Serializing bigdecimal for thrift/parquet

[xrl]

I am retrieving data from a postgres database with diesel. The table's schema is tagged with a Numeric meta-type, which I deserializing in to BigDecimal:

// diesel table definition
table! {
    invoices (id) {
        id -> Int4,
        commission_rate -> Nullable<Numeric>
    }
}

// target rust struct
use bigdecimal::BigDecimal;
use parquet::record::RecordWriter;

#[derive(Queryable, Debug, ParquetRecordWriter)]
pub struct Invoice {
    pub id: i32,
    commission_rate: Option<BigDecimal>,
}

but now I'm trying to figure out what parquet wants me to write out. The parquet logical types have this bit of info about byte representations:

    /// A decimal value.
    /// This may be used to annotate binary or fixed primitive types. The
    /// underlying byte array stores the unscaled value encoded as two's
    /// complement using big-endian byte order (the most significant byte is the
    /// zeroth element).
    ///
    /// This must be accompanied by a (maximum) precision and a scale in the
    /// SchemaElement. The precision specifies the number of digits in the decimal
    /// and the scale stores the location of the decimal point. For example 1.23
    /// would have precision 3 (3 total digits) and scale 2 (the decimal point is
    /// 2 digits over).
    DECIMAL,

I guess the pressing question is, how can I get the big-endian byte representation out of a BigDecimal? Looking over the implementation and it's got a lot of support for data types in but not so much out. Would the project be open to a PR addressing this need?