Optimize API frame helper buffer management (#8805)

Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>

esphome/components/api/api_frame_helper.cpp

@@ -7,20 +7,13 @@
 #include "proto.h"
 #include "api_pb2_size.h"
 #include <cstring>
+#include <cinttypes>
 
 namespace esphome {
 namespace api {
 
 static const char *const TAG = "api.socket";
 
-/// Is the given return value (from write syscalls) a wouldblock error?
-bool is_would_block(ssize_t ret) {
-  if (ret == -1) {
-    return errno == EWOULDBLOCK || errno == EAGAIN;
-  }
-  return ret == 0;
-}
-
 const char *api_error_to_str(APIError err) {
   // not using switch to ensure compiler doesn't try to build a big table out of it
   if (err == APIError::OK) {
@@ -73,92 +66,154 @@ const char *api_error_to_str(APIError err) {
   return "UNKNOWN";
 }
 
-// Common implementation for writing raw data to socket
-template<typename StateEnum>
-APIError APIFrameHelper::write_raw_(const struct iovec *iov, int iovcnt, socket::Socket *socket,
-                                    std::vector<uint8_t> &tx_buf, const std::string &info, StateEnum &state,
-                                    StateEnum failed_state) {
-  // This method writes data to socket or buffers it
+// Helper method to buffer data from IOVs
+void APIFrameHelper::buffer_data_from_iov_(const struct iovec *iov, int iovcnt, uint16_t total_write_len) {
+  SendBuffer buffer;
+  buffer.data.reserve(total_write_len);
+  for (int i = 0; i < iovcnt; i++) {
+    const uint8_t *data = reinterpret_cast<uint8_t *>(iov[i].iov_base);
+    buffer.data.insert(buffer.data.end(), data, data + iov[i].iov_len);
+  }
+  this->tx_buf_.push_back(std::move(buffer));
+}
+
+// This method writes data to socket or buffers it
+APIError APIFrameHelper::write_raw_(const struct iovec *iov, int iovcnt) {
   // Returns APIError::OK if successful (or would block, but data has been buffered)
-  // Returns APIError::SOCKET_WRITE_FAILED if socket write failed, and sets state to failed_state
+  // Returns APIError::SOCKET_WRITE_FAILED if socket write failed, and sets state to FAILED
 
   if (iovcnt == 0)
     return APIError::OK;  // Nothing to do, success
 
-  size_t total_write_len = 0;
+  uint16_t total_write_len = 0;
   for (int i = 0; i < iovcnt; i++) {
 #ifdef HELPER_LOG_PACKETS
     ESP_LOGVV(TAG, "Sending raw: %s",
               format_hex_pretty(reinterpret_cast<uint8_t *>(iov[i].iov_base), iov[i].iov_len).c_str());
 #endif
-    total_write_len += iov[i].iov_len;
+    total_write_len += static_cast<uint16_t>(iov[i].iov_len);
   }
 
-  if (!tx_buf.empty()) {
-    // try to empty tx_buf first
-    while (!tx_buf.empty()) {
-      ssize_t sent = socket->write(tx_buf.data(), tx_buf.size());
-      if (is_would_block(sent)) {
-        break;
-      } else if (sent == -1) {
-        ESP_LOGVV(TAG, "%s: Socket write failed with errno %d", info.c_str(), errno);
-        state = failed_state;
-        return APIError::SOCKET_WRITE_FAILED;  // Socket write failed
-      }
-      // TODO: inefficient if multiple packets in txbuf
-      // replace with deque of buffers
-      tx_buf.erase(tx_buf.begin(), tx_buf.begin() + sent);
+  // Try to send any existing buffered data first if there is any
+  if (!this->tx_buf_.empty()) {
+    APIError send_result = try_send_tx_buf_();
+    // If real error occurred (not just WOULD_BLOCK), return it
+    if (send_result != APIError::OK && send_result != APIError::WOULD_BLOCK) {
+      return send_result;
+    }
+
+    // If there is still data in the buffer, we can't send, buffer
+    // the new data and return
+    if (!this->tx_buf_.empty()) {
+      this->buffer_data_from_iov_(iov, iovcnt, total_write_len);
+      return APIError::OK;  // Success, data buffered
     }
   }
 
-  if (!tx_buf.empty()) {
-    // tx buf not empty, can't write now because then stream would be inconsistent
-    // Reserve space upfront to avoid multiple reallocations
-    tx_buf.reserve(tx_buf.size() + total_write_len);
-    for (int i = 0; i < iovcnt; i++) {
-      tx_buf.insert(tx_buf.end(), reinterpret_cast<uint8_t *>(iov[i].iov_base),
-                    reinterpret_cast<uint8_t *>(iov[i].iov_base) + iov[i].iov_len);
-    }
-    return APIError::OK;  // Success, data buffered
-  }
+  // Try to send directly if no buffered data
+  ssize_t sent = this->socket_->writev(iov, iovcnt);
 
