GoSNMP is a simple SNMP client library, written fully in Go. Currently it only supports GetRequests with single or multiple OIDs.

soniah/gosmp is based on alouca/gosnmp - many thanks to Andreas Louca for starting the project. My version has diverged significantly from Andreas' version:

• the Get function now supports multiple OIDs (thus improving network performance) and has a different method signature
• the NewGoSNMP function has been removed, use Connect instead (see Usage below)
• GoSNMP no longer relies on alouca/gologger - you can use your logger if it conforms to the simple interface - Print and Printf. Otherwise debugging will be discarded (/dev/null).
• the ToBigInt function - useful for treating the returned snmp values as *big.Int (convenient, as SNMP can return int32, uint32, and uint64 values)
• the Partition function - useful when you have a large array of OIDs to run Get() on
• and the largest (but least obvious) feature - TDD (Test Driven Development) was used to correct existing problems and for adding new features. I believe this has improved gosnmp's accuracy and reliability

GoSNMP is still under development, therefore API's may change and bugs will be squashed. You can help by sending packet captures (see Bugs below) or pull requests.

There are two branches on github:

• master - safe to pull from
• dev - unsafe to pull from, as I regularly rewrite history

Sonia Hamilton, sonia@snowfrog.net, http://www.snowfrog.net.

Install via go get:

go get github.com/soniah/gosnmp

See http://godoc.org/github.com/soniah/gosnmp or your local go doc server for full documentation:

cd $GOPATH
godoc -http=:6060 &
$preferred_browser http://localhost:6060/pkg &

Here is code from example/example.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:
        fmt.Printf("string: %s\n", variable.Value.(string))
    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

example/example2.go is similar to example.go, however is uses a custom &GoSNMP rather than g.Default.

The following BER types have been implemented:

• 0x02 Integer
• 0x04 OctetString
• 0x06 ObjectIdentifier
• 0x40 IpAddress
• 0x41 Counter32
• 0x42 Gauge32
• 0x43 TimeTicks
• 0x46 Counter64
• 0x80 NoSuchObject
• 0x81 NoSuchInstance

The following (less common) BER types haven't been implemented, as I ran out of time or haven't been able to find example devices to query:

• 0x00 EndOfContents
• 0x01 Boolean
• 0x03 BitString
• 0x07 ObjectDescription
• 0x44 Opaque
• 0x45 NsapAddress
• 0x47 Uinteger32

Please email me at sonia@snowfrog.net with packet captures containing samples of the missing BER types, or of any other bugs you find. Please include 2 or 3 examples of the missing/faulty BER type, interspersed with a couple of other common BER's eg an Integer, a Counter32 ie about 6 OIDs maximum.

Create your packet captures in the following way:

Expected output, obtained via an snmpget 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

Some of the tests use the Verax Snmp Simulator [1]: download, install and run it with the default configuration. Then, in the gosnmp directory, run these commands (or equivalents for your system):

cd ~/go/src/github.com/soniah/gosnmp
ln -s /usr/local/vxsnmpsimulator/device device

# remove randomising elements from Verax device files
cd device/cisco
sed -i -e 's!\/\/\$.*!!' -e 's!^M!!' cisco_router.txt
sed -i -e 's/\/\/\^int.unq()\^\/\//2/' cisco_router.txt
cd ../os
sed -i -e 's!\/\/\$.*!!' -e 's!^M!!' os-linux-std.txt
sed -i -e 's/\/\/\^int.unq()\^\/\//2/' os-linux-std.txt
cd ~/go/src/github.com/soniah/gosnmp
go test

To run only the Verax tests:

go test -run TestVeraxGet 2>&1 | less

I have noticed that some of the Verax tests randomly fail when using multi-OID Get() requests. I believe these bugs come from Verax not GoSNMP.

To run non-Verax tests:

% grep -h '^func.*Test' *test.go
func TestEnmarshalVarbind(t *testing.T) {
func TestEnmarshalVBL(t *testing.T) {
... <snip>

# for example
go test -run TestEnmarshalMsg

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/soniah/gosnmp | gocov-html > gosnmp.html && firefox gosnmp.html &

[1] http://www.veraxsystems.com/en/products/snmpsimulator

Some parts of the code are borrowed by 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.