## LTN12

The `ltn12` namespace implements the ideas described in LTN012, Filters sources and sinks. This manual simply describes the functions. Please refer to the LTN for a deeper explanation of the functionality provided by this module.

To obtain the `ltn12` namespace, run:

    -- loads the LTN21 module
    local ltn12 = require("ltn12")

### Filters

ltn12.filter.chain(filter1, filter2 [, ... filterN])

Returns a filter that passes all data it receives through each of a series of given filters.

`Filter1` to `filterN` are simple filters.

The function returns the chained filter.

The nesting of filters can be arbitrary. For instance, the useless filter below doesn't do anything but return the data that was passed to it, unaltered.

    -- load required modules
    local ltn12 = require("ltn12")
    local mime = require("mime")

    -- create a silly identity filter
    id = ltn12.filter.chain(
      mime.encode("quoted-printable"),
      mime.encode("base64"),
      mime.decode("base64"),
      mime.decode("quoted-printable")
    )

ltn12.filter.cycle(low [, ctx, extra])

Returns a high-level filter that cycles though a low-level filter by passing it each chunk and updating a context between calls.

`Low` is the low-level filter to be cycled, `ctx` is the initial context and `extra` is any extra argument the low-level filter might take.

The function returns the high-level filter.

    -- load the ltn12 module
    local ltn12 = require("ltn12")

    -- the base64 mime filter factory
    encodet['base64'] = function()
        return ltn12.filter.cycle(b64, "")
    end

### Pumps

ltn12.pump.all(source, sink)

Pumps all data from a `source` to a `sink`.

If successful, the function returns a value that evaluates to `true`. In case of error, the function returns a `false` value, followed by an error message.

ltn12.pump.step(source, sink)

Pumps one chunk of data from a `source` to a `sink`.

If successful, the function returns a value that evaluates to `true`. In case of error, the function returns a `false` value, followed by an error message.

### Sinks

ltn12.sink.chain(filter, sink)

Creates and returns a new sink that passes data through a `filter` before sending it to a given `sink`.

ltn12.sink.error(message)

Creates and returns a sink that aborts transmission with the error `message`.

ltn12.sink.file(handle, message)

Creates a sink that sends data to a file.

`Handle` is a file handle. If `handle` is `nil`, `message` should give the reason for failure.

The function returns a sink that sends all data to the given `handle` and closes the file when done, or a sink that aborts the transmission with the error `message`

In the following example, notice how the prototype is designed to fit nicely with the `io.open` function.

    -- load the ltn12 module
    local ltn12 = require("ltn12")

    -- copy a file
    ltn12.pump.all(
      ltn12.source.file(io.open("original.png")),
      ltn12.sink.file(io.open("copy.png"))
    )

ltn12.sink.null()

Returns a sink that ignores all data it receives.

ltn12.sink.simplify(sink)

Creates and returns a simple sink given a fancy `sink`.

ltn12.sink.table([table])

Creates a sink that stores all chunks in a table. The chunks can later be efficiently concatenated into a single string.

`Table` is used to hold the chunks. If `nil`, the function creates its own table.

The function returns the sink and the table used to store the chunks.

    -- load needed modules
    local http = require("socket.http")
    local ltn12 = require("ltn12")

    -- a simplified http.get function
    function http.get(u)
      local t = {}
      local respt = request{
        url = u,
        sink = ltn12.sink.table(t)
      }
      return table.concat(t), respt.headers, respt.code
    end

### Sources

ltn12.source.cat(source1 [, source2, ..., sourceN])

Creates a new source that produces the concatenation of the data produced by a number of sources.

`Source1` to `sourceN` are the original sources.

The function returns the new source.

ltn12.source.chain(source, filter)

Creates a new `source` that passes data through a `filter` before returning it.

The function returns the new source.

ltn12.source.empty()

Creates and returns an empty source.

ltn12.source.error(message)

Creates and returns a source that aborts transmission with the error `message`.

ltn12.source.file(handle, message)

Creates a source that produces the contents of a file.

`Handle` is a file handle. If `handle` is `nil`, `message` should give the reason for failure.

The function returns a source that reads chunks of data from given `handle` and returns it to the user, closing the file when done, or a source that aborts the transmission with the error `message`

In the following example, notice how the prototype is designed to fit nicely with the `io.open` function.

    -- load the ltn12 module
    local ltn12 = require("ltn12")

    -- copy a file
    ltn12.pump.all(
      ltn12.source.file(io.open("original.png")),
      ltn12.sink.file(io.open("copy.png"))
    )

ltn12.source.simplify(source)

Creates and returns a simple source given a fancy `source`.

ltn12.source.string(string)

Creates and returns a source that produces the contents of a `string`, chunk by chunk.