-  ssize_t sent = socket->writev(iov, iovcnt);
-  if (is_would_block(sent)) {
-    // operation would block, add buffer to tx_buf
-    // Reserve space upfront to avoid multiple reallocations
-    tx_buf.reserve(tx_buf.size() + total_write_len);
-    for (int i = 0; i < iovcnt; i++) {
-      tx_buf.insert(tx_buf.end(), reinterpret_cast<uint8_t *>(iov[i].iov_base),
-                    reinterpret_cast<uint8_t *>(iov[i].iov_base) + iov[i].iov_len);
+  if (sent == -1) {
+    if (errno == EWOULDBLOCK || errno == EAGAIN) {
+      // Socket would block, buffer the data
+      this->buffer_data_from_iov_(iov, iovcnt, total_write_len);
+      return APIError::OK;  // Success, data buffered
     }
-    return APIError::OK;  // Success, data buffered
-  } else if (sent == -1) {
-    // an error occurred
-    ESP_LOGVV(TAG, "%s: Socket write failed with errno %d", info.c_str(), errno);
-    state = failed_state;
+    // Socket error
+    ESP_LOGVV(TAG, "%s: Socket write failed with errno %d", this->info_.c_str(), errno);
+    this->state_ = State::FAILED;
     return APIError::SOCKET_WRITE_FAILED;  // Socket write failed
-  } else if ((size_t) sent != total_write_len) {
-    // partially sent, add end to tx_buf
-    size_t remaining = total_write_len - sent;
-    // Reserve space upfront to avoid multiple reallocations
-    tx_buf.reserve(tx_buf.size() + remaining);
+  } else if (static_cast<uint16_t>(sent) < total_write_len) {
+    // Partially sent, buffer the remaining data
+    SendBuffer buffer;
+    uint16_t to_consume = static_cast<uint16_t>(sent);
+    uint16_t remaining = total_write_len - static_cast<uint16_t>(sent);
+
+    buffer.data.reserve(remaining);
 
-    size_t to_consume = sent;
     for (int i = 0; i < iovcnt; i++) {
       if (to_consume >= iov[i].iov_len) {
-        to_consume -= iov[i].iov_len;
+        // This segment was fully sent
+        to_consume -= static_cast<uint16_t>(iov[i].iov_len);
       } else {
-        tx_buf.insert(tx_buf.end(), reinterpret_cast<uint8_t *>(iov[i].iov_base) + to_consume,
-                      reinterpret_cast<uint8_t *>(iov[i].iov_base) + iov[i].iov_len);
+        // This segment was partially sent or not sent at all
+        const uint8_t *data = reinterpret_cast<uint8_t *>(iov[i].iov_base) + to_consume;
+        uint16_t len = static_cast<uint16_t>(iov[i].iov_len) - to_consume;
+        buffer.data.insert(buffer.data.end(), data, data + len);
         to_consume = 0;
       }
     }
-    return APIError::OK;  // Success, data buffered
+
+    this->tx_buf_.push_back(std::move(buffer));
   }
-  return APIError::OK;  // Success, all data sent
+
+  return APIError::OK;  // Success, all data sent or buffered
 }
 
-#define HELPER_LOG(msg, ...) ESP_LOGVV(TAG, "%s: " msg, info_.c_str(), ##__VA_ARGS__)
+// Common implementation for trying to send buffered data
+// IMPORTANT: Caller MUST ensure tx_buf_ is not empty before calling this method
+APIError APIFrameHelper::try_send_tx_buf_() {
+  // Try to send from tx_buf - we assume it's not empty as it's the caller's responsibility to check
+  bool tx_buf_empty = false;
+  while (!tx_buf_empty) {
+    // Get the first buffer in the queue
+    SendBuffer &front_buffer = this->tx_buf_.front();
+
+    // Try to send the remaining data in this buffer
+    ssize_t sent = this->socket_->write(front_buffer.current_data(), front_buffer.remaining());
+
+    if (sent == -1) {
+      if (errno != EWOULDBLOCK && errno != EAGAIN) {
+        // Real socket error (not just would block)
+        ESP_LOGVV(TAG, "%s: Socket write failed with errno %d", this->info_.c_str(), errno);
+        this->state_ = State::FAILED;
+        return APIError::SOCKET_WRITE_FAILED;  // Socket write failed
+      }
+      // Socket would block, we'll try again later
+      return APIError::WOULD_BLOCK;
+    } else if (sent == 0) {
+      // Nothing sent but not an error
+      return APIError::WOULD_BLOCK;
+    } else if (static_cast<uint16_t>(sent) < front_buffer.remaining()) {
+      // Partially sent, update offset
+      // Cast to ensure no overflow issues with uint16_t
+      front_buffer.offset += static_cast<uint16_t>(sent);
+      return APIError::WOULD_BLOCK;  // Stop processing more buffers if we couldn't send a complete buffer
+    } else {
+      // Buffer completely sent, remove it from the queue
+      this->tx_buf_.pop_front();
+      // Update empty status for the loop condition
+      tx_buf_empty = this->tx_buf_.empty();
+      // Continue loop to try sending the next buffer
+    }
+  }
+
+  return APIError::OK;  // All buffers sent successfully
+}
+
+APIError APIFrameHelper::init_common_() {
+  if (state_ != State::INITIALIZE || this->socket_ == nullptr) {
+    ESP_LOGVV(TAG, "%s: Bad state for init %d", this->info_.c_str(), (int) state_);
+    return APIError::BAD_STATE;
+  }
+  int err = this->socket_->setblocking(false);
+  if (err != 0) {
+    state_ = State::FAILED;
+    ESP_LOGVV(TAG, "%s: Setting nonblocking failed with errno %d", this->info_.c_str(), errno);
+    return APIError::TCP_NONBLOCKING_FAILED;
+  }
+
+  int enable = 1;
+  err = this->socket_->setsockopt(IPPROTO_TCP, TCP_NODELAY, &enable, sizeof(int));
+  if (err != 0) {
+    state_ = State::FAILED;
+    ESP_LOGVV(TAG, "%s: Setting nodelay failed with errno %d", this->info_.c_str(), errno);
+    return APIError::TCP_NODELAY_FAILED;
+  }
+  return APIError::OK;
+}
+
+#define HELPER_LOG(msg, ...) ESP_LOGVV(TAG, "%s: " msg, this->info_.c_str(), ##__VA_ARGS__)
 // uncomment to log raw packets
 //#define HELPER_LOG_PACKETS
 
