ynab-portfolio-monitor/bitcoin/client.go

package bitcoin

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

const apiBaseURL = "https://blockstream.info/api/"

// A client is the structure that will be used to consume the API
// endpoints. It holds the login credentials, http client/transport,
// rate limit information, and the login session timer.
type client struct {
	httpClient *http.Client
	transport  *http.Transport
}

// Send an HTTP GET request, and return the processed response
func (c *client) get(endpoint string, out interface{}, query url.Values) error {
	req, err := http.NewRequest("GET", apiBaseURL+endpoint+"?"+query.Encode(), nil)
	if err != nil {
		return fmt.Errorf("failed to create new GET request: %v", err)
	}

	res, err := c.httpClient.Do(req)
	if err != nil {
		return fmt.Errorf("http GET request failed: %v", err)
	}

	err = c.processResponse(res, out)
	if err != nil {
		return fmt.Errorf("failed to process response: %v", err)
	}
	return nil
}

// processResponse takes the body of an HTTP response, and either returns
// the error code, or unmarshalls the JSON response, extracts
// rate limit info, and places it into the object
// output parameter. This function closes the response body after reading it.
func (c *client) processResponse(res *http.Response, out interface{}) error {
	body, err := io.ReadAll(res.Body)
	res.Body.Close()
	if err != nil {
		return fmt.Errorf("failed to read response body: %v", err)
	}

	if res.StatusCode != 200 && res.StatusCode != 201 {
		return fmt.Errorf("unexpected http status code '%d': %v", res.StatusCode, err)
	}

	err = json.Unmarshal(body, out)
	if err != nil {
		return fmt.Errorf("failed to unmarshal response body: %v", err)
	}
	return nil
}

// newClient is the factory function for clients
func newClient() (*client, error) {
	transport := &http.Transport{
		ResponseHeaderTimeout: 5 * time.Second,
	}

	httpClient := &http.Client{
		Transport: transport,
	}

	// Create a new client
	c := &client{
		httpClient: httpClient,
		transport:  transport,
	}
	return c, nil
}