Implement fallback to softmodem for failed T.38 transmissions

README.md

@@ -61,7 +61,7 @@ curl http://files.freeswitch.org/repo/deb/debian/freeswitch_archive_g0.pub | apt
 
 ```
 apt-get update
-apt-get install hylafax-server freeswitch freeswitch-mod-commands freeswitch-mod-dptools freeswitch-mod-event-socket freeswitch-mod-logfile freeswitch-mod-sofia freeswitch-mod-spandsp freeswitch-mod-timerfd freeswitch-mod-tone-stream freeswitch-sysvinit
+apt-get install hylafax-server freeswitch freeswitch-mod-commands freeswitch-mod-dptools freeswitch-mod-event-socket freeswitch-mod-logfile freeswitch-mod-sofia freeswitch-mod-spandsp freeswitch-mod-timerfd freeswitch-mod-tone-stream freeswitch-mod-db freeswitch-sysvinit
 ```
 
 It is recommended to run gofaxd using a process management system as it doesn't daemonize by itself. A configuration file for the supervisor process control system is provided in the GOfax.IP repository. To use it, the supervisor packae has to be installed:
@@ -178,3 +178,12 @@ The following arguments are provided to the `DynamicConfig` script for outgoing
 * `LocalIdentifier: +1 234 567` will assign a TSI (Transmitting Station Identifier) for this call. The Default TSI can be set in `gofax.conf` in the `ident` parameter.
 * `TagLine: ACME` will assign a header string to be shown on the top of each page. This does not support format strings as used by HylaFAX; if defined a header string is always shown with the current timestamp and page number as set by SpanDSP.
 * `FAXNumber: 1337` will set the outgoing caller id number as used by FreeSWITCH when originating the call. 
+
+### Fallback from T.38 to SpanDSP softmodem
+
+In rare cases we noticed problems with certain remote stations that could not successfully negotiate with some T.38 Gateways we tested. In the case we observed, the remote tried to use T.4 1-D compression with ECM enabled. After disabling T.38 the fax was successfully received. 
+
+To work around this rare sort of problem and improve compatiblity, GOfax.IP can identify failed transmissions and dynamically disable T.38 for the affected remote station and have FreeSWITCH use SpanDSP's pure software fax implementation. The station is identified by caller id and saved in FreeSWITCH's `mod_db`.
+To enable this feature, set `softmodemfallback = false` in `gofax.conf`.
+
+Note that this will only affect all subsequent calls from/to the remote station, assuming that the remote station will retry a failed fax. Entries in the fallback list are persistant and will not be expired by GOfax.IP. It is possible however to manually expire entries. The used `<realm>/<key>/<value>` is `fallback/<callerid>/<unix_timestamp>`, with unix_timestamp being the time when the entry was added. See https://wiki.freeswitch.org/wiki/Mod_db for details. 

config/freeswitch/autoload_configs/db.conf.xml

@@ -0,0 +1,5 @@
+<configuration name="db.conf" description="LIMIT DB Configuration">
+  <settings>
+    <!--<param name="odbc-dsn" value="dsn:user:pass"/>-->
+  </settings>
+</configuration>

config/gofax.conf

@@ -9,6 +9,14 @@ header = "GONICUS LABS"
 ; Enable to get excessive SpanDSP debug messages in FreeSWITCH
 verbose = false
 
+; Disable T.38
+disablet38 = false
+
+; Enable fallback to softmodem for the next call of
+; a caller (identified by caller id) if negotiation using T.38 fails
+; Persistent fallback data is saved in FreeSWITCH's mod_db
+softmodemfallback = false
+
 [hylafax]
 spooldir = /var/spool/hylafax
 

src/gofaxd/server.go

@@ -156,6 +156,22 @@ func (e *EventSocketServer) handler(c *eventsocket.Connection) {
 
 	logger.Logger.Println(channel_uuid, "Logging events for commid", sessionlog.CommId(), "to", sessionlog.Logfile())
 	sessionlog.Log("Inbound channel UUID: ", channel_uuid)
+
+	// Check if T.38 should be disabled
+	disable_t38 := gofaxlib.Config.Freeswitch.DisableT38
+	if disable_t38 {
+		sessionlog.Log("T.38 disabled by configuration")
+	} else {
+		disable_t38, err = gofaxlib.GetSoftmodemFallback(nil, cidnum)
+		if err != nil {
+			sessionlog.Log(err)
+			disable_t38 = false
+		}
+		if disable_t38 {
+			sessionlog.Log(fmt.Sprintf("Softmodem fallback active for caller %s, disabling T.38", cidnum))
+		}
+	}
+
 	sessionlog.Log(fmt.Sprintf("Accepting call to %v from %v <%v> with commid %v", recipient, cidname, cidnum, sessionlog.CommId()))
 
 	if device != nil {
@@ -191,8 +207,12 @@ func (e *EventSocketServer) handler(c *eventsocket.Connection) {
 
 	sessionlog.Log("Rxfax to", filename_abs)
 