@@ -206,23 +261,9 @@ std::string noise_err_to_str(int err) {
 
 /// Initialize the frame helper, returns OK if successful.
 APIError APINoiseFrameHelper::init() {
-  if (state_ != State::INITIALIZE || socket_ == nullptr) {
-    HELPER_LOG("Bad state for init %d", (int) state_);
-    return APIError::BAD_STATE;
-  }
-  int err = socket_->setblocking(false);
-  if (err != 0) {
-    state_ = State::FAILED;
-    HELPER_LOG("Setting nonblocking failed with errno %d", errno);
-    return APIError::TCP_NONBLOCKING_FAILED;
-  }
-
-  int enable = 1;
-  err = socket_->setsockopt(IPPROTO_TCP, TCP_NODELAY, &enable, sizeof(int));
-  if (err != 0) {
-    state_ = State::FAILED;
-    HELPER_LOG("Setting nodelay failed with errno %d", errno);
-    return APIError::TCP_NODELAY_FAILED;
+  APIError err = init_common_();
+  if (err != APIError::OK) {
+    return err;
   }
 
   // init prologue
@@ -234,17 +275,16 @@ APIError APINoiseFrameHelper::init() {
 /// Run through handshake messages (if in that phase)
 APIError APINoiseFrameHelper::loop() {
   APIError err = state_action_();
-  if (err == APIError::WOULD_BLOCK)
-    return APIError::OK;
-  if (err != APIError::OK)
+  if (err != APIError::OK && err != APIError::WOULD_BLOCK) {
     return err;
-  if (!tx_buf_.empty()) {
+  }
+  if (!this->tx_buf_.empty()) {
     err = try_send_tx_buf_();
-    if (err != APIError::OK) {
+    if (err != APIError::OK && err != APIError::WOULD_BLOCK) {
       return err;
     }
   }
-  return APIError::OK;
+  return APIError::OK;  // Convert WOULD_BLOCK to OK to avoid connection termination
 }
 
 /** Read a packet into the rx_buf_. If successful, stores frame data in the frame parameter
@@ -270,8 +310,8 @@ APIError APINoiseFrameHelper::try_read_frame_(ParsedFrame *frame) {
   // read header
   if (rx_header_buf_len_ < 3) {
     // no header information yet
-    size_t to_read = 3 - rx_header_buf_len_;
-    ssize_t received = socket_->read(&rx_header_buf_[rx_header_buf_len_], to_read);
+    uint8_t to_read = 3 - rx_header_buf_len_;
+    ssize_t received = this->socket_->read(&rx_header_buf_[rx_header_buf_len_], to_read);
     if (received == -1) {
       if (errno == EWOULDBLOCK || errno == EAGAIN) {
         return APIError::WOULD_BLOCK;
@@ -284,8 +324,8 @@ APIError APINoiseFrameHelper::try_read_frame_(ParsedFrame *frame) {
       HELPER_LOG("Connection closed");
       return APIError::CONNECTION_CLOSED;
     }
-    rx_header_buf_len_ += received;
-    if ((size_t) received != to_read) {
+    rx_header_buf_len_ += static_cast<uint8_t>(received);
+    if (static_cast<uint8_t>(received) != to_read) {
       // not a full read
       return APIError::WOULD_BLOCK;
     }
@@ -317,8 +357,8 @@ APIError APINoiseFrameHelper::try_read_frame_(ParsedFrame *frame) {
 
   if (rx_buf_len_ < msg_size) {
     // more data to read
-    size_t to_read = msg_size - rx_buf_len_;
-    ssize_t received = socket_->read(&rx_buf_[rx_buf_len_], to_read);
+    uint16_t to_read = msg_size - rx_buf_len_;
+    ssize_t received = this->socket_->read(&rx_buf_[rx_buf_len_], to_read);
     if (received == -1) {
       if (errno == EWOULDBLOCK || errno == EAGAIN) {
         return APIError::WOULD_BLOCK;
@@ -331,8 +371,8 @@ APIError APINoiseFrameHelper::try_read_frame_(ParsedFrame *frame) {
       HELPER_LOG("Connection closed");
       return APIError::CONNECTION_CLOSED;
     }
-    rx_buf_len_ += received;
-    if ((size_t) received != to_read) {
+    rx_buf_len_ += static_cast<uint16_t>(received);
+    if (static_cast<uint16_t>(received) != to_read) {
       // not all read
       return APIError::WOULD_BLOCK;
     }
@@ -381,6 +421,8 @@ APIError APINoiseFrameHelper::state_action_() {
     if (aerr != APIError::OK)
       return aerr;
     // ignore contents, may be used in future for flags
+    // Reserve space for: existing prologue + 2 size bytes + frame data
+    prologue_.reserve(prologue_.size() + 2 + frame.msg.size());
     prologue_.push_back((uint8_t) (frame.msg.size() >> 8));
     prologue_.push_back((uint8_t) frame.msg.size());
     prologue_.insert(prologue_.end(), frame.msg.begin(), frame.msg.end());
@@ -389,16 +431,20 @@ APIError APINoiseFrameHelper::state_action_() {
   }
   if (state_ == State::SERVER_HELLO) {
     // send server hello
+    const std::string &name = App.get_name();
+    const std::string &mac = get_mac_address();
+
     std::vector<uint8_t> msg;
+    // Reserve space for: 1 byte proto + name + null + mac + null
+    msg.reserve(1 + name.size() + 1 + mac.size() + 1);
+
     // chosen proto
     msg.push_back(0x01);
 
     // node name, terminated by null byte
-    const std::string &name = App.get_name();
     const uint8_t *name_ptr = reinterpret_cast<const uint8_t *>(name.c_str());
     msg.insert(msg.end(), name_ptr, name_ptr + name.size() + 1);
     // node mac, terminated by null byte
-    const std::string &mac = get_mac_address();
     const uint8_t *mac_ptr = reinterpret_cast<const uint8_t *>(mac.c_str());
     msg.insert(msg.end(), mac_ptr, mac_ptr + mac.size() + 1);
 
