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plugin.go
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plugin.go
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// The plugin package provides the functionality to both expose a Packer
// plugin binary and to connect to an existing Packer plugin binary.
//
// Packer supports plugins in the form of self-contained external static
// Go binaries. These binaries behave in a certain way (enforced by this
// package) and are connected to in a certain way (also enforced by this
// package).
package plugin
import (
"errors"
"fmt"
"github.com/mitchellh/packer/packer"
packrpc "github.com/mitchellh/packer/packer/rpc"
"log"
"net"
"net/rpc"
"os"
"os/signal"
"runtime"
"strconv"
"sync/atomic"
)
// This is a count of the number of interrupts the process has received.
// This is updated with sync/atomic whenever a SIGINT is received and can
// be checked by the plugin safely to take action.
var Interrupts int32 = 0
const MagicCookieKey = "PACKER_PLUGIN_MAGIC_COOKIE"
const MagicCookieValue = "d602bf8f470bc67ca7faa0386276bbdd4330efaf76d1a219cb4d6991ca9872b2"
// The APIVersion is outputted along with the RPC address. The plugin
// client validates this API version and will show an error if it doesn't
// know how to speak it.
const APIVersion = "1"
// This serves a single RPC connection on the given RPC server on
// a random port.
func serve(server *rpc.Server) (err error) {
log.Printf("Plugin build against Packer '%s'", packer.GitCommit)
if os.Getenv(MagicCookieKey) != MagicCookieValue {
return errors.New("Please do not execute plugins directly. Packer will execute these for you.")
}
// If there is no explicit number of Go threads to use, then set it
if os.Getenv("GOMAXPROCS") == "" {
runtime.GOMAXPROCS(runtime.NumCPU())
}
minPort, err := strconv.ParseInt(os.Getenv("PACKER_PLUGIN_MIN_PORT"), 10, 32)
if err != nil {
return
}
maxPort, err := strconv.ParseInt(os.Getenv("PACKER_PLUGIN_MAX_PORT"), 10, 32)
if err != nil {
return
}
log.Printf("Plugin minimum port: %d\n", minPort)
log.Printf("Plugin maximum port: %d\n", maxPort)
// Set the RPC port range
packrpc.PortRange(int(minPort), int(maxPort))
var address string
var listener net.Listener
for port := minPort; port <= maxPort; port++ {
address = fmt.Sprintf("127.0.0.1:%d", port)
listener, err = net.Listen("tcp", address)
if err != nil {
err = nil
continue
}
break
}
defer listener.Close()
// Output the address to stdout
log.Printf("Plugin address: %s\n", address)
fmt.Printf("%s|%s\n", APIVersion, address)
os.Stdout.Sync()
// Accept a connection
log.Println("Waiting for connection...")
conn, err := listener.Accept()
if err != nil {
log.Printf("Error accepting connection: %s\n", err.Error())
return
}
// Serve a single connection
log.Println("Serving a plugin connection...")
server.ServeConn(conn)
return
}
// Registers a signal handler to swallow and count interrupts so that the
// plugin isn't killed. The main host Packer process is responsible
// for killing the plugins when interrupted.
func countInterrupts() {
ch := make(chan os.Signal, 1)
signal.Notify(ch, os.Interrupt)
go func() {
for {
<-ch
newCount := atomic.AddInt32(&Interrupts, 1)
log.Printf("Received interrupt signal (count: %d). Ignoring.", newCount)
}
}()
}
// Serves a builder from a plugin.
func ServeBuilder(builder packer.Builder) {
log.Println("Preparing to serve a builder plugin...")
server := rpc.NewServer()
packrpc.RegisterBuilder(server, builder)
countInterrupts()
if err := serve(server); err != nil {
log.Printf("ERROR: %s", err)
os.Exit(1)
}
}
// Serves a command from a plugin.
func ServeCommand(command packer.Command) {
log.Println("Preparing to serve a command plugin...")
server := rpc.NewServer()
packrpc.RegisterCommand(server, command)
countInterrupts()
if err := serve(server); err != nil {
log.Printf("ERROR: %s", err)
os.Exit(1)
}
}
// Serves a hook from a plugin.
func ServeHook(hook packer.Hook) {
log.Println("Preparing to serve a hook plugin...")
server := rpc.NewServer()
packrpc.RegisterHook(server, hook)
countInterrupts()
if err := serve(server); err != nil {
log.Printf("ERROR: %s", err)
os.Exit(1)
}
}
// Serves a post-processor from a plugin.
func ServePostProcessor(p packer.PostProcessor) {
log.Println("Preparing to serve a post-processor plugin...")
server := rpc.NewServer()
packrpc.RegisterPostProcessor(server, p)
countInterrupts()
if err := serve(server); err != nil {
log.Printf("ERROR: %s", err)
os.Exit(1)
}
}
// Serves a provisioner from a plugin.
func ServeProvisioner(p packer.Provisioner) {
log.Println("Preparing to serve a provisioner plugin...")
server := rpc.NewServer()
packrpc.RegisterProvisioner(server, p)
countInterrupts()
if err := serve(server); err != nil {
log.Printf("ERROR: %s", err)
os.Exit(1)
}
}
// Tests whether or not the plugin was interrupted or not.
func Interrupted() bool {
return atomic.LoadInt32(&Interrupts) > 0
}