Implement notifications service with shared messaging and email drivers (#36)

backend/notifications/email/http.go

@@ -0,0 +1,54 @@
+package email
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"io"
+	"net/http"
+	"strconv"
+	"time"
+
+	"git.sendico.io/tech/sxchnge/notifications/model"
+)
+
+func (c *client) post(ctx context.Context, key string, payload any) Outcome {
+	body, err := json.Marshal(payload)
+	if err != nil {
+		return Outcome{State: model.Failed, Code: "invalid_payload"}
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.endpoint, bytes.NewReader(body))
+	if err != nil {
+		return Outcome{State: model.Failed, Code: "invalid_provider_config"}
+	}
+	req.Header.Set("Authorization", "Bearer "+c.key)
+	req.Header.Set("Content-Type", "application/json")
+	if key != "" {
+		req.Header.Set("Idempotency-Key", key)
+	}
+	resp, err := c.http.Do(req)
+	if err != nil {
+		return Outcome{State: model.Unknown, Code: "provider_outcome_unknown"}
+	}
+	defer resp.Body.Close()
+	// Discard a bounded response without logging provider-controlled content.
+	_, _ = io.Copy(io.Discard, io.LimitReader(resp.Body, 64<<10))
+	switch {
+	case resp.StatusCode >= 200 && resp.StatusCode < 300:
+		return Outcome{State: model.Accepted}
+	case resp.StatusCode == 429:
+		delay := time.Minute
+		if n, e := strconv.Atoi(resp.Header.Get("Retry-After")); e == nil && n > 0 && n <= 86400 {
+			delay = time.Duration(n) * time.Second
+		} else if date, e := http.ParseTime(resp.Header.Get("Retry-After")); e == nil && time.Until(date) > 0 {
+			delay = time.Until(date)
+		}
+		return Outcome{State: model.RetryWait, Code: "provider_rate_limited", RetryAfter: delay}
+	case resp.StatusCode >= 500 || resp.StatusCode == 408:
+		return Outcome{State: model.Unknown, Code: "provider_outcome_unknown"}
+	case resp.StatusCode == 401 || resp.StatusCode == 403:
+		return Outcome{State: model.Failed, Code: "provider_authentication_failed"}
+	default:
+		return Outcome{State: model.Failed, Code: "provider_rejected"}
+	}
+}