@@ -505,7 +551,6 @@ void APINoiseFrameHelper::send_explicit_handshake_reject_(const std::string &rea
   write_frame_(data.data(), data.size());
   state_ = orig_state;
 }
-
 APIError APINoiseFrameHelper::read_packet(ReadPacketBuffer *buffer) {
   int err;
   APIError aerr;
@@ -533,7 +578,7 @@ APIError APINoiseFrameHelper::read_packet(ReadPacketBuffer *buffer) {
     return APIError::CIPHERSTATE_DECRYPT_FAILED;
   }
 
-  size_t msg_size = mbuf.size;
+  uint16_t msg_size = mbuf.size;
   uint8_t *msg_data = frame.msg.data();
   if (msg_size < 4) {
     state_ = State::FAILED;
@@ -559,7 +604,6 @@ APIError APINoiseFrameHelper::read_packet(ReadPacketBuffer *buffer) {
   buffer->type = type;
   return APIError::OK;
 }
-bool APINoiseFrameHelper::can_write_without_blocking() { return state_ == State::DATA && tx_buf_.empty(); }
 APIError APINoiseFrameHelper::write_protobuf_packet(uint16_t type, ProtoWriteBuffer buffer) {
   int err;
   APIError aerr;
@@ -574,9 +618,9 @@ APIError APINoiseFrameHelper::write_protobuf_packet(uint16_t type, ProtoWriteBuf
 
   std::vector<uint8_t> *raw_buffer = buffer.get_buffer();
   // Message data starts after padding
-  size_t payload_len = raw_buffer->size() - frame_header_padding_;
-  size_t padding = 0;
-  size_t msg_len = 4 + payload_len + padding;
+  uint16_t payload_len = raw_buffer->size() - frame_header_padding_;
+  uint16_t padding = 0;
+  uint16_t msg_len = 4 + payload_len + padding;
 
   // We need to resize to include MAC space, but we already reserved it in create_buffer
   raw_buffer->resize(raw_buffer->size() + frame_footer_size_);
@@ -609,7 +653,7 @@ APIError APINoiseFrameHelper::write_protobuf_packet(uint16_t type, ProtoWriteBuf
     return APIError::CIPHERSTATE_ENCRYPT_FAILED;
   }
 
-  size_t total_len = 3 + mbuf.size;
+  uint16_t total_len = 3 + mbuf.size;
   buf_start[1] = (uint8_t) (mbuf.size >> 8);
   buf_start[2] = (uint8_t) mbuf.size;
 
@@ -620,29 +664,9 @@ APIError APINoiseFrameHelper::write_protobuf_packet(uint16_t type, ProtoWriteBuf
   iov.iov_len = total_len;
 
   // write raw to not have two packets sent if NAGLE disabled
-  return write_raw_(&iov, 1);
+  return this->write_raw_(&iov, 1);
 }
-APIError APINoiseFrameHelper::try_send_tx_buf_() {
-  // try send from tx_buf
-  while (state_ != State::CLOSED && !tx_buf_.empty()) {
-    ssize_t sent = socket_->write(tx_buf_.data(), tx_buf_.size());
-    if (sent == -1) {
-      if (errno == EWOULDBLOCK || errno == EAGAIN)
-        break;
-      state_ = State::FAILED;
-      HELPER_LOG("Socket write failed with errno %d", errno);
-      return APIError::SOCKET_WRITE_FAILED;
-    } else if (sent == 0) {
-      break;
-    }
-    // TODO: inefficient if multiple packets in txbuf
-    // replace with deque of buffers
-    tx_buf_.erase(tx_buf_.begin(), tx_buf_.begin() + sent);
-  }
-
-  return APIError::OK;
-}
-APIError APINoiseFrameHelper::write_frame_(const uint8_t *data, size_t len) {
+APIError APINoiseFrameHelper::write_frame_(const uint8_t *data, uint16_t len) {
   uint8_t header[3];
   header[0] = 0x01;  // indicator
   header[1] = (uint8_t) (len >> 8);
@@ -652,12 +676,12 @@ APIError APINoiseFrameHelper::write_frame_(const uint8_t *data, size_t len) {
   iov[0].iov_base = header;
   iov[0].iov_len = 3;
   if (len == 0) {
-    return write_raw_(iov, 1);
+    return this->write_raw_(iov, 1);
   }
   iov[1].iov_base = const_cast<uint8_t *>(data);
   iov[1].iov_len = len;
 
-  return write_raw_(iov, 2);
+  return this->write_raw_(iov, 2);
 }
 
 /** Initiate the data structures for the handshake.
@@ -752,22 +776,6 @@ APINoiseFrameHelper::~APINoiseFrameHelper() {
   }
 }
 
-APIError APINoiseFrameHelper::close() {
-  state_ = State::CLOSED;
-  int err = socket_->close();
-  if (err == -1)
-    return APIError::CLOSE_FAILED;
-  return APIError::OK;
-}
-APIError APINoiseFrameHelper::shutdown(int how) {
-  int err = socket_->shutdown(how);
-  if (err == -1)
-    return APIError::SHUTDOWN_FAILED;
-  if (how == SHUT_RDWR) {
-    state_ = State::CLOSED;
-  }
-  return APIError::OK;
-}
 extern "C" {
 // declare how noise generates random bytes (here with a good HWRNG based on the RF system)
 void noise_rand_bytes(void *output, size_t len) {
@@ -778,32 +786,15 @@ void noise_rand_bytes(void *output, size_t len) {
 }
 }
 
