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Improve comment about magic word not present. #318

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May 29, 2024
Merged

Improve comment about magic word not present. #318

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9e8e2f3
fix invalid magic word returning nil error
lnogueir May 29, 2024
eef01d8
Revert "fix invalid magic word returning nil error"
lnogueir May 29, 2024
e266bbf
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lnogueir May 29, 2024
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7 changes: 2 additions & 5 deletions parse.go
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Original file line number Diff line number Diff line change
Expand Up @@ -40,9 +40,6 @@ const (
)

var (
// ErrorMagicWord indicates that the magic word was not found in the correct
// location in the DICOM.
ErrorMagicWord = errors.New("error, DICM magic word not found in correct location")
// ErrorMetaElementGroupLength indicates that the MetaElementGroupLength
// was not found where expected in the metadata.
ErrorMetaElementGroupLength = errors.New("MetaElementGroupLength tag not found where expected")
Expand Down Expand Up @@ -281,8 +278,8 @@ func SkipPixelData() ParseOption {
// a PixelData element will be added to the dataset with the
// PixelDataInfo.IntentionallyUnprocessed = true, and the raw bytes of the
// entire PixelData element stored in PixelDataInfo.UnprocessedValueData.
//
// In the future, we may be able to extend this functionality to support
//
// In the future, we may be able to extend this functionality to support
// on-demand processing of elements elsewhere in the library.
func SkipProcessingPixelDataValue() ParseOption {
return func(set *parseOptSet) {
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5 changes: 4 additions & 1 deletion read.go
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Expand Up @@ -20,6 +20,9 @@ import (
)

var (
// ErrorMagicWord indicates that the magic word was not found in the correct
// location in the DICOM.
ErrorMagicWord = errors.New("error, DICM magic word not found in correct location")
// ErrorOWRequiresEvenVL indicates that an element with VR=OW had a not even
// value length which is not allowed.
ErrorOWRequiresEvenVL = errors.New("vr of OW requires even value length")
Expand Down Expand Up @@ -160,7 +163,7 @@ func (r *reader) readHeader() ([]*Element, error) {
return nil, err
}
if string(data[128:]) != magicWord {
return nil, nil
return nil, ErrorMagicWord
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@suyashkumar suyashkumar May 29, 2024 •
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I think the reason for this was the note at L157: namely, if the magic word isn't found we try to parse the Dataset without the preamble: #59. This was reported by folks who had files like this in production! Perhaps we should make the user pass an explicit parse option to trigger this behavior if we think there's harm in doing this as a default.

Of course, parsing without metadata can cause all sorts of problems which may eventually result in an error anyway.

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@wkoszek do y'all recall if this fix actually lead to y'all successfully parsing DICOMs without the header?

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That makes sense. I reverted the commit, but I updated the comment because it's rather unusual to see a function returning nil, nil like that and the comment was a bit hidden up top. Will update PR title

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Agreed, thanks for the update!

}

err = r.rawReader.Skip(128 + 4) // skip preamble + magic word
Expand Down
8 changes: 8 additions & 0 deletions read_test.go
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Expand Up @@ -684,6 +684,14 @@ func headerWithFileMetaInformationGroupLength() (*headerData, error) {
return headerData, nil
}

func TestReadHeader_InvalidMagicWord(t *testing.T) {
notDICOMReader := bufio.NewReader(bytes.NewReader(make([]byte, 128+4)))
r := &reader{rawReader: dicomio.NewReader(notDICOMReader, binary.LittleEndian, dicomio.LimitReadUntilEOF)}
if _, err := r.readHeader(); err != ErrorMagicWord {
t.Fatalf("Expected %v error, got %v", ErrorMagicWord, err)
}
}

func TestReadHeader_TryAllowErrorMetaElementGroupLength(t *testing.T) {
opts := parseOptSet{allowMissingMetaElementGroupLength: true}

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