Data.ByteString.Builder.Internal

bytestring-0.12.2.0: Fast, compact, strict and lazy byte strings with a list interface

Copyright | (c) 2010 - 2011 Simon Meier
License | BSD3-style (see LICENSE)
Maintainer | Simon Meier <iridcode@gmail.com>
Stability | unstable, private
Portability | GHC
Safe Haskell | Unsafe
Language | Haskell2010

Data.ByteString.Builder.Internal

Contents

- Buffer management
- Build signals and steps
- The Builder monoid
  - Primitive combinators
  - Execution
- The Put monad
  - Execution
  - Conversion to and from Builders

Description

- Warning:* this module is internal. If you find that you need it then please contact the maintainers and explain what you are trying to do and discuss what you would need in the public API. It is important that you do this as the module may not be exposed at all in future releases.

Core types and functions for the `Builder` monoid and its generalization, the `Put` monad.

The design of the `Builder` monoid is optimized such that

1. buffers of arbitrary size can be filled as efficiently as possible and
2. sequencing of `Builder`s is as cheap as possible.

We achieve (1) by completely handing over control over writing to the buffer to the `BuildStep` implementing the `Builder`. This `BuildStep` is just told the start and the end of the buffer (represented as a `BufferRange`). Then, the `BuildStep` can write to as big a prefix of this `BufferRange` in any way it desires. If the `BuildStep` is done, the `BufferRange` is full, or a long sequence of bytes should be inserted directly, then the `BuildStep` signals this to its caller using a `BuildSignal`.

We achieve (2) by requiring that every `Builder` is implemented by a `BuildStep` that takes a continuation `BuildStep`, which it calls with the updated `BufferRange` after it is done. Therefore, only two pointers have to be passed in a function call to implement concatenation of `Builder`s. Moreover, many `Builder`s are completely inlined, which enables the compiler to sequence them without a function call and with no boxing at all.

This design gives the implementation of a `Builder` full access to the `IO` monad. Therefore, utmost care has to be taken to not overwrite anything outside the given `BufferRange`s. Moreover, further care has to be taken to ensure that `Builder`s and `Put`s are referentially transparent. See the comments of the `builder` and `put` functions for further information. Note that there are no safety belts at all, when implementing a `Builder` using an `IO` action: you are writing code that might enable the next buffer-overflow attack on a Haskell server!

