Code: Calculating MD5 from a file using Corona

MD5 is very useful to verify the consistency of file, specially after a file transfer. Below I show you how can you calculate the MD5 of file using Lua/Corona.

local function calculateMD5 (filename, systemDirectory)
    
    systemDirectory = systemDirectory or system.DocumentsDirectory -- using DocumentsDirectory as default if param not provided
    
    local crypto = require "crypto"

    local rfilePath = system.pathForFile( filename, systemDirectory  ) 
    if rfilePath == nil then  -- this can be nil when using ResourceDirectory. If using DocumentsDirectory or TemporaryDirectory, it will return "not nil" even if the file does not exist
        print("Error: file does not exist")   -- error
        return false
    end
        
    local rfh = io.open( rfilePath, "rb" )              
    if rfh == nil then
        print("Error: file does not exist")   -- error
        return false
    end
    
    local data = rfh:read( "*a" )
    if not data then
        print( "Error: read error!" )        
        return false
    end
    io.close( rfh )
    
    local hash = crypto.digest( crypto.md5, data )                
    
    return ( hash )   
        
end