feat: publish standalone worker

Separate worker packaging and service lifecycle from the control plane.

checks/ctcp/tcp.go

@@ -0,0 +1,77 @@
+// Package ctcp provides TCP connect / port check functionality for RSMon.
+//
+// Semantics: the check opens a TCP connection to host:port using the
+// dialer's timeout, and reports OK as soon as the kernel-level
+// handshake completes (no banner read, no payload sent). Any dial
+// failure (refused, timed out, network unreachable, no route, ...)
+// is reported as ERR with the underlying error message so operators
+// can distinguish configuration problems from real outages.
+//
+// Settings consumed from models.CheckSettings:
+//   - port (string): TCP port to dial. Defaults to 80 when empty.
+//   - timeout (int, seconds): per-dial budget. Clamped to at least 1s.
+//   - host (string): optional override of the monitor host.
+package ctcp
+
+import (
+	"fmt"
+	"net"
+	"time"
+
+	"rsgit.ru/rsmon/rsmon/app/models"
+)
+
+const (
+	stateOK  = "OK"
+	stateERR = "ERR"
+
+	defaultTimeout = 5 * time.Second
+	minTimeout     = 1 * time.Second
+)
+
+// Perform executes a single TCP connect check.
+func Perform(c *models.Check) *Result {
+	r := &Result{}
+	settings := c.GetSettings()
+
+	host := c.Monitor.Host
+	if settings.Host != "" {
+		host = settings.Host
+	}
+	if host == "" {
+		r.State = stateERR
+		r.Error = fmt.Errorf("tcp: empty host")
+		return r
+	}
+
+	port := settings.Port
+	if port == "" {
+		port = "80"
+	}
+
+	timeout := time.Duration(settings.Timeout) * time.Second
+	if timeout <= 0 {
+		timeout = defaultTimeout
+	}
+	if timeout < minTimeout {
+		timeout = minTimeout
+	}
+
+	addr := net.JoinHostPort(host, port)
+	dialer := &net.Dialer{Timeout: timeout, DualStack: true}
+	start := time.Now()
+	conn, err := dialer.Dial("tcp", addr)
+	r.Duration = time.Since(start)
+	if err != nil {
+		r.State = stateERR
+		r.Error = err
+		return r
+	}
+	r.RemoteAddr = conn.RemoteAddr().String()
+	if closeErr := conn.Close(); closeErr != nil {
+		r.Warnings = append(r.Warnings, fmt.Sprintf("close: %v", closeErr))
+	}
+	r.State = stateOK
+	r.Infos = append(r.Infos, fmt.Sprintf("tcp %s in %.2fms", addr, float64(r.Duration.Microseconds())/1000.0))
+	return r
+}