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server.go
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server.go
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package repl
import (
encjson "encoding/json"
"fmt"
"io"
"io/ioutil"
"math"
"math/rand"
"net"
"os"
"path/filepath"
"strconv"
"strings"
"time"
"github.com/google/uuid"
bencode "github.com/jackpal/bencode-go"
"alda.io/client/generated"
"alda.io/client/json"
log "alda.io/client/logging"
"alda.io/client/model"
"alda.io/client/parser"
"alda.io/client/system"
"alda.io/client/transmitter"
"alda.io/client/util"
)
const midiExportTimeout = 20 * time.Second
type nREPLRequest struct {
conn net.Conn
msg map[string]interface{}
}
// Server is a stateful Alda REPL server object.
type Server struct {
// A short, generated ID that appears in `alda ps` output.
id string
// The Port on which the server listens for nREPL messages from clients.
Port int
// The string of input that is built up over time as clients submit code, line
// by line, to be evaluated and added to the score.
input string
// The stateful score object that should correspond to the input received so
// far.
score *model.Score
// The current index into `score.Events`, representing where to start playing
// any new events that are added to the score when input is added.
eventIndex int
// The server's most recent information about the player process it is using.
player system.PlayerState
// A queue onto which bdecoded messages from clients are placed in one
// routine. In another routine, the messages are handled synchronously, one at
// a time. Therefore, messages can be received asynchronously, but results are
// processed synchronously to avoid concurrency issues due to global state.
requestQueue chan nREPLRequest
}
func (server *Server) stateFile() string {
return system.CachePath("state", "repl-servers", server.id+".json")
}
func (server *Server) respond(
req nREPLRequest, status []string, data map[string]interface{},
) {
if data == nil {
data = make(map[string]interface{})
}
data["status"] = status
if session, present := req.msg["session"]; present {
data["session"] = session
}
if id, present := req.msg["id"]; present {
data["id"] = id
}
log.Info().Interface("data", data).Msg("Sending response.")
if err := bencode.Marshal(req.conn, data); err != nil {
log.Warn().Interface("data", data).Msg("Failed to send response.")
}
}
func (server *Server) respondDone(
req nREPLRequest, data map[string]interface{},
) {
server.respond(req, []string{"done"}, data)
}
func (server *Server) respondErrors(
req nREPLRequest, problems []string, data map[string]interface{},
) {
if data == nil {
data = make(map[string]interface{})
}
data["problems"] = problems
server.respond(req, []string{"done", "error"}, data)
}
func (server *Server) respondError(
req nREPLRequest, problem string, data map[string]interface{},
) {
server.respondErrors(req, []string{problem}, data)
}
func (server *Server) resetState() error {
if server.hasPlayer() {
if err := server.shutdownPlayer(); err != nil {
return err
}
}
server.input = ""
server.score = model.NewScore()
server.eventIndex = 0
return nil
}
// Adapted from: https://www.calhoun.io/creating-random-strings-in-go/
func generateId() string {
const charset = "abcdefghijklmnopqrstuvwxyz"
var seededRand = rand.New(rand.NewSource(time.Now().UnixNano()))
b := make([]byte, 3)
for i := range b {
b[i] = charset[seededRand.Intn(len(charset))]
}
return string(b)
}
// NewServer returns an initialized instance of an Alda REPL server.
func NewServer(port int) *Server {
server := &Server{
id: generateId(),
Port: port,
requestQueue: make(chan nREPLRequest),
}
server.resetState()
return server
}
const nREPLPortFile = ".alda-nrepl-port"
// The nREPL server writes a file called ".alda-nrepl-port" into the current
// directory. This makes it easy for a client started in the same directory to
// discover what port the server is running on.
func (server *Server) writePortFile() {
os.WriteFile(nREPLPortFile, []byte(strconv.Itoa(server.Port)), 0644)
}
func (server *Server) writeStateFile() {
state := system.REPLServerState{ID: server.id, Port: server.Port}
stateJSON, err := encjson.Marshal(state)
if err != nil {
log.Warn().
