cli-sdk-guide

name	cli-sdk-guide
description	Guide for implementing Backend.AI client SDK and CLI (Session, BaseFunction, @api_function, Click commands, Pydantic models, FieldSpec, output handlers, APIConfig, testing)
version	1.0.0
dependencies	["api-guide","tdd-guide"]
tags	["client-sdk","cli","session","api-function","click","pydantic","output-handler"]

CLI/SDK Implementation Guide

Guide for implementing Backend.AI client SDK and CLI with session management, API functions, and Click commands.

Purpose

SDK (Software Development Kit):

• Python library for Backend.AI REST API
• Programmatic access for integrations and automation
• Async-first with sync wrapper for CLI compatibility

CLI (Command Line Interface):

• User-facing commands for Backend.AI operations
• Built on top of SDK functions
• Supports console and JSON output modes

When to use:

• SDK: Building integrations, automation scripts, web dashboards
• CLI: Interactive administration, shell scripts, CI/CD pipelines
• Direct API: Only when SDK doesn't support the operation yet

Architecture Overview

Layers: CLI → SDK → REST API → Manager

Flow: CLI commands call SDK functions through Session, which makes HTTP requests to REST API endpoints.

CLI Layer:

• ExtendedCommandGroup - Command groups with aliases and interrupt handling
• LazyGroup - Lazy loading for faster startup
• CLIContext - Shared state (config, output mode)
• @pass_ctx_obj - CLIContext injection decorator
• FieldSpec - Output field definitions
• BaseOutputHandler - Console/JSON formatters

SDK Layer:

• BaseFunction - Metaclass for API function classes
• @api_function - Decorator for API methods
• AsyncSession - Primary async HTTP session
• Session - Sync wrapper for CLI
• api_session - ContextVar for session context

Data Layer:

• Pydantic models - Request/Response DTOs (future standard)
• attrs classes - Legacy DTOs (current usage in client/cli/types.py)
• New code should use Pydantic (common/dto/)

Config Layer:

• APIConfig - Environment variables and .env file
• CLIContext - CLI state and output handler

SDK Implementation Patterns

Session Management

AsyncSession (Primary):

• Async context manager for API operations
• Manages HTTP client lifecycle, authentication tokens
• Uses api_session ContextVar for context propagation

Session (Sync Wrapper):

• Synchronous wrapper for CLI commands
• Creates async event loop internally
• Same interface as AsyncSession

See:

• client/session.py - Session and AsyncSession implementation
• client/request.py - HTTP request handling
• client/config.py - APIConfig for environment variables

API Function Pattern

@api_function decorator:

• Wraps instance methods as API functions
• Retrieves session from api_session ContextVar
• Handles async/sync execution
• Provides consistent error handling

BaseFunction metaclass:

• Creates function group instances bound to session
• Examples: session.FairShare, session.Admin

Standard operations:

• create_* - POST requests
• get_* - GET single item
• search_* - GET collection with filters
• update_* - PATCH requests
• delete_* - DELETE requests
• purge_* - Permanent deletion

See:

• client/func/base.py - BaseFunction and @api_function
• client/func/fair_share.py - Complete implementation example

Pydantic Models (Future Standard)

Current state:

• attrs - Current usage in client/cli/types.py
• Pydantic - Future standard in common/dto/
• New code should use Pydantic

Why Pydantic:

• Runtime type validation
• Automatic JSON serialization/deserialization
• IDE autocomplete and type checking
• Better error messages

Usage:

• model_dump(mode="json", exclude_none=True) - To JSON dict
• model_validate(data) - From JSON dict
• Handles nested models automatically

See:

• client/func/fair_share.py - Pydantic usage in SDK
• common/dto/fair_share.py - Shared DTO definitions

SDK Implementation Flow

Standard pattern:

1. Define request/response Pydantic models
2. Create method with @api_function decorator
3. Build Request object with endpoint and data
4. Fetch JSON response from session
5. Parse with Response.model_validate(data)
6. Return typed result

See complete example:

• client/func/fair_share.py - All standard operations (create, get, search, update, delete)

CLI Implementation Patterns

Click Command Structure

Command organization:

• ExtendedCommandGroup - Enhanced Click group with interrupt handling
• LazyGroup - Defers module imports until needed
• @pass_ctx_obj - Type-safe CLIContext injection

See:

• client/cli/main.py - Main entry and command groups
• client/cli/extensions.py - @pass_ctx_obj decorator
• client/cli/fair_share/__init__.py - LazyGroup usage

Output Handlers

FieldSpec:

• Defines displayable fields for a model
• Specifies field name, human-readable label, formatters
• Supports nested fields (dot notation) and custom formatters

BaseOutputHandler:

• print_item() - Single item display
• print_list() - Collection display
• print_error() - Error messages
• Implementations: ConsoleOutputHandler (table), JSONOutputHandler

See:

