gosnmp

GoSNMP is an SNMP client library fully written in Go. It provides Get, GetNext, GetBulk, Walk, BulkWalk, Set and Traps. It supports IPv4 and IPv6, using SNMPv1, SNMPv2c or SNMPv3. Builds are tested against linux/amd64 and linux/386.

About

gosnmp was started by Andreas Louca, then completely rewritten by Sonia Hamilton (2012-2020), and now ownership has been transferred to the community at gosnmp/gosnmp.

For support and help, join us in the #snmp channel of Gophers Slack.

Overview

GoSNMP has the following SNMP functions:

• Get (single or multiple OIDs)
• GetNext
• GetBulk (SNMPv2c and SNMPv3 only)
• Walk - retrieves a subtree of values using GETNEXT.
• BulkWalk - retrieves a subtree of values using GETBULK (SNMPv2c and SNMPv3 only).
• BulkWalkAll - similar to BulkWalk but returns a filled array of all values rather than using a callback function to stream results.
• Set - supports Integers and OctetStrings.
• SendTrap - send SNMP TRAPs.
• Listen - act as an NMS for receiving TRAPs.

GoSNMP has the following helper functions:

• ToBigInt - treat returned values as *big.Int
• Partition - facilitates dividing up large slices of OIDs

gosnmp/gosnmp has completely diverged from alouca/gosnmp, your code will require modification in these (and other) locations:

• the Get function has a different method signature
• the NewGoSNMP function has been removed, use Connect instead (see Usage below). Connect uses the GoSNMP struct; gosnmp.Default is provided for you to build on.
• GoSNMP no longer relies on alouca/gologger - you can use your logger if it conforms to the gosnmp.LoggerInterface interface; otherwise debugging will disabled.

type LoggerInterface interface {
    Print(v ...interface{})
    Printf(format string, v ...interface{})
}

To enable logging, you must call gosnmp.NewLogger() function, and pass a pointer to your logging interface, for example with standard *log.Logger:

gosnmp.Default.Logger = gosnmp.NewLogger(log.New(os.Stdout, "", 0))

or

g := &gosnmp.GoSNMP{
    ...
    Logger:    gosnmp.NewLogger(log.New(os.Stdout, "", 0)),
}

You can completely remove the logging code from your application using the golang build tag "gosnmp_nodebug", for example:

go build -tags gosnmp_nodebug

This will completely disable the logging of the gosnmp library, even if the logger interface is specified in the code. This provides a small performance improvement.

Installation

go get github.com/gosnmp/gosnmp

Documentation

https://pkg.go.dev/github.com/gosnmp/gosnmp

Usage

Here is examples/example/main.go, demonstrating how to use GoSNMP:

// Default is a pointer to a GoSNMP struct that contains sensible defaults
// eg port 161, community public, etc
g.Default.Target = "192.168.1.10"
err := g.Default.Connect()
if err != nil {
    log.Fatalf("Connect() err: %v", err)
}
defer g.Default.Conn.Close()

oids := []string{"1.3.6.1.2.1.1.4.0", "1.3.6.1.2.1.1.7.0"}
result, err2 := g.Default.Get(oids) // Get() accepts up to g.MAX_OIDS
if err2 != nil {
    log.Fatalf("Get() err: %v", err2)
}

for i, variable := range result.Variables {
    fmt.Printf("%d: oid: %s ", i, variable.Name)

    // the Value of each variable returned by Get() implements
    // interface{}. You could do a type switch...
    switch variable.Type {
    case g.OctetString:
        bytes := variable.Value.([]byte)
        fmt.Printf("string: %s\n", string(bytes))
    default:
        // ... or often you're just interested in numeric values.
        // ToBigInt() will return the Value as a BigInt, for plugging
        // into your calculations.
        fmt.Printf("number: %d\n", g.ToBigInt(variable.Value))
    }
}

Running this example gives the following output (from my printer):

% go run example.go
0: oid: 1.3.6.1.2.1.1.4.0 string: Administrator
1: oid: 1.3.6.1.2.1.1.7.0 number: 104

• examples/example2.go is similar to example.go, however it uses a custom &GoSNMP rather than g.Default
• examples/walkexample.go demonstrates using BulkWalk
• examples/example3.go demonstrates SNMPv3
• examples/trapserver.go demonstrates writing an SNMP v2c trap server

MIB Parser

I don't have any plans to write a mib parser. Others have suggested https://github.com/sleepinggenius2/gosmi

Contributions

Contributions are welcome, especially ones that have packet captures (see below).

