Expose enable_deflate() so the inflater can be opted out of later

With raw lwIP in the main loop the radio is deaf while a sector is written,
so the ESP8266 and RP2040 keep the client quiet until the block is in flash;
with BSD or lwIP sockets the next block can arrive while this one is written.

esphome/__main__.py

@@ -1289,10 +1289,9 @@ def _choose_ota_platform(config: ConfigType, requested: str | None) -> str:
     The native API uses challenge-response auth with MD5/SHA256 hashing of a
     server-issued nonce, so the password is never sent over the wire; the
     ``web_server`` path uses HTTP Basic auth which transmits credentials in
-    cleartext over the LAN. (The native path also supports gzip compression
-    on ESP8266, where flash space is tight; on ESP32/RP2040/LibreTiny the
-    backend reports ``supports_compression() == false`` and the firmware is
-    sent uncompressed regardless of which platform is used.) Falls back to
+    cleartext over the LAN. (The native path also compresses the upload:
+    gzip on ESP8266 and RP2040, which inflate it at reboot, and a deflate
+    stream on ESP32/LibreTiny, which inflate it as it arrives.) Falls back to
     ``web_server`` only when that is the only available platform.
     """
     # Use a dict (insertion-ordered) instead of a list so error messages and

esphome/components/esphome/ota/__init__.py

@@ -283,10 +283,18 @@ FINAL_VALIDATE_SCHEMA = ota_esphome_final_validate
 
 
 FILTER_SOURCE_FILES = filter_source_files_from_defines(
-    {"ota_esphome_noise.cpp": "USE_OTA_ENCRYPTION"}
+    {
+        "ota_esphome_noise.cpp": "USE_OTA_ENCRYPTION",
+        "ota_esphome_inflate.c": "USE_OTA_DEFLATE",
+    }
 )
 
 
+def enable_deflate() -> None:
+    """Compile the on-the-fly inflater for compressed uploads."""
+    cg.add_define("USE_OTA_DEFLATE")
+
+
 @coroutine_with_priority(CoroPriority.OTA_UPDATES)
 async def to_code(config: ConfigType) -> None:
     var = cg.new_Pvariable(config[CONF_ID])
@@ -305,6 +313,10 @@ async def to_code(config: ConfigType) -> None:
     if config.get(CONF_ALLOW_PARTITION_ACCESS):
         cg.add_define("USE_OTA_PARTITIONS")
 
+    # ESP8266 and RP2040 inflate gzip at reboot; the rest inflate on the fly
+    if not (CORE.is_esp8266 or CORE.is_rp2):
+        enable_deflate()
+
     # One key per device: an api encryption block supplies it (static or
     # runtime) and offers; the ota block only adds the requirement
     api_conf = CORE.config.get(CONF_API) or {}

esphome/components/esphome/ota/ota_esphome.cpp

@@ -24,6 +24,7 @@
 
 #include <cerrno>
 #include <cstdio>
+#include <new>
 #include <sys/time.h>
 
 namespace esphome {
@@ -42,6 +43,8 @@ const noise::NoiseContext &ESPHomeOTAComponent::noise_context_() const {
 static constexpr uint16_t OTA_BLOCK_SIZE = 8192;
 static constexpr uint32_t OTA_SOCKET_TIMEOUT_HANDSHAKE = 20000;  // milliseconds for initial handshake
 static constexpr uint32_t OTA_SOCKET_TIMEOUT_DATA = 90000;       // milliseconds for data transfer
+static constexpr uint32_t OTA_PROGRESS_INTERVAL_MS = 1000;
+static constexpr size_t OTA_SIZE_FIELD_BYTES = 4;  // sizes on the wire are 4 bytes MSB first
 
 // Single-instance pointer — multi-port configs are rejected in final_validate.
 // NOLINTNEXTLINE(cppcoreguidelines-avoid-non-const-global-variables)
@@ -179,12 +182,16 @@ static constexpr uint8_t CLIENT_FEATURE_SUPPORTS_COMPRESSION = 0x01;
 static constexpr uint8_t CLIENT_FEATURE_SUPPORTS_SHA256_AUTH = 0x02;
 static constexpr uint8_t CLIENT_FEATURE_SUPPORTS_EXTENDED_PROTOCOL = 0x04;
 static constexpr uint8_t CLIENT_FEATURE_SUPPORTS_NOISE = 0x08;
+static constexpr uint8_t CLIENT_FEATURE_SUPPORTS_DEFLATE = 0x10;
 // Noise needs the extended protocol: the prologue binds the 2-byte feature ack
 static constexpr uint8_t CLIENT_NOISE_FEATURES =
     CLIENT_FEATURE_SUPPORTS_NOISE | CLIENT_FEATURE_SUPPORTS_EXTENDED_PROTOCOL;
 static constexpr uint8_t SERVER_FEATURE_SUPPORTS_COMPRESSION = 0x01;
 static constexpr uint8_t SERVER_FEATURE_SUPPORTS_PARTITION_ACCESS = 0x02;
 static constexpr uint8_t SERVER_FEATURE_SUPPORTS_NOISE = 0x04;
+// Raw deflate, window <= OTA_INFLATE_WINDOW_SIZE. Binding once offered: the
+// client must then send the image size frame and a deflate stream.
+static constexpr uint8_t SERVER_FEATURE_SUPPORTS_DEFLATE = 0x08;
 
 inline bool ESPHomeOTAComponent::extended_proto_() const {
 #ifdef USE_OTA_ENCRYPTION_REQUIRED
@@ -290,7 +297,7 @@ void ESPHomeOTAComponent::handle_handshake_() {
       this->transition_ota_state_(OTAState::FEATURE_ACK);
 
       const bool supports_compression =
-          (this->ota_features_ & CLIENT_FEATURE_SUPPORTS_COMPRESSION) != 0 && this->backend_->supports_compression();
+          (this->ota_features_ & CLIENT_FEATURE_SUPPORTS_COMPRESSION) != 0 && ota::OTABackend::supports_compression();
 
       // Compose the feature-ack response. When the client negotiates the extended protocol we emit
       // a 2-byte response (marker + server feature flags); otherwise we emit the single-byte
@@ -310,6 +317,17 @@ void ESPHomeOTAComponent::handle_handshake_() {
 #elif defined(USE_OTA_ENCRYPTION)
         // A yaml key always exists: validation rejects the all-zeros key
         this->handshake_buf_[1] |= SERVER_FEATURE_SUPPORTS_NOISE;
+#endif
+#ifdef USE_OTA_DEFLATE
+        // Offered only once the session memory is in hand; else uncompressed
+        if ((this->ota_features_ & CLIENT_FEATURE_SUPPORTS_DEFLATE) != 0) {
+          this->inflate_.reset(new (std::nothrow) InflateSession());
+          if (this->inflate_ != nullptr) {
+            this->handshake_buf_[1] |= SERVER_FEATURE_SUPPORTS_DEFLATE;
+          } else {
+            ESP_LOGW(TAG, "No memory to inflate");
+          }
+        }
 #endif
       } else {
         this->handshake_buf_[0] =
@@ -427,16 +445,11 @@ void ESPHomeOTAComponent::handle_data_() {
   // Backend calls overwrite this with OK; reset to UNKNOWN before any
   // goto error that follows a successful begin()/write()
   ota::OTAResponseTypes error_code = ota::OTA_RESPONSE_ERROR_UNKNOWN;
-  size_t total = 0;
-  uint32_t last_progress = 0;
-  uint32_t last_data_ms = 0;
+  DataTransfer xfer;
   uint8_t buf[OTA_BUFFER_SIZE];
   char *sbuf = reinterpret_cast<char *>(buf);
-  size_t ota_size;
+  size_t image_size;
   ota::OTAType ota_type = ota::OTA_TYPE_UPDATE_APP;
-#if USE_OTA_VERSION == 2
-  size_t size_acknowledged = 0;
-#endif
 
   // Set socket timeouts and blocking mode (see strategy table above)
   struct timeval tv;
@@ -459,14 +472,13 @@ void ESPHomeOTAComponent::handle_data_() {
   }
   ESP_LOGV(TAG, "OTA type is 0x%02x", ota_type);
 
-  // Read size, 4 bytes MSB first
-  if (!this->data_readall_(buf, 4)) {
-    this->log_read_error_(LOG_STR("size"));
+  if (!this->read_size_(buf, xfer.ota_size, LOG_STR("size")))
     goto error;  // NOLINT(cppcoreguidelines-avoid-goto)
-  }
-  ota_size = (static_cast<size_t>(buf[0]) << 24) | (static_cast<size_t>(buf[1]) << 16) |
-             (static_cast<size_t>(buf[2]) << 8) | buf[3];
-  ESP_LOGV(TAG, "Size is %zu bytes", ota_size);
+  image_size = xfer.ota_size;
+#ifdef USE_OTA_DEFLATE
+  if (this->inflate_ != nullptr && !this->read_size_(buf, image_size, LOG_STR("image size")))
+    goto error;  // NOLINT(cppcoreguidelines-avoid-goto)
+#endif
 
 #ifndef USE_OTA_PARTITIONS
   if (ota_type != ota::OTA_TYPE_UPDATE_APP) {
@@ -486,7 +498,7 @@ void ESPHomeOTAComponent::handle_data_() {
 #endif
 
   // begin() returns quickly; flash sectors are erased incrementally during write().
-  error_code = this->backend_->begin(ota_size, ota_type);
+  error_code = this->backend_->begin(image_size, ota_type);
   if (error_code != ota::OTA_RESPONSE_OK)
     goto error;  // NOLINT(cppcoreguidelines-avoid-goto)
 
@@ -506,75 +518,25 @@ void ESPHomeOTAComponent::handle_data_() {
   // Acknowledge MD5 OK - 1 byte
   this->data_write_byte_(ota::OTA_RESPONSE_BIN_MD5_OK);
 
