pacto-plugin-schema-infer

pacto-plugin-schema-infer

A Pacto plugin that reads a service configuration file (JSON, YAML, or TOML) and infers a JSON Schema from it.

Installation

make install

Or download a pre-built binary from the latest release.

Usage

pacto generate schema-infer <bundle-dir> --option file=config.yaml

Arguments

Argument	Description
<bundle-dir>	Path to the Pacto bundle directory containing the service's source code and pacto.yaml. Use . for the current directory.

Example

# Run from the project root
pacto generate schema-infer .  --option file=config.yaml

# Or specify an explicit path
pacto generate schema-infer /path/to/my-service --option file=config.yaml

This generates a config.schema.json file containing the inferred JSON Schema. Reference it in your Pacto contract:

configuration:
  schema: config.schema.json

Version

pacto-plugin-schema-infer --version

Options

Options are passed via --option key=value flags when invoking with Pacto.

file (required)

Path to the configuration file to infer from, relative to the bundle directory.

pacto generate schema-infer . --option file=config.yaml

Supported file extensions: .json, .yaml, .yml, .toml. The extension determines which parser is used. If the extension is not recognized, the plugin exits with an error.

title (optional)

Title for the generated JSON Schema's title field.

• Default: "configuration"

pacto generate schema-infer . --option file=config.yaml --option title="My Service Config"

The output schema always has a fixed output path of config.schema.json.

Supported formats

Format	Extensions	Parser
JSON	.json	encoding/json
YAML	.yaml, .yml	gopkg.in/yaml.v3
TOML	.toml	github.com/BurntSushi/toml

How it works

The plugin parses the configuration file and recursively infers JSON Schema types from the values it finds:

Go type	JSON Schema type
string	string
float64	number
int64 / int	integer
bool	boolean
nil	null
map[string]any	object
[]any	array

All keys found in the sample are marked as required. The root object sets additionalProperties: false.

Note: The generated schema infers types from sample values and marks all present fields as required. Review the output and relax constraints as needed for your use case.

Example

Given config.yaml:

server:
  host: "0.0.0.0"
  port: 8080
  tls: true
logging:
  level: info
  outputs:
    - stdout
    - file

The plugin generates:

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "type": "object",
  "additionalProperties": false,
  "title": "configuration",
  "properties": {
    "server": {
      "type": "object",
      "properties": {
        "host": { "type": "string" },
        "port": { "type": "number" },
        "tls": { "type": "boolean" }
      },
      "required": ["host", "port", "tls"]
    },
    "logging": {
      "type": "object",
      "properties": {
        "level": { "type": "string" },
        "outputs": {
          "type": "array",
          "items": { "type": "string" }
        }
      },
      "required": ["level", "outputs"]
    }
  },
  "required": ["logging", "server"]
}

Development

make build      # Build the binary to dist/
make test       # Run unit tests
make e2e        # Run e2e tests
make coverage   # Run tests with coverage report
make lint       # Check formatting and run go vet
make ci         # Run full CI pipeline
make install    # Install to $GOPATH/bin