OpenAPI to
Go.

// services/default_client.go
package services

import (
	"context"
	"fmt"
	"net/http"

	"github.com/example/payments/models"
)

// DefaultClient is the HTTP client for this service.
type DefaultClient struct {
	httpClient *http.Client
	baseURL    string
}

// NewDefaultClient creates a new DefaultClient instance.
func NewDefaultClient(baseURL string) *DefaultClient {
	return &DefaultClient{
		httpClient: &http.Client{},
		baseURL:    baseURL,
	}
}

func (c *DefaultClient) GetPayment(
	ctx context.Context,
	id string,
	expand string,
) (*models.Payment, error) {
	// ... builds URL, appends ?expand when non-empty
	req, err := http.NewRequestWithContext(ctx, "GET", fullURL, nil)
	if err != nil {
		return nil, fmt.Errorf("failed to create request: %w", err)
	}
	req.Header.Set("Accept", "application/json")

	var result models.Payment
	if err := doRequestJSON(c.httpClient, req, &result); err != nil {
		return nil, err
	}
	return &result, nil
}

// services/api_helpers.go
package services

import (
	"encoding/json"
	"fmt"
	"io"
	"net/http"
)

// doRequestJSON executes the request, checks the status,
// and decodes the JSON body into target.
func doRequestJSON(
	httpClient *http.Client,
	req *http.Request,
	target any,
) error {
	resp, err := httpClient.Do(req)
	if err != nil {
		return fmt.Errorf("failed to execute request: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode >= 400 {
		errBody, _ := io.ReadAll(resp.Body)
		return fmt.Errorf("HTTP %d: %s", resp.StatusCode, string(errBody))
	}
	return json.NewDecoder(resp.Body).Decode(target)
}