Packing Dict{Symbol,Any} corrupts data

[ararslan]

Reproducer:

julia> bad = Dict{Symbol,Any}(:wake_after_sleep_onset => 0, :wake_after_sleep_onset_percentage => 1)
Dict{Symbol,Any} with 2 entries:
  :wake_after_sleep_onset            => 0
  :wake_after_sleep_onset_percentage => 1

julia> io = IOBuffer();

julia> pack(io, bad)

julia> seekstart(io);

julia> unpack(io, Dict{Symbol,Any})
Dict{Symbol,Any} with 2 entries:
  :wake_after_sleep_onset => 0x00
  :wake_after_sleep       => 0x5f

The keys are truncated and the values are wrong. Also note that the value assigned to the key :wake_after_sleep is the code point for an underscore, which would be the continuation of the key name were it completely consumed.

The problem seems to be specific to packing Symbols, as packing as String and unpacking as Symbol works fine:

julia> ok = Dict{String,Any}("wake_after_sleep_onset" => 0, "wake_after_sleep_onset_percentage" => 1)
Dict{String,Any} with 2 entries:
  "wake_after_sleep_onset"            => 0
  "wake_after_sleep_onset_percentage" => 1

julia> io = IOBuffer();

julia> pack(io, ok)

julia> seekstart(io);

julia> unpack(io, Dict{Symbol,Any})
Dict{Symbol,Any} with 2 entries:
  :wake_after_sleep_onset            => 0x00
  :wake_after_sleep_onset_percentage => 0x01

[ararslan]

The issue seems to be with this use of sizeof: https://github.com/JuliaIO/MsgPack.jl/blob/master/src/pack.jl#L185. When x here is a PointerString, sizeof doesn't properly capture the length of the underlying data.