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Add support for branch nodes in local descriptors #47

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Add support for branch nodes in local descriptors #47

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91 changes: 62 additions & 29 deletions pkg/local_descriptors.go
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Original file line number Diff line number Diff line change
Expand Up @@ -34,18 +34,28 @@ type LocalDescriptor struct {
func NewLocalDescriptor(data []byte, formatType FormatType) LocalDescriptor {
switch formatType {
case FormatTypeANSI:
return LocalDescriptor{
Identifier: Identifier(binary.LittleEndian.Uint32(data[:4])),
DataIdentifier: Identifier(binary.LittleEndian.Uint32(data[4 : 4+4])),
LocalDescriptorsIdentifier: Identifier(binary.LittleEndian.Uint32(data[8 : 8+4])),
ld := LocalDescriptor{
Identifier: Identifier(binary.LittleEndian.Uint32(data[:4])),
DataIdentifier: Identifier(binary.LittleEndian.Uint32(data[4 : 4+4])),
}

if len(data) > 8 {
ld.LocalDescriptorsIdentifier = Identifier(binary.LittleEndian.Uint32(data[8 : 8+4]))
}

return ld
default:
// TODO - Reference [MS-PDF] that this is actually 32-bit.
return LocalDescriptor{
Identifier: Identifier(binary.LittleEndian.Uint32(data[:8])),
DataIdentifier: Identifier(binary.LittleEndian.Uint32(data[8 : 8+8])),
LocalDescriptorsIdentifier: Identifier(binary.LittleEndian.Uint32(data[16 : 16+8])),
ld := LocalDescriptor{
Identifier: Identifier(binary.LittleEndian.Uint32(data[:8])),
DataIdentifier: Identifier(binary.LittleEndian.Uint32(data[8 : 8+8])),
}

if len(data) > 16 {
ld.LocalDescriptorsIdentifier = Identifier(binary.LittleEndian.Uint32(data[16 : 16+8]))
}

return ld
}
}

Expand All @@ -54,6 +64,11 @@ func (file *File) GetLocalDescriptors(btreeNodeEntry BTreeNode) ([]LocalDescript
return file.GetLocalDescriptorsFromIdentifier(btreeNodeEntry.LocalDescriptorsIdentifier)
}

const (
SlBlockEntry = 0
SiBlockEntry = 1
)

// GetLocalDescriptorsFromIdentifier returns the local descriptors of the local descriptors identifier.
// References "Local Descriptors".
func (file *File) GetLocalDescriptorsFromIdentifier(localDescriptorsIdentifier Identifier) ([]LocalDescriptor, error) {
Expand Down Expand Up @@ -81,26 +96,18 @@ func (file *File) GetLocalDescriptorsFromIdentifier(localDescriptorsIdentifier I

if _, err := file.Reader.ReadAt(localDescriptorsLevel, localDescriptorsNode.FileOffset+1); err != nil {
return nil, eris.Wrap(err, "failed to read local descriptors level")
} else if localDescriptorsLevel[0] > 0 {
// Haven't seen branch nodes yet.
return nil, ErrLocalDescriptorBranchNode
}

var localDescriptorEntrySize uint8
blockType := localDescriptorsLevel[0]

switch file.FormatType {
case FormatTypeANSI:
localDescriptorEntrySize = 12
default:
localDescriptorEntrySize = 24
}

localDescriptorsEntryCount := make([]byte, 2)
localDescriptorsEntryCountBytes := make([]byte, 2)

if _, err := file.Reader.ReadAt(localDescriptorsEntryCount, localDescriptorsNode.FileOffset+2); err != nil {
if _, err := file.Reader.ReadAt(localDescriptorsEntryCountBytes, localDescriptorsNode.FileOffset+2); err != nil {
return nil, eris.Wrap(err, "failed to get local descriptors entry count")
}

localDescriptorsEntryCount := binary.LittleEndian.Uint16(localDescriptorsEntryCountBytes)

var localDescriptorsEntriesOffset int64

switch file.FormatType {
Expand All @@ -110,18 +117,44 @@ func (file *File) GetLocalDescriptorsFromIdentifier(localDescriptorsIdentifier I
localDescriptorsEntriesOffset = localDescriptorsNode.FileOffset + 8
}

localDescriptorsEntries := make([]byte, binary.LittleEndian.Uint16(localDescriptorsEntryCount)*uint16(localDescriptorEntrySize))
localDescriptors := make([]LocalDescriptor, 0, localDescriptorsEntryCount)

for i := 1; i <= int(localDescriptorsEntryCount); i++ {
var entryDataSize int64
if blockType == SlBlockEntry {
if file.FormatType == FormatTypeANSI {
entryDataSize = 12
} else {
entryDataSize = 24
}
} else {
if file.FormatType == FormatTypeANSI {
entryDataSize = 8
} else {
entryDataSize = 16
}
}

if _, err := file.Reader.ReadAt(localDescriptorsEntries, localDescriptorsEntriesOffset); err != nil {
return nil, eris.Wrap(err, "failed to read local descriptors entries")
}
localDescriptorEntry := make([]byte, entryDataSize)

if _, err := file.Reader.ReadAt(localDescriptorEntry, localDescriptorsEntriesOffset); err != nil {
return nil, eris.Wrap(err, "failed to get local descriptors entry count")
}

localDescriptors := make([]LocalDescriptor, binary.LittleEndian.Uint16(localDescriptorsEntryCount))
localDescriptor := NewLocalDescriptor(localDescriptorEntry, file.FormatType)
if blockType == SlBlockEntry {
localDescriptors = append(localDescriptors, localDescriptor)
} else {
descriptors, err := file.GetLocalDescriptorsFromIdentifier(localDescriptor.DataIdentifier)
if err != nil {
return nil, eris.Wrap(err, "failed to get descriptors from identifier")
}

for i := 0; i < int(binary.LittleEndian.Uint16(localDescriptorsEntryCount)); i++ {
localDescriptorEntry := localDescriptorsEntries[i*int(localDescriptorEntrySize) : (i+1)*int(localDescriptorEntrySize)]
localDescriptors = append(localDescriptors, descriptors...)
}

localDescriptors[i] = NewLocalDescriptor(localDescriptorEntry, file.FormatType)
// Increase the offset so its at the start of the next entry
localDescriptorsEntriesOffset += entryDataSize
}

return localDescriptors, nil
Expand Down