-// Explicit template instantiation for Noise
-template APIError APIFrameHelper::write_raw_<APINoiseFrameHelper::State>(
-    const struct iovec *iov, int iovcnt, socket::Socket *socket, std::vector<uint8_t> &tx_buf_, const std::string &info,
-    APINoiseFrameHelper::State &state, APINoiseFrameHelper::State failed_state);
 #endif  // USE_API_NOISE
 
 #ifdef USE_API_PLAINTEXT
 
 /// Initialize the frame helper, returns OK if successful.
 APIError APIPlaintextFrameHelper::init() {
-  if (state_ != State::INITIALIZE || socket_ == nullptr) {
-    HELPER_LOG("Bad state for init %d", (int) state_);
-    return APIError::BAD_STATE;
-  }
-  int err = socket_->setblocking(false);
-  if (err != 0) {
-    state_ = State::FAILED;
-    HELPER_LOG("Setting nonblocking failed with errno %d", errno);
-    return APIError::TCP_NONBLOCKING_FAILED;
-  }
-  int enable = 1;
-  err = socket_->setsockopt(IPPROTO_TCP, TCP_NODELAY, &enable, sizeof(int));
-  if (err != 0) {
-    state_ = State::FAILED;
-    HELPER_LOG("Setting nodelay failed with errno %d", errno);
-    return APIError::TCP_NODELAY_FAILED;
+  APIError err = init_common_();
+  if (err != APIError::OK) {
+    return err;
   }
 
   state_ = State::DATA;
@@ -814,14 +805,13 @@ APIError APIPlaintextFrameHelper::loop() {
   if (state_ != State::DATA) {
     return APIError::BAD_STATE;
   }
-  // try send pending TX data
-  if (!tx_buf_.empty()) {
+  if (!this->tx_buf_.empty()) {
     APIError err = try_send_tx_buf_();
-    if (err != APIError::OK) {
+    if (err != APIError::OK && err != APIError::WOULD_BLOCK) {
       return err;
     }
   }
-  return APIError::OK;
+  return APIError::OK;  // Convert WOULD_BLOCK to OK to avoid connection termination
 }
 
 /** Read a packet into the rx_buf_. If successful, stores frame data in the frame parameter
@@ -846,7 +836,7 @@ APIError APIPlaintextFrameHelper::try_read_frame_(ParsedFrame *frame) {
     // there is no data on the wire (which is the common case).
     // This results in faster failure detection compared to
     // attempting to read multiple bytes at once.
-    ssize_t received = socket_->read(&data, 1);
+    ssize_t received = this->socket_->read(&data, 1);
     if (received == -1) {
       if (errno == EWOULDBLOCK || errno == EAGAIN) {
         return APIError::WOULD_BLOCK;
@@ -910,14 +900,24 @@ APIError APIPlaintextFrameHelper::try_read_frame_(ParsedFrame *frame) {
       continue;
     }
 
-    rx_header_parsed_len_ = msg_size_varint->as_uint32();
+    if (msg_size_varint->as_uint32() > 65535) {
+      state_ = State::FAILED;
+      HELPER_LOG("Bad packet: message size %" PRIu32 " exceeds maximum 65535", msg_size_varint->as_uint32());
+      return APIError::BAD_DATA_PACKET;
+    }
+    rx_header_parsed_len_ = msg_size_varint->as_uint16();
 
     auto msg_type_varint = ProtoVarInt::parse(&rx_header_buf_[consumed], rx_header_buf_pos_ - 1 - consumed, &consumed);
     if (!msg_type_varint.has_value()) {
       // not enough data there yet
       continue;
     }
-    rx_header_parsed_type_ = msg_type_varint->as_uint32();
+    if (msg_type_varint->as_uint32() > 65535) {
+      state_ = State::FAILED;
+      HELPER_LOG("Bad packet: message type %" PRIu32 " exceeds maximum 65535", msg_type_varint->as_uint32());
+      return APIError::BAD_DATA_PACKET;
+    }
+    rx_header_parsed_type_ = msg_type_varint->as_uint16();
     rx_header_parsed_ = true;
   }
   // header reading done
@@ -929,8 +929,8 @@ APIError APIPlaintextFrameHelper::try_read_frame_(ParsedFrame *frame) {
 
   if (rx_buf_len_ < rx_header_parsed_len_) {
     // more data to read
-    size_t to_read = rx_header_parsed_len_ - rx_buf_len_;
-    ssize_t received = socket_->read(&rx_buf_[rx_buf_len_], to_read);
+    uint16_t to_read = rx_header_parsed_len_ - rx_buf_len_;
+    ssize_t received = this->socket_->read(&rx_buf_[rx_buf_len_], to_read);
     if (received == -1) {
       if (errno == EWOULDBLOCK || errno == EAGAIN) {
         return APIError::WOULD_BLOCK;
@@ -943,8 +943,8 @@ APIError APIPlaintextFrameHelper::try_read_frame_(ParsedFrame *frame) {
       HELPER_LOG("Connection closed");
       return APIError::CONNECTION_CLOSED;
     }
-    rx_buf_len_ += received;
-    if ((size_t) received != to_read) {
+    rx_buf_len_ += static_cast<uint16_t>(received);
+    if (static_cast<uint16_t>(received) != to_read) {
       // not all read
       return APIError::WOULD_BLOCK;
     }
@@ -962,7 +962,6 @@ APIError APIPlaintextFrameHelper::try_read_frame_(ParsedFrame *frame) {
   rx_header_parsed_ = false;
   return APIError::OK;
 }
-
 APIError APIPlaintextFrameHelper::read_packet(ReadPacketBuffer *buffer) {
   APIError aerr;
 
