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