OpenAPI to
Go.

// services/default_client.go
package services

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

	"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 {
	httpClient := &http.Client{}

	return &DefaultClient{
		httpClient: httpClient,
		baseURL:    baseURL,
	}
}

func (c *DefaultClient) GetPayment(ctx context.Context, id string, expand *string) (*models.Payment, error) {
	// ... builds urlPath, appends ?expand when non-nil
	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 HTTP request, checks the status code, and decodes
// the JSON response body into target. Works for both objects and slices.
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)
}