@@ -990,7 +989,7 @@ APIError APIPlaintextFrameHelper::read_packet(ReadPacketBuffer *buffer) {
                          "Bad indicator byte";
       iov[0].iov_base = (void *) msg;
       iov[0].iov_len = 19;
-      write_raw_(iov, 1);
+      this->write_raw_(iov, 1);
     }
     return aerr;
   }
@@ -1001,7 +1000,6 @@ APIError APIPlaintextFrameHelper::read_packet(ReadPacketBuffer *buffer) {
   buffer->type = rx_header_parsed_type_;
   return APIError::OK;
 }
-bool APIPlaintextFrameHelper::can_write_without_blocking() { return state_ == State::DATA && tx_buf_.empty(); }
 APIError APIPlaintextFrameHelper::write_protobuf_packet(uint16_t type, ProtoWriteBuffer buffer) {
   if (state_ != State::DATA) {
     return APIError::BAD_STATE;
@@ -1009,12 +1007,12 @@ APIError APIPlaintextFrameHelper::write_protobuf_packet(uint16_t type, ProtoWrit
 
   std::vector<uint8_t> *raw_buffer = buffer.get_buffer();
   // Message data starts after padding (frame_header_padding_ = 6)
-  size_t payload_len = raw_buffer->size() - frame_header_padding_;
+  uint16_t payload_len = static_cast<uint16_t>(raw_buffer->size() - frame_header_padding_);
 
   // Calculate varint sizes for header components
-  size_t size_varint_len = api::ProtoSize::varint(static_cast<uint32_t>(payload_len));
-  size_t type_varint_len = api::ProtoSize::varint(static_cast<uint32_t>(type));
-  size_t total_header_len = 1 + size_varint_len + type_varint_len;
+  uint8_t size_varint_len = api::ProtoSize::varint(static_cast<uint32_t>(payload_len));
+  uint8_t type_varint_len = api::ProtoSize::varint(static_cast<uint32_t>(type));
+  uint8_t total_header_len = 1 + size_varint_len + type_varint_len;
 
   if (total_header_len > frame_header_padding_) {
     // Header is too large to fit in the padding
@@ -1044,7 +1042,7 @@ APIError APIPlaintextFrameHelper::write_protobuf_packet(uint16_t type, ProtoWrit
   // [4-5]  - Message type varint (2 bytes, for types 128-32767)
   // [6...] - Actual payload data
   uint8_t *buf_start = raw_buffer->data();
-  size_t header_offset = frame_header_padding_ - total_header_len;
+  uint8_t header_offset = frame_header_padding_ - total_header_len;
 
   // Write the plaintext header
   buf_start[header_offset] = 0x00;  // indicator
@@ -1063,46 +1061,7 @@ APIError APIPlaintextFrameHelper::write_protobuf_packet(uint16_t type, ProtoWrit
 
   return write_raw_(&iov, 1);
 }
-APIError APIPlaintextFrameHelper::try_send_tx_buf_() {
-  // try send from tx_buf
-  while (state_ != State::CLOSED && !tx_buf_.empty()) {
-    ssize_t sent = socket_->write(tx_buf_.data(), tx_buf_.size());
-    if (is_would_block(sent)) {
-      break;
-    } else if (sent == -1) {
-      state_ = State::FAILED;
-      HELPER_LOG("Socket write failed with errno %d", errno);
-      return APIError::SOCKET_WRITE_FAILED;
-    }
-    // TODO: inefficient if multiple packets in txbuf
-    // replace with deque of buffers
-    tx_buf_.erase(tx_buf_.begin(), tx_buf_.begin() + sent);
-  }
 
-  return APIError::OK;
-}
-
-APIError APIPlaintextFrameHelper::close() {
-  state_ = State::CLOSED;
-  int err = socket_->close();
-  if (err == -1)
-    return APIError::CLOSE_FAILED;
-  return APIError::OK;
-}
-APIError APIPlaintextFrameHelper::shutdown(int how) {
-  int err = socket_->shutdown(how);
-  if (err == -1)
-    return APIError::SHUTDOWN_FAILED;
-  if (how == SHUT_RDWR) {
-    state_ = State::CLOSED;
-  }
-  return APIError::OK;
-}
-
-// Explicit template instantiation for Plaintext
-template APIError APIFrameHelper::write_raw_<APIPlaintextFrameHelper::State>(
-    const struct iovec *iov, int iovcnt, socket::Socket *socket, std::vector<uint8_t> &tx_buf_, const std::string &info,
-    APIPlaintextFrameHelper::State &state, APIPlaintextFrameHelper::State failed_state);
 #endif  // USE_API_PLAINTEXT
 
 }  // namespace api

esphome/components/api/api_frame_helper.h

@@ -21,15 +21,8 @@ class ProtoWriteBuffer;
 struct ReadPacketBuffer {
   std::vector<uint8_t> container;
   uint16_t type;
-  size_t data_offset;
-  size_t data_len;
-};
-
-struct PacketBuffer {
-  const std::vector<uint8_t> container;
-  uint16_t type;
-  uint8_t data_offset;
-  uint8_t data_len;
+  uint16_t data_offset;
+  uint16_t data_len;
 };
 
 enum class APIError : int {
@@ -62,38 +55,117 @@ const char *api_error_to_str(APIError err);
 