-	c.Execute("set", "fax_enable_t38_request=true", true)
-	c.Execute("set", "fax_enable_t38=true", true)
+	if disable_t38 {
+		c.Execute("set", "fax_enable_t38=false", true)
+	} else {
+		c.Execute("set", "fax_enable_t38_request=true", true)
+		c.Execute("set", "fax_enable_t38=true", true)
+	}
 	c.Execute("set", fmt.Sprintf("fax_ident=%s", csi), true)
 	c.Execute("rxfax", filename_abs, true)
 
@@ -253,6 +273,36 @@ EventLoop:
 		sessionlog.Log(err)
 	}
 
+	// If reception failed:
+	// Check if softmodem fallback should be enabled on the next call
+	if gofaxlib.Config.Freeswitch.SoftmodemFallback && !result.Success {
+		var activate_fallback bool
+
+		if result.NegotiateCount > 1 {
+			// Activate fallback if negotiation was repeated
+			sessionlog.Log(fmt.Sprintf("Fax failed with %d negotiations, enabling softmodem fallback for calls from/to %s.", result.NegotiateCount, cidnum))
+			activate_fallback = true
+		} else {
+			var badrows uint
+			for _, p := range result.PageResults {
+				badrows += p.BadRows
+			}
+			if badrows > 0 {
+				// Activate fallback if any bad rows were present
+				sessionlog.Log(fmt.Sprintf("Fax failed with %d bad rows in %d pages, enabling softmodem fallback for calls from/to %s.", badrows, result.TransferredPages, cidnum))
+				activate_fallback = true
+			}
+		}
+
+		if activate_fallback {
+			err = gofaxlib.SetSoftmodemFallback(nil, cidnum, true)
+			if err != nil {
+				sessionlog.Log(err)
+			}
+		}
+
+	}
+
 	// Process received file
 	rcvdcmd := gofaxlib.Config.Gofaxd.FaxRcvdCmd
 	if rcvdcmd == "" {

src/gofaxlib/config.go

@@ -29,12 +29,14 @@ var (
 
 type config struct {
 	Freeswitch struct {
-		Socket   string
-		Password string
-		Gateway  []string
-		Ident    string
-		Header   string
-		Verbose  bool
+		Socket            string
+		Password          string
+		Gateway           []string
+		Ident             string
+		Header            string
+		Verbose           bool
+		DisableT38        bool
+		SoftmodemFallback bool
 	}
 	Hylafax struct {
 		Spooldir   string

src/gofaxlib/faxresult.go

@@ -90,6 +90,7 @@ type FaxResult struct {
 	ResultText       string
 	Success          bool
 	TransferRate     uint
+	NegotiateCount   uint
 
 	PageResults []PageResult
 }
@@ -123,6 +124,7 @@ func (f *FaxResult) AddEvent(ev *eventsocket.Event) {
 		case "spandsp::rxfaxnegociateresult":
 			fallthrough
 		case "spandsp::txfaxnegociateresult":
+			f.NegotiateCount++
 			if ecm := ev.Get("Fax-Ecm-Used"); ecm == "on" {
 				f.Ecm = true
 			}

src/gofaxlib/fsdb.go

@@ -0,0 +1,39 @@
+package gofaxlib
+
+import (
+	"fmt"
+	"github.com/fiorix/go-eventsocket/eventsocket"
+)
+
+func FreeSwitchDBInsert(c *eventsocket.Connection, realm string, key string, value string) error {
+	_, err := c.Send(fmt.Sprintf("api db insert/%s/%s/%s", realm, key, value))
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func FreeSwitchDBDelete(c *eventsocket.Connection, realm string, key string) error {
+	_, err := c.Send(fmt.Sprintf("api db delete/%s/%s", realm, key))
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func FreeSwitchDBSelect(c *eventsocket.Connection, realm string, key string) (string, error) {
+	result, err := c.Send(fmt.Sprintf("api db select/%s/%s", realm, key))
+	if err != nil {
+		return "", err
+	}
+	return result.Body, nil
+}
+
+func FreeSwitchDBExists(c *eventsocket.Connection, realm string, key string) (bool, error) {
+	result, err := c.Send(fmt.Sprintf("api db exists/%s/%s", realm, key))
+	if err != nil {
+		return false, err
+	}
+
+	return result.Body == "true", nil
+}

