+) -> JsValue {
+    js_error(&format!(
+        "unexpected response type during {context}: expected {:?}, got {:?}; raw {}; parsed {}",
+        expected_type,
+        response_type,
+        raw_frame_preview(response),
+        parsed
+    ))
+}
+
 #[wasm_bindgen]
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum ConnectionState {
@@ -33,17 +56,27 @@ pub struct ConnectionConfig {
 impl ConnectionConfig {
     #[wasm_bindgen(constructor)]
     pub fn new(url: String) -> Self {
-        Self { url, server_certificate_hashes: None, client_id: 0 }
+        Self {
+            url,
+            server_certificate_hashes: None,
+            client_id: 0,
+        }
     }
 
     #[wasm_bindgen(getter)]
-    pub fn url(&self) -> String { self.url.clone() }
+    pub fn url(&self) -> String {
+        self.url.clone()
+    }
 
     #[wasm_bindgen(setter)]
-    pub fn set_client_id(&mut self, id: u64) { self.client_id = id; }
+    pub fn set_client_id(&mut self, id: u64) {
+        self.client_id = id;
+    }
 
     #[wasm_bindgen(getter)]
-    pub fn client_id(&self) -> u64 { self.client_id }
+    pub fn client_id(&self) -> u64 {
+        self.client_id
+    }
 
     #[wasm_bindgen(setter)]
     pub fn set_server_certificate_hashes(&mut self, hashes: Vec<String>) {
@@ -79,24 +112,29 @@ impl WasmClient {
 
     #[wasm_bindgen]
     pub fn is_supported() -> bool {
-        js_sys::Reflect::has(&js_sys::global(), &JsValue::from_str("WebTransport"))
+        js_sys::Reflect::has(&js_sys::global(), &JsValue::from_str("WebTransport")).unwrap_or(false)
-            .unwrap_or(false)
     }
 
     #[wasm_bindgen(getter)]
-    pub fn state(&self) -> u8 { self.state.get() as u8 }
+    pub fn state(&self) -> u8 {
+        self.state.get() as u8
+    }
 
     /// Unauthenticated connect (sends basic Identification, enables receive loop).
     #[wasm_bindgen]
     pub async fn connect(&mut self, config: &ConnectionConfig) -> Result<(), JsValue> {
         self.set_state(ConnectionState::Connecting);
-        let transport = WasmTransport::connect(&config.url, config.server_certificate_hashes.clone()).await?;
+        let transport =
+            WasmTransport::connect(&config.url, config.server_certificate_hashes.clone()).await?;
         let inner = transport.inner().clone();
 
         let version_str = format!("{}", PROTOCOL_VERSION);
         let ident = CommunicationValue::new(CommunicationType::Identification)
             .add_typed_default(DataType::Version, DataValue::Str(version_str))
-            .add_typed_default(DataType::Id, DataValue::UnsignedNumber(config.client_id as u128));
+            .add_typed_default(
+                DataType::Id,
+                DataValue::UnsignedNumber(config.client_id as u128),
+            );
         transport.send_frame(&ident.to_bytes()).await?;
 
         self.transport = Some(transport);
@@ -106,7 +144,9 @@ impl WasmClient {
         let on_msg = self.on_message.clone();
         let on_err = self.on_error.clone();
         wasm_bindgen_futures::spawn_local(async move {
-            WasmTransport::from_inner(inner).receive_loop(on_msg, on_err).await;
+            WasmTransport::from_inner(inner)
+                .receive_loop(on_msg, on_err)
+                .await;
             state.set(ConnectionState::Disconnected);
         });
         Ok(())
@@ -137,8 +177,7 @@ impl WasmClient {
 
         let version_str = format!("{}", PROTOCOL_VERSION);
         let mut nonce_bytes = [0u8; 16];
-        getrandom::fill(&mut nonce_bytes)
+        getrandom::fill(&mut nonce_bytes).map_err(|_| js_error("rng failed"))?;
-            .map_err(|_| js_error("rng failed"))?;
         let client_nonce = u128::from_be_bytes(nonce_bytes);
 
