read the TCP reply length and return a number

src/main.rs

@@ -62,11 +62,13 @@ fn main() -> anyhow::Result<()> {
         let _ = mdm.tcp_connect("51.158.66.64", 9988)?;
         let _ = mdm.tcp_send("aaaaa")?;
         thread::sleep(Duration::from_millis(1000));
-        let _ = mdm.tcp_receive_query_len()?;
-        let reply = mdm.tcp_receive(6)?;
-        println!("+++++++++++++++++++++++++++++++++");
-        println!("{}", reply);
         println!("+++++++++++++++++++++++++++++++++");
+        let size = mdm.tcp_receive_reply_len()?;
+        println!("{}", size);
+        //println!("+++++++++++++++++++++++++++++++++");
+        //let reply = mdm.tcp_receive(size)?;
+        //println!("{}", reply);
+        //println!("+++++++++++++++++++++++++++++++++");
         let _ = mdm.tcp_close_connection()?;
     }
 

src/modem.rs

@@ -256,19 +256,26 @@ impl<UART: serial::Uart> Modem<UART> {
         Ok(())
     }
 
-
-    pub fn tcp_receive_query_len(&mut self) -> Result<()> {
-        self.send_command(Command::tcp_receive_query_len())?;
-        Ok(())
-    }
-
     pub fn tcp_send(&mut self, payload: &str) -> Result<()> {
         self.send_data(payload)?;
         Ok(())
     }
 
-    pub fn tcp_receive(&mut self, size: usize) -> Result<String> {
-        self.send_command(Command::tcp_receive(size))
+    pub fn tcp_receive_reply_len(&mut self) -> Result<usize> {
+        let reply = self.send_command(Command::tcp_receive_query_len())?;
+        reply.lines()
+            .filter(|line| line.contains("+CIPRXGET: 4"))
+            .next()
+            .ok_or(ModemError::CommandError("reply not found :/".to_string()))
+            .map(|line| {
+                line.split(',')
+                    .into_iter()
+                    .last()
+                    .unwrap_or("x")
+                    .parse::<usize>()
+                    .map_err(|_| ModemError::CommandError(format!("response size should be a number, got {}", line)))
+            })
+            .unwrap_or(Err(ModemError::CommandError(format!("received 0 elements from parsing"))))
     }
 
     pub fn tcp_close_connection(&mut self) -> Result<String> {