add err output when server failed to start

in same time than the port was opened.
Rename function into `wait_for_server` according.

src/server.rs

@@ -1,7 +1,7 @@
-use crate::server::utils::{get_free_port, wait_for_port};
+use crate::server::utils::{get_free_port, wait_for_server};
 use mktemp::Temp;
 use std::io::{self, Cursor, Read};
-use std::process::{Child, Stdio};
+use std::process::{Child, ExitStatus, Stdio};
 use thiserror::Error;
 use zip::{result::ZipError, ZipArchive};
 
@@ -13,6 +13,15 @@ pub enum Error {
     #[error("Get an available port failed")]
     GetFreePort(#[source] io::Error),
 
+    #[error("Server exit with `{status}`")]
+    ServerExitWithStatus { status: ExitStatus },
+
+    #[error("Server exit with `{status}` :\n{msg}")]
+    ServerExitWithError { status: ExitStatus, msg: String },
+
+    #[error("Error append during check grammalecte-server status")]
+    ServerCheckStatus(#[source] io::Error),
+
     #[error("Port {port} did not open in time!")]
     WaitPortOpen { port: u16 },
 
@@ -80,16 +89,16 @@ impl EmbeddedServer {
         log::info!("Will execute file {}", server_file);
 
         // Start server
-        let child = std::process::Command::new("/usr/bin/python3")
+        let mut child = std::process::Command::new("/usr/bin/python3")
             .arg(server_file)
             .arg("-p")
             .arg(port.to_string())
             .stdout(Stdio::null())
-            .stderr(Stdio::null())
+            .stderr(Stdio::piped())
             .spawn()
             .map_err(Error::StartServerProcess)?;
 
-        wait_for_port(port)?;
+        wait_for_server(&mut child, port)?;
 
         Ok(Self {
             _srv_dir: dest,
@@ -111,9 +120,11 @@ impl Drop for EmbeddedServer {
 }
 
 mod utils {
-    use std::time::Duration;
-
     use super::Error;
+    use std::fmt::Write;
+    use std::io::{BufRead, BufReader};
+    use std::process::Child;
+    use std::time::Duration;
 
     /// Get a free port
     pub fn get_free_port() -> u16 {
@@ -130,8 +141,9 @@ mod utils {
         port
     }
 
-    pub fn wait_for_port(port: u16) -> Result<(), Error> {
+    pub fn wait_for_server(child: &mut Child, port: u16) -> Result<(), Error> {
         for _ in 0..50 {
+            check_server(child)?;
             if port_scanner::scan_port(port) {
                 return Ok(());
             }
@@ -140,4 +152,28 @@ mod utils {
 
         Err(Error::WaitPortOpen { port })
     }
+
+    fn check_server(child: &mut Child) -> Result<(), Error> {
+        match child.try_wait().map_err(Error::ServerCheckStatus)? {
+            None => Ok(()), // Continue
+            Some(status) => {
+                if let Some(err) = child.stderr.take() {
+                    let mut msg = format!("grammalecte-server exit with `{status}`");
+                    writeln!(&mut msg, " :").unwrap();
+                    let err = BufReader::new(err);
+                    err.lines().for_each(|line| match line {
+                        Ok(line) => {
+                            writeln!(&mut msg, "\t{}", line).unwrap();
+                        }
+                        Err(err) => {
+                            writeln!(&mut msg, "__{err:?}").unwrap();
+                        }
+                    });
+                    Err(Error::ServerExitWithError { status, msg })
+                } else {
+                    Err(Error::ServerExitWithStatus { status })
+                }
+            }
+        }
+    }
 }