io - Reading whole files in Lua

Question

I am trying to read a full mp3 file in order to read out the id3 tags. That's when I noticed that file:read("*a") apparently does not read the full file but rather a small part. So I tried to build some kind of workaround in order to get the content of the whole file:

function readAll(file)
    local f = io.open(file, "r")
    local content = ""
    local length = 0

    while f:read(0) ~= "" do
        local current = f:read("*all")

        print(#current, length)
        length = length + #current

        content = content .. current
    end

    return content
end

for my testfile, this shows that 256 reading operations are performed, reading a total of ~113kB (the whole file is ~7MB). Though this should be enough to read most id3 tags, I wonder why Lua behaves in this way (especially because it does not when reading large textbased files such as *.obj or *.ase). Is there any explanation for this behaviour or maybe a solution to reliably read the whole file?

Answer 1

I must be missing something but I fail to see why a loop is needed. This should work (but you'd better add error handling in case the file cannot be opened):

function readAll(file)
    local f = assert(io.open(file, "rb"))
    local content = f:read("*all")
    f:close()
    return content
end