[skip-changelog] Added discovery.Discovery object to handle communication with pluggable discoveries (#1029)

* Pluggable Discovery handler: first implementation

* Added 'discovery_client' (for debugging discoveries)

* Added 'event' mode in PluggableDiscovery

* discovery_client now supports multiple discoveries

* Added ID to PluggableDiscovery

* Added PluggableDiscovery.String() implementation

* Fixed TestDiscoveryStdioHandling

* Fixed discovery test run on Windows

It really takes that long for messages to go back and forth.
I don't know if there is a simpler way to reduce stdio buffering time.

Author: cmaglie

Diff for: arduino/discovery/discovery.go

@@ -0,0 +1,306 @@
+// This file is part of arduino-cli.
+//
+// Copyright 2020 ARDUINO SA (http://www.arduino.cc/)
+//
+// This software is released under the GNU General Public License version 3,
+// which covers the main part of arduino-cli.
+// The terms of this license can be found at:
+// https://www.gnu.org/licenses/gpl-3.0.en.html
+//
+// You can be released from the requirements of the above licenses by purchasing
+// a commercial license. Buying such a license is mandatory if you want to
+// modify or otherwise use the software for commercial activities involving the
+// Arduino software without disclosing the source code of your own applications.
+// To purchase a commercial license, send an email to [email protected].
+
+package discovery
+
+import (
+	"encoding/json"
+	"io"
+	"sync"
+	"time"
+
+	"github.com/arduino/arduino-cli/executils"
+	"github.com/arduino/go-properties-orderedmap"
+	"github.com/pkg/errors"
+)
+
+// PluggableDiscovery is a tool that detects communication ports to interact
+// with the boards.
+type PluggableDiscovery struct {
+	id                   string
+	args                 []string
+	process              *executils.Process
+	outgoingCommandsPipe io.Writer
+	incomingMessagesChan <-chan *discoveryMessage
+
+	// All the following fields are guarded by statusMutex
+	statusMutex           sync.Mutex
+	incomingMessagesError error
+	alive                 bool
+	eventsMode            bool
+	eventChan             chan<- *Event
+	cachedPorts           map[string]*Port
+}
+
+type discoveryMessage struct {
+	EventType string  `json:"eventType"`
+	Message   string  `json:"message"`
+	Ports     []*Port `json:"ports"`
+	Port      *Port   `json:"port"`
+}
+
+// Port containts metadata about a port to connect to a board.
+type Port struct {
+	Address                  string          `json:"address"`
+	AddressLabel             string          `json:"label"`
+	Protocol                 string          `json:"protocol"`
+	ProtocolLabel            string          `json:"protocolLabel"`
+	Properties               *properties.Map `json:"prefs"`
+	IdentificationProperties *properties.Map `json:"identificationPrefs"`
+}
+
+func (p *Port) String() string {
+	if p == nil {
+		return "none"
+	}
+	return p.Address
+}
+
+// Event is a pluggable discovery event
+type Event struct {
+	Type string
+	Port *Port
+}
+
+// New create and connect to the given pluggable discovery
+func New(id string, args ...string) (*PluggableDiscovery, error) {
+	proc, err := executils.NewProcess(args...)
+	if err != nil {
+		return nil, err
+	}
+	stdout, err := proc.StdoutPipe()
+	if err != nil {
+		return nil, err
+	}
+	stdin, err := proc.StdinPipe()
+	if err != nil {
+		return nil, err
+	}
+	if err := proc.Start(); err != nil {
+		return nil, err
+	}
+	messageChan := make(chan *discoveryMessage)
+	disc := &PluggableDiscovery{
+		id:                   id,
+		process:              proc,
+		incomingMessagesChan: messageChan,
+		outgoingCommandsPipe: stdin,
+		alive:                true,
+	}
+	go disc.jsonDecodeLoop(stdout, messageChan)
+	return disc, nil
+}
+
+// GetID returns the identifier for this discovery
+func (disc *PluggableDiscovery) GetID() string {
+	return disc.id
+}
+
+func (disc *PluggableDiscovery) String() string {
+	return disc.id
+}
+
+func (disc *PluggableDiscovery) jsonDecodeLoop(in io.Reader, outChan chan<- *discoveryMessage) {
+	decoder := json.NewDecoder(in)
+	closeAndReportError := func(err error) {
+		disc.statusMutex.Lock()
+		disc.alive = false
+		disc.incomingMessagesError = err
+		disc.statusMutex.Unlock()
+		close(outChan)
+	}
+	for {
+		var msg discoveryMessage
+		if err := decoder.Decode(&msg); err != nil {
+			closeAndReportError(err)
+			return
+		}
+
+		if msg.EventType == "add" {
+			if msg.Port == nil {
+				closeAndReportError(errors.New("invalid 'add' message: missing port"))
+				return
+			}
+			disc.statusMutex.Lock()
+			disc.cachedPorts[msg.Port.Address] = msg.Port
+			if disc.eventChan != nil {
+				disc.eventChan <- &Event{"add", msg.Port}
+			}
+			disc.statusMutex.Unlock()
+		} else if msg.EventType == "remove" {
+			if msg.Port == nil {
+				closeAndReportError(errors.New("invalid 'remove' message: missing port"))
+				return
+			}
+			disc.statusMutex.Lock()
+			delete(disc.cachedPorts, msg.Port.Address)
+			if disc.eventChan != nil {
+				disc.eventChan <- &Event{"remove", msg.Port}
+			}
+			disc.statusMutex.Unlock()
+		} else {
+			outChan <- &msg
+		}
+	}
+}
+
+// IsAlive return true if the discovery process is running and so is able to receive commands
