go-libvirt-plain/README.md

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====

Package `go-libvirt` provides a pure Go interface for interacting with libvirt.

Rather than using libvirt's C bindings, this package makes use of
libvirt's RPC interface, as documented [here](https://libvirt.org/internals/rpc.html).
Connections to the libvirt server may be local, or remote. RPC packets are encoded
using the XDR standard as defined by [RFC 4506](https://tools.ietf.org/html/rfc4506.html).

libvirt's RPC interface is quite extensive, and changes from one version to the next, so
this project uses a code generator to build the go bindings. The code generator should
be run whenever you want to build go-libvirt for a new version of libvirt. To do this,
you'll need to set an environment variable `LIBVIRT_SOURCE` to the directory containing
the untarred libvirt sources, and then run `go generate ./...` from the go-libvirt directory.
The code generator consumes [src/remote/remote_protocol.x](https://github.com/libvirt/libvirt/blob/master/src/remote/remote_protocol.x)
and produces go bindings for all the remote procedures defined there.

[Pull requests are welcome](https://github.com/digitalocean/go-libvirt/blob/master/CONTRIBUTING.md)!

How to Use This Library
-----------------------

Once you've vendored go-libvirt into your project, you'll probably want to call
some libvirt functions. There's some example code below showing how to connect
to libvirt and make one such call, but once you get past the introduction you'll
next want to call some other libvirt functions. How do you find them?

Start with the [libvirt API reference](https://libvirt.org/html/index.html).
Let's say you want to gracefully shutdown a VM, and after reading through the
libvirt docs you determine that virDomainShutdown() is the function you want to
call to do that. Where's that function in go-libvirt? We transform the names
slightly when building the go bindings. There's no need for a global prefix like
"vir" in Go, since all our functions are inside the package namespace, so we
drop it. That means the Go function for `virDomainShutdown()` is just `DomainShutdown()`,
and sure enough, you can find the Go function `DomainShutdown()` in libvirt.gen.go,
with parameters and return values equivalent to those documented in the API
reference.

Suppose you then decide you need more control over your shutdown, so you switch
over to `virDomainShutdownFlags()`. As its name suggests, this function takes a
flag parameter which has possible values specified in an enum called
`virDomainShutdownFlagValues`. Flag types like this are a little tricky for the
code generator, because the C functions just take an integer type - only the
libvirt documentation actually ties the flags to the enum types. In most cases
though we're able to generate a wrapper function with a distinct flag type,
making it easier for Go tooling to suggest possible flag values while you're
working. Checking the documentation for this function:

`godoc github.com/digitalocean/go-libvirt DomainShutdownFlags`

returns this:

`func (l *Libvirt) DomainShutdownFlags(Dom Domain, Flags DomainShutdownFlagValues) (err error)`

If you want to see the possible flag values, `godoc` can help again:

```
$ godoc github.com/digitalocean/go-libvirt DomainShutdownFlagValues

type DomainShutdownFlagValues int32
    DomainShutdownFlagValues as declared in libvirt/libvirt-domain.h:1121

const (
    DomainShutdownDefault      DomainShutdownFlagValues = iota
    DomainShutdownAcpiPowerBtn DomainShutdownFlagValues = 1
    DomainShutdownGuestAgent   DomainShutdownFlagValues = 2
    DomainShutdownInitctl      DomainShutdownFlagValues = 4
    DomainShutdownSignal       DomainShutdownFlagValues = 8
    DomainShutdownParavirt     DomainShutdownFlagValues = 16
)
    DomainShutdownFlagValues enumeration from libvirt/libvirt-domain.h:1121
```

One other suggestion: most of the code in go-libvirt is now generated, but a few
hand-written routines still exist in libvirt.go, and wrap calls to the generated
code with slightly different parameters or return values. We suggest avoiding
these hand-written routines and calling the generated routines in libvirt.gen.go
instead. Over time these handwritten routines will be removed from go-libvirt.

Warning
-------

The libvirt project strongly recommends *against* talking to the RPC interface
directly. They consider it to be a private implementation detail with the
possibility of being entirely rearchitected in the future.

While these package are reasonably well-tested and have seen some use inside of
DigitalOcean, there may be subtle bugs which could cause the packages to act
in unexpected ways.  Use at your own risk!

In addition, the API is not considered stable at this time.  If you would like
to include package `libvirt` in a project, we highly recommend vendoring it into
your project.

Example
-------

```go
package main

import (
	"fmt"
	"log"
	"net"
	"time"

	"github.com/digitalocean/go-libvirt"
)

func main() {
	// This dials libvirt on the local machine, but you can substitute the first
	// two parameters with "tcp", "<ip address>:<port>" to connect to libvirt on
	// a remote machine.
	c, err := net.DialTimeout("unix", "/var/run/libvirt/libvirt-sock", 2*time.Second)
	if err != nil {
		log.Fatalf("failed to dial libvirt: %v", err)
	}

	l := libvirt.New(c)
	if err := l.Connect(); err != nil {
		log.Fatalf("failed to connect: %v", err)
	}

	v, err := l.Version()
	if err != nil {
		log.Fatalf("failed to retrieve libvirt version: %v", err)
	}
	fmt.Println("Version:", v)

	domains, err := l.Domains()
	if err != nil {
		log.Fatalf("failed to retrieve domains: %v", err)
	}

	fmt.Println("ID\tName\t\tUUID")
	fmt.Printf("--------------------------------------------------------\n")
	for _, d := range domains {
		fmt.Printf("%d\t%s\t%x\n", d.ID, d.Name, d.UUID)
	}

	if err := l.Disconnect(); err != nil {
		log.Fatal("failed to disconnect: %v", err)
	}
}

```

```
Version: 1.3.4
ID	Name		UUID
--------------------------------------------------------
1	Test-1		dc329f87d4de47198cfd2e21c6105b01
2	Test-2		dc229f87d4de47198cfd2e21c6105b01
```