api-custom-commands

How to author custom commands for the api CLI using the co-generated SDK.

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tessl review fix ./seed/cli/file-upload-openapi/.agents/skills/custom-commands/SKILL.md

Custom Commands for `api`

Overview

The api CLI supports user-authored custom commands that are compiled into the binary alongside the auto-generated API commands. Custom commands get a fully-wired SDK client that inherits the CLI's auth, retries, TLS, base URL, and global headers — zero configuration required.

Architecture

cli/api/custom.rs    ← Your command handlers (protected by .fernignore)
cli/api/sdk.rs       ← Generated bridge: client() + block_on()
cli/api/main.rs      ← Generated entrypoint (calls custom::register)
api-sdk/             ← Co-generated typed SDK crate
api-types/           ← Co-generated typed model crate

Adding a Custom Command

1. Edit `cli/api/custom.rs`

This file is protected by .fernignore — fern generate will never overwrite it. Register commands in the register() function:

use api_sdk::api::*;

pub fn register(app: CliApp) -> CliApp {
    let app = app.command(
        clap::Command::new("upload-file")
            .about("Upload a file to the database")
        ,
        |matches, ctx| {
            let client = super::sdk::client(ctx);
            let result = super::sdk::block_on(
                client.file_upload_example.upload_file(),
            )?;
            println!("{}", serde_json::to_string_pretty(&result).unwrap());
            Ok(())
        },
    );
    app
}

Then build and test:

cargo build
api upload-file

2. Available SDK Clients

The super::sdk::client(ctx) call returns a api_sdk::api::Client with the following sub-clients:

Field	Type	Description
`client.file_upload_example`	`api_sdk::api::FileUploadExampleClient`	file_upload_example operations

3. Key Patterns

Get the SDK client (execution-sharing, fully authenticated):

let client = super::sdk::client(ctx);

Run an async SDK call from a sync handler:

let result = super::sdk::block_on(
    client.some_resource.some_method(args),
)?;

Use typed models for request/response serialization:

use api_sdk::api::*;

Regeneration Safety

File	Regenerated?	Notes
`cli/api/custom.rs`	No	Protected by `.fernignore`
`cli/api/sdk.rs`	Yes	Bridges AppContext → SDK client
`cli/api/main.rs`	Yes	Calls `custom::register(app)`
`api-sdk/`	Yes	Co-generated typed SDK crate
`api-types/`	Yes	Co-generated typed models

After running fern generate, your custom.rs is preserved. All generated code (SDK, types, glue, main.rs) is updated to match the latest API spec. If the SDK surface changes (renamed methods, new sub-clients), update your custom.rs to match.

Build & Test

# Build the CLI (includes custom commands)
cargo build

# Run your custom command
api <your-command> [args]

# Run with verbose output for debugging
RUST_LOG=debug api <your-command> [args]

Repository: fern-api/fern
Path: seed/cli/file-upload-openapi/.agents/skills/custom-commands/SKILL.md
Commit: 134b13f

Last updated: 2 days ago
First committed: about 1 month ago

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