Make extracting payload from response more explicit

It's written in the sensors data sheet but I did not remember this after
looking into the code after quite some time.

src/sht4x.rs

@@ -7,6 +7,7 @@ use core::marker::PhantomData;
 use embedded_hal::{delay::DelayNs, i2c::I2c};
 use sensirion_i2c::i2c;
 
+const PAYLOAD_LEN: usize = 4;
 pub(crate) const RESPONSE_LEN: usize = 6;
 
 /// Driver for STH4x sensors.
@@ -108,7 +109,7 @@ where
 
         self.write_command_and_delay_for_execution(command, delay)?;
         let response = self.read_response()?;
-        let raw = sensor_data_from_response(&response);
+        let raw = sensor_data_from_response(response);
 
         Ok(raw)
     }
@@ -133,7 +134,7 @@ where
 
         self.write_command_and_delay_for_execution(command, delay)?;
         let response = self.read_response()?;
-        let raw = sensor_data_from_response(&response);
+        let raw = sensor_data_from_response(response);
 
         Ok(raw)
     }
@@ -142,7 +143,7 @@ where
     pub fn serial_number(&mut self, delay: &mut D) -> Result<u32, Error<I::Error>> {
         self.write_command_and_delay_for_execution(Command::SerialNumber, delay)?;
         let response = self.read_response()?;
-        Ok(serial_number_from_response(&response))
+        Ok(serial_number_from_response(response))
     }
 
     /// Performs a soft reset of the sensor.
@@ -172,13 +173,21 @@ where
     }
 }
 
-pub(crate) fn sensor_data_from_response(response: &[u8; RESPONSE_LEN]) -> SensorData {
+fn response_payload(response: [u8; RESPONSE_LEN]) -> [u8; PAYLOAD_LEN] {
+    // Response data comes in chunks of three bytes: [MSB, LSB, CRC]. The CRCs got already checked
+    // by sensirion_i2c::read_words_with_crc. So we just have to extract the payload data here.
+    [response[0], response[1], response[3], response[4]]
+}
+
+pub(crate) fn sensor_data_from_response(response: [u8; RESPONSE_LEN]) -> SensorData {
+    let payload = response_payload(response);
     SensorData {
-        temperature: u16::from_be_bytes([response[0], response[1]]),
-        humidity: u16::from_be_bytes([response[3], response[4]]),
+        temperature: u16::from_be_bytes([payload[0], payload[1]]),
+        humidity: u16::from_be_bytes([payload[2], payload[3]]),
     }
 }
 
-pub(crate) fn serial_number_from_response(response: &[u8; RESPONSE_LEN]) -> u32 {
-    u32::from_be_bytes([response[0], response[1], response[3], response[4]])
+pub(crate) fn serial_number_from_response(response: [u8; RESPONSE_LEN]) -> u32 {
+    let payload = response_payload(response);
+    u32::from_be_bytes(payload)
 }

src/sht4x_async.rs

@@ -89,7 +89,7 @@ where
         self.write_command_and_delay_for_execution(command, delay)
             .await?;
         let response = self.read_response().await?;
-        let raw = crate::sht4x::sensor_data_from_response(&response);
+        let raw = crate::sht4x::sensor_data_from_response(response);
 
         Ok(raw)
     }
@@ -115,7 +115,7 @@ where
         self.write_command_and_delay_for_execution(command, delay)
             .await?;
         let response = self.read_response().await?;
-        let raw = crate::sht4x::sensor_data_from_response(&response);
+        let raw = crate::sht4x::sensor_data_from_response(response);
 
         Ok(raw)
     }
@@ -125,7 +125,7 @@ where
         self.write_command_and_delay_for_execution(Command::SerialNumber, delay)
             .await?;
         let response = self.read_response().await?;
-        Ok(crate::sht4x::serial_number_from_response(&response))
+        Ok(crate::sht4x::serial_number_from_response(response))
     }
 
     /// Performs a soft reset of the sensor.