106 lines
3.2 KiB
Lua
106 lines
3.2 KiB
Lua
-- primitive for reading files from a file system (or, later, network)
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-- returns an object or nil on error
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-- read lines from the object using .read() with args similar to file:read()
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-- read() will indicate end of file by returning nil.
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function start_reading(fs, filename)
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local infile = io.open(filename)
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if infile == nil then return nil end
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return {
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read = coroutine.wrap(function(format)
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while true do
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if format == nil then format = '*l' end
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format = coroutine.yield(infile:read(format))
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end
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end),
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}
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end
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-- fake file object with the same 'shape' as that returned by start_reading
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function fake_file_stream(s)
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local i = 1
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local max = string.len(s)
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return {
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read = function(format)
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if i > max then
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return nil
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end
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if type(format) == 'number' then
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local result = s:sub(i, i+format-1)
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i = i+format
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return result
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elseif format == '*a' then
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local result = s:sub(i)
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i = max+1
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return result
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elseif format == '*l' then
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local start = i
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while i <= max do
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if s:sub(i, i) == '\n' then
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break
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end
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i = i+1
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end
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local result = s:sub(start, i)
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i = i+1
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return result
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elseif format == '*n' then
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error('fake file streams: *n not yet supported')
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end
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end,
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}
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end
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function test_fake_file_system()
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local s = fake_file_stream('abcdefgh\nijk\nlmn')
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check_eq(s.read(1), 'a', 'fake_file_system: 1 char')
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check_eq(s.read(1), 'b', 'fake_file_system: 1 more char')
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check_eq(s.read(3), 'cde', 'fake_file_system: multiple chars')
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check_eq(s.read('*l'), 'fgh\n', 'fake_file_system: line')
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check_eq(s.read('*a'), 'ijk\nlmn', 'fake_file_system: all')
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end
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-- primitive for writing files to a file system (or, later, network)
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-- returns an object or nil on error
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-- write to the object using .write()
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-- indicate you're done writing by calling .close()
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-- file will not be externally visible until .close()
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function start_writing(fs, filename)
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if filename == nil then
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error('start_writing requires two arguments: a file-system (nil for real disk) and a filename')
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end
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local initial_filename = temporary_filename_in_same_volume(filename)
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local outfile = io.open(initial_filename, 'w')
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if outfile == nil then return nil end
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return {
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write = coroutine.wrap(function(x)
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while true do
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x = coroutine.yield(outfile:write(x))
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end
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end),
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close = function()
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outfile:close()
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os.rename(initial_filename, filename)
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end,
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}
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end
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function temporary_filename_in_same_volume(filename)
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-- opening in same directory will hopefully keep it on the same volume,
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-- so that a future rename works
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local i = 1
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while true do
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temporary_filename = 'teliva_tmp_'..filename..'_'..i
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if io.open(temporary_filename) == nil then
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-- file doesn't exist yet; create a placeholder and return it
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local handle = io.open(temporary_filename, 'w')
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if handle == nil then
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-- HERE: if an app doesn't have permissions, attempts to write to disk eventually get here
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error("this is unexpected; I can't create temporary files..")
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end
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handle:close()
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return temporary_filename
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end
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i = i+1
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end
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end
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