Initial release

src/backend.go

@@ -0,0 +1,101 @@
+package main
+
+import (
+	"crypto/tls"
+	"fmt"
+	"net/http"
+)
+
+// Backend connects to a backend (https)
+// and forward requests from frontend
+type Backend interface {
+	IsPrimary() (bool, error)
+	IsReplica() (bool, error)
+}
+
+// NewBackend creates a backend from a driver, a connection string
+// and an optional interval for caching values
+func NewBackend(config BackendConfig, cache Cache) Backend {
+	if config.Host == "" {
+		config.Host = "localhost"
+	}
+	if config.Port == 0 {
+		config.Port = 80
+	}
+	if config.Scheme == "" {
+		config.Scheme = "http"
+	}
+
+	b := &HTTPBackend{
+		host:   config.Host,
+		port:   config.Port,
+		scheme: config.Scheme,
+		cache:  cache,
+	}
+
+	tr := &http.Transport{
+		TLSClientConfig: &tls.Config{InsecureSkipVerify: config.Insecure},
+	}
+	b.client = &http.Client{Transport: tr}
+	return b
+}
+
+// HTTPBackend will request a backend with HTTP(s) protocol
+type HTTPBackend struct {
+	cache  Cache
+	host   string
+	port   int
+	scheme string
+	client *http.Client
+}
+
+func (b HTTPBackend) baseURL() string {
+	return fmt.Sprintf("%s://%s:%d", b.scheme, b.host, b.port)
+}
+
+// request search into the cache to find the given key
+// then eventually creates a HTTP/HTTPS request on backend and
+// cache response for further requests
+func (b HTTPBackend) request(key string) (bool, error) {
+	state, err := b.cache.Get(key)
+	if err != nil {
+		Warning("could not get key %s from cache: %v", key, err)
+		return false, err
+	}
+
+	if state == nil {
+		url := b.baseURL() + "/" + key
+
+		Debug("GET %s", url)
+		response, err := b.client.Get(url)
+		if err != nil {
+			Warning("could not request remote backend: %v", err)
+			return false, err
+		}
+		defer response.Body.Close()
+
+		if response.StatusCode == http.StatusOK {
+			state = true
+		} else {
+			state = false
+		}
+
+		err = b.cache.Set(key, state)
+		if err != nil {
+			Warning("could not save %s key to cache: %v", key, err)
+			return false, err
+		}
+	}
+
+	return state.(bool), nil
+}
+
+// IsPrimary will call /master route on patroni API
+func (b HTTPBackend) IsPrimary() (bool, error) {
+	return b.request("master")
+}
+
+// IsReplica will call /replica route on patroni API
+func (b HTTPBackend) IsReplica() (bool, error) {
+	return b.request("replica")
+}