-  // Track when we last received data so a silently-vanished peer (no FIN/RST
-  // delivered, e.g. uploader killed mid-transfer or NAT/router dropped state)
-  // can't wedge the device indefinitely. Without this, the loop only exits
-  // on actual data, EOF, or a non-EWOULDBLOCK error from read(), and lwIP
-  // TCP keepalive isn't enabled here.
-  last_data_ms = millis();
-  while (total < ota_size) {
-    if (millis() - last_data_ms > OTA_SOCKET_TIMEOUT_DATA) {
-      ESP_LOGW(TAG, "No data received for %u ms", (unsigned) OTA_SOCKET_TIMEOUT_DATA);
-      error_code = ota::OTA_RESPONSE_ERROR_UNKNOWN;
+  xfer.last_data_ms = millis();
+#ifdef USE_OTA_DEFLATE
+  if (this->inflate_ != nullptr) {
+    error_code = this->inflate_data_(buf, image_size, xfer);
+    if (error_code != ota::OTA_RESPONSE_OK)
       goto error;  // NOLINT(cppcoreguidelines-avoid-goto)
-    }
-    size_t remaining = ota_size - total;
-    size_t requested = remaining < OTA_BUFFER_SIZE ? remaining : OTA_BUFFER_SIZE;
-    ssize_t read;
-#ifdef USE_OTA_ENCRYPTION
-    if (this->noise_ != nullptr) {
-      // One frame per call; noise_read_data_ waits internally (readall_), so
-      // there is no would-block retry here and failures are already logged.
-      read = this->noise_read_data_(buf, requested);
-      if (read <= 0) {
+  } else
+#endif
+  {
+    while (xfer.total < xfer.ota_size) {
+      ssize_t read = this->receive_data_(buf, xfer);
+      if (read < 0) {
         error_code = ota::OTA_RESPONSE_ERROR_UNKNOWN;
         goto error;  // NOLINT(cppcoreguidelines-avoid-goto)
       }
-    } else
-#endif
-    {
-      read = this->client_->read(buf, requested);
-      if (read == -1) {
-        const int err = errno;
-        if (this->would_block_(err)) {
-          // read() already waited up to SO_RCVTIMEO for data, just feed WDT
-          App.feed_wdt();
-          continue;
-        }
-        ESP_LOGW(TAG, "Read err %d", err);
-        error_code = ota::OTA_RESPONSE_ERROR_UNKNOWN;
+      error_code = this->write_flash_(buf, read);
+      if (error_code != ota::OTA_RESPONSE_OK)
         goto error;  // NOLINT(cppcoreguidelines-avoid-goto)
-      } else if (read == 0) {
-        ESP_LOGW(TAG, "Remote closed");
-        error_code = ota::OTA_RESPONSE_ERROR_UNKNOWN;
-        goto error;  // NOLINT(cppcoreguidelines-avoid-goto)
-      }
-    }
-
-    last_data_ms = millis();
-    error_code = this->backend_->write(buf, read);
-    if (error_code != ota::OTA_RESPONSE_OK) {
-      ESP_LOGW(TAG, "Flash write err %d", error_code);
-      goto error;  // NOLINT(cppcoreguidelines-avoid-goto)
-    }
-    total += read;
-#if USE_OTA_VERSION == 2
-    while (size_acknowledged + OTA_BLOCK_SIZE <= total || (total == ota_size && size_acknowledged < ota_size)) {
-      this->data_write_byte_(ota::OTA_RESPONSE_CHUNK_OK);
-      size_acknowledged += OTA_BLOCK_SIZE;
-    }
-#endif
-
-    uint32_t now = millis();
-    if (now - last_progress > 1000) {
-      last_progress = now;
-      float percentage = (total * 100.0f) / ota_size;
-      ESP_LOGD(TAG, "Progress: %0.1f%%", percentage);
-#ifdef USE_OTA_STATE_LISTENER
-      this->notify_state_(ota::OTA_IN_PROGRESS, percentage, 0);
-#endif
-      // feed watchdog and give other tasks a chance to run
-      this->yield_and_feed_watchdog_();
+      this->ack_written_(xfer);
     }
   }
 
@@ -771,6 +733,169 @@ bool ESPHomeOTAComponent::try_write_(size_t to_write, const LogString *desc) {
   return this->handshake_buf_pos_ >= to_write;
 }
 
+bool ESPHomeOTAComponent::read_size_(uint8_t *buf, size_t &size, const LogString *desc) {
+  if (!this->data_readall_(buf, OTA_SIZE_FIELD_BYTES)) {
+    this->log_read_error_(desc);
+    return false;
+  }
+  size = encode_uint32(buf[0], buf[1], buf[2], buf[3]);
+  ESP_LOGV(TAG, "%s is %zu bytes", LOG_STR_ARG(desc), size);
+  return true;
+}
+
+ota::OTAResponseTypes ESPHomeOTAComponent::write_flash_(uint8_t *data, size_t len) {
+  ota::OTAResponseTypes result = this->backend_->write(data, len);
+  if (result != ota::OTA_RESPONSE_OK) {
+    ESP_LOGW(TAG, "Flash write err %d", result);
+  }
+  return result;
+}
+
+ssize_t ESPHomeOTAComponent::receive_data_(uint8_t *buf, DataTransfer &xfer) {
+  const size_t remaining = xfer.ota_size - xfer.total;
+  const size_t requested = std::min(remaining, OTA_BUFFER_SIZE);
+  ssize_t read;
+  for (;;) {
+    // A silently-vanished peer (no FIN/RST delivered, e.g. uploader killed
+    // mid-transfer or NAT/router dropped state) must not wedge the device:
+    // read() only fails on EOF or a real error, and lwIP TCP keepalive isn't
+    // enabled here.
+    if (millis() - xfer.last_data_ms > OTA_SOCKET_TIMEOUT_DATA) {
+      ESP_LOGW(TAG, "No data received for %u ms", (unsigned) OTA_SOCKET_TIMEOUT_DATA);
+      return -1;
+    }
+#ifdef USE_OTA_ENCRYPTION
+    if (this->noise_ != nullptr) {
+      // One frame per call; noise_read_data_ waits internally (readall_), so
+      // there is no would-block retry here and failures are already logged.
+      read = this->noise_read_data_(buf, requested);
+      if (read <= 0)
+        return -1;
+      break;
+    }
+#endif
+    read = this->client_->read(buf, requested);
+    if (read > 0)
+      break;
+    if (read == 0) {
+      this->log_remote_closed_(LOG_STR("data"));
+      return -1;
+    }
+    if (!this->would_block_(errno)) {
+      this->log_socket_error_(LOG_STR("data"));
+      return -1;
+    }
+    // read() already waited up to SO_RCVTIMEO for data, just feed WDT
+    App.feed_wdt();
+  }
+
+  const uint32_t now = millis();
+  xfer.last_data_ms = now;
+  xfer.total += read;
+  this->ack_received_(xfer);
+  if (now - xfer.last_progress > OTA_PROGRESS_INTERVAL_MS) {
+    xfer.last_progress = now;
+    float percentage = (xfer.total * 100.0f) / xfer.ota_size;
+    ESP_LOGD(TAG, "Progress: %0.1f%%", percentage);
+#ifdef USE_OTA_STATE_LISTENER
+    this->notify_state_(ota::OTA_IN_PROGRESS, percentage, 0);
+#endif
+    // feed watchdog and give other tasks a chance to run
+    this->yield_and_feed_watchdog_();
+  }
+  return read;
+}
+
+void ESPHomeOTAComponent::send_chunk_acks_(DataTransfer &xfer) {
+#if USE_OTA_VERSION == 2
+  while (xfer.acknowledged + OTA_BLOCK_SIZE <= xfer.total ||
+         (xfer.total == xfer.ota_size && xfer.acknowledged < xfer.ota_size)) {
+    this->data_write_byte_(ota::OTA_RESPONSE_CHUNK_OK);
+    xfer.acknowledged += OTA_BLOCK_SIZE;
+  }
+#endif
+}
+
+#ifdef USE_OTA_DEFLATE
+// The window doubles as the output buffer; flushed bytes stay as back
+// reference history for the next windowful.
+ota::OTAResponseTypes ESPHomeOTAComponent::inflate_flush_(InflateSession &session) {
+  const size_t produced = session.dest - session.window;
+  const size_t pending = produced - session.flushed;
+  if (pending == 0)
+    return ota::OTA_RESPONSE_OK;
+  if (pending > session.image_size - session.written) {
+    ESP_LOGW(TAG, "Inflate overrun");
+    return ota::OTA_RESPONSE_ERROR_UNKNOWN;
+  }
+  ota::OTAResponseTypes result = this->write_flash_(session.window + session.flushed, pending);
+  if (result != ota::OTA_RESPONSE_OK)
+    return result;
+  session.flushed = produced;
+  session.written += pending;
+  // A compressible region yields many windows per socket read
+  App.feed_wdt();
+  this->ack_written_(*session.xfer);
+  return ota::OTA_RESPONSE_OK;
+}
+
+ota::OTAResponseTypes ESPHomeOTAComponent::inflate_data_(uint8_t *in, size_t image_size, DataTransfer &xfer) {
+  InflateSession &session = *this->inflate_;
+  session.self = this;
+  session.xfer = &xfer;
+  session.in = in;
+  session.image_size = image_size;
+  session.written = 0;
+  session.error = ota::OTA_RESPONSE_OK;
+  ota_inflate_init(&session, session.window, OTA_INFLATE_WINDOW_SIZE);
+  // Where the ack must follow the write, flush and ack before waiting for
+  // input, or the client waits for an ack while the decoder waits for data
+  session.source_read_cb = [](OtaInflateState *d) -> int {
+    auto *s = static_cast<InflateSession *>(d);
+    if (ACK_AFTER_WRITE) {
+      s->error = s->self->inflate_flush_(*s);
+      if (s->error != ota::OTA_RESPONSE_OK)
+        return -1;
+    }
+    // More input than announced; reported by the size check below
+    if (s->xfer->total >= s->xfer->ota_size)
+      return -1;
+    ssize_t read = s->self->receive_data_(s->in, *s->xfer);
+    if (read <= 0) {
+      // Already logged by receive_data_
+      s->error = ota::OTA_RESPONSE_ERROR_UNKNOWN;
+      return -1;
+    }
+    d->source = s->in + 1;
+    d->source_limit = s->in + read;
+    return s->in[0];
+  };
+
+  int res;
+  do {
+    // The ring index wrapped to 0 exactly when the window filled
+    session.dest = session.window;
+    session.dest_limit = session.window + OTA_INFLATE_WINDOW_SIZE;
+    session.flushed = 0;
+    res = ota_inflate(&session);
+    // A stored block keeps emitting zeros after a failed read, hence eof
+    if (res < 0 || session.eof)
+      break;
+    session.error = this->inflate_flush_(session);
+  } while (res != OTA_INFLATE_DONE && session.error == ota::OTA_RESPONSE_OK);
+
+  // Transport and flash failures are logged where they happen
+  if (session.error != ota::OTA_RESPONSE_OK)
+    return session.error;
+  if (res != OTA_INFLATE_DONE || session.written != image_size || xfer.total != xfer.ota_size) {
+    ESP_LOGW(TAG, "Inflate err %d", res);
+    return ota::OTA_RESPONSE_ERROR_UNKNOWN;
+  }
+  ESP_LOGD(TAG, "Inflated %zu bytes from %zu", session.written, xfer.total);
+  return ota::OTA_RESPONSE_OK;
+}
+#endif  // USE_OTA_DEFLATE
+
 void ESPHomeOTAComponent::cleanup_connection_() {
   this->client_->close();
   this->client_ = nullptr;
@@ -784,6 +909,9 @@ void ESPHomeOTAComponent::cleanup_connection_() {
 #endif
 #ifdef USE_OTA_ENCRYPTION
   this->noise_ = nullptr;
+#endif
+#ifdef USE_OTA_DEFLATE
+  this->inflate_ = nullptr;
 #endif
   // Intentionally no disable_loop() — letting loop() run one more iteration catches
   // any connection that queued on the listener mid-session (otherwise the wake flag,

esphome/components/esphome/ota/ota_esphome.h

@@ -7,6 +7,9 @@
 #ifdef USE_OTA_ENCRYPTION
 #include "esphome/components/noise/noise_handshake.h"
 #endif
+#ifdef USE_OTA_DEFLATE
+#include "ota_esphome_inflate.h"
+#endif
 #include "esphome/core/helpers.h"
 #include "esphome/core/log.h"
 #include "esphome/core/preferences.h"
@@ -119,6 +122,38 @@ class ESPHomeOTAComponent final : public ota::OTAComponent {
     return this->readall_(buf, len);
   }
 
+  // Upload accounting shared by the data loop and the inflate read callback
+  struct DataTransfer {
+    size_t ota_size{0};  // bytes the client sends
+    size_t total{0};     // bytes received so far
+#if USE_OTA_VERSION == 2
+    size_t acknowledged{0};
+#endif
+    uint32_t last_data_ms{0};
+    uint32_t last_progress{0};
+  };
+  // Up to OTA_BUFFER_SIZE bytes into buf; returns bytes read, -1 on failure (logged)
+  inline ssize_t receive_data_(uint8_t *buf, DataTransfer &xfer);
+  // Raw lwIP cannot service the radio during a sector write, so the ack waits
+  // for the write there; a socket task lets the next block arrive meanwhile
+#ifdef USE_SOCKET_IMPL_LWIP_TCP
+  static constexpr bool ACK_AFTER_WRITE = true;
+#else
+  static constexpr bool ACK_AFTER_WRITE = false;
+#endif
+  void send_chunk_acks_(DataTransfer &xfer);
+  inline void ack_received_(DataTransfer &xfer) {
+    if (!ACK_AFTER_WRITE)
+      this->send_chunk_acks_(xfer);
+  }
+  inline void ack_written_(DataTransfer &xfer) {
+    if (ACK_AFTER_WRITE)
+      this->send_chunk_acks_(xfer);
+  }
+  inline bool read_size_(uint8_t *buf, size_t &size, const LogString *desc);
+  // Writes to the backend and logs a failure
+  inline ota::OTAResponseTypes write_flash_(uint8_t *data, size_t len);
+
   bool try_read_(size_t to_read, const LogString *desc);
   bool try_write_(size_t to_write, const LogString *desc);
 
