feat: user roles - admins and users limited to the machines given to them, user editor with machines, password sign-in and its lock; direct address without Cloudflare as the agents' fallback and in the installer; version 0.1.2

internal/agent/hosts.go

@@ -0,0 +1,170 @@
+package agent
+
+import (
+	"context"
+	"log"
+	"net/http"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/x-grk/longpolling-remote-access/internal/proto"
+)
+
+// The server can be reached at two addresses: the main one (behind
+// Cloudflare, say) and a direct one that goes to the server itself. The
+// direct one comes from the installer or, for agents installed before it was
+// set, from the server, and is kept in the state file. When the address in
+// use has been out of reach for a while the agent tries the other; on the
+// direct one it keeps checking the main one and goes back when it answers.
+
+const (
+	// switchAfter is how long the address in use may fail before the other
+	// is tried.
+	switchAfter = 30 * time.Second
+	// mainCheck is how often the main address is checked from the direct one.
+	mainCheck = 5 * time.Minute
+)
+
+type hostState struct {
+	mu        sync.Mutex
+	cur       string
+	downSince time.Time
+	changed   bool // the address changed: the WebSocket goes there at once
+}
+
+// host is the server address in use now.
+func (a *Agent) host() string {
+	a.hosts.mu.Lock()
+	defer a.hosts.mu.Unlock()
+	if a.hosts.cur == "" {
+		return a.cfg.Host
+	}
+	return a.hosts.cur
+}
+
+// fallback is the direct address: the installer's, else the one the server
+// told.
+func (a *Agent) fallback() string {
+	if a.cfg.Fallback != "" {
+		return a.cfg.Fallback
+	}
+	a.stateMu.Lock()
+	defer a.stateMu.Unlock()
+	return a.state.Fallback
+}
+
+// learnFallback keeps the direct address the server tells.
+func (a *Agent) learnFallback(v string) {
+	v = strings.TrimRight(strings.TrimSpace(v), "/")
+	if v == "" || a.cfg.Fallback != "" {
+		return
+	}
+	a.stateMu.Lock()
+	same := a.state.Fallback == v
+	if !same {
+		a.state.Fallback = v
+	}
+	a.stateMu.Unlock()
+	if !same {
+		log.Printf("direct address: %s", v)
+		_ = a.saveState()
+	}
+}
+
+// setHost moves to addr: requests go there from now on, and the WebSocket
+// is dropped to reconnect there.
+func (a *Agent) setHost(addr string) {
+	a.hosts.mu.Lock()
+	if a.hosts.cur == addr || (a.hosts.cur == "" && addr == a.cfg.Host) {
+		a.hosts.mu.Unlock()
+		return
+	}
+	a.hosts.cur, a.hosts.downSince, a.hosts.changed = addr, time.Time{}, true
+	a.hosts.mu.Unlock()
+	log.Printf("server address: %s", addr)
+	if l := a.link.Load(); l != nil {
+		l.close()
+	}
+}
+
+// hostChanged reports, once, that the address changed.
+func (a *Agent) hostChanged() bool {
+	a.hosts.mu.Lock()
+	defer a.hosts.mu.Unlock()
+	c := a.hosts.changed
+	a.hosts.changed = false
+	return c
+}
+
+// reached notes the server answered; failed notes it did not, and after
+// switchAfter of that moves to the other address.
+func (a *Agent) reached() {
+	a.hosts.mu.Lock()
+	a.hosts.downSince = time.Time{}
+	a.hosts.mu.Unlock()
+}
+
+func (a *Agent) failed() {
+	fb := a.fallback()
+	if fb == "" || fb == a.cfg.Host {
+		return
+	}
+	a.hosts.mu.Lock()
+	now := time.Now()
+	if a.hosts.downSince.IsZero() {
+		a.hosts.downSince = now
+		a.hosts.mu.Unlock()
+		return
+	}
+	long := now.Sub(a.hosts.downSince) >= switchAfter
+	cur := a.hosts.cur
+	a.hosts.mu.Unlock()
+	if !long {
+		return
+	}
+	next := fb
+	if cur == fb {
+		next = a.cfg.Host
+	}
+	log.Printf("server out of reach for %s, trying %s", switchAfter, next)
+	a.setHost(next)
+}
+
+// watchMain moves back to the main address once it answers again.
+func (a *Agent) watchMain(ctx context.Context) {
+	t := time.NewTicker(mainCheck)
+	defer t.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-t.C:
+		}
+		if a.host() == a.cfg.Host {
+			continue
+		}
+		if a.reachableAt(ctx, a.cfg.Host) {
+			log.Printf("main address answers again")
+			a.setHost(a.cfg.Host)
+		}
+	}
+}
+
+// reachableAt reports whether the server answers a quick request at base.
+func (a *Agent) reachableAt(ctx context.Context, base string) bool {
+	ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
+	defer cancel()
+	req, _ := http.NewRequestWithContext(ctx, http.MethodGet, base+"/api/agent/config", nil)
+	a.authHeaders(req)
+	resp, err := a.http.Do(req)
+	if err != nil {
+		return false
+	}
+	resp.Body.Close()
+	if resp.StatusCode < 300 {
+		a.learnFallback(resp.Header.Get(proto.FallbackHeader))
+		return true
+	}
+	return false
+}