• client/output/types.py - FieldSpec and BaseOutputHandler protocol
• client/output/fields.py - Field utilities
• client/cli/fair_share/commands.py - FieldSpec definitions and usage

CLI + SDK Integration

Pattern:

• Click command → Session context → SDK function → REST API
• Catch BackendAIError exceptions
• Use ctx.output.print_error() for consistent formatting
• Exit with appropriate ExitCode

Error handling:

• All exceptions inherit from BackendAIError
• Exit codes from ExitCode enum (OK=0, FAILURE=1, INVALID_ARGUMENT=2, PERMISSION_DENIED=3)
• ctx.output.print_error() handles both console and JSON modes

See:

• client/cli/fair_share/commands.py - Complete CLI integration
• client/cli/types.py - CLIContext and ExitCode
• client/exceptions.py - Exception hierarchy

Common Patterns

Pattern	SDK	CLI
Session	async with AsyncSession()	with Session() (sync wrapper)
Request	Request("POST", "/endpoint", json={...})	SDK handles internally
Response	Response.model_validate(data)	SDK returns parsed model
Output	Return Pydantic model	ctx.output.print_item() or print_list()
Error	Raise BackendAIError subclass	print_error() + sys.exit(ExitCode)
Config	APIConfig() reads environment	Passed via CLIContext
Async	Always async (async def, await)	Sync wrapper handles internally

Implementation Checklist

When implementing new CLI/SDK feature:

1. ✅ Implement REST API (/api-guide)

   • Handler with standard operations
   • Proper error responses

2. ✅ Define Pydantic models

   • Request DTOs in common/dto/
   • Response DTOs shared with API layer

3. ✅ Implement SDK function

   • Add method to appropriate function group
   • Use @api_function decorator
   • Handle all operations (create, get, search, update, delete)

4. ✅ Define FieldSpec

   • List displayable fields
   • Add formatters for complex types
   • Consider both console and JSON output

5. ✅ Implement CLI commands

   • Add Click command group
   • Map options/arguments to SDK calls
   • Handle errors with proper exit codes

6. ✅ Write tests (/tdd-guide)

   • SDK: Mock HTTP responses (pytest-aiohttp)
   • CLI: Use CliRunner, mock SDK functions (not HTTP)
   • Verify request/response serialization

7. ✅ Update documentation

   • Add usage examples to README
   • Document new CLI commands

Testing

SDK tests:

• Mock HTTP responses with pytest-aiohttp
• Test request serialization and response parsing
• Verify Pydantic model validation

CLI tests:

• Use Click's CliRunner for command invocation
• Mock SDK functions (not HTTP layer)
• Test output formatting and exit codes

See:

• /tdd-guide skill for testing workflow
• tests/unit/client/ - Test examples

Reference Files

Complete implementations:

• client/func/fair_share.py - Full SDK with Pydantic models
• client/cli/fair_share/commands.py - Full CLI with all patterns

Architecture components:

• client/session.py - Session and AsyncSession
• client/func/base.py - @api_function and BaseFunction
• client/cli/main.py - CLI entry point
• client/cli/extensions.py - @pass_ctx_obj decorator
• client/output/types.py - FieldSpec and output handlers
• client/config.py - APIConfig
• client/cli/types.py - CLIContext and ExitCode
• client/exceptions.py - Exception hierarchy

V2 SDK/CLI (New Pattern)

All new SDK/CLI work MUST use the v2 pattern.

V2 SDK Client (client/v2/domains_v2/)

• Inherits BaseDomainClient, receives BackendAIAuthClient via constructor
• Uses v2 DTOs from common/dto/manager/v2/ exclusively
• typed_request() handles serialization and response parsing
• Registry: V2ClientRegistry (client/v2/v2_registry.py) with @cached_property per domain

V2 CLI (client/cli/v2/)

Command pattern: ./bai [admin] {entity} [{sub-entity}] {operation}

• admin_ SDK methods → commands under ./bai admin {entity} ...
• Non-admin methods → ./bai {entity} ...
• Entity names are singular (domain, user, agent)
• Each entity has its own directory with __init__.py + commands.py
• Admin commands in admin/{entity}.py
• Sub-entities as separate Click sub-groups (e.g., revision, channel, role)
• Construct Pydantic DTOs with explicit field arguments (never kwargs unpacking)
• Filter options are domain-specific CLI args (--name-contains, --status, etc.)
• --order-by field:direction supports multiple values
• Config from ~/.backend.ai/ via load_v2_config() → V2ConnectionConfig dataclass

V2 Config (~/.backend.ai/)

• config.toml — endpoint, endpoint_type, api_version
• credentials.toml — access_key, secret_key
• session/cookie.dat — webserver session cookie (login/logout)

Related skills:

• /api-guide - REST API implementation (prerequisite)
• /tdd-guide - Testing workflow
• /local-dev - Service management and CLI testing