         // Build signature payload: version || client_id || client_nonce
@@ -149,17 +188,22 @@ impl WasmClient {
 
         let signer = mtp_crypto::Ed25519Signer::new(&keyring.sig_cl_secret_key)
             .map_err(|e| js_error(&format!("signer creation failed: {}", e)))?;
-        let signature = signer.sign(&sig_payload)
+        let signature = signer
+            .sign(&sig_payload)
             .map_err(|e| js_error(&format!("signature failed: {}", e)))?;
 
         let frame = CommunicationValue::new(CommunicationType::Identification)
             .add_typed_default(DataType::Version, DataValue::Str(version_str))
             .add_typed_default(DataType::Id, DataValue::UnsignedNumber(client_id as u128))
-            .add_typed_default(DataType::ClientNonce, DataValue::UnsignedNumber(client_nonce))
+            .add_typed_default(
+                DataType::ClientNonce,
+                DataValue::UnsignedNumber(client_nonce),
+            )
             .add_typed_default(DataType::Signature, DataValue::Bytes(signature))
             .to_bytes();
 
-        let transport = WasmTransport::connect(&config.url, config.server_certificate_hashes.clone()).await?;
+        let transport =
+            WasmTransport::connect(&config.url, config.server_certificate_hashes.clone()).await?;
         let inner = transport.inner().clone();
         transport.send_frame(&frame).await?;
 
@@ -171,7 +215,13 @@ impl WasmClient {
         let resp_type = resp_comm.get_type();
         let expected_type = CommunicationTypeId(16); // IdentificationResponse
         if resp_type != expected_type {
-            return Err(js_error("unexpected response type"));
+            return Err(unexpected_response_type_error(
+                "auth_connect",
+                expected_type,
+                resp_type,
+                &response,
+                &resp_comm,
+            ));
         }
 
         if resp_comm.get_data(DataTypeId(11)) != &DataValue::BoolTrue {
@@ -197,7 +247,9 @@ impl WasmClient {
         let on_msg = self.on_message.clone();
         let on_err = self.on_error.clone();
         wasm_bindgen_futures::spawn_local(async move {
-            WasmTransport::from_inner(inner).receive_loop(on_msg, on_err).await;
+            WasmTransport::from_inner(inner)
+                .receive_loop(on_msg, on_err)
+                .await;
             state.set(ConnectionState::Disconnected);
         });
 
@@ -227,8 +279,7 @@ impl WasmClient {
 
         let version_str = format!("{}", PROTOCOL_VERSION);
         let mut nonce_bytes = [0u8; 16];
-        getrandom::fill(&mut nonce_bytes)
+        getrandom::fill(&mut nonce_bytes).map_err(|_| js_error("rng failed"))?;
-            .map_err(|_| js_error("rng failed"))?;
         let client_nonce = u128::from_be_bytes(nonce_bytes);
 
         let pk_bytes = keyring.public_key_bundle().as_bytes();
@@ -241,17 +292,22 @@ impl WasmClient {
 
         let signer = mtp_crypto::Ed25519Signer::new(&keyring.sig_cl_secret_key)
             .map_err(|e| js_error(&format!("signer creation failed: {}", e)))?;
-        let signature = signer.sign(&sig_payload)
+        let signature = signer
+            .sign(&sig_payload)
             .map_err(|e| js_error(&format!("signature failed: {}", e)))?;
 
         let frame = CommunicationValue::new(CommunicationType::Register)
             .add_typed_default(DataType::Version, DataValue::Str(version_str))
-            .add_typed_default(DataType::ClientNonce, DataValue::UnsignedNumber(client_nonce))
+            .add_typed_default(
+                DataType::ClientNonce,
+                DataValue::UnsignedNumber(client_nonce),
+            )
             .add_typed_default(DataType::PublicKeys, DataValue::Bytes(pk_bytes))
             .add_typed_default(DataType::Signature, DataValue::Bytes(signature))
             .to_bytes();
 
