Accept target and sub_target in module config

README.md

@@ -78,10 +78,18 @@ Flags:
       --[no-]version             Show application version.
 
 ```
-Visit http://localhost:9602/modbus?target=1.2.3.4:502&module=fake&sub_target=1 where 1.2.3.4:502 is the IP and port number of the modbus IP device to get metrics from,
-while module and sub_target parameters specify which module and subtarget to use from the config file.
+Visit http://localhost:9602/modbus?module=fake&target=1.2.3.4:502&sub_target=1 where:
+
+- the `module` parameter specifies which module to use from the config file;
+- the `target` parameter specifies the IP and port number of the modbus IP device to get metrics from, e.g. `1.2.3.4:502`;
+- the `sub_target` specifies the slave address/id to use in the modbus request;
+
 If your device doesn't use sub-targets you can usually just set it to 1.
 
+Note `target` and `sub_target` may be provided per-module in the config,
+in which case the respective value in the request is ignored.
+This is useful e.g. if you only have one device per module and don't want to accept the IP address in the request.
+
 Visit http://localhost:9602/metrics to get the metrics of the exporter itself.
 
 ## Configuration File

config/config.go

@@ -62,6 +62,8 @@ type ListTargets map[string]*Module
 type Module struct {
 	Name        string         `yaml:"name"`
 	Protocol    ModbusProtocol `yaml:"protocol"`
+	Target      *string        `yaml:"target"`
+	SubTarget   *uint8         `yaml:"subTarget"`
 	Timeout     int            `yaml:"timeout"`
 	Baudrate    int            `yaml:"baudrate"`
 	Databits    int            `yaml:"databits"`

modbus.yml

@@ -3,6 +3,15 @@ modules:
     # Module name, needs to be passed as parameter by Prometheus.
   - name: "fake"
     protocol: 'tcp/ip'
+
+    # IP and port number of the modbus IP device to get metrics from.
+    # Optinal. If specified, this value is used and the target HTTP request parameter is ignored.
+    # target: "1.2.3.4:502"
+
+    # Modbus slave address/id to use
+    # Optional. If specified, this value is used and the sub_target HTTP request parameter is ignored.
+    # subTarget: 0
+
     # Certain modbus devices need special timing workarounds
     workarounds:
       # Sleep a certain time after the TCP connection is established

modbus_exporter.go

@@ -88,32 +88,45 @@ func scrapeHandler(e *modbus.Exporter, w http.ResponseWriter, r *http.Request, l
 		http.Error(w, "'module' parameter must be specified", http.StatusBadRequest)
 		return
 	}
-
-	if !e.GetConfig().HasModule(moduleName) {
+	module := e.GetConfig().GetModule(moduleName)
+	if module == nil {
 		http.Error(w, fmt.Sprintf("module '%v' not defined in configuration file", moduleName), http.StatusBadRequest)
 		return
 	}
 
-	target := r.URL.Query().Get("target")
-	if target == "" {
-		http.Error(w, "'target' parameter must be specified", http.StatusBadRequest)
-		return
+	var target string
+	if module.Target == nil {
+		target = r.URL.Query().Get("target")
+		if target == "" {
+			http.Error(w, "'target' parameter must be specified", http.StatusBadRequest)
+			return
+		}
+	} else {
+		target = *module.Target
 	}
 
-	sT := r.URL.Query().Get("sub_target")
-	if sT == "" {
-		http.Error(w, "'sub_target' parameter must be specified", http.StatusBadRequest)
-		return
-	}
+	var subTarget uint8
+	if module.SubTarget == nil {
+		sT := r.URL.Query().Get("sub_target")
+		if sT == "" {
+			http.Error(w, "'sub_target' parameter must be specified", http.StatusBadRequest)
+			return
+		}
 
-	subTarget, err := strconv.ParseUint(sT, 10, 32)
-	if err != nil {
-		http.Error(w, fmt.Sprintf("'sub_target' parameter must be a valid integer: %v", err), http.StatusBadRequest)
-		return
-	}
-	if subTarget > 255 {
-		http.Error(w, fmt.Sprintf("'sub_target' parameter must be from 0 to 255. Invalid value: %d", subTarget), http.StatusBadRequest)
-		return
+		parsedSubTarget, err := strconv.ParseUint(sT, 10, 32)
+		if err != nil {
+			http.Error(w, fmt.Sprintf("'sub_target' parameter must be a valid integer: %v", err), http.StatusBadRequest)
+			return
+		}
+
+		if parsedSubTarget > 255 {
+			http.Error(w, fmt.Sprintf("'sub_target' parameter must be from 0 to 255. Invalid value: %d", parsedSubTarget), http.StatusBadRequest)
+			return
+		}
+
+		subTarget = byte(parsedSubTarget)
+	} else {
+		subTarget = *module.SubTarget
 	}
 
 	level.Info(logger).Log("msg", "got scrape request", "module", moduleName, "target", target, "sub_target", subTarget)