Handle panic when ipmi_sensor input gets bad input (influxdata#4937)

plugins/inputs/ipmi_sensor/ipmi.go

@@ -4,6 +4,7 @@ import (
 	"bufio"
 	"bytes"
 	"fmt"
+	"log"
 	"os/exec"
 	"regexp"
 	"strconv"
@@ -228,7 +229,12 @@ func parseV2(acc telegraf.Accumulator, hostname string, cmdOut []byte, measured_
 func extractFieldsFromRegex(re *regexp.Regexp, input string) map[string]string {
 	submatches := re.FindStringSubmatch(input)
 	results := make(map[string]string)
-	for i, name := range re.SubexpNames() {
+	subexpNames := re.SubexpNames()
+	if len(subexpNames) > len(submatches) {
+		log.Printf("D! No matches found in '%s'", input)
+		return results
+	}
+	for i, name := range subexpNames {
 		if name != input && name != "" && input != "" {
 			results[name] = trim(submatches[i])
 		}

plugins/inputs/ipmi_sensor/ipmi_test.go

@@ -572,3 +572,41 @@ Power Supply 1   | 03h | ok  | 10.1 | 110 Watts, Presence detected
 	}
 	os.Exit(0)
 }
+
+func TestExtractFields(t *testing.T) {
+	v1Data := `Ambient Temp     | 20 degrees C      | ok
+Altitude         | 80 feet           | ok
+Avg Power        | 210 Watts         | ok
+Planar 3.3V      | 3.29 Volts        | ok
+Planar 5V        | 4.90 Volts        | ok
+Planar 12V       | 12.04 Volts       | ok
+B                | 0x00              | ok
+Unable to send command: Invalid argument
+ECC Corr Err     | Not Readable      | ns
+Unable to send command: Invalid argument
+ECC Uncorr Err   | Not Readable      | ns
+Unable to send command: Invalid argument
+`
+
+	v2Data := `SEL              | 72h | ns  |  7.1 | No Reading
+Intrusion        | 73h | ok  |  7.1 |
+Fan1             | 30h | ok  |  7.1 | 5040 RPM
+Inlet Temp       | 04h | ok  |  7.1 | 25 degrees C
+USB Cable Pres   | 50h | ok  |  7.1 | Connected
+Unable to send command: Invalid argument
+Current 1        | 6Ah | ok  | 10.1 | 7.20 Amps
+Unable to send command: Invalid argument
+Power Supply 1   | 03h | ok  | 10.1 | 110 Watts, Presence detected
+`
+
+	tests := []string{
+		v1Data,
+		v2Data,
+	}
+
+	for i := range tests {
+		t.Logf("Checking v%d data...", i+1)
+		extractFieldsFromRegex(re_v1_parse_line, tests[i])
+		extractFieldsFromRegex(re_v2_parse_line, tests[i])
+	}
+}