From 139498937a97c258581bf5efe1c2925d348f828d Mon Sep 17 00:00:00 2001
From: Wiard van Rij <5786097+wiardvanrij@users.noreply.github.com>
Date: Mon, 7 Dec 2020 22:45:06 +0100
Subject: [PATCH] Add support to convert snmp hex strings to integers (#8426)

---
 plugins/inputs/snmp/README.md    | 24 ++++++++++------
 plugins/inputs/snmp/snmp.go      | 47 ++++++++++++++++++++++++++++----
 plugins/inputs/snmp/snmp_test.go |  6 ++++
 3 files changed, 62 insertions(+), 15 deletions(-)

diff --git a/plugins/inputs/snmp/README.md b/plugins/inputs/snmp/README.md
index ea6e7a95b..0eb0ac31a 100644
--- a/plugins/inputs/snmp/README.md
+++ b/plugins/inputs/snmp/README.md
@@ -113,15 +113,21 @@ option operate similar to the `snmpget` utility.
     # is_tag = false
 
     ## Apply one of the following conversions to the variable value:
-    ##   float(X) Convert the input value into a float and divides by the
-    ##            Xth power of 10. Effectively just moves the decimal left
-    ##            X places. For example a value of `123` with `float(2)`
-    ##            will result in `1.23`.
-    ##   float:   Convert the value into a float with no adjustment. Same
-    ##            as `float(0)`.
-    ##   int:     Convert the value into an integer.
-    ##   hwaddr:  Convert the value to a MAC address.
-    ##   ipaddr:  Convert the value to an IP address.
+    ##   float(X):    Convert the input value into a float and divides by the
+    ##                Xth power of 10. Effectively just moves the decimal left
+    ##                X places. For example a value of `123` with `float(2)`
+    ##                will result in `1.23`.
+    ##   float:       Convert the value into a float with no adjustment. Same
+    ##                as `float(0)`.
+    ##   int:         Convert the value into an integer.
+    ##   hwaddr:      Convert the value to a MAC address.
+    ##   ipaddr:      Convert the value to an IP address.
+    ##   hextoint:X:Y Convert a hex string value to integer. Where X is the Endian
+    ##                and Y the bit size. For example: hextoint:LittleEndian:uint64
+    ##                or hextoint:BigEndian:uint32. Valid options for the Endian are:
+    ##                BigEndian and LittleEndian. For the bit size: uint16, uint32
+    ##                and uint64.
+    ##                      
     # conversion = ""
 ```
 
diff --git a/plugins/inputs/snmp/snmp.go b/plugins/inputs/snmp/snmp.go
index 623c9ba61..f8fa50004 100644
--- a/plugins/inputs/snmp/snmp.go
+++ b/plugins/inputs/snmp/snmp.go
@@ -3,6 +3,7 @@ package snmp
 import (
 	"bufio"
 	"bytes"
+	"encoding/binary"
 	"fmt"
 	"log"
 	"math"
@@ -574,12 +575,6 @@ func (s *Snmp) getConnection(idx int) (snmpConnection, error) {
 }
 
 // fieldConvert converts from any type according to the conv specification
-//  "float"/"float(0)" will convert the value into a float.
-//  "float(X)" will convert the value into a float, and then move the decimal before Xth right-most digit.
-//  "int" will convert the value into an integer.
-//  "hwaddr" will convert the value into a MAC address.
-//  "ipaddr" will convert the value into into an IP address.
-//  "" will convert a byte slice into a string.
 func fieldConvert(conv string, v interface{}) (interface{}, error) {
 	if conv == "" {
 		if bs, ok := v.([]byte); ok {
@@ -671,6 +666,46 @@ func fieldConvert(conv string, v interface{}) (interface{}, error) {
 		return v, nil
 	}
 
+	split := strings.Split(conv, ":")
+	if split[0] == "hextoint" && len(split) == 3 {
+
+		endian := split[1]
+		bit := split[2]
+
+		bv, ok := v.([]byte)
+		if !ok {
+			return v, nil
+		}
+
+		if endian == "LittleEndian" {
+			switch bit {
+			case "uint64":
+				v = binary.LittleEndian.Uint64(bv)
+			case "uint32":
+				v = binary.LittleEndian.Uint32(bv)
+			case "uint16":
+				v = binary.LittleEndian.Uint16(bv)
+			default:
+				return nil, fmt.Errorf("invalid bit value (%s) for hex to int conversion", bit)
+			}
+		} else if endian == "BigEndian" {
+			switch bit {
+			case "uint64":
+				v = binary.BigEndian.Uint64(bv)
+			case "uint32":
+				v = binary.BigEndian.Uint32(bv)
+			case "uint16":
+				v = binary.BigEndian.Uint16(bv)
+			default:
+				return nil, fmt.Errorf("invalid bit value (%s) for hex to int conversion", bit)
+			}
+		} else {
+			return nil, fmt.Errorf("invalid Endian value (%s) for hex to int conversion", endian)
+		}
+
+		return v, nil
+	}
+
 	if conv == "ipaddr" {
 		var ipbs []byte
 
diff --git a/plugins/inputs/snmp/snmp_test.go b/plugins/inputs/snmp/snmp_test.go
index 8368ed738..199fbe83c 100644
--- a/plugins/inputs/snmp/snmp_test.go
+++ b/plugins/inputs/snmp/snmp_test.go
@@ -739,6 +739,12 @@ func TestFieldConvert(t *testing.T) {
 		{[]byte("abcd"), "ipaddr", "97.98.99.100"},
 		{"abcd", "ipaddr", "97.98.99.100"},
 		{[]byte("abcdefghijklmnop"), "ipaddr", "6162:6364:6566:6768:696a:6b6c:6d6e:6f70"},
+		{[]byte{0x00, 0x09, 0x3E, 0xE3, 0xF6, 0xD5, 0x3B, 0x60}, "hextoint:BigEndian:uint64", uint64(2602423610063712)},
+		{[]byte{0x00, 0x09, 0x3E, 0xE3}, "hextoint:BigEndian:uint32", uint32(605923)},
+		{[]byte{0x00, 0x09}, "hextoint:BigEndian:uint16", uint16(9)},
+		{[]byte{0x00, 0x09, 0x3E, 0xE3, 0xF6, 0xD5, 0x3B, 0x60}, "hextoint:LittleEndian:uint64", uint64(6934371307618175232)},
+		{[]byte{0x00, 0x09, 0x3E, 0xE3}, "hextoint:LittleEndian:uint32", uint32(3812493568)},
+		{[]byte{0x00, 0x09}, "hextoint:LittleEndian:uint16", uint16(2304)},
 	}
 
 	for _, tc := range testTable {