From 589447abafcc719a15b3904d90a87f83470bf2e7 Mon Sep 17 00:00:00 2001
From: Joerg Epping <56630628+joerg-git@users.noreply.github.com>
Date: Tue, 18 Oct 2022 20:42:18 +0200
Subject: [PATCH] feat(inputs.modbus): add config option to pause after connect
 (#11983)

---
 etc/telegraf.conf                             | 2 ++
 etc/telegraf_windows.conf                     | 2 ++
 plugins/inputs/modbus/README.md               | 8 +++++---
 plugins/inputs/modbus/modbus.go               | 9 +++++++--
 plugins/inputs/modbus/sample.conf             | 2 ++
 plugins/inputs/modbus/sample_general_end.conf | 2 ++
 6 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/etc/telegraf.conf b/etc/telegraf.conf
index 89ee352a5..e52c5fb06 100644
--- a/etc/telegraf.conf
+++ b/etc/telegraf.conf
@@ -5970,6 +5970,8 @@
 #
 #   ## Enable workarounds required by some devices to work correctly
 #   # [inputs.modbus.workarounds]
+#     ## Pause after connect delays the first request by the specified time. This might be necessary for (slow) devices.
+#     # pause_after_connect = "0ms"
 #     ## Pause between read requests sent to the device. This might be necessary for (slow) serial devices.
 #     # pause_between_requests = "0ms"
 #     ## Close the connection after every gather cycle. Usually the plugin closes the connection after a certain
diff --git a/etc/telegraf_windows.conf b/etc/telegraf_windows.conf
index 8e9791aa9..e0ff4e028 100644
--- a/etc/telegraf_windows.conf
+++ b/etc/telegraf_windows.conf
@@ -5764,6 +5764,8 @@
 #
 #   ## Enable workarounds required by some devices to work correctly
 #   # [inputs.modbus.workarounds]
+#     ## Pause after connect delays the first request by the specified time. This might be necessary for (slow) devices.
+#     # pause_after_connect = "0ms"
 #     ## Pause between read requests sent to the device. This might be necessary for (slow) serial devices.
 #     # pause_between_requests = "0ms"
 #     ## Close the connection after every gather cycle. Usually the plugin closes the connection after a certain
diff --git a/plugins/inputs/modbus/README.md b/plugins/inputs/modbus/README.md
index 432036506..256bdf45a 100644
--- a/plugins/inputs/modbus/README.md
+++ b/plugins/inputs/modbus/README.md
@@ -196,6 +196,8 @@ Registers via Modbus TCP or Modbus RTU/ASCII.
 
   ## Enable workarounds required by some devices to work correctly
   # [inputs.modbus.workarounds]
+    ## Pause after connect delays the first request by the specified time. This might be necessary for (slow) devices.
+    # pause_after_connect = "0ms"
     ## Pause between read requests sent to the device. This might be necessary for (slow) serial devices.
     # pause_between_requests = "0ms"
     ## Close the connection after every gather cycle. Usually the plugin closes the connection after a certain
@@ -211,9 +213,9 @@ those debug messages, Telegraf has to be started with debugging enabled
 (i.e. with the `--debug` option). Please be aware that connection tracing will
 produce a lot of messages and should __NOT__ be used in production environments.
 
-Please use `pause_between_requests` with care. Ensure the total gather time,
-including the pause(s), does not exceed the configured collection interval. Note
-that pauses add up if multiple requests are sent!
+Please use `pause_after_connect` / `pause_between_requests` with care. Ensure
+the total gather time, including the pause(s), does not exceed the configured
+collection interval. Note that pauses add up if multiple requests are sent!
 
 ## Configuration styles
 
diff --git a/plugins/inputs/modbus/modbus.go b/plugins/inputs/modbus/modbus.go
index 26e42e882..7aeb25b47 100644
--- a/plugins/inputs/modbus/modbus.go
+++ b/plugins/inputs/modbus/modbus.go
@@ -24,8 +24,9 @@ var sampleConfigStart string
 var sampleConfigEnd string
 
 type ModbusWorkarounds struct {
-	PollPause        config.Duration `toml:"pause_between_requests"`
-	CloseAfterGather bool            `toml:"close_connection_after_gather"`
+	AfterConnectPause config.Duration `toml:"pause_after_connect"`
+	PollPause         config.Duration `toml:"pause_between_requests"`
+	CloseAfterGather  bool            `toml:"close_connection_after_gather"`
 }
 
 // Modbus holds all data relevant to the plugin
@@ -265,6 +266,10 @@ func (m *Modbus) initClient() error {
 func (m *Modbus) connect() error {
 	err := m.handler.Connect()
 	m.isConnected = err == nil
+	if m.isConnected && m.Workarounds.AfterConnectPause != 0 {
+		nextRequest := time.Now().Add(time.Duration(m.Workarounds.AfterConnectPause))
+		time.Sleep(time.Until(nextRequest))
+	}
 	return err
 }
 
diff --git a/plugins/inputs/modbus/sample.conf b/plugins/inputs/modbus/sample.conf
index 8fe908ed0..cf1216be2 100644
--- a/plugins/inputs/modbus/sample.conf
+++ b/plugins/inputs/modbus/sample.conf
@@ -188,6 +188,8 @@
 
   ## Enable workarounds required by some devices to work correctly
   # [inputs.modbus.workarounds]
+    ## Pause after connect delays the first request by the specified time. This might be necessary for (slow) devices.
+    # pause_after_connect = "0ms"
     ## Pause between read requests sent to the device. This might be necessary for (slow) serial devices.
     # pause_between_requests = "0ms"
     ## Close the connection after every gather cycle. Usually the plugin closes the connection after a certain
diff --git a/plugins/inputs/modbus/sample_general_end.conf b/plugins/inputs/modbus/sample_general_end.conf
index f6245caed..3f58b336b 100644
--- a/plugins/inputs/modbus/sample_general_end.conf
+++ b/plugins/inputs/modbus/sample_general_end.conf
@@ -1,5 +1,7 @@
   ## Enable workarounds required by some devices to work correctly
   # [inputs.modbus.workarounds]
+    ## Pause after connect delays the first request by the specified time. This might be necessary for (slow) devices.
+    # pause_after_connect = "0ms"
     ## Pause between read requests sent to the device. This might be necessary for (slow) serial devices.
     # pause_between_requests = "0ms"
     ## Close the connection after every gather cycle. Usually the plugin closes the connection after a certain