static bool TryReadMetaData(MemoryMappedFile file, long size, out Metadata metadata, out string error)
{
if (size < FeatherMagic.MAGIC_HEADER_SIZE * 2)
{
metadata = default(Metadata);
error = $"File too small ({size:N0} bytes) to be a valid feather file";
return(false);
}
using (var accessor = file.CreateViewAccessor())
{
var leadingHeader = accessor.ReadInt32(0);
if (leadingHeader != FeatherMagic.MAGIC_HEADER)
{
metadata = default(Metadata);
error = $"Magic header malformed";
return(false);
}
var trailingHeader = accessor.ReadInt32(size - FeatherMagic.MAGIC_HEADER_SIZE);
if (trailingHeader != FeatherMagic.MAGIC_HEADER)
{
metadata = default(Metadata);
error = $"Magic footer malformed";
return(false);
}
var metadataSize = accessor.ReadUInt32(size - FeatherMagic.MAGIC_HEADER_SIZE - sizeof(uint));
var metadataStart = size - FeatherMagic.MAGIC_HEADER_SIZE - sizeof(uint) - metadataSize;
if (metadataStart < FeatherMagic.MAGIC_HEADER_SIZE || metadataSize > int.MaxValue)
{
metadata = default(Metadata);
error = $"Metadata size ({metadataSize:N0}) is invalid";
return(false);
}
var metadataBytes = new byte[metadataSize];
accessor.ReadArray(metadataStart, metadataBytes, 0, (int)metadataSize);
// note: It'd be nice to not actually use flatbuffers for this,
// kind of a heavy (re)build dependency for reading, like, 4
// things
var metadataBuffer = new ByteBuffer(metadataBytes);
var metadataCTable = CTable.GetRootAsCTable(metadataBuffer);
if (metadataCTable.Version != FeatherMagic.FEATHER_VERSION)
{
error = $"Unexpected version {metadataCTable.Version}, only {FeatherMagic.FEATHER_VERSION} is supported";
metadata = default(Metadata);
return(false);
}
if (metadataCTable.ColumnsLength <= 0)
{
error = $"Invalid number of columns: {metadataCTable.ColumnsLength:N0}";
metadata = default(Metadata);
return(false);
}
var columnSpecs = new ColumnSpec[metadataCTable.ColumnsLength];
for (var i = 0; i < columnSpecs.Length; i++)
{
var metadataColumn = metadataCTable.Columns(i).Value;
var name = metadataColumn.Name;
var metadataType = metadataColumn.MetadataType;
string[] categoryLevels = null;
DateTimePrecisionType precision = default(DateTimePrecisionType);
var arrayDetails = metadataColumn.Values.Value;
var effectiveType = arrayDetails.Type;
switch (metadataType)
{
case TypeMetadata.CategoryMetadata:
if (!TryReadCategoryLevels(accessor, ref metadataColumn, out categoryLevels, out error))
{
metadata = default(Metadata);
return(false);
}
break;
case TypeMetadata.TimestampMetadata:
if (arrayDetails.Type != feather.fbs.Type.INT64)
{
metadata = default(Metadata);
error = $"Column {name} has Timestamp metadata, but isn't backed by an Int64 array";
return(false);
}
if (!TryReadTimestampPrecision(ref metadataColumn, out precision, out error))
{
metadata = default(Metadata);
return(false);
}
// note: this type is spec'd (https://github.com/wesm/feather/blob/master/cpp/src/feather/metadata.fbs#L25),
// but it looks like R always writes it as an int64?
// Possibly a bug.
effectiveType = feather.fbs.Type.TIMESTAMP;
break;
case TypeMetadata.TimeMetadata:
if (arrayDetails.Type != feather.fbs.Type.INT64)
{
metadata = default(Metadata);
error = $"Column {name} has Time metadata, but isn't backed by an Int64 array";
return(false);
}
if (!TryReadTimePrecision(ref metadataColumn, out precision, out error))
{
metadata = default(Metadata);
return(false);
}
// note: this type is spec'd (https://github.com/wesm/feather/blob/master/cpp/src/feather/metadata.fbs#L27),
// but it looks like R always writes it as an int64?
// Possibly a bug.
effectiveType = feather.fbs.Type.TIME;
break;
case TypeMetadata.DateMetadata:
if (arrayDetails.Type != feather.fbs.Type.INT32)
{
metadata = default(Metadata);
error = $"Column {name} has Time metadata, but isn't backed by an Int32 array";
return(false);
}
// note: this type is spec'd (https://github.com/wesm/feather/blob/master/cpp/src/feather/metadata.fbs#L26),
// but it looks like R always writes it as an int32?
// Possibly a bug.
effectiveType = feather.fbs.Type.DATE;
break;
case TypeMetadata.NONE: break;
}
ColumnSpec column;
if (!TryMakeColumnSpec(name, effectiveType, ref arrayDetails, categoryLevels, precision, out column, out error))
{
metadata = default(Metadata);
return(false);
}
columnSpecs[i] = column;
}
metadata =
new Metadata
{
Columns = columnSpecs,
NumRows = metadataCTable.NumRows
};
error = null;
return(true);
}
}