@@ -171,6 +206,31 @@ class ESPHomeOTAComponent final : public ota::OTAComponent {
   static_assert(OTA_BUFFER_SIZE >= NOISE_CLIENT_MAX_PLAINTEXT + noise::MAC_SIZE,
                 "OTA_BUFFER_SIZE must fit a full encrypted data frame");
 #endif
+#ifdef USE_OTA_DEFLATE
+  // At least 1 << espota2.DEFLATE_WINDOW_BITS; also the inflate output buffer
+  static constexpr size_t OTA_INFLATE_WINDOW_SIZE = 4096;
+  // Heap-allocated only while a deflate upload is negotiated; the decoder
+  // state is the base so the read callback can recover the session
+  struct InflateSession : OtaInflateState {
+    ESPHomeOTAComponent *self;
+    DataTransfer *xfer;
+    uint8_t *in;  // caller's buffer for the compressed input, valid during inflate_data_
+    size_t image_size;
+    size_t written;               // inflated bytes in flash
+    size_t flushed;               // bytes of the current window already in flash
+    ota::OTAResponseTypes error;  // first failure inside the read callback
+    uint8_t window[OTA_INFLATE_WINDOW_SIZE];
+  };
+#ifndef CLANG_TIDY  // static analysis sets every define at once
+  static_assert(!ota::OTABackend::supports_compression(),
+                "USE_OTA_DEFLATE is for backends that cannot store a gzip image");
+#endif
+  // Writes the decoded bytes not yet in flash without moving dest
+  ota::OTAResponseTypes inflate_flush_(InflateSession &session);
+  ota::OTAResponseTypes inflate_data_(uint8_t *in, size_t image_size, DataTransfer &xfer);
+  std::unique_ptr<InflateSession> inflate_;
+#endif
+
   static constexpr uint8_t MAGIC_BYTES[5] = {0x6C, 0x26, 0xF7, 0x5C, 0x45};
   // Derived from the feature byte; storing it would pad the trailing bytes
   bool extended_proto_() const;

esphome/components/esphome/ota/ota_esphome_inflate.c

@@ -0,0 +1,498 @@
+/*
+ * uzlib  -  tiny deflate/inflate library (deflate, gzip, zlib)
+ *
+ * Copyright (c) 2003 by Joergen Ibsen / Jibz
+ * All Rights Reserved
+ * http://www.ibsensoftware.com/
+ *
+ * Copyright (c) 2014-2018 by Paul Sokolovsky
+ *
+ * This software is provided 'as-is', without any express
+ * or implied warranty.  In no event will the authors be
+ * held liable for any damages arising from the use of
+ * this software.
+ *
+ * Permission is granted to anyone to use this software
+ * for any purpose, including commercial applications,
+ * and to alter it and redistribute it freely, subject to
+ * the following restrictions:
+ *
+ * 1. The origin of this software must not be
+ *    misrepresented; you must not claim that you
+ *    wrote the original software. If you use this
+ *    software in a product, an acknowledgment in
+ *    the product documentation would be appreciated
+ *    but is not required.
+ *
+ * 2. Altered source versions must be plainly marked
+ *    as such, and must not be misrepresented as
+ *    being the original software.
+ *
+ * 3. This notice may not be removed or altered from
+ *    any source distribution.
+ */
+
+/*
+ * Altered for ESPHome: this is the raw deflate decoder from uzlib's
+ * tinflate.c (v2.9.5) with the gzip/zlib header parsers, checksums,
+ * runtime table builder and in-memory (non ring window) output path
+ * removed, and the public names prefixed with ota_inflate.
+ */
+
+#include "ota_esphome_inflate.h"
+
+#include <stddef.h>
+
+#define TINF_OK OTA_INFLATE_OK
+#define TINF_DONE OTA_INFLATE_DONE
+#define TINF_DATA_ERROR OTA_INFLATE_DATA_ERROR
+#define TINF_DICT_ERROR OTA_INFLATE_DICT_ERROR
+#define TINF_DATA struct OtaInflateState
+#define TINF_TREE struct OtaInflateTree
+#define TINF_ARRAY_SIZE(arr) (sizeof(arr) / sizeof(*(arr)))
+
+/* every output byte also goes into the ring window */
+#define TINF_PUT(d, c) \
+  { \
+    *d->dest++ = c; \
+    d->dict_ring[d->dict_idx++] = c; \
+    if (d->dict_idx == d->dict_size) \
+      d->dict_idx = 0; \
+  }
+
+/* --------------------------------------------------- *
+ * -- constant tables (upstream builds them at runtime) -- *
+ * --------------------------------------------------- */
+
+static const unsigned char LENGTH_BITS[30] = {0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2,
+                                              2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5};
+static const unsigned short LENGTH_BASE[30] = {3,  4,  5,  6,  7,  8,  9,  10, 11,  13,  15,  17,  19,  23, 27,
+                                               31, 35, 43, 51, 59, 67, 83, 99, 115, 131, 163, 195, 227, 258};
+
+static const unsigned char DIST_BITS[30] = {0, 0, 0, 0, 1, 1, 2, 2,  3,  3,  4,  4,  5,  5,  6,
+                                            6, 7, 7, 8, 8, 9, 9, 10, 10, 11, 11, 12, 12, 13, 13};
+static const unsigned short DIST_BASE[30] = {1,    2,    3,    4,    5,    7,    9,    13,    17,    25,
+                                             33,   49,   65,   97,   129,  193,  257,  385,   513,   769,
+                                             1025, 1537, 2049, 3073, 4097, 6145, 8193, 12289, 16385, 24577};
+
+/* special ordering of code length codes */
+static const unsigned char CLCIDX[] = {16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15};
+
+/* ----------------------- *
+ * -- utility functions -- *
+ * ----------------------- */
+
+/* given an array of code lengths, build a tree */
+static void tinf_build_tree(TINF_TREE *t, const unsigned char *lengths, unsigned int num) {
+  unsigned short offs[16];
+  unsigned int i, sum;
+
+  /* clear code length count table */
+  for (i = 0; i < 16; ++i)
+    t->table[i] = 0;
+
+  /* scan symbol lengths, and sum code length counts */
+  for (i = 0; i < num; ++i)
+    t->table[lengths[i]]++;
+
+  /* In the lengths array, 0 means unused code. So, t->table[0] now contains
+     number of unused codes. But table's purpose is to contain # of codes of
+     particular length, and there're 0 codes of length 0. */
+  t->table[0] = 0;
+
+  /* compute offset table for distribution sort */
+  for (sum = 0, i = 0; i < 16; ++i) {
+    offs[i] = sum;
+    sum += t->table[i];
+  }
+
+  /* create code->symbol translation table (symbols sorted by code) */
+  for (i = 0; i < num; ++i) {
+    if (lengths[i])
+      t->trans[offs[lengths[i]]++] = i;
+  }
+}
+
+/* ---------------------- *
+ * -- decode functions -- *
+ * ---------------------- */
+
+static unsigned char uzlib_get_byte(TINF_DATA *d) {
+  /* If end of source buffer is not reached, return next byte from source
+     buffer. */
+  if (d->source < d->source_limit) {
+    return *d->source++;
+  }
+
+  /* Otherwise if there's callback and we haven't seen EOF yet, try to
+     read next byte using it. (Note: the callback can also update ->source
+     and ->source_limit). */
+  if (!d->eof) {
+    int val = d->source_read_cb(d);
+    if (val >= 0) {
+      return (unsigned char) val;
+    }
+  }
+
+  /* Otherwise, we hit EOF (either from ->source_read_cb() or from exhaustion
+     of the buffer), and it will be "sticky", i.e. further calls to this
+     function will end up here too. */
+  d->eof = true;
+
+  return 0;
+}
+
+/* get one bit from source stream */
+static int tinf_getbit(TINF_DATA *d) {
+  unsigned int bit;
+
+  /* check if tag is empty */
+  if (!d->bitcount--) {
+    /* load next tag */
+    d->tag = uzlib_get_byte(d);
+    d->bitcount = 7;
+  }
+
+  /* shift bit out of tag */
+  bit = d->tag & 0x01;
+  d->tag >>= 1;
+
+  return bit;
+}
+
+/* read a num bit value from a stream and add base */
+static unsigned int tinf_read_bits(TINF_DATA *d, int num, int base) {
+  unsigned int val = 0;
+
+  /* read num bits */
+  if (num) {
+    unsigned int limit = 1 << (num);
+    unsigned int mask;
+
+    for (mask = 1; mask < limit; mask *= 2)
+      if (tinf_getbit(d))
+        val += mask;
+  }
+
+  return val + base;
+}
+
+/* given a data stream and a tree, decode a symbol */
+static int tinf_decode_symbol(TINF_DATA *d, TINF_TREE *t) {
+  int sum = 0, cur = 0, len = 0;
+
+  /* get more bits while code value is above sum */
+  do {
+    cur = 2 * cur + tinf_getbit(d);
+
+    if (++len == TINF_ARRAY_SIZE(t->table)) {
+      return TINF_DATA_ERROR;
+    }
+
+    sum += t->table[len];
+    cur -= t->table[len];
+
+  } while (cur >= 0);
+
+  sum += cur;
+  if (sum < 0 || sum >= t->size) {
+    return TINF_DATA_ERROR;
+  }
+
+  return t->trans[sum];
+}
+
+/* given a data stream, decode dynamic trees from it */
+static int tinf_decode_trees(TINF_DATA *d, TINF_TREE *lt, TINF_TREE *dt) {
+  /* code lengths for 288 literal/len symbols and 32 dist symbols */
+  unsigned char lengths[288 + 32];
+  unsigned int hlit, hdist, hclen, hlimit;
+  unsigned int i, num, length;
+
+  /* get 5 bits HLIT (257-286) */
+  hlit = tinf_read_bits(d, 5, 257);
+
+  /* get 5 bits HDIST (1-32) */
+  hdist = tinf_read_bits(d, 5, 1);
+
+  /* get 4 bits HCLEN (4-19) */
+  hclen = tinf_read_bits(d, 4, 4);
+
+  for (i = 0; i < 19; ++i)
+    lengths[i] = 0;
+
+  /* read code lengths for code length alphabet */
+  for (i = 0; i < hclen; ++i) {
+    /* get 3 bits code length (0-7) */
+    unsigned int clen = tinf_read_bits(d, 3, 0);
+
+    lengths[CLCIDX[i]] = clen;
+  }
+
+  /* build code length tree, temporarily use length tree */
+  tinf_build_tree(lt, lengths, 19);
+
+  /* decode code lengths for the dynamic trees */
+  hlimit = hlit + hdist;
+  for (num = 0; num < hlimit;) {
+    int sym = tinf_decode_symbol(d, lt);
+    unsigned char fill_value = 0;
+    int lbits, lbase = 3;
+
+    /* error decoding */
+    if (sym < 0)
+      return sym;
+
+    switch (sym) {
+      case 16:
+        /* copy previous code length 3-6 times (read 2 bits) */
+        if (num == 0)
+          return TINF_DATA_ERROR;
+        fill_value = lengths[num - 1];
+        lbits = 2;
+        break;
+      case 17:
+        /* repeat code length 0 for 3-10 times (read 3 bits) */
+        lbits = 3;
+        break;
+      case 18:
+        /* repeat code length 0 for 11-138 times (read 7 bits) */
+        lbits = 7;
+        lbase = 11;
+        break;
+      default:
+        /* values 0-15 represent the actual code lengths */
+        lengths[num++] = sym;
+        /* continue the for loop */
+        continue;
+    }
+
+    /* special code length 16-18 are handled here */
+    length = tinf_read_bits(d, lbits, lbase);
+    if (num + length > hlimit)
+      return TINF_DATA_ERROR;
+    for (; length; --length) {
+      lengths[num++] = fill_value;
+    }
+  }
+
+  /* Check that there's "end of block" symbol */
+  if (lengths[256] == 0) {
+    return TINF_DATA_ERROR;
+  }
+
+  /* build dynamic trees */
+  tinf_build_tree(lt, lengths, hlit);
+  tinf_build_tree(dt, lengths + hlit, hdist);
+
+  return TINF_OK;
+}
+
+/* build the fixed huffman trees (RFC 1951 3.2.6) through the generic tree
+   builder; altered from upstream, which unrolls them by hand */
+static void tinf_build_fixed_trees(TINF_TREE *lt, TINF_TREE *dt) {
+  unsigned char lengths[288];
+  unsigned int i;
+
+  for (i = 0; i < 144; ++i)
+    lengths[i] = 8;
+  for (; i < 256; ++i)
+    lengths[i] = 9;
+  for (; i < 280; ++i)
+    lengths[i] = 7;
+  for (; i < 288; ++i)
+    lengths[i] = 8;
+  tinf_build_tree(lt, lengths, 288);
+
+  for (i = 0; i < 32; ++i)
+    lengths[i] = 5;
+  tinf_build_tree(dt, lengths, 32);
+}
+
+/* ----------------------------- *
+ * -- block inflate functions -- *
+ * ----------------------------- */
+
+/* given a stream and two trees, inflate next chunk of output (a byte or more) */
+static int tinf_inflate_block_data(TINF_DATA *d, TINF_TREE *lt, TINF_TREE *dt) {
+  if (d->curlen == 0) {
+    unsigned int offs;
+    int dist;
+    int sym = tinf_decode_symbol(d, lt);
+
+    if (d->eof) {
+      return TINF_DATA_ERROR;
+    }
+
+    if (sym < 0) {
+      return sym;
+    }
+
+    /* literal byte */
+    if (sym < 256) {
+      TINF_PUT(d, sym);
+      return TINF_OK;
+    }
+
+    /* end of block */
+    if (sym == 256) {
+      return TINF_DONE;
+    }
+
+    /* substring from sliding dictionary */
+    sym -= 257;
+    if (sym >= 29) {
+      return TINF_DATA_ERROR;
+    }
+
+    /* possibly get more bits from length code */
+    d->curlen = tinf_read_bits(d, LENGTH_BITS[sym], LENGTH_BASE[sym]);
+
+    dist = tinf_decode_symbol(d, dt);
+    if (dist < 0 || dist >= 30) {
+      return TINF_DATA_ERROR;
+    }
+
+    /* possibly get more bits from distance code */
+    offs = tinf_read_bits(d, DIST_BITS[dist], DIST_BASE[dist]);
+
+    /* calculate and validate actual LZ offset to use */
+    if (offs > d->dict_size) {
+      return TINF_DICT_ERROR;
+    }
+    /* Note: we don't try to catch offset which points to not yet filled
+       part of the dictionary here. Doing so would require keeping another
+       variable to track "filled in" size of the dictionary. Appearance of
+       such an offset cannot lead to accessing memory outside of the
+       dictionary buffer, and clients which don't want to leak unrelated
+       information, should explicitly initialize dictionary buffer passed
+       to uzlib. */
+
+    d->lz_off = d->dict_idx - offs;
+    if (d->lz_off < 0) {
+      d->lz_off += d->dict_size;
+    }
+  }
+
+  /* copy next byte from dict substring */
+  TINF_PUT(d, d->dict_ring[d->lz_off]);
+  if ((unsigned) ++d->lz_off == d->dict_size) {
+    d->lz_off = 0;
+  }
+  d->curlen--;
+  return TINF_OK;
+}
+
+/* inflate next byte from uncompressed block of data */
+static int tinf_inflate_uncompressed_block(TINF_DATA *d) {
+  if (d->curlen == 0) {
+    unsigned int length, invlength;
+
+    /* get length */
+    length = uzlib_get_byte(d);
+    length += 256 * uzlib_get_byte(d);
+    /* get one's complement of length */
+    invlength = uzlib_get_byte(d);
+    invlength += 256 * uzlib_get_byte(d);
+    /* check length */
+    if (length != (~invlength & 0x0000ffff))
+      return TINF_DATA_ERROR;
+
+    /* increment length to properly return TINF_DONE below, without
+       producing data at the same time */
+    d->curlen = length + 1;
+
+    /* make sure we start next block on a byte boundary */
+    d->bitcount = 0;
+  }
+
+  if (--d->curlen == 0) {
+    return TINF_DONE;
+  }
+
+  unsigned char c = uzlib_get_byte(d);
+  TINF_PUT(d, c);
+  return TINF_OK;
+}
+
+/* ---------------------- *
+ * -- public functions -- *
+ * ---------------------- */
+
+/* initialize decompression structure */
+void ota_inflate_init(TINF_DATA *d, unsigned char *dict, unsigned int dict_len) {
+  d->source = NULL;
+  d->source_limit = NULL;
+  d->tag = 0;
+  d->eof = 0;
+  d->bitcount = 0;
+  d->lz_off = 0;
+  d->bfinal = 0;
+  d->btype = -1;
+  d->dict_size = dict_len;
+  d->dict_ring = dict;
+  d->dict_idx = 0;
+  d->curlen = 0;
+  d->ltree.trans = d->ltrans;
+  d->ltree.size = TINF_ARRAY_SIZE(d->ltrans);
+  d->dtree.trans = d->dtrans;
+  d->dtree.size = TINF_ARRAY_SIZE(d->dtrans);
+}
+
+/* inflate next output bytes from compressed stream */
+int ota_inflate(TINF_DATA *d) {
+  do {
+    int res;
+
+    /* start a new block */
+    if (d->btype == -1) {
+      int old_btype;
+    next_blk:
+      old_btype = d->btype;
+      /* read final block flag */
+      d->bfinal = tinf_getbit(d);
+      /* read block type (2 bits) */
+      d->btype = tinf_read_bits(d, 2, 0);
+
+      if (d->btype == 1 && old_btype != 1) {
+        /* build fixed huffman trees */
+        tinf_build_fixed_trees(&d->ltree, &d->dtree);
+      } else if (d->btype == 2) {
+        /* decode trees from stream */
+        res = tinf_decode_trees(d, &d->ltree, &d->dtree);
+        if (res != TINF_OK) {
+          return res;
+        }
+      }
+    }
+
+    /* process current block */
+    switch (d->btype) {
+      case 0:
+        /* decompress uncompressed block */
+        res = tinf_inflate_uncompressed_block(d);
+        break;
+      case 1:
+      case 2:
+        /* decompress block with fixed/dynamic huffman trees */
+        /* trees were decoded previously, so it's the same routine for both */
+        res = tinf_inflate_block_data(d, &d->ltree, &d->dtree);
+        break;
+      default:
+        return TINF_DATA_ERROR;
+    }
+
+    if (res == TINF_DONE && !d->bfinal) {
+      /* the block has ended (without producing more data), but we
+         can't return without data, so start procesing next block */
+      goto next_blk;
+    }
+
+    if (res != TINF_OK) {
+      return res;
+    }
+
+  } while (d->dest < d->dest_limit);
+
+  return TINF_OK;
+}