src/gofaxlib/softmodemfallback.go

@@ -0,0 +1,50 @@
+package gofaxlib
+
+import (
+	"fmt"
+	"github.com/fiorix/go-eventsocket/eventsocket"
+	"time"
+)
+
+const (
+	MOD_DB_FALLBACK_REALM = "fallback"
+)
+
+func GetSoftmodemFallback(c *eventsocket.Connection, cidnum string) (bool, error) {
+	if !Config.Freeswitch.SoftmodemFallback || cidnum == "" {
+		return false, nil
+	}
+
+	var err error
+	if c == nil {
+		c, err = eventsocket.Dial(Config.Freeswitch.Socket, Config.Freeswitch.Password)
+		if err != nil {
+			return false, err
+		}
+		defer c.Close()
+	}
+
+	exists, err := FreeSwitchDBExists(c, MOD_DB_FALLBACK_REALM, cidnum)
+	if err != nil {
+		return false, err
+	}
+
+	return exists, nil
+}
+
+func SetSoftmodemFallback(c *eventsocket.Connection, cidnum string, enabled bool) error {
+	if !Config.Freeswitch.SoftmodemFallback || cidnum == "" {
+		return nil
+	}
+
+	var err error
+	if c == nil {
+		c, err = eventsocket.Dial(Config.Freeswitch.Socket, Config.Freeswitch.Password)
+		if err != nil {
+			return err
+		}
+		defer c.Close()
+	}
+
+	return FreeSwitchDBInsert(c, MOD_DB_FALLBACK_REALM, cidnum, fmt.Sprintf("%d", time.Now().Unix()))
+}

src/gofaxsend/transmission.go

@@ -96,6 +96,21 @@ func (t *transmission) start() {
 		return
 	}
 
+	// Check if T.38 should be disabled
+	disable_t38 := gofaxlib.Config.Freeswitch.DisableT38
+	if disable_t38 {
+		t.sessionlog.Log("T.38 disabled by configuration")
+	} else {
+		disable_t38, err = gofaxlib.GetSoftmodemFallback(t.conn, t.faxjob.Number)
+		if err != nil {
+			t.sessionlog.Log(err)
+			disable_t38 = false
+		}
+		if disable_t38 {
+			t.sessionlog.Log(fmt.Sprintf("Softmodem fallback active for destination %s, disabling T.38", t.faxjob.Number))
+		}
+	}
+
 	// Assemble dialstring
 	ds_variables_map := map[string]string{
 		"ignore_early_media":           "true",
@@ -108,6 +123,12 @@ func (t *transmission) start() {
 		"fax_verbose":                  strconv.FormatBool(gofaxlib.Config.Freeswitch.Verbose),
 	}
 
+	if disable_t38 {
+		ds_variables_map["fax_enable_t38"] = "false"
+	} else {
+		ds_variables_map["fax_enable_t38"] = "true"
+	}
+
 	ds_variables_pairs := make([]string, len(ds_variables_map))
 	i := 0
 	for k, v := range ds_variables_map {
@@ -152,6 +173,37 @@ func (t *transmission) start() {
 		case ev := <-es.Events():
 			result.AddEvent(ev)
 			if result.Hangupcause != "" {
+
+				// If transmission failed:
+				// Check if softmodem fallback should be enabled on the next call
+				if gofaxlib.Config.Freeswitch.SoftmodemFallback && !result.Success {
+					var activate_fallback bool
+
+					if result.NegotiateCount > 1 {
+						// Activate fallback if negotiation was repeated
+						t.sessionlog.Log(fmt.Sprintf("Fax failed with %d negotiations, enabling softmodem fallback for calls from/to %s.", result.NegotiateCount, t.faxjob.Number))
+						activate_fallback = true
+					} else {
+						var badrows uint
+						for _, p := range result.PageResults {
+							badrows += p.BadRows
+						}
+						if badrows > 0 {
+							// Activate fallback if any bad rows were present
+							t.sessionlog.Log(fmt.Sprintf("Fax failed with %d bad rows in %d pages, enabling softmodem fallback for calls from/to %s.", badrows, result.TransferredPages, t.faxjob.Number))
+							activate_fallback = true
+						}
+					}
+
+					if activate_fallback {
+						err = gofaxlib.SetSoftmodemFallback(t.conn, t.faxjob.Number, true)
+						if err != nil {
+							t.sessionlog.Log(err)
+						}
+					}
+
+				}
+
 				t.resultChan <- result
 				return
 			}