+// and produce events.
+func (disc *PluggableDiscovery) IsAlive() bool {
+	disc.statusMutex.Lock()
+	defer disc.statusMutex.Unlock()
+	return disc.alive
+}
+
+// IsEventMode return true if the discovery is in "events" mode
+func (disc *PluggableDiscovery) IsEventMode() bool {
+	disc.statusMutex.Lock()
+	defer disc.statusMutex.Unlock()
+	return disc.eventsMode
+}
+
+func (disc *PluggableDiscovery) waitMessage(timeout time.Duration) (*discoveryMessage, error) {
+	select {
+	case msg := <-disc.incomingMessagesChan:
+		if msg == nil {
+			// channel has been closed
+			disc.statusMutex.Lock()
+			defer disc.statusMutex.Unlock()
+			return nil, disc.incomingMessagesError
+		}
+		return msg, nil
+	case <-time.After(timeout):
+		return nil, errors.New("timeout")
+	}
+}
+
+func (disc *PluggableDiscovery) sendCommand(command string) error {
+	if n, err := disc.outgoingCommandsPipe.Write([]byte(command)); err != nil {
+		return err
+	} else if n < len(command) {
+		return disc.sendCommand(command[n:])
+	} else {
+		return nil
+	}
+}
+
+// Start initializes and start the discovery internal subroutines. This command must be
+// called before List or StartSync.
+func (disc *PluggableDiscovery) Start() error {
+	if err := disc.sendCommand("START\n"); err != nil {
+		return err
+	}
+	if msg, err := disc.waitMessage(time.Second * 10); err != nil {
+		return err
+	} else if msg.EventType != "start" {
+		return errors.Errorf("communication out of sync, expected 'start', received '%s'", msg.EventType)
+	} else if msg.Message != "OK" {
+		return errors.Errorf("command failed: %s", msg.Message)
+	}
+	return nil
+}
+
+// Stop stops the discovery internal subroutines and possibly free the internally
+// used resources. This command should be called if the client wants to pause the
+// discovery for a while.
+func (disc *PluggableDiscovery) Stop() error {
+	if err := disc.sendCommand("STOP\n"); err != nil {
+		return err
+	}
+	if msg, err := disc.waitMessage(time.Second * 10); err != nil {
+		return err
+	} else if msg.EventType != "stop" {
+		return errors.Errorf("communication out of sync, expected 'stop', received '%s'", msg.EventType)
+	} else if msg.Message != "OK" {
+		return errors.Errorf("command failed: %s", msg.Message)
+	}
+	return nil
+}
+
+// Quit terminates the discovery. No more commands can be accepted by the discovery.
+func (disc *PluggableDiscovery) Quit() error {
+	if err := disc.sendCommand("QUIT\n"); err != nil {
+		return err
+	}
+	if msg, err := disc.waitMessage(time.Second * 10); err != nil {
+		return err
+	} else if msg.EventType != "quit" {
+		return errors.Errorf("communication out of sync, expected 'quit', received '%s'", msg.EventType)
+	} else if msg.Message != "OK" {
+		return errors.Errorf("command failed: %s", msg.Message)
+	}
+	return nil
+}
+
+// List executes an enumeration of the ports and returns a list of the available
+// ports at the moment of the call.
+func (disc *PluggableDiscovery) List() ([]*Port, error) {
+	if err := disc.sendCommand("LIST\n"); err != nil {
+		return nil, err
+	}
+	if msg, err := disc.waitMessage(time.Second * 10); err != nil {
+		return nil, err
+	} else if msg.EventType != "list" {
+		return nil, errors.Errorf("communication out of sync, expected 'list', received '%s'", msg.EventType)
+	} else {
+		return msg.Ports, nil
+	}
+}
+
+// EventChannel creates a channel used to receive events from the pluggable discovery.
+// The event channel must be consumed as quickly as possible since it may block the
+// discovery if it becomes full. The channel size is configurable.
+func (disc *PluggableDiscovery) EventChannel(size int) <-chan *Event {
+	c := make(chan *Event, size)
+	disc.statusMutex.Lock()
+	defer disc.statusMutex.Unlock()
+	disc.eventChan = c
+	return c
+}
+
+// StartSync puts the discovery in "events" mode: the discovery will send "add"
+// and "remove" events each time a new port is detected or removed respectively.
+// After calling StartSync an initial burst of "add" events may be generated to
+// report all the ports available at the moment of the start.
+func (disc *PluggableDiscovery) StartSync() error {
+	disc.statusMutex.Lock()
+	defer disc.statusMutex.Unlock()
+
+	if disc.eventsMode {
+		return errors.New("already in events mode")
+	}
+	if err := disc.sendCommand("START_SYNC\n"); err != nil {
+		return err
+	}
+
+	// START_SYNC does not give any response
+
+	disc.eventsMode = true
+	disc.cachedPorts = map[string]*Port{}
+	return nil
+}
+
+// ListSync returns a list of the available ports. The list is a cache of all the
+// add/remove events happened from the StartSync call and it will not consume any
+// resource from the underliying discovery.
+func (disc *PluggableDiscovery) ListSync() []*Port {
+	disc.statusMutex.Lock()
+	defer disc.statusMutex.Unlock()
+	res := []*Port{}
+	for _, port := range disc.cachedPorts {
+		res = append(res, port)
+	}
+	return res
+}

Diff for: arduino/discovery/discovery_client/go.mod

@@ -0,0 +1,10 @@
+module github.com/arduino/arduino-cli/arduino/discovery/discovery_client
+
+go 1.14
+
+replace github.com/arduino/arduino-cli => ../../..
+
+require (
+	github.com/arduino/arduino-cli v0.0.0-00010101000000-000000000000
+	github.com/gizak/termui/v3 v3.1.0
+)