Add support for downstream CHATHISTORY

This adds support for the WIP (at the time of this commit)
draft/chathistory extension, based on the draft at [1] and the
additional comments at [2].

This gets the history by parsing the chat logs, and is therefore only
enabled when the logs are enabled and the log path is configured.

Getting the history only from the logs adds some restrictions:
- we cannot get history by msgid (those are not logged)
- we cannot get the users masks (maybe they could be inferred from the
  JOIN etc, but it is not worth the effort and would not work every
  time)

The regular soju network history is not sent to clients that support
draft/chathistory, so that they can fetch what they need by manually
calling CHATHISTORY.

The only supported command is BEFORE for now, because that is the only
required command for an app that offers an "infinite history scrollback"
feature.

Regarding implementation, rather than reading the file from the end in
reverse, we simply start from the beginning of each log file, store each
PRIVMSG into a ring, then add the last lines of that ring into the
history we'll return later. The message parsing implementation must be
kept somewhat fast because an app could potentially request thousands of
messages in several files. Here we are using simple sscanf and indexOf
rather than regexps.

In case some log files do not contain any message (for example because
the user had not joined a channel at that time), we try up to a 100 days
of empty log files before giving up.

[1]: https://github.com/prawnsalad/ircv3-specifications/pull/3/files
[2]: https://github.com/ircv3/ircv3-specifications/pull/393/files#r350210018

downstream.go

@@ -45,6 +45,13 @@ func newNeedMoreParamsError(cmd string) ircError {
 	}}
 }
 
+func newChatHistoryError(subcommand string, target string) ircError {
+	return ircError{&irc.Message{
+		Command: "FAIL",
+		Params:  []string{"CHATHISTORY", "MESSAGE_ERROR", subcommand, target, "Messages could not be retrieved"},
+	}}
+}
+
 var errAuthFailed = ircError{&irc.Message{
 	Command: irc.ERR_PASSWDMISMATCH,
 	Params:  []string{"*", "Invalid username or password"},
@@ -107,6 +114,9 @@ func newDownstreamConn(srv *Server, netConn net.Conn, id uint64) *downstreamConn
 	for k, v := range permanentDownstreamCaps {
 		dc.supportedCaps[k] = v
 	}
+	if srv.LogPath != "" {
+		dc.supportedCaps["draft/chathistory"] = ""
+	}
 	return dc
 }
 
@@ -785,6 +795,7 @@ func (dc *downstreamConn) welcome() error {
 		Params:  []string{dc.nick, dc.srv.Hostname, "soju", "aiwroO", "OovaimnqpsrtklbeI"},
 	})
 	// TODO: RPL_ISUPPORT
+	// TODO: send CHATHISTORY in RPL_ISUPPORT when implemented
 	dc.SendMessage(&irc.Message{
 		Prefix:  dc.srv.prefix(),
 		Command: irc.ERR_NOMOTD,
@@ -825,6 +836,9 @@ func (dc *downstreamConn) welcome() error {
 }
 