-        let transport = WasmTransport::connect(&config.url, config.server_certificate_hashes.clone()).await?;
+        let transport =
+            WasmTransport::connect(&config.url, config.server_certificate_hashes.clone()).await?;
         let inner = transport.inner().clone();
         transport.send_frame(&frame).await?;
 
@@ -262,7 +318,13 @@ impl WasmClient {
         let resp_type = resp_comm.get_type();
         let expected_type = CommunicationTypeId(18); // RegisterResponse
         if resp_type != expected_type {
-            return Err(js_error("unexpected response type"));
+            return Err(unexpected_response_type_error(
+                "auth_register",
+                expected_type,
+                resp_type,
+                &response,
+                &resp_comm,
+            ));
         }
 
         if resp_comm.get_data(DataTypeId(11)) != &DataValue::BoolTrue {
@@ -286,7 +348,9 @@ impl WasmClient {
         let on_msg = self.on_message.clone();
         let on_err = self.on_error.clone();
         wasm_bindgen_futures::spawn_local(async move {
-            WasmTransport::from_inner(inner).receive_loop(on_msg, on_err).await;
+            WasmTransport::from_inner(inner)
+                .receive_loop(on_msg, on_err)
+                .await;
             state.set(ConnectionState::Disconnected);
         });
 
@@ -303,16 +367,17 @@ impl WasmClient {
 
     #[wasm_bindgen]
     pub fn disconnect(&mut self) {
-        if let Some(t) = &self.transport { t.close(); }
+        if let Some(t) = &self.transport {
+            t.close();
+        }
         self.transport = None;
         self.set_state(ConnectionState::Disconnected);
     }
 
     fn set_state(&self, new_state: ConnectionState) {
         self.state.set(new_state);
-        let _ = self.on_state_change.call1(
+        let _ = self
-            &JsValue::NULL,
+            .on_state_change
-            &JsValue::from(new_state as u8),
+            .call1(&JsValue::NULL, &JsValue::from(new_state as u8));
-        );
     }
 }

wasm/src/message.rs

@@ -1,27 +1,23 @@
 use wasm_bindgen::prelude::*;
 
-use mtp_codec::{
+use mtp_codec::{CommunicationType, CommunicationValue, DataType, DataTypeId, DataValue};
-    CommunicationType, CommunicationValue, DataType, DataTypeId, DataValue,
+use mtp_crypto::{ChaCha20Poly1305, Ed25519Signer, Keyring, SigAlgorithm, derive_encryption_key};
-};
 use mtp_type_map::communication_type_name;
-use mtp_crypto::{
-    ChaCha20Poly1305, Ed25519Signer, Keyring, SigAlgorithm,
-    derive_encryption_key,
-};
 
 use crate::error::js_error;
 
 /// Build a simple Ping frame with description, timestamp, and optional data.
 #[wasm_bindgen]
-pub fn build_ping_frame(
+pub fn build_ping_frame(client_id: u64, description: &str, timestamp: u64, data: &[u8]) -> Vec<u8> {
-    client_id: u64,
-    description: &str,
-    timestamp: u64,
-    data: &[u8],
-) -> Vec<u8> {
     let mut msg = CommunicationValue::new(CommunicationType::Ping)
-        .add_typed_default(DataType::Description, DataValue::Str(description.to_string()))
+        .add_typed_default(
-        .add_typed_default(DataType::Timestamp, DataValue::UnsignedNumber(timestamp as u128))
+            DataType::Description,
+            DataValue::Str(description.to_string()),
+        )
+        .add_typed_default(
+            DataType::Timestamp,
+            DataValue::UnsignedNumber(timestamp as u128),
+        )
         .with_sender(client_id);
 