esphome/components/esphome/ota/ota_esphome_inflate.h

@@ -0,0 +1,66 @@
+#pragma once
+// Raw deflate decoder cut down from uzlib (https://github.com/pfalcon/uzlib,
+// zlib licence, see the .c file); output goes through a ring window.
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+enum OtaInflateResult {
+  OTA_INFLATE_OK = 0,   /* more data produced, call again */
+  OTA_INFLATE_DONE = 1, /* end of compressed stream reached */
+  OTA_INFLATE_DATA_ERROR = -3,
+  OTA_INFLATE_DICT_ERROR = -5,
+};
+
+struct OtaInflateTree {
+  uint16_t table[16]; /* table of code length counts */
+  uint16_t *trans;    /* code -> symbol translation table, size entries */
+  uint16_t size;
+};
+
+struct OtaInflateState {
+  /* Next byte in the input buffer and one past its end */
+  const unsigned char *source;
+  const unsigned char *source_limit;
+  /* Called when source is exhausted; returns the next byte or -1 at EOF.
+     It may refill source/source_limit for buffered operation. */
+  int (*source_read_cb)(struct OtaInflateState *d);
+
+  unsigned int tag;
+  unsigned int bitcount;
+
+  /* Output cursor and one past the end of the output buffer */
+  unsigned char *dest;
+  unsigned char *dest_limit;
+
+  bool eof;
+
+  int btype;
+  int bfinal;
+  unsigned int curlen;
+  int lz_off;
+  /* Ring window holding the last dict_size output bytes for back references */
+  unsigned char *dict_ring;
+  unsigned int dict_size;
+  unsigned int dict_idx;
+
+  struct OtaInflateTree ltree; /* dynamic length/symbol tree */
+  struct OtaInflateTree dtree; /* dynamic distance tree */
+  uint16_t ltrans[288];
+  uint16_t dtrans[32]; /* the distance alphabet has 30 symbols, so the tree is kept small */
+};
+
+/* dict must cover the encoder's window (its largest back reference) */
+void ota_inflate_init(struct OtaInflateState *d, unsigned char *dict, unsigned int dict_len);
+/* Fills dest up to dest_limit (OK) or to the end of the stream (DONE). dest may
+   alias dict only if dest_limit - dest == dict_len and dest is reset to dict
+   exactly when a call returns OK, so the ring index and dest stay in lockstep */
+int ota_inflate(struct OtaInflateState *d);
+
+#ifdef __cplusplus
+}
+#endif

esphome/components/ota/ota_backend.h

@@ -7,6 +7,7 @@
 #include <concepts>
 #include <cstddef>
 #include <cstdint>
+#include <type_traits>
 
 #ifdef USE_OTA_STATE_LISTENER
 #include <vector>
@@ -102,6 +103,8 @@ enum OTAType : uint8_t {
 // - set_update_md5: expected digest of the incoming image, hex string.
 // - write: consume the next chunk; end: finalize and mark bootable.
 // - abort: safe to call in any state, including after end().
+// - supports_compression: constexpr, whether a gzip image is stored as is and
+//   inflated at reboot.
 template<typename T>
 concept OTABackendContract = requires(T backend, size_t image_size, uint8_t *data, size_t len, const char *md5) {
   { backend.begin(image_size, OTA_TYPE_UPDATE_APP) } -> std::same_as<OTAResponseTypes>;
@@ -110,7 +113,9 @@ concept OTABackendContract = requires(T backend, size_t image_size, uint8_t *dat
   { backend.write(data, len) } -> std::same_as<OTAResponseTypes>;
   { backend.end() } -> std::same_as<OTAResponseTypes>;
   backend.abort();
-  { backend.supports_compression() } -> std::same_as<bool>;
+  { T::supports_compression() } -> std::same_as<bool>;
+  // The value must be a constant expression
+  typename std::bool_constant<T::supports_compression()>;
 };
 
