Writing data from curl request using LibCURL

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LibCURL is a fairly low level library, so you will need to write your own handler function to receive and convert the data from the C format.

function curl_write_cb(curlbuf::Ptr{Cvoid}, s::Csize_t, n::Csize_t, p_ctxt::Ptr{Cvoid})::Csize_t
    sz = s * n
    data = Array{UInt8}(undef, sz)

    ccall(:memcpy, Ptr{Cvoid}, (Ptr{Cvoid}, Ptr{Cvoid}, UInt64), data, curlbuf, sz)

    if p_ctxt == C_NULL
        j_ctxt = nothing
    else
        j_ctxt = unsafe_pointer_to_objref(p_ctxt)
    end

    append!(j_ctxt, data)

    sz
end

curl = curl_easy_init()

curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, @cfunction(curl_write_cb, Csize_t, (Ptr{Cvoid}, Csize_t, Csize_t, Ptr{Cvoid})))

buffer = UInt8[]

curl_easy_setopt(curl, CURLOPT_WRITEDATA,  pointer_from_objref(buffer))

curl_easy_setopt(curl, CURLOPT_URL, url)

GC.@preserve buffer begin
    res = curl_easy_perform(curl)
end

# At this point buffer will contain all the data read from the network

To learn more, you’ll need to read the CURL API docs at libcurl - API

It is written for C as the LibCURL.jl library is a thin wrapper around the C library.