fix: stuck on "Connecting..."

CHANGELOG.md

@@ -21,6 +21,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Fix Windows connection issue by aligning reset sequence with `esptool` including RTS/DTR workaround (#999)
 - Fix board-info misreporting the crystal frequency of ESP32-C5 (#1005)
+- Fix `esptool flash` getting stuck on `Sync` command
 
 ### Removed
 

espflash/src/command.rs

@@ -20,6 +20,9 @@ const SYNC_TIMEOUT: Duration = Duration::from_millis(100);
 const FLASH_DEFLATE_END_TIMEOUT: Duration = Duration::from_secs(10);
 const FLASH_MD5_TIMEOUT_PER_MB: Duration = Duration::from_secs(8);
 
+const SYNC_MAX_LEN: u64 = 44;
+const DEFAULT_MAX_LEN: u64 = 8 * 1024 * 1024; // 8Mi by default
+
 /// Input data for SYNC command (36 bytes: 0x07 0x07 0x12 0x20, followed by
 /// 32 x 0x55)
 const SYNC_FRAME: [u8; 36] = [
@@ -211,6 +214,14 @@ impl CommandType {
             _ => self.timeout(),
         }
     }
+
+    /// Return a max response length for the given [`CommandType`]
+    pub fn max_response_len(&self) -> u64 {
+        match self {
+            CommandType::Sync => SYNC_MAX_LEN,
+            _ => DEFAULT_MAX_LEN,
+        }
+    }
 }
 
 /// Available commands

espflash/src/connection/mod.rs

@@ -369,7 +369,7 @@ impl Connection {
             sleep(Duration::from_millis(10));
 
             for _ in 0..MAX_CONNECT_ATTEMPTS {
-                match connection.read_response()? {
+                match connection.read_response_for_command(CommandType::Sync)? {
                     Some(response) if response.return_op == CommandType::Sync as u8 => {
                         if response.status == 1 {
                             connection.flush().ok();
@@ -542,9 +542,21 @@ impl Connection {
         Ok(Some(header))
     }
 
+    /// Reads the response from a serial port for a [`CommandType`].
+    pub fn read_response_for_command(
+        &mut self,
+        ty: CommandType,
+    ) -> Result<Option<CommandResponse>, Error> {
+        self.read_response_bounded(ty.max_response_len())
+            .for_command(ty)
+    }
+
     /// Reads the response from a serial port.
-    pub fn read_response(&mut self) -> Result<Option<CommandResponse>, Error> {
-        match self.read(10)? {
+    pub fn read_response_bounded(
+        &mut self,
+        max_len: u64,
+    ) -> Result<Option<CommandResponse>, Error> {
+        match self.read_bounded(10, max_len)? {
             None => Ok(None),
             Some(response) => {
                 // Here is what esptool does: https://github.com/espressif/esptool/blob/81b2eaee261aed0d3d754e32c57959d6b235bfed/esptool/loader.py#L518
@@ -631,7 +643,7 @@ impl Connection {
         let ty = command.command_type();
         self.write_command(command).for_command(ty)?;
         for _ in 0..100 {
-            match self.read_response().for_command(ty)? {
+            match self.read_response_for_command(ty)? {
                 Some(response) if response.return_op == ty as u8 => {
                     return if response.status != 0 {
                         let _error = self.flush();
@@ -693,11 +705,21 @@ impl Connection {
         self.write_reg(addr, masked_old_value | masked_new_value, None)
     }
 
-    /// Reads a register command with a timeout.
+    /// Reads a register command.
     pub(crate) fn read(&mut self, len: usize) -> Result<Option<Vec<u8>>, Error> {
+        self.read_bounded(len, u64::MAX)
+    }
+
+    /// Reads a register command at most `max_len` bytes long.
+    pub(crate) fn read_bounded(
+        &mut self,
+        len: usize,
+        max_len: u64,
+    ) -> Result<Option<Vec<u8>>, Error> {
         let mut tmp = Vec::with_capacity(1024);
+        let mut serial = (&mut self.serial).take(max_len);
         loop {
-            self.decoder.decode(&mut self.serial, &mut tmp)?;
+            self.decoder.decode(&mut serial, &mut tmp)?;
             if tmp.len() >= len {
                 return Ok(Some(tmp));
             }