 /** Listener interface for OTA state changes.

esphome/components/ota/ota_backend_arduino_libretiny.h

@@ -13,7 +13,7 @@ class ArduinoLibreTinyOTABackend final {
   OTAResponseTypes write(uint8_t *data, size_t len);
   OTAResponseTypes end();
   void abort();
-  bool supports_compression() { return false; }
+  static constexpr bool supports_compression() { return false; }
 
  private:
   bool md5_set_{false};

esphome/components/ota/ota_backend_arduino_rp2.h

@@ -6,6 +6,8 @@
 #include "esphome/core/defines.h"
 #include "esphome/core/macros.h"
 
+#include <RP2040Version.h>
+
 namespace esphome::ota {
 
 class ArduinoRP2OTABackend final {
@@ -15,7 +17,12 @@ class ArduinoRP2OTABackend final {
   OTAResponseTypes write(uint8_t *data, size_t len);
   OTAResponseTypes end();
   void abort();
-  bool supports_compression() { return false; }
+  // The core's OTA stub inflates a staged gzip image at reboot, on every chip
+  // from 4.0.3 (ESPHome pins 6.0.0). begin() only sees the gzip size; the
+  // inflated size is known when the stub reads the trailer.
+  static constexpr bool supports_compression() {
+    return VERSION_CODE(ARDUINO_PICO_MAJOR, ARDUINO_PICO_MINOR, ARDUINO_PICO_REVISION) >= VERSION_CODE(4, 0, 3);
+  }
 
  private:
   bool md5_set_{false};

esphome/components/ota/ota_backend_esp8266.h

@@ -20,7 +20,7 @@ class ESP8266OTABackend final {
   OTAResponseTypes end();
   void abort();
   // Compression supported in all ESP8266 Arduino versions ESPHome supports (>= 2.7.0)
-  bool supports_compression() { return true; }
+  static constexpr bool supports_compression() { return true; }
 
  protected:
   /// Erase flash sector if current address is at sector boundary

esphome/components/ota/ota_backend_esp_idf.h

@@ -33,7 +33,7 @@ class IDFOTABackend final {
   OTAResponseTypes write(uint8_t *data, size_t len);
   OTAResponseTypes end();
   void abort();
-  bool supports_compression() { return false; }
+  static constexpr bool supports_compression() { return false; }
 
  protected:
 #ifdef USE_OTA_PARTITIONS

esphome/components/ota/ota_backend_factory.h

@@ -25,7 +25,7 @@ struct StubOTABackend {
   OTAResponseTypes write(uint8_t *data, size_t len) { return OTA_RESPONSE_ERROR_UNKNOWN; }
   OTAResponseTypes end() { return OTA_RESPONSE_ERROR_UNKNOWN; }
   void abort() {}
-  bool supports_compression() { return false; }
+  static constexpr bool supports_compression() { return false; }
 };
 std::unique_ptr<StubOTABackend> make_ota_backend();
 }  // namespace esphome::ota
@@ -33,6 +33,7 @@ std::unique_ptr<StubOTABackend> make_ota_backend();
 
 namespace esphome::ota {
 using OTABackendPtr = decltype(make_ota_backend());
-static_assert(OTABackendContract<OTABackendPtr::element_type>,
+using OTABackend = OTABackendPtr::element_type;
+static_assert(OTABackendContract<OTABackend>,
               "The platform's OTA backend is missing part of the backend surface (ota_backend.h)");
 }  // namespace esphome::ota

esphome/components/ota/ota_backend_host.h

@@ -19,7 +19,7 @@ class HostOTABackend final {
   OTAResponseTypes write(uint8_t *data, size_t len);
   OTAResponseTypes end();
   void abort();
-  bool supports_compression() { return false; }
+  static constexpr bool supports_compression() { return false; }
 
  protected:
   md5::MD5Digest md5_{};

esphome/core/defines.h

@@ -244,6 +244,7 @@
 #define USE_RUNTIME_IMAGE_QOI
 #define USE_RUNTIME_STATS
 #define USE_OTA
+#define USE_OTA_DEFLATE
 #define USE_OTA_ENCRYPTION
 #define USE_OTA_ENCRYPTION_FROM_API
 #define USE_OTA_ENCRYPTION_PROVISIONED

esphome/espota2.py

@@ -11,6 +11,7 @@ import secrets
 import socket
 import time
 from typing import Any
+import zlib
 
 from esphome.core import EsphomeError
 from esphome.helpers import ProgressBar, resolve_ip_address
@@ -65,9 +66,15 @@ CLIENT_FEATURE_SUPPORTS_COMPRESSION = 0x01
 CLIENT_FEATURE_SUPPORTS_SHA256_AUTH = 0x02
 CLIENT_FEATURE_SUPPORTS_EXTENDED_PROTOCOL = 0x04
 CLIENT_FEATURE_SUPPORTS_NOISE = 0x08
+CLIENT_FEATURE_SUPPORTS_DEFLATE = 0x10
 SERVER_FEATURE_SUPPORTS_COMPRESSION = 0x01
 SERVER_FEATURE_SUPPORTS_PARTITION_ACCESS = 0x02
 SERVER_FEATURE_SUPPORTS_NOISE = 0x04
+# Binding once offered: the device then expects the image size and a deflate stream
+SERVER_FEATURE_SUPPORTS_DEFLATE = 0x08
+
+# Wire constant: the deflate bit promises a 4 KB window (OTA_INFLATE_WINDOW_SIZE)
+DEFLATE_WINDOW_BITS = 12
 
 NOISE_FRAME_INDICATOR = 0x01
 NOISE_HANDSHAKE_OK = 0x00
@@ -87,6 +94,9 @@ _SUPPORTED_OTA_TYPES: frozenset[int] = frozenset(
 )
 
 UPLOAD_BLOCK_SIZE = 8192
+# Sizes on the wire are 4 bytes MSB first
+SIZE_FIELD_BYTES = 4
+COMPRESS_LEVEL = 9
 UPLOAD_BUFFER_SIZE = UPLOAD_BLOCK_SIZE * 8
 
 # Flaky Wi-Fi links often drop the first OTA attempt, and the device may need time
@@ -547,6 +557,7 @@ def perform_ota(
         CLIENT_FEATURE_SUPPORTS_COMPRESSION
         | CLIENT_FEATURE_SUPPORTS_SHA256_AUTH
         | CLIENT_FEATURE_SUPPORTS_EXTENDED_PROTOCOL
+        | CLIENT_FEATURE_SUPPORTS_DEFLATE
     )
     if noise_psk:
         features_to_send |= CLIENT_FEATURE_SUPPORTS_NOISE
@@ -640,8 +651,16 @@ def perform_ota(
                 f"retry {flag_name}."
             )
 
-    if features & SERVER_FEATURE_SUPPORTS_COMPRESSION:
-        upload_contents = gzip.compress(file_contents, compresslevel=9)
+    deflate = bool(extended_proto and features & SERVER_FEATURE_SUPPORTS_DEFLATE)
+    if deflate:
+        # The device inflates while receiving through a small ring window
+        upload_contents = zlib.compress(
+            file_contents, COMPRESS_LEVEL, wbits=-DEFLATE_WINDOW_BITS
+        )
+        _LOGGER.info("Compressed to %s bytes (deflate)", len(upload_contents))
+    elif features & SERVER_FEATURE_SUPPORTS_COMPRESSION:
+        # The device stores the gzip file and inflates it when it reboots
+        upload_contents = gzip.compress(file_contents, compresslevel=COMPRESS_LEVEL)
         _LOGGER.info("Compressed to %s bytes", len(upload_contents))
     else:
         upload_contents = file_contents
@@ -701,22 +720,20 @@ def perform_ota(
         send_check(sock, ota_type, "ota type")
 
     upload_size = len(upload_contents)
-    upload_size_encoded = [
-        (upload_size >> 24) & 0xFF,
-        (upload_size >> 16) & 0xFF,
-        (upload_size >> 8) & 0xFF,
-        (upload_size >> 0) & 0xFF,
-    ]
     # The device erases flash between receiving the size and acking the
     # prepare, so this window shows the erase cost (near zero when the
     # device erases lazily during the upload)
     prepare_start = time.perf_counter()
-    send_check(sock, upload_size_encoded, "binary size")
+    send_check(sock, upload_size.to_bytes(SIZE_FIELD_BYTES, "big"), "binary size")
+    if deflate:
+        # Own frame: an encrypted session carries one field per frame
+        send_check(sock, file_size.to_bytes(SIZE_FIELD_BYTES, "big"), "image size")
     receive_exactly(sock, 1, "update prepare result", RESPONSE_UPDATE_PREPARE_OK)
     prepare_duration = time.perf_counter() - prepare_start
     _LOGGER.info("Preparing for upload took %.2f seconds", prepare_duration)
 
-    upload_md5 = hashlib.md5(upload_contents).hexdigest()
+    # The device hashes what it writes: the inflated image, else the received bytes
+    upload_md5 = hashlib.md5(file_contents if deflate else upload_contents).hexdigest()
     _LOGGER.debug("MD5 of upload is %s", upload_md5)
 
     send_check(sock, upload_md5, "file checksum")

script/ci-custom.py

@@ -823,6 +823,8 @@ def lint_relative_py_import(fname: Path, line, col, content):
         # neither can live in a C++ namespace.
         "esphome/components/esp32_hosted/esp_now_hosted.cpp",
         "esphome/components/esp32_hosted/esp_now_hosted_rpc.h",
+        # C header shared with the vendored decoder
+        "esphome/components/esphome/ota/ota_esphome_inflate.h",
     ],
 )
 def lint_namespace(fname: Path, content: str) -> str | None:

tests/components/esphome/__init__.py

@@ -0,0 +1,12 @@
+from esphome.loader import FileResource
+from tests.testing_helpers import ComponentManifestOverride
+
+
+def override_manifest(manifest: ComponentManifestOverride) -> None:
+    # to_code emits the component count the application needs
+    manifest.enable_codegen()
+    # Only the decoder is under test; its ota platform is not in this build
+    manifest.resources = manifest.resources + [
+        FileResource("esphome.components.esphome", "ota/ota_esphome_inflate.c"),
+        FileResource("esphome.components.esphome", "ota/ota_esphome_inflate.h"),
+    ]

