Step 4: Pre-Flight

Purpose

The Pre-Flight step runs initial validation checks on the submission and prepares the code for grading. It acts as the final "gatekeeper" that ensures both the file structure is correct and the code is in an executable state (e.g., compiled).

This step performs three main functions: 1. Asset injection: Injecting grader-owned static files (datasets, test fixtures) from S3 into the sandbox. 2. Required files check: Ensuring all mandatory files defined in the assignment configuration exist. 3. Setup commands execution: Running compilation or initialization scripts (e.g., javac, npm install, gcc) inside the sandbox.

How It Works

The step execution follows these logic gates:

1. Asset Injection: If the setup_config contains an assets list, the PreFlightService resolves each asset via the AssetSourceResolver. Assets are fetched from S3 and injected into the container's /tmp directory using a secure Base64-encoded exec_run method (fully compatible with gVisor).

2. Required Files Check: It compares the files in the submission against the list provided in the required_files section of the setup_config for the submission's language.

3. Setup Commands Execution: If the setup_config contains setup_commands, they are executed sequentially within the sandbox created in Step 3.

   • Stop on Failure: If any command fails (non-zero or invalid response), the step stops immediately and fails the entire pre-flight check. Subsequent commands are not executed.
   • Setup commands are orchestrated via the SandboxService.

If both checks pass, the step succeeds and the pipeline continues to Step 5: Grade.

Dependencies

Step	What It Needs
Sandbox	Requires the SandboxContainer to execute setup commands

Input

Source	Data
Constructor	setup_config: dict — language-keyed setup configuration
Pipeline	StepName.SANDBOX → SandboxContainer
Pipeline	pipeline_exec.submission → submission files and language

Output

Field	Type	Description
data	None	This step does not produce data for downstream steps
status	StepStatus.SUCCESS	Required files exist and all setup commands passed

Language-Specific Configuration

The setup_config defines mandatory files and commands for each language:

{
  "python": {
    "required_files": ["main.py"],
    "setup_commands": []
  },
  "java": {
    "required_files": ["Calculator.java"],
    "setup_commands": ["javac Calculator.java"]
  }
}

Failure Scenarios

• Missing required file → StepStatus.FAIL listing missing files.
• Setup Command Failed → StepStatus.FAIL with the command's exit code, stdout, and stderr.
• No Sandbox → StepStatus.FAIL if setup commands exist but no sandbox was provided.

Next Step

After verification and compilation, the pipeline proceeds to Step 5: Grade to execute the actual test functions.

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Source

autograder/steps/pre_flight_step.py → PreFlightStep

autograder/services/pre_flight_service.py → PreFlightService

autograder/services/sandbox_service.py → SandboxService