132 lines
3.7 KiB
Markdown
132 lines
3.7 KiB
Markdown
# pipe Module
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| Since | Origin / Contributor | Maintainer | Source |
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| :----- | :-------------------- | :---------- | :------ |
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| 2019-07-18 | [Terry Ellison](https://github.com/TerryE) | [Terry Ellison](https://github.com/TerryE) | [pipe.c](../../app/modules/pipe.c)|
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The pipe module provides a RAM-efficient means of passing character stream of records from one Lua
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task to another.
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## pipe.create()
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Create a pipe.
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#### Syntax
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`pobj = pipe.create([CB_function],[task_priority])`
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#### Parameters
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- `CB_function` optional reader callback which is called through the `node.task.post()` when the pipe is written to. If the CB returns a boolean, then the reposting action is forced: it is reposted if true and not if false. If the return is nil or omitted then the deault is to repost if a pipe write has occured since the last call.
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- `task_priority` See `ǹode.task.post()`
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#### Returns
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A pipe resource.
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## pobj:read()
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Read a record from a pipe object.
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Note that the recommended method of reading from a pipe is to use a reader function as described below.
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#### Syntax
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`pobj:read([size/end_char])`
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#### Parameters
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- `size/end_char`
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- If numeric then a string of `size` length will be returned from the pipe.
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- If a string then this is a single character delimiter, followed by an optional "+" flag. The delimiter is used as an end-of-record to split the character stream into separate records. If the flag "+" is specified then the delimiter is also returned at the end of the record, otherwise it is discarded.
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- If omitted, then this defaults to `"\n+"`
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Note that if the last record in the pipe is missing a delimiter or is too short, then it is still returned, emptying the pipe.
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#### Returns
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A string or `nil` if the pipe is empty
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#### Example
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```lua
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line = pobj:read('\n')
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line = pobj:read(50)
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```
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## pobj:reader()
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Returns a Lua **iterator** function for a pipe object. This is as described in the
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[Lua Language: For Statement](http://www.lua.org/manual/5.1/manual.html#2.4.5). \(Note that the
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`state` and `object` variables mentioned in 2.5.4 are optional and default to `nil`, so this
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conforms to the`for` iterator syntax and works in a for because it maintains the state and `pobj`
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internally as upvalues.
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An emptied pipe takes up minimal RAM resources (an empty Lua array), and just like any other array
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this is reclaimed if all variables referencing it go out of scope or are over-written. Note
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that any reader iterators that you have created also refer to the pipe as an upval, so you will
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need to discard these to descope the pipe array.
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#### Syntax
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`myFunc = pobj:reader([size/end_char])`
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#### Parameters
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- `size/end_char` as for `pobj:read()`
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#### Returns
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- `myFunc` iterator function
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#### Examples
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- used in `for` loop:
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```lua
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for rec in p:reader() do print(rec) end
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-- or
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fp = p:reader()
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-- ...
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for rec in fp do print(rec) end
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```
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- used in callback task:
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```Lua
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do
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local pipe_reader = p:reader(1400)
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local function flush(sk) -- Upvals flush, pipe_reader
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local next = pipe_reader()
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if next then
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sk:send(next, flush)
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else
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sk:on('sent') -- dereference to allow GC
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flush = nil
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end
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end
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flush()
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end
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```
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## pobj:unread()
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Write a string to the head of a pipe object. This can be used to back-out a previous read.
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#### Syntax
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`pobj:unread(s)`
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#### Parameters
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`s` Any input string. Note that with all Lua strings, these may contain all character values including "\0".
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#### Returns
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Nothing
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#### Example
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```Lua
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a=p:read()
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p:unread(a) -- restores pipe to state before the read
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```
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## pobj:write()
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Write a string to a pipe object.
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#### Syntax
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`pobj:write(s)`
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#### Parameters
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`s` Any input string. Note that with all Lua strings, these may contain all character values including "\0".
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#### Returns
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Nothing
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