tests/components/esphome/test_ota_inflate.cpp

@@ -0,0 +1,323 @@
+#include <gtest/gtest.h>
+
+#include <cstdint>
+#include <cstring>
+#include <vector>
+
+#include "esphome/components/esphome/ota/ota_esphome_inflate.h"
+
+namespace esphome::testing {
+
+// build_plain() compressed with the CLI's window (espota2.DEFLATE_WINDOW_BITS):
+//   DEFLATED = zlib.compress(plain, 9, wbits=-12)
+//   STORED = zlib.compress(plain[:300], 0, wbits=-12)
+static const uint8_t DEFLATED[] = {
+    0xed, 0xc8, 0xf7, 0x3f, 0xd4, 0x0f, 0x03, 0x00, 0x70, 0x67, 0xaf, 0x4b, 0x67, 0x66, 0x9f, 0x90, 0x91, 0x11, 0xc2,
+    0x11, 0x91, 0xb8, 0xb3, 0xf7, 0x3a, 0xd9, 0x5f, 0x4e, 0x99, 0x67, 0x1e, 0xce, 0x8a, 0xac, 0xec, 0x59, 0xb8, 0xc2,
+    0x95, 0x5d, 0x56, 0x42, 0x67, 0x73, 0x46, 0xf6, 0xca, 0xce, 0xc8, 0xc8, 0xc8, 0x91, 0x8a, 0x7c, 0x2f, 0x7a, 0xfe,
+    0x86, 0xe7, 0x87, 0xe7, 0x87, 0xe7, 0xf5, 0xfa, 0xbc, 0x7f, 0x7c, 0xbb, 0x07, 0xa2, 0x1f, 0xfa, 0xf9, 0xb8, 0x43,
+    0xfd, 0x82, 0x5c, 0xa0, 0x6e, 0xee, 0x28, 0x6f, 0x97, 0x20, 0x77, 0xa8, 0x3b, 0x70, 0xc0, 0x01, 0x07, 0x1c, 0x70,
+    0xc0, 0x01, 0x07, 0x1c, 0x70, 0xc0, 0x01, 0x07, 0x1c, 0x70, 0xc0, 0x01, 0x07, 0x1c, 0x70, 0xc0, 0x01, 0x07, 0x1c,
+    0x70, 0xc0, 0x01, 0xf7, 0x5f, 0xdd, 0x40, 0xd4, 0x63, 0x2f, 0x03, 0xf2, 0x17, 0xb2, 0xe5, 0x69, 0xc7, 0x5a, 0x04,
+    0xdf, 0x46, 0x22, 0xa8, 0x4b, 0x6e, 0xd5, 0x3a, 0x80, 0x05, 0xe1, 0x81, 0x4a, 0x44, 0x56, 0x27, 0xa9, 0x21, 0xf7,
+    0xad, 0xd9, 0xb0, 0xd3, 0xf1, 0xa5, 0x0b, 0x6a, 0x96, 0x56, 0xb2, 0xca, 0xb5, 0xee, 0x0f, 0x96, 0x28, 0xc3, 0x9e,
+    0x8f, 0x6e, 0xf2, 0x84, 0xa4, 0x3b, 0x2d, 0x16, 0x64, 0x08, 0x6a, 0x28, 0x91, 0xee, 0x87, 0x1a, 0x81, 0xff, 0xed,
+    0x2c, 0x5f, 0xda, 0x4a, 0x48, 0x5f, 0x91, 0xf0, 0x31, 0xfe, 0x6b, 0xbd, 0x81, 0x86, 0x92, 0x33, 0x1a, 0x6c, 0x69,
+    0x32, 0xfb, 0x19, 0x56, 0x2c, 0xc6, 0xaa, 0xef, 0xe8, 0x16, 0x98, 0xcf, 0x98, 0xbf, 0xa0, 0x2d, 0xde, 0x7f, 0xdf,
+    0x4b, 0xcb, 0xf6, 0x5c, 0xaf, 0x11, 0x24, 0xf0, 0x46, 0x3e, 0x49, 0x0e, 0x67, 0x0e, 0xcf, 0xf3, 0x57, 0xca, 0xb0,
+    0x39, 0x55, 0xe1, 0xe7, 0xfc, 0x37, 0x29, 0xe8, 0xd7, 0xf3, 0x08, 0x2e, 0xfb, 0x7b, 0x6d, 0x3e, 0xfe, 0xe9, 0x2c,
+    0x68, 0xe4, 0x20, 0x88, 0x57, 0x56, 0x41, 0x3d, 0xab, 0x9b, 0xbf, 0x0c, 0x0c, 0xae, 0x51, 0x48, 0x8b, 0x72, 0xcc,
+    0xb8, 0xbb, 0xf3, 0x30, 0xa8, 0x5c, 0xb5, 0xa1, 0x2f, 0x07, 0x52, 0xe9, 0x36, 0xb8, 0x3c, 0xbc, 0xee, 0xbc, 0xf1,
+    0xa3, 0x8b, 0x81, 0xc2, 0x03, 0xbf, 0x29, 0x5a, 0x22, 0x24, 0x97, 0xf8, 0xc9, 0xb5, 0xbf, 0xd2, 0x24, 0x4a, 0x86,
+    0xc1, 0x2b, 0xb7, 0xb8, 0xde, 0xa7, 0xea, 0xa5, 0x1d, 0x13, 0x1c, 0x1d, 0xd3, 0x3c, 0x81, 0x60, 0x2e, 0x2f, 0x93,
+    0x5c, 0x78, 0x43, 0x2e, 0x39, 0x68, 0x09, 0x13, 0x09, 0x10, 0xce, 0xd6, 0x8d, 0xe9, 0x2f, 0xaf, 0x88, 0x6f, 0x99,
+    0x4f, 0xcd, 0xdc, 0xaa, 0xf9, 0x47, 0xdb, 0x1c, 0xb5, 0x89, 0x53, 0x10, 0x3d, 0x77, 0xac, 0x26, 0x04, 0x3a, 0x3b,
+    0x18, 0xf8, 0x47, 0x75, 0x56, 0xa5, 0xda, 0x70, 0xfb, 0xf7, 0x0d, 0x3b, 0x6e, 0x4b, 0x2a, 0xbc, 0x49, 0x32, 0x43,
+    0x95, 0x62, 0x83, 0x3d, 0xdc, 0x0a, 0x1f, 0x1d, 0xf9, 0x59, 0x6b, 0x95, 0xf0, 0x9b, 0xf5, 0x53, 0x9e, 0xb5, 0x65,
+    0xeb, 0x74, 0xfa, 0x81, 0x9b, 0x61, 0xa3, 0x57, 0x2f, 0xda, 0x2c, 0xcd, 0xf8, 0xb0, 0x74, 0xb9, 0x62, 0x39, 0x91,
+    0xd9, 0x7d, 0xb3, 0x03, 0x65, 0x2e, 0x66, 0x20, 0x18, 0xac, 0xa2, 0xeb, 0x3b, 0x35, 0x98, 0xa3, 0x28, 0x46, 0x30,
+    0xee, 0xd3, 0xeb, 0x47, 0x49, 0x11, 0xc5, 0xcd, 0xa0, 0xa5, 0x1c, 0x2e, 0x9d, 0x14, 0xd6, 0x46, 0x4a, 0x05, 0x7b,
+    0xd3, 0xb9, 0x0d, 0xeb, 0xd7, 0x6f, 0xb5, 0xf4, 0xed, 0x3f, 0x27, 0xb8, 0xec, 0x51, 0xb1, 0x6e, 0xb0, 0x14, 0xed,
+    0xdf, 0x90, 0x72, 0x59, 0x71, 0xd5, 0xf5, 0xf2, 0x61, 0x5f, 0xa7, 0x8a, 0xd7, 0x0f, 0x80, 0x2f, 0xe5, 0x0f, 0x45,
+    0xf2, 0x4d, 0xd1, 0xdc, 0xdd, 0xce, 0x46, 0xdf, 0x77, 0xf2, 0xa6, 0xa2, 0x79, 0x77, 0xf0, 0x0e, 0xaa, 0x68, 0x14,
+    0x85, 0x32, 0x05, 0x29, 0x75, 0x2b, 0x6c, 0xb0, 0x7c, 0x84, 0xc9, 0xec, 0x49, 0x70, 0x9b, 0x38, 0x36, 0x4c, 0xe9,
+    0xa5, 0xdc, 0xb1, 0xb8, 0x28, 0xd6, 0x20, 0x89, 0x8a, 0x2a, 0x62, 0xc1, 0x90, 0x3a, 0x43, 0x48, 0xaa, 0xfc, 0xec,
+    0x52, 0xf4, 0x02, 0xa7, 0xcd, 0x46, 0xf9, 0x78, 0x64, 0x4f, 0xad, 0x6b, 0x17, 0xdb, 0x56, 0xa2, 0xa1, 0x6a, 0xcf,
+    0x3b, 0x66, 0x64, 0x01, 0xc2, 0xd6, 0xae, 0x23, 0x34, 0x82, 0x60, 0x0a, 0x3a, 0xe4, 0xdd, 0x7f, 0xaa, 0x97, 0x44,
+    0x9a, 0x63, 0x8f, 0xaf, 0xa9, 0x97, 0x5a, 0x55, 0xcc, 0x81, 0x48, 0x83, 0xf8, 0xe6, 0xc5, 0xef, 0xdf, 0xfa, 0x5a,
+    0x4f, 0x7f, 0x18, 0x56, 0xc0, 0x66, 0x36, 0xad, 0x8a, 0x79, 0xab, 0xde, 0xf4, 0x7b, 0x70, 0x98, 0xea, 0xfa, 0xf4,
+    0xc7, 0x01, 0x31, 0x16, 0xea, 0xf1, 0x70, 0x8d, 0xee, 0x87, 0x52, 0x13, 0x01, 0x9e, 0x0c, 0xbd, 0x5a, 0x14, 0x01,
+    0x8e, 0xf7, 0x6e, 0xff, 0xce, 0x7f, 0xa4, 0xd1, 0xa1, 0x6a, 0x9b, 0x95, 0xb2, 0x31, 0x8a, 0x6f, 0xc8, 0xfe, 0x8c,
+    0x29, 0x55, 0xbc, 0xfc, 0x61, 0xd0, 0xde, 0xb0, 0xa9, 0x0c, 0x01, 0x0f, 0xba, 0x77, 0x7e, 0x77, 0xd9, 0x76, 0xa4,
+    0xfd, 0xab, 0x38, 0x18, 0x92, 0xec, 0xf0, 0xd3, 0x57, 0x7f, 0xf4, 0xbd, 0x65, 0xd4, 0x77, 0x8e, 0xa1, 0x92, 0x82,
+    0x0c, 0x7b, 0x34, 0xd3, 0x11, 0xfb, 0xc0, 0x36, 0x23, 0x8e, 0xbb, 0x89, 0xdf, 0x70, 0xdc, 0x9a, 0x76, 0x45, 0x0b,
+    0x22, 0xfa, 0x35, 0xdf, 0x8f, 0x45, 0x48, 0x7d, 0xed, 0xdc, 0x06, 0x01, 0x5e, 0xbb, 0xe9, 0xf9, 0x07, 0x93, 0xf6,
+    0x69, 0x6f, 0xf1, 0xfc, 0xfd, 0xfa, 0x41, 0xc0, 0x13, 0x9e, 0x74, 0x2d, 0x76, 0xfe, 0xa7, 0xbe, 0x4e, 0xd9, 0xaa,
+    0x64, 0xa6, 0xed, 0xd3, 0xad, 0xee, 0x62, 0x9d, 0x39, 0xc9, 0xb8, 0xae, 0x86, 0x31, 0x4f, 0x62, 0x57, 0xea, 0xea,
+    0x5a, 0xe3, 0x59, 0xd8, 0x99, 0xb3, 0xcd, 0x9f, 0x3b, 0xea, 0x58, 0x99, 0x11, 0xdc, 0x3d, 0xac, 0x58, 0xd9, 0xa6,
+    0xae, 0x2d, 0x07, 0x1d, 0xd7, 0xfa, 0x87, 0x78, 0xa7, 0x7f, 0x2a, 0x4f, 0x25, 0x58, 0xef, 0x53, 0x78, 0x2e, 0x93,
+    0xdc, 0x44, 0xcc, 0x53, 0x88, 0x77, 0x1c, 0xda, 0x14, 0xaf, 0xe1, 0x67, 0x92, 0xff, 0x36, 0x96, 0x20, 0x6f, 0x9d,
+    0x2c, 0x7f, 0xea, 0x31, 0xf2, 0x34, 0x50, 0xc2, 0x39, 0x84, 0xee, 0x4c, 0xbe, 0xca, 0x06, 0x6f, 0x67, 0x42, 0xea,
+    0x13, 0x58, 0xee, 0xdd, 0x8e, 0x29, 0x4f, 0xee, 0xd8, 0x93, 0x0d, 0x45, 0x80, 0x4d, 0xf3, 0x12, 0x79, 0xbb, 0x36,
+    0xa3, 0x73, 0x95, 0x95, 0xb6, 0xfc, 0x54, 0x60, 0xb2, 0xcc, 0x71, 0xaa, 0xf1, 0x6b, 0x66, 0xed, 0xba, 0x8b, 0xd6,
+    0x6d, 0x61, 0x79, 0x61, 0x1d, 0xb3, 0xba, 0xa6, 0x2f, 0xaa, 0xdc, 0x1d, 0xb8, 0x22, 0xd8, 0x98, 0x58, 0xed, 0x4d,
+    0x3c, 0xea, 0xa9, 0x37, 0x5e, 0x5e, 0x7b, 0x47, 0xa1, 0x7a, 0x39, 0x42, 0xe4, 0x3b, 0xbb, 0x69, 0x0a, 0x8b, 0x32,
+    0x6e, 0x63, 0xeb, 0x87, 0xf6, 0x5d, 0xaa, 0xbf, 0xbe, 0xc5, 0xb2, 0x85, 0x60, 0xdc, 0x32, 0x07, 0x85, 0x73, 0x3d,
+    0x96, 0x8b, 0x89, 0x71, 0x52, 0xb4, 0x93, 0xe6, 0x18, 0xad, 0xbf, 0xce, 0x21, 0x1d, 0x33, 0xb5, 0xb3, 0x35, 0x6a,
+    0x5b, 0xe7, 0x47, 0x13, 0x19, 0x8f, 0x53, 0xf4, 0x0c, 0x2a, 0x39, 0x16, 0x37, 0x39, 0x3b, 0x5f, 0x81, 0x51, 0xbc,
+    0x23, 0x92, 0x2c, 0x8d, 0xbf, 0x2f, 0xee, 0xbf, 0xed, 0x9d, 0x3f, 0xe0, 0x16, 0x21, 0x5a, 0x57, 0xa6, 0x8c, 0x58,
+    0x7a, 0xd5, 0xa1, 0x6d, 0xed, 0xe8, 0x90, 0x97, 0x14, 0xb4, 0x6b, 0xa5, 0x3b, 0xd7, 0x90, 0x84, 0x9e, 0x07, 0xc2,
+    0x7f, 0x1e, 0x08, 0xa0, 0x6f, 0x69, 0xf1, 0xcc, 0x4e, 0xca, 0x07, 0x64, 0xa2, 0xb4, 0xbc, 0x5f, 0xe0, 0xa7, 0x0e,
+    0x31, 0x77, 0x6f, 0x35, 0xd7, 0x66, 0x83, 0x5d, 0x64, 0x4e, 0xf1, 0x3c, 0x7a, 0xcb, 0xa5, 0xfc, 0xc9, 0x95, 0xab,
+    0x27, 0x30, 0x6b, 0x82, 0x57, 0xcd, 0xb0, 0x85, 0x9d, 0xc5, 0xa9, 0x0f, 0xdb, 0xe3, 0x5a, 0xc1, 0xb2, 0x3f, 0xfa,
+    0xea, 0xf3, 0x3a, 0xa0, 0xe4, 0xad, 0xd7, 0x14, 0xcf, 0x4f, 0xc9, 0x46, 0x09, 0x6e, 0x70, 0x27, 0xe4, 0x9b, 0x5f,
