req.go

package req

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

const (
	defaultBaseURL = "https://www.registreentreprises.gouv.qc.ca"
	userAgent      = "github.com/quebec/req"
)

// Client is an HTTP client used to interact with the API
type Client struct {
	client *http.Client

	// Base URL for API requests. Defaults to the Registre des Entreprises
	// du Québec base URL.
	BaseURL *url.URL

	// User agent used when communicating.
	UserAgent string
}

// NewClient returns a new API client. If a nil httpClient is provided,
// http.DefaultClient will be used.
func NewClient(httpClient *http.Client) *Client {
	if httpClient == nil {
		httpClient = http.DefaultClient
	}
	baseURL, _ := url.Parse(defaultBaseURL)

	return &Client{client: httpClient, BaseURL: baseURL}
}

// NewRequest creates an API request. A relative URL can be provided in urlStr,
// in which case it is resolved relative to the BaseURL of the Client.
// Relative URLs should always be specified without a preceding slash. If
// specified, the value pointed to by body is JSON encoded and included as the
// request body.
func (c *Client) NewRequest(method, urlStr string, body interface{}) (*http.Request, error) {
	rel, err := url.Parse(urlStr)
	if err != nil {
		return nil, err
	}

	u := c.BaseURL.ResolveReference(rel)

	var buf io.ReadWriter
	if body != nil {
		buf = new(bytes.Buffer)
		err := json.NewEncoder(buf).Encode(body)
		if err != nil {
			return nil, err
		}
	}

	req, err := http.NewRequest(method, u.String(), buf)
	if err != nil {
		return nil, err
	}

	req.Header.Add("Content-Type", "application/json; charset=UTF-8")
	req.Header.Add("User-Agent", c.UserAgent)

	if c.UserAgent == "" {
		req.Header.Add("User-Agent", userAgent)
	}

	return req, nil
}

// Do sends an API request and returns the API response.  The API response is
// JSON decoded and stored in the value pointed to by v, or returned as an
// error if an API error has occurred.  If v implements the io.Writer
// interface, the raw response body will be written to v, without attempting to
// first decode it.
func (c *Client) Do(req *http.Request, v interface{}) error {
	resp, err := c.client.Do(req)
	if err != nil {
		return err
	}

	defer resp.Body.Close()

	err = CheckResponse(resp)
	if err != nil {
		return err
	}

	if v != nil {
		if w, ok := v.(io.Writer); ok {
			io.Copy(w, resp.Body)
		} else {
			err = json.NewDecoder(resp.Body).Decode(v)
		}
	}
	return err
}

// CheckResponse checks the API response for errors, and returns them if
// present. A response is considered an error if it has a status code outside
// the 200 range. API error responses are expected to have either no response
// body, or a JSON response body that maps to ErrorResponse.  Any other
// response body will be silently ignored.
func CheckResponse(r *http.Response) error {
	if c := r.StatusCode; 200 <= c && c <= 299 {
		return nil
	}
	errorResponse := &ErrorResponse{Response: r}
	data, err := ioutil.ReadAll(r.Body)
	if err == nil && data != nil {
		json.Unmarshal(data, &errorResponse)
	}
	return errorResponse
}

// An ErrorResponse is the error format returned by the API
type ErrorResponse struct {
	Response      *http.Response // HTTP response that caused this error
	ExceptionType string         `json:"ExceptionType"`
	Message       string         `json:"Message"`
	StackTrace    string         `json:"StackTrace"`
}

func (r *ErrorResponse) Error() string {
	return fmt.Sprintf("%v %v: %d %v",
		r.Response.Request.Method, r.Response.Request.URL,
		r.Response.StatusCode, r.Message)
}