 class APIFrameHelper {
  public:
+  APIFrameHelper() = default;
+  explicit APIFrameHelper(std::unique_ptr<socket::Socket> socket) : socket_owned_(std::move(socket)) {
+    socket_ = socket_owned_.get();
+  }
   virtual ~APIFrameHelper() = default;
   virtual APIError init() = 0;
   virtual APIError loop() = 0;
   virtual APIError read_packet(ReadPacketBuffer *buffer) = 0;
-  virtual bool can_write_without_blocking() = 0;
-  virtual APIError write_protobuf_packet(uint16_t type, ProtoWriteBuffer buffer) = 0;
-  virtual std::string getpeername() = 0;
-  virtual int getpeername(struct sockaddr *addr, socklen_t *addrlen) = 0;
-  virtual APIError close() = 0;
-  virtual APIError shutdown(int how) = 0;
+  bool can_write_without_blocking() { return state_ == State::DATA && tx_buf_.empty(); }
+  std::string getpeername() { return socket_->getpeername(); }
+  int getpeername(struct sockaddr *addr, socklen_t *addrlen) { return socket_->getpeername(addr, addrlen); }
+  APIError close() {
+    state_ = State::CLOSED;
+    int err = this->socket_->close();
+    if (err == -1)
+      return APIError::CLOSE_FAILED;
+    return APIError::OK;
+  }
+  APIError shutdown(int how) {
+    int err = this->socket_->shutdown(how);
+    if (err == -1)
+      return APIError::SHUTDOWN_FAILED;
+    if (how == SHUT_RDWR) {
+      state_ = State::CLOSED;
+    }
+    return APIError::OK;
+  }
   // Give this helper a name for logging
-  virtual void set_log_info(std::string info) = 0;
+  void set_log_info(std::string info) { info_ = std::move(info); }
+  virtual APIError write_protobuf_packet(uint16_t type, ProtoWriteBuffer buffer) = 0;
   // Get the frame header padding required by this protocol
   virtual uint8_t frame_header_padding() = 0;
   // Get the frame footer size required by this protocol
   virtual uint8_t frame_footer_size() = 0;
 
  protected:
+  // Struct for holding parsed frame data
+  struct ParsedFrame {
+    std::vector<uint8_t> msg;
+  };
+
+  // Buffer containing data to be sent
+  struct SendBuffer {
+    std::vector<uint8_t> data;
+    uint16_t offset{0};  // Current offset within the buffer (uint16_t to reduce memory usage)
+
+    // Using uint16_t reduces memory usage since ESPHome API messages are limited to 64KB max
+    uint16_t remaining() const { return static_cast<uint16_t>(data.size()) - offset; }
+    const uint8_t *current_data() const { return data.data() + offset; }
+  };
+
+  // Queue of data buffers to be sent
+  std::deque<SendBuffer> tx_buf_;
+
+  // Common state enum for all frame helpers
+  // Note: Not all states are used by all implementations
+  // - INITIALIZE: Used by both Noise and Plaintext
+  // - CLIENT_HELLO, SERVER_HELLO, HANDSHAKE: Only used by Noise protocol
+  // - DATA: Used by both Noise and Plaintext
+  // - CLOSED: Used by both Noise and Plaintext
+  // - FAILED: Used by both Noise and Plaintext
+  // - EXPLICIT_REJECT: Only used by Noise protocol
+  enum class State {
+    INITIALIZE = 1,
+    CLIENT_HELLO = 2,  // Noise only
+    SERVER_HELLO = 3,  // Noise only
+    HANDSHAKE = 4,     // Noise only
+    DATA = 5,
+    CLOSED = 6,
+    FAILED = 7,
+    EXPLICIT_REJECT = 8,  // Noise only
+  };
+
+  // Current state of the frame helper
+  State state_{State::INITIALIZE};
+
+  // Helper name for logging
+  std::string info_;
+
+  // Socket for communication
+  socket::Socket *socket_{nullptr};
+  std::unique_ptr<socket::Socket> socket_owned_;
+
   // Common implementation for writing raw data to socket
+  APIError write_raw_(const struct iovec *iov, int iovcnt);
+
+  // Try to send data from the tx buffer
+  APIError try_send_tx_buf_();
+
+  // Helper method to buffer data from IOVs
+  void buffer_data_from_iov_(const struct iovec *iov, int iovcnt, uint16_t total_write_len);
   template<typename StateEnum>
   APIError write_raw_(const struct iovec *iov, int iovcnt, socket::Socket *socket, std::vector<uint8_t> &tx_buf,
                       const std::string &info, StateEnum &state, StateEnum failed_state);
 
   uint8_t frame_header_padding_{0};
   uint8_t frame_footer_size_{0};
+
+  // Receive buffer for reading frame data
+  std::vector<uint8_t> rx_buf_;
+  uint16_t rx_buf_len_ = 0;
+
+  // Common initialization for both plaintext and noise protocols
+  APIError init_common_();
 };
 
 #ifdef USE_API_NOISE
 class APINoiseFrameHelper : public APIFrameHelper {
  public:
   APINoiseFrameHelper(std::unique_ptr<socket::Socket> socket, std::shared_ptr<APINoiseContext> ctx)
-      : socket_(std::move(socket)), ctx_(std::move(ctx)) {
+      : APIFrameHelper(std::move(socket)), ctx_(std::move(ctx)) {
     // Noise header structure:
     // Pos 0: indicator (0x01)
     // Pos 1-2: encrypted payload size (16-bit big-endian)
@@ -105,49 +177,25 @@ class APINoiseFrameHelper : public APIFrameHelper {
   APIError init() override;
   APIError loop() override;
   APIError read_packet(ReadPacketBuffer *buffer) override;
-  bool can_write_without_blocking() override;
   APIError write_protobuf_packet(uint16_t type, ProtoWriteBuffer buffer) override;
-  std::string getpeername() override { return this->socket_->getpeername(); }
-  int getpeername(struct sockaddr *addr, socklen_t *addrlen) override {
-    return this->socket_->getpeername(addr, addrlen);
-  }
-  APIError close() override;
-  APIError shutdown(int how) override;
-  // Give this helper a name for logging
-  void set_log_info(std::string info) override { info_ = std::move(info); }
   // Get the frame header padding required by this protocol
   uint8_t frame_header_padding() override { return frame_header_padding_; }
   // Get the frame footer size required by this protocol
   uint8_t frame_footer_size() override { return frame_footer_size_; }
 