+    0x61, 0x4a, 0xb2, 0xfb, 0xc3, 0xf0, 0x3a, 0x53, 0x38, 0x2a, 0x59, 0x48, 0x2b, 0xab, 0x21, 0x64, 0x1a, 0x1c, 0x90,
+    0xb6, 0x69, 0xbb, 0x89, 0xe3, 0x9a, 0x12, 0xb7, 0xfd, 0x47, 0xcc, 0x57, 0xdb, 0x2b, 0xf6, 0x35, 0xe1, 0x79, 0xe0,
+    0xbf, 0x6d, 0x7f, 0x71, 0x3c, 0x21, 0x27, 0x82, 0x12, 0x05, 0xae, 0x43, 0x11, 0x0f, 0xc8, 0xe7, 0x3c, 0xf0, 0x0b,
+    0xe4, 0x69, 0xff, 0xb2, 0xda, 0x9e, 0x7f, 0xfe, 0xa4, 0x3f, 0xdf, 0x02, 0x58, 0xaa, 0x60, 0xd2, 0x8e, 0xd5, 0x6c,
+    0x92, 0x22, 0x38, 0xb1, 0xd2, 0x84, 0x80, 0xea, 0xce, 0xfe, 0x34, 0x79, 0xd6, 0x94, 0xb0, 0xad, 0x51, 0x67, 0x65,
+    0xf5, 0xab, 0xd5, 0x18, 0x05, 0x92, 0x8a, 0x24, 0x36, 0xc2, 0xc4, 0x99, 0xad, 0x0d, 0x26, 0xb8, 0x70, 0xea, 0x5b,
+    0x74, 0x35, 0x6a, 0xfa, 0xac, 0x97, 0xd8, 0x4c, 0x08, 0x6d, 0xc1, 0xfe, 0x60, 0xe4, 0xd4, 0x8f, 0x93, 0xd4, 0xaf,
+    0xa2, 0xec, 0xb8, 0x71, 0xf6, 0xcb, 0x3f, 0xdc, 0x3e, 0x42, 0xca, 0xe2, 0x8d, 0xb9, 0x0a, 0x2c, 0xef, 0xb6, 0x18,
+    0x75, 0x46, 0x8a, 0x2b, 0x21, 0xeb, 0xc5, 0x12, 0x4d, 0xd7, 0xb8, 0x8e, 0x6c, 0xec, 0x9d, 0x12, 0xde, 0xa5, 0x45,
+    0xab, 0xc4, 0x26, 0x47, 0xfa, 0x57, 0xad, 0x78, 0x4c, 0x5e, 0x87, 0x0b, 0x42, 0x6a, 0xbe, 0xef, 0xbd, 0xbc, 0xe5,
+    0xd7, 0x4c, 0x3a, 0x0f, 0x96, 0x29, 0xcb, 0x45, 0x46, 0x3f, 0x8a, 0x31, 0xda, 0x8d, 0x7f, 0x89, 0xa4, 0xd6, 0xb4,
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+    0xd8, 0x40, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    0xfe, 0xe7, 0xdc, 0x03, 0xd1, 0x0f, 0xfd, 0x7c, 0xdc, 0xa1, 0x7e, 0x41, 0x2e, 0x50, 0x37, 0x77, 0x94, 0xb7, 0x4b,
+    0x90, 0x3b, 0x14, 0x38, 0xe0, 0x80, 0x03, 0x0e, 0x38, 0xe0, 0x80, 0xfb, 0xff, 0xba, 0xff, 0x00,
+};
+
+static const uint8_t STORED[] = {
+    0x01, 0x2c, 0x01, 0xd3, 0xfe, 0x65, 0x73, 0x70, 0x68, 0x6f, 0x6d, 0x65, 0x20, 0x6f, 0x74, 0x61, 0x20, 0x64,
+    0x65, 0x66, 0x6c, 0x61, 0x74, 0x65, 0x20, 0x65, 0x73, 0x70, 0x68, 0x6f, 0x6d, 0x65, 0x20, 0x6f, 0x74, 0x61,
+    0x20, 0x64, 0x65, 0x66, 0x6c, 0x61, 0x74, 0x65, 0x20, 0x65, 0x73, 0x70, 0x68, 0x6f, 0x6d, 0x65, 0x20, 0x6f,
+    0x74, 0x61, 0x20, 0x64, 0x65, 0x66, 0x6c, 0x61, 0x74, 0x65, 0x20, 0x65, 0x73, 0x70, 0x68, 0x6f, 0x6d, 0x65,
+    0x20, 0x6f, 0x74, 0x61, 0x20, 0x64, 0x65, 0x66, 0x6c, 0x61, 0x74, 0x65, 0x20, 0x65, 0x73, 0x70, 0x68, 0x6f,
+    0x6d, 0x65, 0x20, 0x6f, 0x74, 0x61, 0x20, 0x64, 0x65, 0x66, 0x6c, 0x61, 0x74, 0x65, 0x20, 0x65, 0x73, 0x70,
+    0x68, 0x6f, 0x6d, 0x65, 0x20, 0x6f, 0x74, 0x61, 0x20, 0x64, 0x65, 0x66, 0x6c, 0x61, 0x74, 0x65, 0x20, 0x65,
+    0x73, 0x70, 0x68, 0x6f, 0x6d, 0x65, 0x20, 0x6f, 0x74, 0x61, 0x20, 0x64, 0x65, 0x66, 0x6c, 0x61, 0x74, 0x65,
+    0x20, 0x65, 0x73, 0x70, 0x68, 0x6f, 0x6d, 0x65, 0x20, 0x6f, 0x74, 0x61, 0x20, 0x64, 0x65, 0x66, 0x6c, 0x61,
+    0x74, 0x65, 0x20, 0x65, 0x73, 0x70, 0x68, 0x6f, 0x6d, 0x65, 0x20, 0x6f, 0x74, 0x61, 0x20, 0x64, 0x65, 0x66,
+    0x6c, 0x61, 0x74, 0x65, 0x20, 0x65, 0x73, 0x70, 0x68, 0x6f, 0x6d, 0x65, 0x20, 0x6f, 0x74, 0x61, 0x20, 0x64,
+    0x65, 0x66, 0x6c, 0x61, 0x74, 0x65, 0x20, 0x65, 0x73, 0x70, 0x68, 0x6f, 0x6d, 0x65, 0x20, 0x6f, 0x74, 0x61,
+    0x20, 0x64, 0x65, 0x66, 0x6c, 0x61, 0x74, 0x65, 0x20, 0x65, 0x73, 0x70, 0x68, 0x6f, 0x6d, 0x65, 0x20, 0x6f,
+    0x74, 0x61, 0x20, 0x64, 0x65, 0x66, 0x6c, 0x61, 0x74, 0x65, 0x20, 0x65, 0x73, 0x70, 0x68, 0x6f, 0x6d, 0x65,
+    0x20, 0x6f, 0x74, 0x61, 0x20, 0x64, 0x65, 0x66, 0x6c, 0x61, 0x74, 0x65, 0x20, 0x65, 0x73, 0x70, 0x68, 0x6f,
+    0x6d, 0x65, 0x20, 0x6f, 0x74, 0x61, 0x20, 0x64, 0x65, 0x66, 0x6c, 0x61, 0x74, 0x65, 0x20, 0x65, 0x73, 0x70,
+    0x68, 0x6f, 0x6d, 0x65, 0x20, 0x6f, 0x74, 0x61, 0x20, 0x64, 0x65, 0x66, 0x6c, 0x61, 0x74, 0x65, 0x20,
+};
+
+static constexpr size_t WINDOW = 4096;
+static constexpr size_t PLAIN_SIZE = 16000;
+
+static uint8_t lcg_next(uint32_t &x) {
+  x = (x * 1103515245u + 12345u) & 0x7fffffffu;
+  return (x >> 16) & 0xff;
+}
+
+static std::vector<uint8_t> build_plain() {
+  std::vector<uint8_t> plain;
+  const char *text = "esphome ota deflate ";
+  for (int i = 0; i < 300; i++)
+    plain.insert(plain.end(), text, text + strlen(text));
+  uint32_t x = 1;
+  for (int i = 0; i < 3000; i++)
+    plain.push_back(lcg_next(x));
+  plain.insert(plain.end(), 5000, 0);
+  for (int i = 0; i < 100; i++)
+    plain.insert(plain.end(), text, text + strlen(text));
+  return plain;
+}
+
+// Mirrors the OTA session: chunked input through the read callback, window as output
+struct Session : OtaInflateState {
+  const uint8_t *in;
+  size_t in_len;
+  size_t in_pos;
+  size_t chunk;
+  std::vector<uint8_t> out;
+  uint8_t window[WINDOW];
+};
+
+static int read_cb(OtaInflateState *d) {
+  auto *s = static_cast<Session *>(d);
+  if (s->in_pos >= s->in_len)
+    return -1;
+  size_t n = std::min(s->chunk, s->in_len - s->in_pos);
+  d->source = s->in + s->in_pos + 1;
+  d->source_limit = s->in + s->in_pos + n;
+  s->in_pos += n;
+  return s->in[s->in_pos - n];
+}
+
+// Inflates the whole input; returns the decoder result and fills s.out
+static int inflate_all(Session &s, const uint8_t *in, size_t in_len, size_t chunk) {
+  s.in = in;
+  s.in_len = in_len;
+  s.in_pos = 0;
+  s.chunk = chunk;
+  s.out.clear();
+  memset(s.window, 0, sizeof(s.window));
+  ota_inflate_init(&s, s.window, WINDOW);
+  s.source_read_cb = read_cb;
+  int res;
+  do {
+    s.dest = s.window;
+    s.dest_limit = s.window + WINDOW;
+    res = ota_inflate(&s);
+    if (res < 0 || s.eof)
+      return res < 0 ? res : OTA_INFLATE_DATA_ERROR;
+    s.out.insert(s.out.end(), s.window, s.dest);
+    if (s.out.size() > PLAIN_SIZE)
+      return OTA_INFLATE_DATA_ERROR;
+  } while (res != OTA_INFLATE_DONE);
+  return res;
+}
+
+TEST(OtaInflate, RoundTripThroughWindow) {
+  auto s = std::make_unique<Session>();
+  ASSERT_EQ(inflate_all(*s, DEFLATED, sizeof(DEFLATED), 1040), OTA_INFLATE_DONE);
+  EXPECT_EQ(s->out, build_plain());
+  EXPECT_EQ(s->in_pos, sizeof(DEFLATED));
+}
+
+TEST(OtaInflate, SmallReadChunks) {
+  auto s = std::make_unique<Session>();
+  ASSERT_EQ(inflate_all(*s, DEFLATED, sizeof(DEFLATED), 7), OTA_INFLATE_DONE);
+  EXPECT_EQ(s->out, build_plain());
+}
+
+TEST(OtaInflate, StoredBlock) {
+  auto s = std::make_unique<Session>();
+  ASSERT_EQ(inflate_all(*s, STORED, sizeof(STORED), 64), OTA_INFLATE_DONE);
+  auto plain = build_plain();
+  plain.resize(300);
+  EXPECT_EQ(s->out, plain);
+}
+
+TEST(OtaInflate, TruncatedStreamFails) {
+  auto s = std::make_unique<Session>();
+  for (size_t cut : {size_t{1}, size_t{100}, size_t{1000}, sizeof(DEFLATED) - 1}) {
+    EXPECT_LT(inflate_all(*s, DEFLATED, cut, 1040), 0) << "cut at " << cut;
+    EXPECT_LE(s->out.size(), PLAIN_SIZE);
+  }
+}
+
+TEST(OtaInflate, TruncatedStoredBlockFails) {
+  auto s = std::make_unique<Session>();
+  EXPECT_LT(inflate_all(*s, STORED, sizeof(STORED) - 50, 64), 0);
+}
+
+TEST(OtaInflate, CorruptStreamsNeverEscapeTheWindow) {
+  // Flipped bytes and garbage; the sanitizers check the decoder stays in bounds
+  auto s = std::make_unique<Session>();
+  std::vector<uint8_t> bad(DEFLATED, DEFLATED + sizeof(DEFLATED));
+  for (size_t i = 0; i < bad.size(); i += 3) {
+    bad[i] ^= 0x5a;
+    inflate_all(*s, bad.data(), bad.size(), 1040);
+    bad[i] ^= 0x5a;
+  }
+  uint32_t x = 99;
+  std::vector<uint8_t> garbage(2000);
+  for (int round = 0; round < 50; round++) {
+    for (auto &b : garbage)
+      b = lcg_next(x);
+    inflate_all(*s, garbage.data(), garbage.size(), 1040);
+  }
+}
+
+}  // namespace esphome::testing

