fix snmp emitting empty fields

closes #1848
closes #1835

CHANGELOG.md

@@ -44,6 +44,7 @@
 - [#1702](https://github.com/influxdata/telegraf/issues/1702): sqlserver, fix issue when case sensitive collation is activated.
 - [#1823](https://github.com/influxdata/telegraf/issues/1823): Fix huge allocations in http_listener when dealing with huge payloads.
 - [#1833](https://github.com/influxdata/telegraf/issues/1833): Fix translating SNMP fields not in MIB.
+- [#1835](https://github.com/influxdata/telegraf/issues/1835): Fix SNMP emitting empty fields.
 
 ## v1.0.1 [unreleased]
 

plugins/inputs/snmp/snmp.go

@@ -460,13 +460,15 @@ func (t Table) Build(gs snmpConnection, walk bool) (*RTable, error) {
 			// index, and being added on the same row.
 			if pkt, err := gs.Get([]string{oid}); err != nil {
 				return nil, Errorf(err, "performing get")
-			} else if pkt != nil && len(pkt.Variables) > 0 && pkt.Variables[0].Type != gosnmp.NoSuchObject {
+			} else if pkt != nil && len(pkt.Variables) > 0 && pkt.Variables[0].Type != gosnmp.NoSuchObject && pkt.Variables[0].Type != gosnmp.NoSuchInstance {
 				ent := pkt.Variables[0]
 				fv, err := fieldConvert(f.Conversion, ent.Value)
 				if err != nil {
 					return nil, Errorf(err, "converting %q", ent.Value)
 				}
-				ifv[""] = fv
+				if fvs, ok := fv.(string); !ok || fvs != "" {
+					ifv[""] = fv
+				}
 			}
 		} else {
 			err := gs.Walk(oid, func(ent gosnmp.SnmpPDU) error {
@@ -487,7 +489,9 @@ func (t Table) Build(gs snmpConnection, walk bool) (*RTable, error) {
 				if err != nil {
 					return Errorf(err, "converting %q", ent.Value)
 				}
-				ifv[idx] = fv
+				if fvs, ok := fv.(string); !ok || fvs != "" {
+					ifv[idx] = fv
+				}
 				return nil
 			})
 			if err != nil {

plugins/inputs/snmp/snmp_test.go

@@ -62,12 +62,15 @@ var tsc = &testSNMPConnection{
 	values: map[string]interface{}{
 		".1.0.0.0.1.1.0":     "foo",
 		".1.0.0.0.1.1.1":     []byte("bar"),
+		".1.0.0.0.1.1.2":     []byte(""),
 		".1.0.0.0.1.102":     "bad",
 		".1.0.0.0.1.2.0":     1,
 		".1.0.0.0.1.2.1":     2,
+		".1.0.0.0.1.2.2":     0,
 		".1.0.0.0.1.3.0":     "0.123",
 		".1.0.0.0.1.3.1":     "0.456",
-		".1.0.0.0.1.3.2":     "9.999",
+		".1.0.0.0.1.3.2":     "0.000",
+		".1.0.0.0.1.3.3":     "9.999",
 		".1.0.0.0.1.4.0":     123456,
 		".1.0.0.1.1":         "baz",
 		".1.0.0.1.2":         234,
@@ -426,6 +429,14 @@ func TestTableBuild_noWalk(t *testing.T) {
 				Oid:   ".1.0.0.1.2",
 				IsTag: true,
 			},
+			{
+				Name: "empty",
+				Oid:  ".1.0.0.0.1.1.2",
+			},
+			{
+				Name: "noexist",
+				Oid:  ".1.2.3.4.5",
+			},
 		},
 	}