  protected:
-  struct ParsedFrame {
-    std::vector<uint8_t> msg;
-  };
-
   APIError state_action_();
   APIError try_read_frame_(ParsedFrame *frame);
-  APIError try_send_tx_buf_();
-  APIError write_frame_(const uint8_t *data, size_t len);
-  inline APIError write_raw_(const struct iovec *iov, int iovcnt) {
-    return APIFrameHelper::write_raw_(iov, iovcnt, socket_.get(), tx_buf_, info_, state_, State::FAILED);
-  }
+  APIError write_frame_(const uint8_t *data, uint16_t len);
   APIError init_handshake_();
   APIError check_handshake_finished_();
   void send_explicit_handshake_reject_(const std::string &reason);
-
-  std::unique_ptr<socket::Socket> socket_;
-
-  std::string info_;
   // Fixed-size header buffer for noise protocol:
   // 1 byte for indicator + 2 bytes for message size (16-bit value, not varint)
   // Note: Maximum message size is 65535, with a limit of 128 bytes during handshake phase
   uint8_t rx_header_buf_[3];
-  size_t rx_header_buf_len_ = 0;
-  std::vector<uint8_t> rx_buf_;
-  size_t rx_buf_len_ = 0;
+  uint8_t rx_header_buf_len_ = 0;
 
-  std::vector<uint8_t> tx_buf_;
   std::vector<uint8_t> prologue_;
 
   std::shared_ptr<APINoiseContext> ctx_;
@@ -155,24 +203,13 @@ class APINoiseFrameHelper : public APIFrameHelper {
   NoiseCipherState *send_cipher_{nullptr};
   NoiseCipherState *recv_cipher_{nullptr};
   NoiseProtocolId nid_;
-
-  enum class State {
-    INITIALIZE = 1,
-    CLIENT_HELLO = 2,
-    SERVER_HELLO = 3,
-    HANDSHAKE = 4,
-    DATA = 5,
-    CLOSED = 6,
-    FAILED = 7,
-    EXPLICIT_REJECT = 8,
-  } state_ = State::INITIALIZE;
 };
 #endif  // USE_API_NOISE
 
 #ifdef USE_API_PLAINTEXT
 class APIPlaintextFrameHelper : public APIFrameHelper {
  public:
-  APIPlaintextFrameHelper(std::unique_ptr<socket::Socket> socket) : socket_(std::move(socket)) {
+  APIPlaintextFrameHelper(std::unique_ptr<socket::Socket> socket) : APIFrameHelper(std::move(socket)) {
     // Plaintext header structure (worst case):
     // Pos 0: indicator (0x00)
     // Pos 1-3: payload size varint (up to 3 bytes)
@@ -184,35 +221,13 @@ class APIPlaintextFrameHelper : public APIFrameHelper {
   APIError init() override;
   APIError loop() override;
   APIError read_packet(ReadPacketBuffer *buffer) override;
-  bool can_write_without_blocking() override;
   APIError write_protobuf_packet(uint16_t type, ProtoWriteBuffer buffer) override;
-  std::string getpeername() override { return this->socket_->getpeername(); }
-  int getpeername(struct sockaddr *addr, socklen_t *addrlen) override {
-    return this->socket_->getpeername(addr, addrlen);
-  }
-  APIError close() override;
-  APIError shutdown(int how) override;
-  // Give this helper a name for logging
-  void set_log_info(std::string info) override { info_ = std::move(info); }
-  // Get the frame header padding required by this protocol
   uint8_t frame_header_padding() override { return frame_header_padding_; }
   // Get the frame footer size required by this protocol
   uint8_t frame_footer_size() override { return frame_footer_size_; }
 
  protected:
-  struct ParsedFrame {
-    std::vector<uint8_t> msg;
-  };
-
   APIError try_read_frame_(ParsedFrame *frame);
-  APIError try_send_tx_buf_();
-  inline APIError write_raw_(const struct iovec *iov, int iovcnt) {
-    return APIFrameHelper::write_raw_(iov, iovcnt, socket_.get(), tx_buf_, info_, state_, State::FAILED);
-  }
-
-  std::unique_ptr<socket::Socket> socket_;
-
-  std::string info_;
   // Fixed-size header buffer for plaintext protocol:
   // We only need space for the two varints since we validate the indicator byte separately.
   // To match noise protocol's maximum message size (65535), we need:
@@ -224,20 +239,8 @@ class APIPlaintextFrameHelper : public APIFrameHelper {
   uint8_t rx_header_buf_[5];  // 5 bytes for varints (3 for size + 2 for type)
   uint8_t rx_header_buf_pos_ = 0;
   bool rx_header_parsed_ = false;
-  uint32_t rx_header_parsed_type_ = 0;
-  uint32_t rx_header_parsed_len_ = 0;
-
-  std::vector<uint8_t> rx_buf_;
-  size_t rx_buf_len_ = 0;
-
-  std::vector<uint8_t> tx_buf_;
-
-  enum class State {
-    INITIALIZE = 1,
-    DATA = 2,
-    CLOSED = 3,
-    FAILED = 4,
-  } state_ = State::INITIALIZE;
+  uint16_t rx_header_parsed_type_ = 0;
+  uint16_t rx_header_parsed_len_ = 0;
 };
 #endif
 

esphome/components/api/proto.h

@@ -55,6 +55,7 @@ class ProtoVarInt {
     return {};  // Incomplete or invalid varint
   }
 
+  uint16_t as_uint16() const { return this->value_; }
   uint32_t as_uint32() const { return this->value_; }
   uint64_t as_uint64() const { return this->value_; }
   bool as_bool() const { return this->value_; }