 func (dc *downstreamConn) sendNetworkHistory(net *network) {
+	if dc.caps["draft/chathistory"] {
+		return
+	}
 	for target, history := range net.history {
 		if ch, ok := net.channels[target]; ok && ch.Detached {
 			continue
@@ -1510,6 +1524,106 @@ func (dc *downstreamConn) handleMessageRegistered(msg *irc.Message) error {
 			Command: "INVITE",
 			Params:  []string{upstreamUser, upstreamChannel},
 		})
+	case "CHATHISTORY":
+		var subcommand string
+		if err := parseMessageParams(msg, &subcommand); err != nil {
+			return err
+		}
+		var target, criteria, limitStr string
+		if err := parseMessageParams(msg, nil, &target, &criteria, &limitStr); err != nil {
+			return ircError{&irc.Message{
+				Command: "FAIL",
+				Params:  []string{"CHATHISTORY", "NEED_MORE_PARAMS", subcommand, "Missing parameters"},
+			}}
+		}
+
+		if dc.srv.LogPath == "" {
+			return ircError{&irc.Message{
+				Command: irc.ERR_UNKNOWNCOMMAND,
+				Params:  []string{dc.nick, subcommand, "Unknown command"},
+			}}
+		}
+
+		uc, entity, err := dc.unmarshalEntity(target)
+		if err != nil {
+			return err
+		}
+
+		// TODO: support msgid criteria
+		criteriaParts := strings.SplitN(criteria, "=", 2)
+		if len(criteriaParts) != 2 || criteriaParts[0] != "timestamp" {
+			return ircError{&irc.Message{
+				Command: "FAIL",
+				Params:  []string{"CHATHISTORY", "UNKNOWN_CRITERIA", criteria, "Unknown criteria"},
+			}}
+		}
+
+		timestamp, err := time.Parse(serverTimeLayout, criteriaParts[1])
+		if err != nil {
+			return ircError{&irc.Message{
+				Command: "FAIL",
+				Params:  []string{"CHATHISTORY", "INVALID_CRITERIA", criteria, "Invalid criteria"},
+			}}
+		}
+
+		limit, err := strconv.Atoi(limitStr)
+		if err != nil || limit < 0 || limit > dc.srv.HistoryLimit {
+			return ircError{&irc.Message{
+				Command: "FAIL",
+				Params:  []string{"CHATHISTORY", "INVALID_LIMIT", limitStr, "Invalid limit"},
+			}}
+		}
+
+		switch subcommand {
+		case "BEFORE":
+			batchRef := "history"
+			dc.SendMessage(&irc.Message{
+				Prefix:  dc.srv.prefix(),
+				Command: "BATCH",
+				Params:  []string{"+" + batchRef, "chathistory", target},
+			})
+
+			history := make([]*irc.Message, limit)
+			remaining := limit
+
+			tries := 0
+			for remaining > 0 {
+				buf, err := parseMessagesBefore(uc.network, entity, timestamp, remaining)
+				if err != nil {
+					dc.logger.Printf("failed parsing log messages for chathistory: %v", err)
+					return newChatHistoryError(subcommand, target)
+				}
+				if len(buf) == 0 {
+					tries++
+					if tries >= 100 {
+						break
+					}
+				} else {
+					tries = 0
+				}
+				copy(history[remaining-len(buf):], buf)
+				remaining -= len(buf)
+				year, month, day := timestamp.Date()
+				timestamp = time.Date(year, month, day, 0, 0, 0, 0, timestamp.Location()).Add(-1)
+			}
+
+			for _, m := range history[remaining:] {
+				m.Tags["batch"] = irc.TagValue(batchRef)
+				dc.SendMessage(dc.marshalMessage(m, uc.network))
+			}
+
+			dc.SendMessage(&irc.Message{
+				Prefix:  dc.srv.prefix(),
+				Command: "BATCH",
+				Params:  []string{"-" + batchRef},
+			})
+		default:
+			// TODO: support AFTER, LATEST, BETWEEN
+			return ircError{&irc.Message{
+				Command: "FAIL",
+				Params:  []string{"CHATHISTORY", "UNKNOWN_COMMAND", subcommand, "Unknown command"},
+			}}
+		}
 	default:
 		dc.logger.Printf("unhandled message: %v", msg)
 		return newUnknownCommandError(msg.Command)

logger.go

@@ -1,6 +1,7 @@
 package soju
 
 import (
+	"bufio"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -132,3 +133,74 @@ func formatMessage(msg *irc.Message) string {
 		return ""
 	}
 }
+
+func parseMessagesBefore(network *network, entity string, timestamp time.Time, limit int) ([]*irc.Message, error) {
+	year, month, day := timestamp.Date()
+	path := logPath(network, entity, timestamp)
+	f, err := os.Open(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, nil
+		}
+		return nil, err
+	}
+	defer f.Close()
+
+	historyRing := make([]*irc.Message, limit)
+	cur := 0
+
+	sc := bufio.NewScanner(f)
+	for sc.Scan() {
+		line := sc.Text()
+		var hour, minute, second int
+		_, err := fmt.Sscanf(line, "[%02d:%02d:%02d] ", &hour, &minute, &second)
+		if err != nil {
+			return nil, err
+		}
+		message := line[11:]
+		// TODO: support NOTICE
+		if !strings.HasPrefix(message, "<") {
+			continue
+		}
+		i := strings.Index(message, "> ")
+		if i == -1 {
+			continue
+		}
+		t := time.Date(year, month, day, hour, minute, second, 0, time.Local)
+		if !t.Before(timestamp) {
+			break
+		}
+
+		sender := message[1:i]
+		text := message[i+2:]
+		historyRing[cur%limit] = &irc.Message{
+			Tags: map[string]irc.TagValue{
+				"time": irc.TagValue(t.UTC().Format(serverTimeLayout)),
+			},
+			Prefix: &irc.Prefix{
+				Name: sender,
+			},
+			Command: "PRIVMSG",
+			Params:  []string{entity, text},
+		}
+		cur++
+	}
+	if sc.Err() != nil {
+		return nil, sc.Err()
+	}
+
+	n := limit
+	if cur < limit {
+		n = cur
+	}
+	start := (cur - n + limit) % limit
+
+	if start+n <= limit { // ring doesnt wrap
+		return historyRing[start : start+n], nil
+	} else { // ring wraps
+		history := make([]*irc.Message, n)
+		r := copy(history, historyRing[start:])
+		copy(history[r:], historyRing[:n-r])
+		return history, nil
+	}
+}

server.go

@@ -41,6 +41,7 @@ type Server struct {
 	Hostname     string
 	Logger       Logger
 	RingCap      int
+	HistoryLimit int
 	LogPath      string
 	Debug        bool
 
@@ -54,6 +55,7 @@ func NewServer(db *DB) *Server {
 	return &Server{
 		Logger:       log.New(log.Writer(), "", log.LstdFlags),
 		RingCap:      4096,
+		HistoryLimit: 1000,
 		users:        make(map[string]*user),
 		db:           db,
 	}