Err(err).
Interface("state", state).
Msg("Failed to serialize REPL state JSON.")
return
}
stateFile := server.stateFile()
if err := os.MkdirAll(filepath.Dir(stateFile), os.ModePerm); err != nil {
log.Warn().
Err(err).
Msg("Failed to create parent directories for REPL server state file.")
}
if err := os.WriteFile(stateFile, stateJSON, 0644); err != nil {
log.Warn().
Err(err).
Msg("Failed to write REPL server state file.")
}
}
func (server *Server) touchStateFile() {
now := time.Now()
if err := os.Chtimes(server.stateFile(), now, now); err != nil {
log.Warn().
Err(err).
Msg("Failed to touch REPL server state file.")
}
}
func (server *Server) manageStateFile() {
// NOTE: We don't yet have a use case for exposing information about the
// server that updates regularly. Therefore, to avoid doing unnecessary work,
// we will just write the state file once and then we'll just continuously
// update the last modified time without re-writing the file.
server.writeStateFile()
for {
server.touchStateFile()
time.Sleep(10 * time.Second)
}
}
func (server *Server) removePortFile() {
os.Remove(nREPLPortFile)
}
func (server *Server) removeStateFile() {
os.Remove(server.stateFile())
}
// Close cleans up after a server is done serving.
//
// This includes actions like removing the nREPL port file.
func (server *Server) Close() {
server.removePortFile()
server.removeStateFile()
}
// RunServer creates a running Alda REPL server instance and returns it.
//
// Returns an error if something goes wrong.
//
// NOTE: The caller is responsible for calling `Close()` on the server instance
// when it is no longer needed. Otherwise, resources like the .alda-nrepl-port
// file will not be cleaned up.
func RunServer(port int) (*Server, error) {
server := NewServer(port)
l, err := net.Listen("tcp", "localhost:"+strconv.Itoa(server.Port))
if err != nil {
return nil, err
}
// This writes an .alda-nrepl-port file, which gets cleaned up when `Close()`
// is invoked.
server.writePortFile()
// Continuously writes a state file so that this REPL server can be included
// in the output of `alda ps`. This file also gets cleaned up by `Close()`.
go server.manageStateFile()
// See repl/player_management.go
go server.managePlayers()
go server.listen(l)
go server.handleRequests()
return server, nil
}
// Runs in a loop, listening for bencoded messages from clients, "bdecoding"
// them, and putting them on a channel to be handled by another routine.
//
// The processing of messages must be synchronous in order to avoid concurrency
// issues because all clients share the same (global) server state. The
// receiving of messages, however, is asynchronous, so that the transmission of
// the next message isn't blocked by the handling of the previous one.
func (server *Server) listen(l net.Listener) {
defer l.Close()
fmt.Printf(
"nREPL server started on port %d on host %s - nrepl://%s:%d\n",
server.Port,
"localhost",
"localhost",
server.Port,
)
for {
conn, err := l.Accept()
if err != nil {
log.Warn().Int("port", server.Port).Msg("Failed to accept connection.")
continue
}
// We do this part (receiving and bdecoding bytes from the connection) in a
// goroutine so that we can avoid blocking and immediately start waiting for
// the next connection. That way, the message receiving part can be
// asynchronous, even though we proceed to process the messages
// synchronously by putting them onto a queue.
go func() {
defer conn.Close()
for {
decoded, err := bencode.Decode(conn)
// I think this means the client disconnected? So assuming I'm right
// about that, we should stop reading and close the connection.
if err == io.EOF {
break
}
if err != nil {
log.Warn().
Int("port", server.Port).
Err(err).
Msg("Failed to bdecode message from connection.")
// If we fail to bdecode a message from the connection, then we bail
// out and close the connection. I'm not 100% sure if this is the
// right thing to do, but it seems reasonable, I guess.
return
}
switch msg := decoded.(type) {
default:
log.Warn().