Synopsis

- data Buffer = Buffer !(ForeignPtr Word8) !BufferRange
- data BufferRange = BufferRange !(Ptr Word8) !(Ptr Word8)
- newBuffer :: Int -> IO Buffer
- bufferSize :: Buffer -> Int
- byteStringFromBuffer :: Buffer -> StrictByteString
- data ChunkIOStream a
  - = Finished Buffer a
  - | Yield1 StrictByteString (IO (ChunkIOStream a))
- buildStepToCIOS :: AllocationStrategy -> BuildStep a -> IO (ChunkIOStream a)
- ciosUnitToLazyByteString :: AllocationStrategy -> LazyByteString -> ChunkIOStream () -> LazyByteString
- ciosToLazyByteString :: AllocationStrategy -> (a -> (b, LazyByteString)) -> ChunkIOStream a -> (b, LazyByteString)
- data BuildSignal a
- type BuildStep a = BufferRange -> IO (BuildSignal a)
- finalBuildStep :: BuildStep ()
- done :: Ptr Word8 -> a -> BuildSignal a
- bufferFull :: Int -> Ptr Word8 -> BuildStep a -> BuildSignal a
- insertChunk :: Ptr Word8 -> StrictByteString -> BuildStep a -> BuildSignal a
- fillWithBuildStep :: BuildStep a -> (Ptr Word8 -> a -> IO b) -> (Ptr Word8 -> Int -> BuildStep a -> IO b) -> (Ptr Word8 -> StrictByteString -> BuildStep a -> IO b) -> BufferRange -> IO b
- data Builder
- builder :: (forall r. BuildStep r -> BuildStep r) -> Builder
- runBuilder :: Builder -> BuildStep ()
- runBuilderWith :: Builder -> BuildStep a -> BuildStep a
- empty :: Builder
- append :: Builder -> Builder -> Builder
- flush :: Builder
- ensureFree :: Int -> Builder
- byteStringCopy :: StrictByteString -> Builder
- byteStringInsert :: StrictByteString -> Builder
- byteStringThreshold :: Int -> StrictByteString -> Builder
- lazyByteStringCopy :: LazyByteString -> Builder
- lazyByteStringInsert :: LazyByteString -> Builder
- lazyByteStringThreshold :: Int -> LazyByteString -> Builder
- shortByteString :: ShortByteString -> Builder
- maximalCopySize :: Int
- byteString :: StrictByteString -> Builder
- lazyByteString :: LazyByteString -> Builder
- toLazyByteString :: Builder -> LazyByteString
- toLazyByteStringWith :: AllocationStrategy -> LazyByteString -> Builder -> LazyByteString
- data AllocationStrategy
- safeStrategy :: Int -> Int -> AllocationStrategy
- untrimmedStrategy :: Int -> Int -> AllocationStrategy
- customStrategy :: (Maybe (Buffer, Int) -> IO Buffer) -> Int -> (Int -> Int -> Bool) -> AllocationStrategy
- smallChunkSize :: Int
- defaultChunkSize :: Int
- chunkOverhead :: Int
- data Put a
- put :: (forall r. (a -> BuildStep r) -> BuildStep r) -> Put a
- runPut :: Put a -> BuildStep a
- putToLazyByteString :: Put a -> (a, LazyByteString)
- putToLazyByteStringWith :: AllocationStrategy -> (a -> (b, LazyByteString)) -> Put a -> (b, LazyByteString)
- hPut :: Handle -> Put a -> IO a
- putBuilder :: Builder -> Put ()
- fromPut :: Put () -> Builder

# Buffer management

data Buffer Source #

A `Buffer` together with the `BufferRange` of free bytes. The filled space starts at offset 0 and ends at the first free byte.

Constructors

Buffer !(ForeignPtr Word8) !BufferRange |

#### Instances

Instances details

NFData Buffer Source # | Like the `NFData` instance for `StrictByteString`, this does not force the `ForeignPtrContents` field of the underlying `ForeignPtr`. Since: bytestring-0.12.2.0
Instance details Defined in Data.ByteString.Builder.Internal Methods rnf :: Buffer -> () Source #

data BufferRange Source #

A range of bytes in a buffer represented by the pointer to the first byte of the range and the pointer to the first byte after the range.

Constructors

BufferRange !(Ptr Word8) !(Ptr Word8) |

#### Instances

Instances details

NFData BufferRange Source # | Since: bytestring-0.12.2.0
Instance details Defined in Data.ByteString.Builder.Internal Methods rnf :: BufferRange -> () Source #

newBuffer :: Int -> IO Buffer Source #

Allocate a new buffer of the given size.

bufferSize :: Buffer -> Int Source #

Combined size of the filled and free space in the buffer.

byteStringFromBuffer :: Buffer -> StrictByteString Source #

Convert the filled part of a `Buffer` to a `StrictByteString`.

data ChunkIOStream a Source #

A stream of chunks that are constructed in the `IO` monad.

This datatype serves as the common interface for the buffer-by-buffer execution of a `BuildStep` by `buildStepToCIOS`. Typical users of this interface are `ciosToLazyByteString` or iteratee-style libraries like `enumerator`.

