Added algorithm to read header

Project.toml

@@ -3,6 +3,9 @@ uuid = "5099a4e5-7ef4-45c0-baf4-116637be075d"
 authors = ["Jake Windle"]
 version = "1.0.0-DEV"
 
+[deps]
+BitConverter = "3a3ce9e8-98e7-11e9-0fa0-055639f146d3"
+
 [compat]
 julia = "1"
 

src/header.jl

@@ -1,13 +1,51 @@
 struct FITHeader
     sz::UInt8
+using Base: sizeof_ios_t
+    protocol::UInt8
+    version::AbstractVector{<:Real}
+    size::Real
+    type::AbstractVector{<:Real}
+    crc::AbstractVector{<:Real}
 end
 
+"""
+    length in bytes
+"""
+const DATA_SIZE_LENGTH = 4
+
 """
     read_header(fit_file::IOStream)
 
 Read the header of the given fit file, and return a FITHeader struct
 """
 function read_header(fit_file::IOStream)::FITHeader
-    sz = read(fit_file, 1; all=false)
+    sz = read(fit_file, 1; all=false)[1]
-    FITHeader(sz[1])
+    protocol = read(fit_file, 1; all=false)[1]
+    version = read(fit_file, 2; all=false)
+    size = read_data_size!(read(fit_file, 4; all=false))
+    type = read(fit_file, 4; all=false)
+    crc = read(fit_file, 2; all=false)
+
+    FITHeader(sz, protocol, version, size, type, crc)
+end
+
+"""
+    read_data_size(size::Vector{UInt8})::Real
+
+FIT headers have a data size field, with 4 bytes.
+"""
+function read_data_size!(size::Vector{UInt8})::Real
+    data_size::Int64 = 0
+    size = Int64.(size)
+
+    for i ∈ 0:length(size) - 1
+        data_size += size[1 + i] << (8 * i)
+    end
+    data_size
+end
+
+function test_read_header()
+    open("test.FIT", "r") do f
+        read_header(f)
+    end
 end