handle-user-output
Guide for producing user-facing output in this Rust project. NEVER use println!, eprintln!, print!, eprint!, or direct stdout/stderr access. Always use UserOutput via the execution context or ProgressReporter in controllers. Covers the sink-based output architecture, stdout vs stderr channel strategy, ProgressReporter for multi-step operations, verbosity control, and themes. Use when writing any user-visible output, progress messages, errors, or results. Triggers on "println", "print output", "user output", "UserOutput", "ProgressReporter", "display result", "output message", or "progress message".
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- handle-user-output
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- Guide for producing user-facing output in this Rust project. NEVER use println!, eprintln!, print!, eprint!, or direct stdout/stderr access. Always use UserOutput via the execution context or ProgressReporter in controllers. Covers the sink-based output architecture, stdout vs stderr channel strategy, ProgressReporter for multi-step operations, verbosity control, and themes. Use when writing any user-visible output, progress messages, errors, or results. Triggers on "println", "print output", "user output", "UserOutput", "ProgressReporter", "display result", "output message", or "progress message".
- metadata
- {"author":"torrust","version":"1.0"}
# Handling User Output
## Golden Rule
**NEVER write directly to stdout/stderr.**
```rust
// ❌ FORBIDDEN
println!("Processing...");
eprintln!("Error occurred");
std::io::stdout().write_all(b"data").unwrap();
```
```rust
// ✅ CORRECT — use UserOutput
let user_output = ctx.user_output();
user_output.lock().borrow_mut().progress("Processing...");
user_output.lock().borrow_mut().error("Error occurred");
user_output.lock().borrow_mut().result("data");
```
## In Controllers: Use ProgressReporter
Controllers use `ProgressReporter` (not `UserOutput` directly):
```rust
use crate::presentation::views::progress::ProgressReporter;
use crate::presentation::views::UserOutput;
pub struct ConfigureCommandController {
progress: ProgressReporter,
}
impl ConfigureCommandController {
pub fn new(user_output: Arc<ReentrantMutex<RefCell<UserOutput>>>) -> Self {
Self {
progress: ProgressReporter::new(user_output, 3), // 3 total steps
}
}
pub fn execute(&mut self) -> Result<(), Error> {
self.progress.start_step("Validating environment")?;
// ... do work ...
self.progress.complete_step(Some("Environment name validated: my-env"))?;
self.progress.start_step("Configuring infrastructure")?;
// ... do work ...
self.progress.complete_step(None)?;
Ok(())
}
}
```
## Channel Strategy (stdout vs stderr)
| Channel | Use for |
| ---------- | ----------------------------------------------- |
| **stdout** | Final results, structured data (JSON), pipeline |
| **stderr** | Progress, status updates, warnings, errors |
This enables piping: `deployer create env | jq .status`
## Why This Architecture?
- **Testability**: Output captured and asserted in tests
- **Verbosity control**: Centralized filtering
- **Theme support**: emoji/plain/ASCII themes
- **Channel routing**: Automatic stdout vs stderr
## Reference
Full guide: [`docs/contributing/output-handling.md`](../../docs/contributing/output-handling.md)
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