Msg("Unable to process request; it isn't a map[string]interface{}")
case map[string]interface{}:
// Strings seem to become byte arrays somewhere in the process of
// marshaling and unmarshaling to bencode. I don't have a use-case for
// dealing with byte arrays, I only want to deal with strings, so
// let's go ahead and do the conversion here.
for k, v := range msg {
switch vv := v.(type) {
case []byte:
msg[k] = string(vv)
}
}
log.Info().
Interface("decodedRequest", msg).
Msg("Request received.")
server.requestQueue <- nREPLRequest{conn: conn, msg: msg}
}
}
}()
}
}
var describeResponse = map[string]interface{}{
"versions": map[string]interface{}{
"alda": map[string]interface{}{
"version-string": generated.ClientVersion,
},
},
}
func init() {
describedOps := map[string]interface{}{}
for op := range ops {
// It isn't clear what information we should include in the value, so we're
// just making it an empty map. I noticed that the Clojure nREPL server does
// the same thing.
describedOps[op] = map[string]interface{}{}
}
describeResponse["ops"] = describedOps
}
var ops = map[string]func(*Server, nREPLRequest){
// NOTE: This is mostly for general nREPL protocol adherence. Sessions don't
// have much meaning to an Alda REPL server. For now, we just fake it by
// generating a session ID and giving it to the client.
"clone": func(server *Server, req nREPLRequest) {
server.respondDone(req, map[string]interface{}{
"new-session": uuid.New().String(),
})
},
// NOTE: This is for nREPL protocol adherence.
"describe": func(server *Server, req nREPLRequest) {
server.respondDone(req, describeResponse)
},
// NOTE: This is just for nREPL protocol adherence. It isn't clear to me yet
// if there should be a distinct "eval" operation that does something
// meaningful. So for now, we're just responding with a shrug.
"eval": func(server *Server, req nREPLRequest) {
server.respondDone(req, map[string]interface{}{"value": "¯\\_(ツ)_/¯"})
},
"eval-and-play": func(server *Server, req nREPLRequest) {
errors := validateRequest(
req.msg,
requestFieldSpec{name: "code", valueType: typeString, required: true},
)
if len(errors) > 0 {
server.respondErrors(req, errors, nil)
return
}
input := req.msg["code"].(string)
if err := server.evalAndPlay(input); err != nil {
server.respondError(req, err.Error(), nil)
return
}
server.respondDone(req, nil)
},
"export": func(server *Server, req nREPLRequest) {
binaryData, err := server.export()
if err != nil {
server.respondError(req, err.Error(), nil)
return
}
server.respondDone(req, map[string]interface{}{"binary-data": binaryData})
},
"instruments": func(server *Server, req nREPLRequest) {
server.respondDone(req, map[string]interface{}{
"instruments": model.InstrumentsList(),
})
},
"load": func(server *Server, req nREPLRequest) {
errors := validateRequest(
req.msg,
requestFieldSpec{name: "code", valueType: typeString, required: true},
)
if len(errors) > 0 {
server.respondErrors(req, errors, nil)
return
}
input := req.msg["code"].(string)
if err := server.load(input); err != nil {
server.respondError(req, err.Error(), nil)
return
}
server.respondDone(req, nil)
},
"new-score": func(server *Server, req nREPLRequest) {
if err := server.resetState(); err != nil {
server.respondError(req, err.Error(), nil)
return
}
server.respondDone(req, nil)
},
"replay": func(server *Server, req nREPLRequest) {
transmitOpts := []transmitter.TransmissionOption{}
from, hit := req.msg["from"]
if hit {
switch f := from.(type) {
case string:
transmitOpts = append(transmitOpts, transmitter.TransmitFrom(f))
}
}
to, hit := req.msg["to"]
if hit {
switch t := to.(type) {
case string:
transmitOpts = append(transmitOpts, transmitter.TransmitTo(t))
}
}
if err := server.replay(transmitOpts...); err != nil {
server.respondError(req, err.Error(), nil)
return
}
server.respondDone(req, nil)
},
"score-data": func(server *Server, req nREPLRequest) {
server.respondDone(req, map[string]interface{}{
"data": server.score.JSON().String(),
})
},
"score-events": func(server *Server, req nREPLRequest) {
