Initila commit

shelly/client.go

@@ -0,0 +1,83 @@
+// Package shelly provides HTTP communication shared by Shelly product implementations.
+package shelly
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+)
+
+const maxErrorBodySize = 4 * 1024
+
+// StatusClient is consumed by product collectors and can be replaced in tests.
+type StatusClient interface {
+	GetStatus(context.Context, any) error
+}
+
+// Client fetches status data from one Shelly device.
+type Client struct {
+	baseURL    *url.URL
+	username   string
+	password   string
+	httpClient *http.Client
+}
+
+// NewClient creates a client that uses HTTP Basic Authentication when credentials are set.
+func NewClient(rawURL, username, password string, timeout time.Duration) (*Client, error) {
+	baseURL, err := url.Parse(rawURL)
+	if err != nil {
+		return nil, fmt.Errorf("parse Shelly URL: %w", err)
+	}
+
+	return &Client{
+		baseURL:  baseURL,
+		username: username,
+		password: password,
+		httpClient: &http.Client{
+			Timeout: timeout,
+		},
+	}, nil
+}
+
+// GetStatus decodes the /status response into destination.
+func (c *Client) GetStatus(ctx context.Context, destination any) error {
+	statusURL := *c.baseURL
+	statusURL.Path = strings.TrimRight(statusURL.Path, "/") + "/status"
+	statusURL.RawQuery = ""
+	statusURL.Fragment = ""
+
+	request, err := http.NewRequestWithContext(ctx, http.MethodGet, statusURL.String(), nil)
+	if err != nil {
+		return fmt.Errorf("create status request: %w", err)
+	}
+	request.Header.Set("Accept", "application/json")
+	request.Header.Set("User-Agent", "shelly-exporter")
+	if c.username != "" || c.password != "" {
+		request.SetBasicAuth(c.username, c.password)
+	}
+
+	response, err := c.httpClient.Do(request)
+	if err != nil {
+		return fmt.Errorf("request %s: %w", statusURL.String(), err)
+	}
+	defer response.Body.Close()
+
+	if response.StatusCode < http.StatusOK || response.StatusCode >= http.StatusMultipleChoices {
+		body, _ := io.ReadAll(io.LimitReader(response.Body, maxErrorBodySize))
+		message := strings.TrimSpace(string(body))
+		if message == "" {
+			return fmt.Errorf("request %s returned %s", statusURL.String(), response.Status)
+		}
+		return fmt.Errorf("request %s returned %s: %s", statusURL.String(), response.Status, message)
+	}
+
+	if err := json.NewDecoder(response.Body).Decode(destination); err != nil {
+		return fmt.Errorf("decode response from %s: %w", statusURL.String(), err)
+	}
+	return nil
+}