Retries, timeout, version configurable per job

This makes retries, timeout and SNMP version configurable per job. It
overrides the module's equivalent WalkParams if they're present as query
attributes.

Partially addresses: prometheus#762

main.go

@@ -19,6 +19,7 @@ import (
 	_ "net/http/pprof"
 	"os"
 	"os/signal"
+	"strconv"
 	"sync"
 	"syscall"
 	"time"
@@ -84,8 +85,68 @@ func handler(w http.ResponseWriter, r *http.Request, logger log.Logger) {
 	if moduleName == "" {
 		moduleName = "if_mib"
 	}
+
+	timeout := query.Get("timeout")
+	if len(query["timeout"]) > 1 {
+		http.Error(w, "'timeout' parameter must only be specified once", 400)
+		snmpRequestErrors.Inc()
+		return
+	}
+	var ptimeout *time.Duration
+	if timeout != "" {
+		p, err := time.ParseDuration(timeout)
+		if err != nil {
+			http.Error(w, "'timeout' parameter must be a valid Go duration string", 400)
+			snmpRequestErrors.Inc()
+			return
+		}
+		ptimeout = &p
+	}
+	retries := query.Get("retries")
+	if len(query["retries"]) > 1 {
+		http.Error(w, "'retries' parameter must only be specified once", 400)
+		snmpRequestErrors.Inc()
+		return
+	}
+	var pretries *int
+	if retries != "" {
+		i, err := strconv.ParseInt(retries, 0, 64)
+		if err != nil {
+			http.Error(w, "'retries' parameter must be an integer", 400)
+			snmpRequestErrors.Inc()
+			return
+		}
+		ii := int(i)
+		pretries = &ii
+	}
+	version := query.Get("version")
+	if len(query["version"]) > 1 {
+		http.Error(w, "'version' parameter must only be specified once", 400)
+		snmpRequestErrors.Inc()
+		return
+	}
+	var pversion *int
+	if version != "" {
+		i, err := strconv.ParseInt(version, 0, 64)
+		if err != nil {
+			http.Error(w, "'version' parameter must be an integer", 400)
+			snmpRequestErrors.Inc()
+			return
+		}
+		ii := int(i)
+		pversion = &ii
+	}
 	sc.RLock()
 	module, ok := (*(sc.C))[moduleName]
+	if ptimeout != nil {
+		module.WalkParams.Timeout = *ptimeout
+	}
+	if pretries != nil {
+		module.WalkParams.Retries = pretries
+	}
+	if pversion != nil {
+		module.WalkParams.Version = *pversion
+	}
 	sc.RUnlock()
 	if !ok {
 		http.Error(w, fmt.Sprintf("Unknown module '%s'", moduleName), 400)