ast, err := parser.ParseString(server.input)
if err != nil {
server.respondError(req, err.Error(), nil)
return
}
scoreUpdates, err := ast.Updates()
if err != nil {
server.respondError(req, err.Error(), nil)
return
}
updates := json.Array()
for _, update := range scoreUpdates {
updates.ArrayAppend(update.JSON())
}
server.respondDone(req, map[string]interface{}{"events": updates.String()})
},
"score-ast": func(server *Server, req nREPLRequest) {
ast, err := parser.ParseString(server.input)
if err != nil {
server.respondError(req, err.Error(), nil)
return
}
server.respondDone(req, map[string]interface{}{"ast": ast.JSON().String()})
},
"score-text": func(server *Server, req nREPLRequest) {
server.respondDone(req, map[string]interface{}{"text": server.input})
},
"stop": func(server *Server, req nREPLRequest) {
if err := server.withTransmitter(
func(transmitter transmitter.OSCTransmitter) error {
log.Info().
Interface("player", server.player).
Msg("Sending \"stop\" message to player process.")
return transmitter.TransmitStopMessage()
},
); err != nil {
server.respondError(req, err.Error(), nil)
return
}
server.respondDone(req, nil)
},
}
// Runs in a loop, handling requests from the queue as they come in in a
// synchronous fashion, one at a time.
func (server *Server) handleRequests() {
for req := range server.requestQueue {
errors := validateRequest(
req.msg,
requestFieldSpec{name: "op", valueType: typeString, required: true},
)
if len(errors) > 0 {
server.respondErrors(req, errors, nil)
continue
}
op := req.msg["op"].(string)
handler, supported := ops[op]
if !supported {
server.respond(req, []string{"done", "error", "unknown-op"}, nil)
continue
}
handler(server, req)
}
}
// Parses a string of `input`, updates the server's score and related state, and
// returns a list of transmission options that would make it so that we're
// transmitting only the new events that resulted from this string of input.
func (server *Server) updateScoreWithInput(
input string,
) ([]transmitter.TransmissionOption, error) {
// Take note of the current offsets of all parts in the score, for the purpose
// of synchronization. (See below where we use the transmitter.SyncOffsets
// option when transmitting the score.)
partOffsets := server.score.PartOffsets()
// Take note of the current `eventIndex` value, so that we know where to start
// playing from when we want to play the new events.
eventIndex := server.eventIndex
ast, err := parser.ParseString(input)
if err != nil {
return nil, err
}
scoreUpdates, err := ast.Updates()
if err != nil {
return nil, err
}
if err := server.score.Update(scoreUpdates...); err != nil {
return nil, err
}
// Add the provided `input` to our total string of input representing the
// entire score.
server.input += strings.TrimSpace(input) + "\n"
// Update the starting index so that the next invocation of `evalAndPlay` for
// this same score will result in only playing newly added events.
server.eventIndex = len(server.score.Events)
return []transmitter.TransmissionOption{
// Transmit only the new events, i.e. events added as a result of parsing
// the provided `input` and applying the resulting updates to the score.
transmitter.TransmitFromIndex(eventIndex),
// The previous offset of each part is subtracted from any new events for
// that part. The effect is that we "synchronize" that part with the events
// that we already sent to the player. For example, if a client submits the
// following code:
//
// piano: c d e f
//
// Followed by (sometime before the 4 notes above finish playing):
//
// piano: g a b > c
//
// Then the notes `c d e f g a b > c` will be played in time.
transmitter.SyncOffsets(partOffsets),
}, nil
}
func (server *Server) evalAndPlay(
input string, additionalTransmitOpts ...transmitter.TransmissionOption,
) error {
return server.withTransmitter(
func(transmitter transmitter.OSCTransmitter) error {
transmitOpts, err := server.updateScoreWithInput(input)
if err != nil {
return err
}
log.Info().
