tormoder · tormoder · Feb 5, 2021 · Jan 2, 2021 · Feb 5, 2021
diff --git a/consts.go b/consts.go
@@ -57,14 +57,13 @@ const (
 	localMesgNumMask   byte = 0x0F
 
 	maxLocalMesgs byte = localMesgNumMask + 1
-	maxFieldSize  byte = 255
 
 	littleEndian byte = 0x00
 	bigEndian    byte = 0x01
 
 	bytesForCRC     byte = 2
 	headerSizeCRC   byte = 14
-	headerSizeNoCRC byte = (headerSizeCRC - bytesForCRC)
+	headerSizeNoCRC byte = headerSizeCRC - bytesForCRC
 
 	fitDataTypeString string = ".FIT"
 

diff --git a/reader.go b/reader.go
@@ -29,7 +29,7 @@ type decoder struct {
 	}
 
 	crc     dyncrc16.Hash16
-	tmp     [maxFieldSize]byte
+	tmp     [255 * 3]byte
 	defmsgs [maxLocalMesgs]*defmsg
 
 	timestamp      uint32
@@ -434,7 +434,7 @@ func (d *decoder) parseDefinitionMessage(recordHeader byte) (*defmsg, error) {
 		return &dm, nil
 	}
 
-	if err = d.readFull(d.tmp[0 : 3*dm.fields]); err != nil {
+	if err = d.readFull(d.tmp[0 : 3*uint16(dm.fields)]); err != nil {
 		return nil, fmt.Errorf("error parsing fields: %v", err)
 	}
 

diff --git a/reader_files_test.go b/reader_files_test.go
@@ -203,6 +203,16 @@ var decodeTestFiles = [...]struct {
 		false,
 		"",
 	},
+	{
+		"bpg",
+		"garmin.fit",
+		false,
+		8578045933883478770,
+		true,
+		tdoNone,
+		false,
+		"Has a definition message with number of fields >85",
+	},
 	{
 		"corrupt",
 		"activity-filecrc.fit",

diff --git a/testdata/bpg/garmin.fit b/testdata/bpg/garmin.fit
diff --git a/testdata/bpg/garmin.fit.golden.gz b/testdata/bpg/garmin.fit.golden.gz
diff --git a/writer.go b/writer.go
@@ -280,11 +280,30 @@ func (e *encoder) encodeFile(file reflect.Value) error {
 			for j := 0; j < v.Len(); j++ {
 				v2 := reflect.Indirect(v.Index(j))
 
-				if j == 0 {
-					def = getEncodeMesgDef(v2, 0)
-					err := e.writeDefMesg(def)
-					if err != nil {
-						return err
+				// Not necessary that the first message will have all defined fields that may appear in the following messages
+				// So we have to build a model first by iterating though all the message and collecting valid definition fields
+				if def == nil {
+					// map to collect field definitions
+					mfields := make(map[byte]*field)
+					for k := 0; k < v.Len(); k++ {
+						r := reflect.Indirect(v.Index(k))
+						def = getEncodeMesgDef(r, 0)
+						for _, f := range def.fields {
+							mfields[f.num] = f
+						}
+					}
+					// should not be nil at this point, but just in case
+					if def != nil {
+						def.fields = make([]*field, 0, len(mfields))
+						for _, f := range mfields {
+							def.fields = append(def.fields, f)
+						}
+						err := e.writeDefMesg(def)
+						if err != nil {
+							return err
+						}
+					} else {
+						return fmt.Errorf("cannot create definition message for %+v", v.Interface())
 					}
 				}