     if !data.is_empty() {
@@ -55,7 +51,8 @@ pub fn build_demo_message(client_id: u64, keyring_bytes: &[u8]) -> Result<Vec<u8
         (DataTypeId(2), DataValue::UnsignedNumber(42)),
     ]);
     let mut dv_enc = inner_enc;
-    dv_enc.encrypt_container(&cipher, b"demo-aad")
+    dv_enc
+        .encrypt_container(&cipher, b"demo-aad")
         .ok_or_else(|| js_error("encryption failed"))?;
 
     // Signed container
@@ -64,23 +61,34 @@ pub fn build_demo_message(client_id: u64, keyring_bytes: &[u8]) -> Result<Vec<u8
         (DataTypeId(2), DataValue::UnsignedNumber(99)),
     ]);
     let mut dv_sig = inner_sig;
-    dv_sig.sign_container(SigAlgorithm::ED25519, &signer)
+    dv_sig
+        .sign_container(SigAlgorithm::ED25519, &signer)
         .ok_or_else(|| js_error("signing failed"))?;
 
     // Signed + encrypted container
     let inner_sec = DataValue::Container(vec![
-        (DataTypeId(1), DataValue::Str("signed+encrypted payload".into())),
+        (
+            DataTypeId(1),
+            DataValue::Str("signed+encrypted payload".into()),
+        ),
         (DataTypeId(2), DataValue::UnsignedNumber(7)),
     ]);
     let mut dv_sec = inner_sec;
-    dv_sec.sign_and_encrypt_container(SigAlgorithm::ED25519, &signer, &cipher, b"demo-aad")
+    dv_sec
+        .sign_and_encrypt_container(SigAlgorithm::ED25519, &signer, &cipher, b"demo-aad")
         .ok_or_else(|| js_error("sign+encrypt failed"))?;
 
     let timestamp = js_sys::Date::now() as u64;
 
     let msg = CommunicationValue::new(CommunicationType::Ping)
-        .add_typed_default(DataType::Description, DataValue::Str("MTP WASM Demo".into()))
+        .add_typed_default(
-        .add_typed_default(DataType::Timestamp, DataValue::UnsignedNumber(timestamp as u128))
+            DataType::Description,
+            DataValue::Str("MTP WASM Demo".into()),
+        )
+        .add_typed_default(
+            DataType::Timestamp,
+            DataValue::UnsignedNumber(timestamp as u128),
+        )
         .add_typed_default(DataType::Version, DataValue::Str("demo-wasm".into()))
         .with_sender(client_id);
 
@@ -174,7 +182,11 @@ pub fn parse_response_frame(frame: &[u8]) -> Result<String, JsValue> {
 
     let obj = js_sys::Object::new();
 
-    let _ = js_sys::Reflect::set(&obj, &JsValue::from_str("_id"), &JsValue::from(comm.get_id()));
+    let _ = js_sys::Reflect::set(
+        &obj,
+        &JsValue::from_str("_id"),
+        &JsValue::from(comm.get_id()),
+    );
 
     let type_name = communication_type_name(comm.get_type().0).unwrap_or("Unknown");
     let _ = js_sys::Reflect::set(
@@ -200,12 +212,21 @@ pub fn parse_response_frame(frame: &[u8]) -> Result<String, JsValue> {
         }
     }
 
-    let stringified = js_sys::JSON::stringify(&obj)
+    let stringified =
-        .map_err(|_| js_error("JSON stringify failed"))?;
+        js_sys::JSON::stringify(&obj).map_err(|_| js_error("JSON stringify failed"))?;
-    stringified.as_string()
+    stringified
+        .as_string()
         .ok_or_else(|| js_error("JSON stringify result not a string"))
 }
 