Interface("player", server.player).
Msg("Sending OSC messages to player.")
return transmitter.TransmitScore(
server.score,
(append(transmitOpts, additionalTransmitOpts...))...,
)
},
)
}
func (server *Server) load(input string) error {
if err := server.resetState(); err != nil {
return err
}
return server.withTransmitter(
func(t transmitter.OSCTransmitter) error {
transmitOpts, err := server.updateScoreWithInput(input)
if err != nil {
return err
}
transmitOpts = append(transmitOpts, transmitter.LoadOnly())
log.Info().
Interface("player", server.player).
Msg("Transmitting score to player.")
err = t.TransmitScore(server.score, transmitOpts...)
if err != nil {
return err
}
newOffset := int32(0)
for _, offset := range server.score.PartOffsets() {
offsetRounded := int32(math.Round(offset))
if offsetRounded > newOffset {
newOffset = offsetRounded
}
}
log.Info().
Interface("player", server.player).
Int32("newOffset", newOffset).
Msg("Transmitting new offset to player.")
return t.TransmitOffsetMessage(newOffset)
},
)
}
func (server *Server) reload() error {
return server.load(server.input)
}
func (server *Server) replay(
transmitOpts ...transmitter.TransmissionOption,
) error {
// `input` is the one thing about the server state that we DON'T want to
// reset, so we keep track of it here. After we reset the state, we invoke
// `server.evalAndPlay` on this input, which has the effect of both playing it
// and re-adding it to the state of the server.
input := server.input
// We reset the server state here so that we can re-transmit the score "from
// scratch" (or just re-transmit the part that we want to hear, if `from`
// and/or `to` parameters are provided). This makes it so that what we hear
// corresponds more directly to the input entered so far.
//
// An alternative would be to tell the player to rewind to offset 0 and play
// the sequence from the beginning, but that would preserve the pauses in
// between the user entering each line of REPL input, which we are presuming
// is not what the user wants. (This would also be a departure from the
// behavior of `:play` in the Alda v1 REPL.)
if err := server.resetState(); err != nil {
return err
}
// At this point, the `managePlayers` loop should find a replacement for the
// player, and this should generally happen quickly. `server.evalAndPlay` will
// handle the case that a player process isn't immediately available, so it's
// OK for us to call it immediately after resetting the state.
return server.evalAndPlay(input, transmitOpts...)
}
// Reloads the score into a fresh player, sends a "MIDI export" message to the
// player, waits for the player to write the MIDI file, reads the file, and
// returns the bytes in the file.
//
// Returns an error if something goes wrong somewhere along the way.
func (server *Server) export() ([]byte, error) {
// Reloading the score is important because of the subtleties of the tempo
// messages in the MIDI sequence.
//
// When we're evaluating Alda code interactively at the REPL, we suppress
// tempo messages because they serve no immediate purpose.
//
// When it comes time to export the score, we reload the input into the MIDI
// sequencer, which does include sending tempo messages, so that the MIDI
// sequence includes tempo changes in the places where we want them.
if err := server.reload(); err != nil {
return nil, err
}
tmpdir, err := ioutil.TempDir("", "alda-repl-server")
if err != nil {
return nil, err
}
midiFilename := filepath.Join(
tmpdir, fmt.Sprintf(
"export-%d-%d.mid",
time.Now().Unix(),
rand.Intn(10000),
),
)
if err := server.withTransmitter(
func(transmitter transmitter.OSCTransmitter) error {
return transmitter.TransmitMidiExportMessage(midiFilename)
},
); err != nil {
return nil, err
}
var midiFile *os.File
if err := util.Await(
func() error {
mf, err := os.Open(midiFilename)
if err != nil {
return err
}
midiFile = mf
return nil
},
midiExportTimeout,
); err != nil {
return nil, err
}
return ioutil.ReadAll(midiFile)
}