If you've never contributed to a Go project before, here is an example workflow.

1. fork this repo on the GitHub webpage
2. go get github.com/gosnmp/gosnmp
3. cd $GOPATH/src/github.com/gosnmp/gosnmp
4. git remote rename origin upstream
5. git remote add origin git@github.com:/gosnmp.git
6. git checkout -b development
7. git push -u origin development (setup where you push to, check it works)

Packet Captures

Create your packet captures in the following way:

Expected output, obtained via an snmp command. For example:

% snmpget -On -v2c -c public 203.50.251.17 1.3.6.1.2.1.1.7.0 \
  1.3.6.1.2.1.2.2.1.2.6 1.3.6.1.2.1.2.2.1.5.3
.1.3.6.1.2.1.1.7.0 = INTEGER: 78
.1.3.6.1.2.1.2.2.1.2.6 = STRING: GigabitEthernet0
.1.3.6.1.2.1.2.2.1.5.3 = Gauge32: 4294967295

A packet capture, obtained while running the snmpget. For example:

sudo tcpdump -s 0 -i eth0 -w foo.pcap host 203.50.251.17 and port 161

Bugs

Rane's document SNMP: Simple? Network Management Protocol was useful when learning the SNMP protocol.

Please create an issue on Github with packet captures (upload capture to Google Drive, Dropbox, or similar) containing samples of missing BER types, or of any other bugs you find. If possible, please include 2 or 3 examples of the missing/faulty BER type.

The following BER types have been implemented:

• 0x00 UnknownType
• 0x01 Boolean
• 0x02 Integer
• 0x03 BitString
• 0x04 OctetString
• 0x05 Null
• 0x06 ObjectIdentifier
• 0x07 ObjectDescription
• 0x40 IPAddress (IPv4 & IPv6)
• 0x41 Counter32
• 0x42 Gauge32
• 0x43 TimeTicks
• 0x44 Opaque (Float & Double)
• 0x45 NsapAddress
• 0x46 Counter64
• 0x47 Uinteger32
• 0x78 OpaqueFloat
• 0x79 OpaqueDouble
• 0x80 NoSuchObject
• 0x81 NoSuchInstance
• 0x82 EndOfMibView

Running the Tests

Local testing in Docker

docker build -t gosnmp/gosnmp:latest .
docker run -it gosnmp/gosnmp:latest

or

export GOSNMP_TARGET=1.2.3.4
export GOSNMP_PORT=161
export GOSNMP_TARGET_IPV4=1.2.3.4
export GOSNMP_PORT_IPV4=161
export GOSNMP_TARGET_IPV6='0:0:0:0:0:ffff:102:304'
export GOSNMP_PORT_IPV6=161
go test -v -tags all        # for example
go test -v -tags helper     # for example

Tests are grouped as follows:

• Unit tests (validating data packing and marshalling):
  • marshal_test.go
  • misc_test.go
• Public API consistency tests:
  • gosnmp_api_test.go
• End-to-end integration tests:
  • generic_e2e_test.go

The generic end-to-end integration test generic_e2e_test.go should work against any SNMP MIB-2 compliant host (e.g. a router, NAS box, printer).

Mocks were generated using:

mockgen -source=interface.go -destination=mocks/gosnmp_mock.go -package=mocks

However they're currently removed, as they were breaking linting.

To profile cpu usage:

go test -cpuprofile cpu.out
go test -c
go tool pprof gosnmp.test cpu.out

To profile memory usage:

go test -memprofile mem.out
go test -c
go tool pprof gosnmp.test mem.out

To check test coverage:

go get github.com/axw/gocov/gocov
go get github.com/matm/gocov-html
gocov test github.com/gosnmp/gosnmp | gocov-html > gosnmp.html && firefox gosnmp.html &

To measure the performance of password hash caching:

Password hash caching can be disabled during benchmark tests by using the golang build tag "gosnmp_nopwdcache", so:

go build -tags gosnmp_nopwdcache -bench=Benchmark.*Hash

will benchmark the code without password hash caching. Removing the tag will run the benchmark with caching enabled (default behavior of package).

License

Parts of the code are taken from the Golang project (specifically some functions for unmarshaling BER responses), which are under the same terms and conditions as the Go language. The rest of the code is under a BSD license.

See the LICENSE file for more details.

The remaining code is Copyright 2012 the GoSNMP Authors - see AUTHORS.md for a list of authors.