+/// Parse any MTP frame into the human-readable CommunicationValue display form.
+#[wasm_bindgen]
+pub fn format_frame(frame: &[u8]) -> Result<String, JsValue> {
+    let comm = CommunicationValue::from_bytes(frame)
+        .map_err(|e| js_error(&format!("parse failed: {}", e)))?;
+    Ok(comm.to_string())
+}
+
 #[cfg(test)]
 #[cfg(target_arch = "wasm32")]
 mod tests {
@@ -219,8 +240,14 @@ mod tests {
 
         assert_eq!(cv.get_type(), CommunicationTypeId(19)); // Ping
         assert_eq!(cv.get_sender(), 42);
-        assert_eq!(cv.get_data(DataTypeId(4)), &DataValue::Str("test-ping".into()));
+        assert_eq!(
-        assert_eq!(cv.get_data(DataTypeId(5)), &DataValue::UnsignedNumber(1234567890));
+            cv.get_data(DataTypeId(4)),
+            &DataValue::Str("test-ping".into())
+        );
+        assert_eq!(
+            cv.get_data(DataTypeId(5)),
+            &DataValue::UnsignedNumber(1234567890)
+        );
     }
 
     #[wasm_bindgen_test]
@@ -231,9 +258,15 @@ mod tests {
 
         assert_eq!(cv.get_type(), CommunicationTypeId(19));
         assert_eq!(cv.get_sender(), 99);
-        assert_eq!(cv.get_data(DataTypeId(4)), &DataValue::Str("with-data".into()));
+        assert_eq!(
+            cv.get_data(DataTypeId(4)),
+            &DataValue::Str("with-data".into())
+        );
         assert_eq!(cv.get_data(DataTypeId(5)), &DataValue::UnsignedNumber(555));
-        assert_eq!(cv.get_data(DataTypeId(6)), &DataValue::Bytes(payload.to_vec()));
+        assert_eq!(
+            cv.get_data(DataTypeId(6)),
+            &DataValue::Bytes(payload.to_vec())
+        );
     }
 
     #[wasm_bindgen_test]
@@ -264,7 +297,10 @@ mod tests {
 
         assert_eq!(cv.get_type(), CommunicationTypeId(19)); // Ping
         assert_eq!(cv.get_sender(), 7);
-        assert_eq!(cv.get_data(DataTypeId(4)), &DataValue::Str("MTP WASM Demo".into()));
+        assert_eq!(
+            cv.get_data(DataTypeId(4)),
+            &DataValue::Str("MTP WASM Demo".into())
+        );
     }
 
     #[wasm_bindgen_test]
@@ -287,11 +323,13 @@ mod tests {
         let result = parse_auth_response(&resp).expect("parse failed");
 
         let connected = js_sys::Reflect::get(&result, &"connected".into())
-            .ok().and_then(|v| v.as_bool());
+            .ok()
+            .and_then(|v| v.as_bool());
         assert_eq!(connected, Some(true));
 
         let id = js_sys::Reflect::get(&result, &"assignedId".into())
-            .ok().and_then(|v| v.as_f64());
+            .ok()
+            .and_then(|v| v.as_f64());
         assert_eq!(id, Some(42.0));
     }
 
@@ -304,7 +342,8 @@ mod tests {
         let result = parse_auth_response(&resp).expect("parse failed");
 
         let connected = js_sys::Reflect::get(&result, &"connected".into())
-            .ok().and_then(|v| v.as_bool());
+            .ok()
+            .and_then(|v| v.as_bool());
         assert_eq!(connected, Some(false));
 
         // rejected should have no assignedId

wasm/src/transport.rs

@@ -5,6 +5,8 @@ use web_sys::{WebTransport, WebTransportHash, WebTransportOptions};
 
 use crate::error::js_error;
 
