From 8cfc5ff44b09f964a84da6e33e9e2e73cd7db3af Mon Sep 17 00:00:00 2001
From: Hikmatulloh Hari Mukti <muktihaz@gmail.com>
Date: Mon, 23 Sep 2024 15:40:33 +0700
Subject: [PATCH] fix: deocder peek file_id

---
 decoder/decoder.go      | 11 +++--------
 decoder/decoder_test.go | 41 -----------------------------------------
 2 files changed, 3 insertions(+), 49 deletions(-)

diff --git a/decoder/decoder.go b/decoder/decoder.go
index 2d6b986f..58c8ec33 100644
--- a/decoder/decoder.go
+++ b/decoder/decoder.go
@@ -42,7 +42,6 @@ const (
 	ErrMesgDefMissing = errorString("message definition missing") // NOTE: Kept exported since it's used by RawDecoder
 
 	errInvalidBaseType = errorString("invalid basetype")
-	errMissingFileId   = errorString("missing file_id")
 )
 
 // Decoder is FIT file decoder. See New() for details.
@@ -343,7 +342,8 @@ func (d *Decoder) PeekFileHeader() (*proto.FileHeader, error) {
 }
 
 // PeekFileId decodes only up to FileId message without decoding the whole reader.
-// FileId message should be the first message of any FIT file, otherwise return an error.
+// The FileId is expected to be present as the first message; however, we don't validate this,
+// as it's an edge case that occurs when a FIT file is poorly encoded.
 //
 // If we choose to continue, Decode picks up where this left then continue decoding next messages instead of starting from zero.
 func (d *Decoder) PeekFileId() (*mesgdef.FileId, error) {
@@ -353,16 +353,11 @@ func (d *Decoder) PeekFileId() (*mesgdef.FileId, error) {
 	if d.err = d.decodeFileHeaderOnce(); d.err != nil {
 		return nil, d.err
 	}
-	for len(d.messages) == 0 {
+	for d.fileId == nil {
 		if d.err = d.decodeMessage(); d.err != nil {
 			return nil, d.err
 		}
 	}
-	if d.fileId == nil {
-		mesg := &d.messages[0]
-		return nil, fmt.Errorf("expect file_id as first mesg, got: %s(%d): %w",
-			mesg.Num, mesg.Num, errMissingFileId)
-	}
 	return d.fileId, nil
 }
 
diff --git a/decoder/decoder_test.go b/decoder/decoder_test.go
index a8a00baa..42c4fca8 100644
--- a/decoder/decoder_test.go
+++ b/decoder/decoder_test.go
@@ -432,47 +432,6 @@ func TestPeekFileId(t *testing.T) {
 			fileId: mesgdef.NewFileId(&fit.Messages[0]),
 			err:    io.EOF,
 		},
-		{
-			name: "peek file id returned non file_id message",
-			r: func() io.Reader {
-				fileId := mesgdef.NewRecord(nil).SetDistance(0)
-				mesg := fileId.ToMesg(nil)
-				mesgb, _ := mesg.MarshalAppend(nil, proto.LittleEndian)
-				mesgDef, _ := proto.NewMessageDefinition(&mesg)
-				mesgDefb, _ := mesgDef.MarshalAppend(nil)
-
-				fileHeaderb, _ := (&proto.FileHeader{
-					Size:            12,
-					ProtocolVersion: proto.V1,
-					ProfileVersion:  profile.Version,
-					DataSize:        uint32(len(mesgDefb) + len(mesgb)),
-					DataType:        proto.DataTypeFIT,
-				}).MarshalAppend(nil)
-
-				buf := append(mesgDefb, mesgb...)
-				crc := crc16.New(nil)
-				crc.Write(buf)
-
-				buf = append(fileHeaderb, buf...)
-				buf = binary.LittleEndian.AppendUint16(buf, crc.Sum16())
-
-				buf, cur := buf, 0
-				return fnReader(func(b []byte) (n int, err error) {
-					m := len(buf)
-					if cur >= m { // only decode header
-						return 0, io.EOF
-					}
-					if cur+len(b) < m {
-						m = cur + len(b)
-					}
-					n = copy(b, buf[cur:m])
-					cur += n
-					return
-				})
-			}(),
-			fileId: nil,
-			err:    errMissingFileId,
-		},
 	}
 
 	for i, tc := range tt {