tests/components/ota/test.bk72xx-ard.yaml

@@ -0,0 +1 @@
+<<: !include common.yaml

tests/components/ota/test_backend_contract.cpp

@@ -14,7 +14,7 @@ struct MinimalBackend {
   OTAResponseTypes write(uint8_t *data, size_t len) { return OTA_RESPONSE_OK; }
   OTAResponseTypes end() { return OTA_RESPONSE_OK; }
   void abort() {}
-  bool supports_compression() { return false; }
+  static constexpr bool supports_compression() { return false; }
 };
 static_assert(OTABackendContract<MinimalBackend>);
 

tests/integration/test_host_ota.py

@@ -180,10 +180,14 @@ async def test_host_ota_self_update(
         )
     )
     staged = asyncio.Event()
+    inflated = asyncio.Event()
 
     def on_log(line: str) -> None:
         if "OTA staged at" in line:
             staged.set()
+        # The host backend cannot store gzip, so the upload negotiates deflate
+        if "Inflated " in line and " bytes from " in line:
+            inflated.set()
         dev.on_log(line)
 
     async with run_binary(dev.binary_path, line_callback=on_log) as (proc, _lines):
@@ -195,6 +199,7 @@ async def test_host_ota_self_update(
 
         await dev.ota(None, None, "espota2 reported failure")
         assert staged.is_set()
+        assert inflated.is_set(), "upload was not deflate compressed"
 
         async with wait_and_connect_api_client(port=dev.api_port) as client:
             info_after = await client.device_info()

tests/unit_tests/test_espota2.py

@@ -12,6 +12,7 @@ from pathlib import Path
 import socket
 import struct
 from unittest.mock import Mock, call, patch
+import zlib
 
 import pytest
 from pytest import CaptureFixture
@@ -354,6 +355,7 @@ def test_perform_ota_successful_md5_auth(
                 espota2.CLIENT_FEATURE_SUPPORTS_COMPRESSION
                 | espota2.CLIENT_FEATURE_SUPPORTS_SHA256_AUTH
                 | espota2.CLIENT_FEATURE_SUPPORTS_EXTENDED_PROTOCOL
+                | espota2.CLIENT_FEATURE_SUPPORTS_DEFLATE
             ]
         )
     )
@@ -598,12 +600,16 @@ def test_perform_ota_upload_error(mock_socket: Mock, mock_file: io.BytesIO) -> N
         espota2.perform_ota(mock_socket, None, mock_file, "test.bin")
 
 
-def _no_auth_handshake(version: int) -> list[bytes]:
+def _no_auth_handshake(version: int, server_features: int | None = None) -> list[bytes]:
     """Recv responses for a handshake without auth, up to the MD5 check."""
+    if server_features is None:
+        features = [bytes([espota2.RESPONSE_HEADER_OK])]
+    else:
+        features = [bytes([espota2.RESPONSE_FEATURE_FLAGS]), bytes([server_features])]
     return [
         bytes([espota2.RESPONSE_OK]),  # First byte of version response
         bytes([version]),  # Version number
-        bytes([espota2.RESPONSE_HEADER_OK]),  # Features response
+        *features,
         bytes([espota2.RESPONSE_AUTH_OK]),  # No auth required
         bytes([espota2.RESPONSE_UPDATE_PREPARE_OK]),  # Binary size OK
         bytes([espota2.RESPONSE_BIN_MD5_OK]),  # MD5 checksum OK
@@ -1051,6 +1057,7 @@ def test_perform_ota_successful_sha256_auth(
                 espota2.CLIENT_FEATURE_SUPPORTS_COMPRESSION
                 | espota2.CLIENT_FEATURE_SUPPORTS_SHA256_AUTH
                 | espota2.CLIENT_FEATURE_SUPPORTS_EXTENDED_PROTOCOL
+                | espota2.CLIENT_FEATURE_SUPPORTS_DEFLATE
             ]
         )
     )
@@ -1107,6 +1114,7 @@ def test_perform_ota_sha256_fallback_to_md5(
                 espota2.CLIENT_FEATURE_SUPPORTS_COMPRESSION
                 | espota2.CLIENT_FEATURE_SUPPORTS_SHA256_AUTH
                 | espota2.CLIENT_FEATURE_SUPPORTS_EXTENDED_PROTOCOL
+                | espota2.CLIENT_FEATURE_SUPPORTS_DEFLATE
             ]
         )
     )
@@ -1216,6 +1224,7 @@ def test_perform_ota_extended_protocol_app(
                 espota2.CLIENT_FEATURE_SUPPORTS_COMPRESSION
                 | espota2.CLIENT_FEATURE_SUPPORTS_SHA256_AUTH
                 | espota2.CLIENT_FEATURE_SUPPORTS_EXTENDED_PROTOCOL
+                | espota2.CLIENT_FEATURE_SUPPORTS_DEFLATE
             ]
         )
     )
@@ -1276,6 +1285,7 @@ def test_perform_ota_successful_partition_table(
                 espota2.CLIENT_FEATURE_SUPPORTS_COMPRESSION
                 | espota2.CLIENT_FEATURE_SUPPORTS_SHA256_AUTH
                 | espota2.CLIENT_FEATURE_SUPPORTS_EXTENDED_PROTOCOL
+                | espota2.CLIENT_FEATURE_SUPPORTS_DEFLATE
             ]
         )
     )
@@ -1504,3 +1514,40 @@ def test_check_error_passes_non_error_when_expect_is_none() -> None:
     espota2.check_error([espota2.RESPONSE_OK], None)
     espota2.check_error([espota2.RESPONSE_HEADER_OK], None)
     espota2.check_error([espota2.RESPONSE_FEATURE_FLAGS], None)
+
+
+# Device replies after the MD5 check for a one-chunk upload
+_UPLOAD_TAIL = [
+    bytes([espota2.RESPONSE_CHUNK_OK]),
+    bytes([espota2.RESPONSE_RECEIVE_OK]),
+    bytes([espota2.RESPONSE_UPDATE_END_OK]),
+]
+
+
+@pytest.mark.usefixtures("mock_time")
+@pytest.mark.parametrize(
+    "server_features",
+    [
+        espota2.SERVER_FEATURE_SUPPORTS_DEFLATE,
+        # Binding offer: deflate wins over gzip
+        espota2.SERVER_FEATURE_SUPPORTS_DEFLATE
+        | espota2.SERVER_FEATURE_SUPPORTS_COMPRESSION,
+    ],
+)
+def test_perform_ota_with_deflate(mock_socket: Mock, server_features: int) -> None:
+    """The device gets a raw deflate stream, both sizes and the image MD5."""
+    original_content = b"firmware" * 100
+    mock_socket.recv.side_effect = (
+        _no_auth_handshake(espota2.OTA_VERSION_2_0, server_features) + _UPLOAD_TAIL
+    )
+
+    espota2.perform_ota(mock_socket, None, io.BytesIO(original_content), "test.bin")
+
+    sent = [c[0][0] for c in mock_socket.sendall.call_args_list]
+    # magic, features, ota type, size, image size, md5, data, end ack
+    sent_size = struct.unpack(">I", sent[3])[0]
+    assert sent[4] == len(original_content).to_bytes(espota2.SIZE_FIELD_BYTES, "big")
+    payload = sent[6]
+    assert len(payload) == sent_size < len(original_content)
+    assert zlib.decompress(payload, -espota2.DEFLATE_WINDOW_BITS) == original_content
+    assert sent[5] == hashlib.md5(original_content).hexdigest().encode()