+const CLOSE_FRAME_LEN: u32 = u32::MAX;
+
 /// Given a `SendStream` (old API with `.writable` or new API where stream IS a WritableStream),
 /// return the object to call `.getWriter()` on.
 fn resolve_stream_writable(send_stream: &JsValue) -> Result<JsValue, JsValue> {
@@ -199,10 +201,17 @@ impl WasmTransport {
             }
 
             if buffer.len() >= 4 {
-                let frame_len =
+                let frame_len = u32::from_be_bytes([buffer[0], buffer[1], buffer[2], buffer[3]]);
-                    u32::from_be_bytes([buffer[0], buffer[1], buffer[2], buffer[3]]) as usize;
+                if frame_len == CLOSE_FRAME_LEN {
-                if 4 + frame_len <= buffer.len() {
+                    return Err(js_error("connection closed before frame"));
-                    return Ok(buffer[4..4 + frame_len].to_vec());
+                }
+
+                let frame_len = frame_len as usize;
+                let Some(frame_end) = 4usize.checked_add(frame_len) else {
+                    return Err(js_error("invalid frame length"));
+                };
+                if frame_end <= buffer.len() {
+                    return Ok(buffer[4..frame_end].to_vec());
                 }
             }
         }
@@ -230,13 +239,7 @@ impl WasmTransport {
             let result = match read_fn.call0(&reader_val) {
                 Ok(p) => match JsFuture::from(p.unchecked_into::<js_sys::Promise>()).await {
                     Ok(v) => v,
-                    Err(e) => {
+                    Err(_) => break,
-                        let _ = on_error.call1(
-                            &JsValue::NULL,
-                            &JsValue::from_str(&format!("read stream failed: {:?}", e)),
-                        );
-                        break;
-                    }
                 },
                 Err(_) => break,
             };
@@ -302,29 +305,43 @@ impl WasmTransport {
 
             // Extract all complete frames from the buffer
             while buffer.len() >= 4 {
-                let frame_len =
+                let frame_len = u32::from_be_bytes([buffer[0], buffer[1], buffer[2], buffer[3]]);
-                    u32::from_be_bytes([buffer[0], buffer[1], buffer[2], buffer[3]]) as usize;
+                if frame_len == CLOSE_FRAME_LEN {
-                if 4 + frame_len > buffer.len() {
+                    return Ok(());
+                }
+
+                let frame_len = frame_len as usize;
+                let Some(frame_end) = 4usize.checked_add(frame_len) else {
+                    return Err(js_error("invalid frame length"));
+                };
+                if frame_end > buffer.len() {
                     break;
                 }
-                let frame = buffer[4..4 + frame_len].to_vec();
+                let frame = buffer[4..frame_end].to_vec();
                 let arr = js_sys::Uint8Array::from(&frame[..]);
                 let _ = on_message.call1(&JsValue::NULL, &arr);
-                buffer.drain(..4 + frame_len);
+                buffer.drain(..frame_end);
             }
         }
 
         // Process any remaining complete frames after stream closes
         while buffer.len() >= 4 {
-            let frame_len =
+            let frame_len = u32::from_be_bytes([buffer[0], buffer[1], buffer[2], buffer[3]]);
-                u32::from_be_bytes([buffer[0], buffer[1], buffer[2], buffer[3]]) as usize;
+            if frame_len == CLOSE_FRAME_LEN {
-            if 4 + frame_len > buffer.len() {
+                return Ok(());
+            }
+
+            let frame_len = frame_len as usize;
+            let Some(frame_end) = 4usize.checked_add(frame_len) else {
+                return Err(js_error("invalid frame length"));
+            };
+            if frame_end > buffer.len() {
                 break;
             }
-            let frame = buffer[4..4 + frame_len].to_vec();
+            let frame = buffer[4..frame_end].to_vec();
             let arr = js_sys::Uint8Array::from(&frame[..]);
             let _ = on_message.call1(&JsValue::NULL, &arr);
-            buffer.drain(..4 + frame_len);
+            buffer.drain(..frame_end);
         }
 
         Ok(())