cram/container/block: Decode fails when the block is empty

[zaeleus]

Some encoders like CRAMtools write empty blocks, i.e., a block with an uncompressed size of 0. This is rather unconventional, but the CRAM spec does not define whether this is legal or not. The question is posed in samtools/hts-specs#680.

An example of data like this can be seen with SAMEA3302751.alt_bwamem_GRCh38DH.20200922.Finnish.simons.cram.

(lldb) p *self
(noodles_cram::container::block::Block) $0 = {
  compression_method = Rans4x8
  content_type = ExternalData
  content_id = {
    0 = 5
  }
  uncompressed_len = 0
  data = {
    ptr = 0x00005555557a6b38
    len = 0
    data = {
      p = {
        value = 0x0000000000000000
      }
    }
    vtable = 0x0000555555821df0
  }
}
(lldb) c
Process 494871 resuming
Error: Error { kind: UnexpectedEof, message: "failed to fill whole buffer" }
Process 494871 exited with status = 1 (0x00000001)

This was originally reported by @claymcleod.

[zaeleus]

Closed by 65dafbb.