Use CMD exec form with an ENTRYPOINT (#487)

* use CMD exec form with an entrypoint

* lint

src/nixpacks/builder/docker/dockerfile_generation.rs

@@ -162,7 +162,10 @@ impl DockerfileGenerator for BuildPlan {
 
         let dockerfile = formatdoc! {"
             FROM {base_image}
+
+            ENTRYPOINT [\"/bin/bash\", \"-l\", \"-c\"]
             WORKDIR {APP_DIR}
+
             {assets_copy_cmd}
 
             {dockerfile_phases_str}
@@ -228,9 +231,7 @@ impl DockerfileGenerator for StartPhase {
         _output: &OutputDir,
     ) -> Result<String> {
         let start_cmd = match &self.cmd {
-            Some(cmd) => {
-                format!("CMD {}", cmd)
-            }
+            Some(cmd) => utils::get_exec_command(cmd),
             None => "".to_string(),
         };
 

src/nixpacks/builder/docker/utils.rs

@@ -46,6 +46,12 @@ pub fn get_copy_from_command(from: &str, files: &[String], app_dir: &str) -> Str
     }
 }
 
+pub fn get_exec_command(command: &str) -> String {
+    let params = command.replace('\"', "\\\"");
+
+    format!("CMD [\"{}\"]", params)
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -99,4 +105,22 @@ mod tests {
             get_copy_from_command(from, &files, app_dir)
         );
     }
+
+    #[test]
+    fn test_get_exec_cmd() {
+        assert_eq!(
+            "CMD [\"command1\"]".to_string(),
+            get_exec_command("command1")
+        );
+
+        assert_eq!(
+            "CMD [\"command1 command2\"]".to_string(),
+            get_exec_command("command1 command2")
+        );
+
+        assert_eq!(
+            "CMD [\"command1 command2 -l \\\"asdf\\\"\"]".to_string(),
+            get_exec_command("command1 command2 -l \"asdf\"")
+        );
+    }
 }