writer() ->
writer
Create a new wire format writer
Returns a builder-based writer that accumulates bytes into an
internal table. Provides methods for writing DNS wire format
primitives (u8, u16, u32, bytes), compressed names, and
character-strings. Use output() to get the accumulated bytes
as a string. Use patch_u16(offset, val) for header fixups.
The writer maintains a compression table for name compression: when writing the same domain name suffix twice, the second occurrence is replaced with a 2-byte pointer.