# Reading FlatBuffer from mmaped file

**URL:** <https://discourse.julialang.org/t/reading-flatbuffer-from-mmaped-file/14739>\
**Category:** New to Julia\
**Tags:** question\
**Created:** [September 9, 2018, 5:25pm UTC](https://discourse.julialang.org/t/reading-flatbuffer-from-mmaped-file/14739 "2018-09-09T17:25:30Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![gabomgp](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/gabomgp/32/1918_2.png) [@gabomgp](https://discourse.julialang.org/u/gabomgp)\
**Post date:** [September 9, 2018, 5:25pm UTC](https://discourse.julialang.org/t/reading-flatbuffer-from-mmaped-file/14739/1 "2018-09-09T17:25:30Z")

</div>

I want to read a custom format written from python and used as IPC format between a python backend and a Angular frontend. The IPC format is based in Arrow Stream IPC Format. I have many Arrow tables (each one is based in a table or view from the database) with a footer written using a custom Flatbuffer format. The footer says the offset and name of each Arrow Table. So, as first step, I want to read that footer from a mmaped file, but i can’t find how to do that.

The documentation in:

[http://juliadata.github.io/FlatBuffers.jl/stable/](http://juliadata.github.io/FlatBuffers.jl/stable/)

Says I have to use a function “read” to read the flatbuffer, but i cant find that funcion. A similar function exists:

```julia
readbuffer(t::Array{UInt8,1}, pos::Int64, ::Type{T})

```

So, the question is: is there a example to read a flatbuffers buffer from a Array{UInt8, 1} or from a mmaped file?

EDIT: Sorry, the function read exists, but i don’t viewed it because autocomplete in Jupyter is not showing it, but if I test with Flatbuffers.read, there is a function read. But, when a pass a Array{UInt8, 1} to that function, the message showed is:

```
MethodError: no method matching read(::Array{UInt8,1})
Closest candidates are:
  read(!Matched::Base.DevNullStream, !Matched::Type{UInt8}) at coreio.jl:12
  read(!Matched::IOStream) at iostream.jl:481
  read(!Matched::IOStream, !Matched::Type{UInt8}) at iostream.jl:393

```

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<div class="post-metadata">

**Author:** ![quinnj](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/quinnj/32/11_2.png) [@quinnj](https://discourse.julialang.org/u/quinnj)\
**Post date:** [September 9, 2018, 9:32pm UTC](https://discourse.julialang.org/t/reading-flatbuffer-from-mmaped-file/14739/2 "2018-09-09T21:32:26Z")

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flatbuffers are build according to a specific “schema”, so if you know the schema type of the flatbuffer, file, the answer here is to call `FlatBuffers(FlatBufferType, bytes)`.

On a related note, there is the [Arrow.jl](https://github.com/ExpandingMan/Arrow.jl) repo that supports reading the in-memory arrow format (though I dont’ believe it quite handles all the IPC formats yet). In any case, that would probably be a good package to reference since it’s doing a similar thing to what you’re after for the in-memory structure.