OpenAPI Generator

A Go implementation of the OpenAPI Generator inspired by the original Java-based project.

Why

I ran into issues with Java dependencies and performance in large projects, and many issues stay unresolved in the repository for a long time. I want to build something simpler, easier to maintain, and portable as a single binary with minimal dependencies.

Features

• Single binary for easy installation and use
• Fast generation times without JVM overhead
• Load specs from local files or remote URLs
• Command-line interface compatible with the original OpenAPI Generator
• Supports OpenAPI 3.x and Swagger 2.0 specifications (auto-converts 2.0 → 3.x)

Generators

Currently implemented:

• typescript-fetch

Installation

go install github.com/xseman/openapi-generator/cmd/openapi-generator@latest

Usage

openapi-generator generate \
  -i openapi.yaml \
  -g <template> \
  -o ./generated \
  -p key=value \
  -c config.yaml \
  --verbose

Template-Specific Usage:

• typescript-fetch

CLI Options

Option	Short	Description
--input-spec	-i	Location of the OpenAPI spec (file or URL)
--generator-name	-g	Generator to use (currently: typescript-fetch)
--output	-o	Output directory
--config	-c	Configuration file (JSON/YAML)
--template-dir	-t	Custom template directory
--additional-properties	-p	Key=value pairs for generator options
--skip-validate-spec		Skip OpenAPI spec validation
--verbose	-v	Enable verbose output

Note: For generator-specific options, see the template documentation (e.g., typescript-fetch options).

Architecture

Generation Pipeline

%%{init: {'theme': 'neutral' } }%%
sequenceDiagram
    participant CLI
    participant Parser
    participant Config
    participant Codegen
    participant Templates

    CLI->>Parser: Load Spec (YAML/JSON)
    Parser-->>Parser: Convert Swagger 2.0 to OpenAPI 3.x
    Parser-->>CLI: Parsed Spec

    CLI->>Config: Merge CLI + File Config
    Config-->>CLI: Resolved Options

    CLI->>Codegen: Transform to CodegenModels
    Codegen-->>Codegen: Map Types & Properties
    Codegen-->>Codegen: Extract Operations
    Codegen-->>CLI: Codegen Models

    CLI->>Templates: Render API Classes
    Templates-->>CLI: Generated API Files

    CLI->>Templates: Render Models
    Templates-->>CLI: Generated Model Files

    CLI->>Templates: Render Supporting Files
    Templates-->>CLI: Runtime & Configuration Files

Loading

Core Components

Component	Package	Description
Parser	internal/parser	Parses OpenAPI 2.0/3.x specs using kin-openapi
Codegen	internal/codegen	Data structures mirroring Java's CodegenModel
Generator	internal/generator	Generator interface and implementations
Template	internal/template	Mustache template engine with lambdas
Config	internal/config	Configuration structs for generators

Dependencies

Library	Purpose
github.com/getkin/kin-openapi	OpenAPI 3.x and 2.0 parsing
github.com/cbroglie/mustache	Mustache template rendering
github.com/spf13/cobra	CLI framework

Development

# Build
go build -o openapi-generator ./cmd/openapi-generator

# Run tests
go test ./...

# Generate from a spec
./openapi-generator generate \
    -i petstore.yaml \
    -g typescript-fetch \
    -o ./out

# List available generators
./openapi-generator list

# Show config options for a generator
./openapi-generator config-help typescript-fetch