1 files changed, 68 insertions, 0 deletions
diff --git a/sd_daemon/watchdog.go b/sd_daemon/watchdog.go
new file mode 100644
index 0000000..b32f470
--- /dev/null
+++ b/sd_daemon/watchdog.go
@@ -0,0 +1,68 @@
+// Copyright 2016 CoreOS, Inc.
+// Copyright 2016 Luke Shumaker
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sd_daemon
+
+import (
+	"os"
+	"strconv"
+	"time"
+)
+
+// WatchdogEnabled returns how often the process is expected to send a
+// keep-alive notification to the service manager.
+//
+//     Notify(0, false, "WATCHDOG=1", nil) // send keep-alive notification
+//
+// If unsetEnv is true, then (regardless of whether the function call
+// itself succeeds or not) it will unset the environmental variables
+// WATCHDOG_USEC and WATCHDOG_PID, which will cause further calls to
+// this function to fail.
+//
+// If an error is returned, then the duration is 0.  If the service
+// manager is not expecting a keep-alive notification from this
+// process (or if this has already been called with unsetEnv=true),
+// then ErrDisabled is returned.  If there is an error parsing the
+// service manager's watchdog request, then an appropriate other error
+// is returned.
+func WatchdogEnabled(unsetEnv bool) (time.Duration, error) {
+	if unsetEnv {
+		defer func() {
+			_ = os.Unsetenv("WATCHDOG_USEC")
+			_ = os.Unsetenv("WATCHDOG_PID")
+		}()
+	}
+
+	usecStr, haveUsec := os.LookupEnv("WATCHDOG_USEC")
+	if !haveUsec {
+		return 0, ErrDisabled
+	}
+	usec, err := strconv.ParseInt(usecStr, 10, 64)
+	if err != nil || usec < 0 {
+		return 0, err
+	}
+
+	if pidStr, havePid := os.LookupEnv("WATCHDOG_PID"); havePid {
+		pid, err := strconv.Atoi(pidStr)
+		if err != nil {
+			return 0, err
+		}
+		if pid != os.Getpid() {
+			return 0, ErrDisabled
+		}
+	}
+
+	return time.Duration(usec) * time.Microsecond, nil
+}