Constructors

Finished Buffer a | The partially filled last buffer together with the result.
Yield1 StrictByteString (IO (ChunkIOStream a)) | Yield a non-empty `StrictByteString`.

buildStepToCIOS Source #

Arguments

:: AllocationStrategy | Buffer allocation strategy to use
-> BuildStep a | `BuildStep` to execute
-> IO (ChunkIOStream a) |

Convert a `BuildStep` to a `ChunkIOStream` stream by executing it on `Buffer`s allocated according to the given `AllocationStrategy`.

ciosUnitToLazyByteString :: AllocationStrategy -> LazyByteString -> ChunkIOStream () -> LazyByteString Source #

Convert a ``ChunkIOStream` ()` to a `LazyByteString` using `unsafeDupablePerformIO`.

ciosToLazyByteString :: AllocationStrategy -> (a -> (b, LazyByteString)) -> ChunkIOStream a -> (b, LazyByteString) Source #

Convert a `ChunkIOStream` to a lazy tuple of the result and the written `LazyByteString` using `unsafeDupablePerformIO`.

# Build signals and steps

data BuildSignal a Source #

`BuildSignal`s abstract signals to the caller of a `BuildStep`. There are three signals: `done`, `bufferFull`, or 'insertChunks signals

type BuildStep a = BufferRange -> IO (BuildSignal a) Source #

`BuildStep`s may be called *multiple times* and they must not rise an async. exception.

finalBuildStep :: BuildStep () Source #

The final build step that returns the `done` signal.

done Source #

Arguments

:: Ptr Word8 | Next free byte in current `BufferRange`
-> a | Computed value
-> BuildSignal a |

Signal that the current `BuildStep` is done and has computed a value.

bufferFull Source #

Arguments

:: Int | Minimal size of next `BufferRange`.
-> Ptr Word8 | Next free byte in current `BufferRange`.
-> BuildStep a | `BuildStep` to run on the next `BufferRange`. This `BuildStep` may assume that it is called with a `BufferRange` of at least the required minimal size; i.e., the caller of this `BuildStep` must guarantee this.
-> BuildSignal a |

Signal that the current buffer is full.

insertChunk Source #

Arguments

:: Ptr Word8 | Next free byte in current `BufferRange`
-> StrictByteString | Chunk to insert.
-> BuildStep a | `BuildStep` to run on next `BufferRange`
-> BuildSignal a |

Signal that a `StrictByteString` chunk should be inserted directly.

fillWithBuildStep Source #

Arguments

:: BuildStep a | Build step to use for filling the `BufferRange`.
-> (Ptr Word8 -> a -> IO b) | Handling the `done` signal
-> (Ptr Word8 -> Int -> BuildStep a -> IO b) | Handling the `bufferFull` signal
-> (Ptr Word8 -> StrictByteString -> BuildStep a -> IO b) | Handling the `insertChunk` signal
-> BufferRange | Buffer range to fill.
-> IO b | Value computed while filling this `BufferRange`.

Fill a `BufferRange` using a `BuildStep`.

# The Builder monoid

data Builder Source #

`Builder`s denote sequences of bytes. They are `Monoid`s where `mempty` is the zero-length sequence and `mappend` is concatenation, which runs in O(1).

#### Instances

Instances details

Monoid Builder Source # |
Instance details Defined in Data.ByteString.Builder.Internal Methods mempty :: Builder # mappend :: Builder -> Builder -> Builder # mconcat :: [Builder] -> Builder #
Semigroup Builder Source # |
Instance details Defined in Data.ByteString.Builder.Internal Methods (<>) :: Builder -> Builder -> Builder # sconcat :: NonEmpty Builder -> Builder # stimes :: Integral b => b -> Builder -> Builder #
IsString Builder Source # |
Instance details Defined in Data.ByteString.Builder Methods fromString :: String -> Builder #
IsList Builder Source # | For long or infinite lists use `fromList` because it uses `LazyByteString` otherwise use `fromListN` which uses `StrictByteString`.
Instance details Defined in Data.ByteString.Builder.Internal Associated Types
type Item Builder |
Instance details Defined in Data.ByteString.Builder.Internal type Item Builder = Word8
Methods fromList :: [Item Builder] -> Builder # fromListN :: Int -> [Item Builder] -> Builder # toList :: Builder -> [Item Builder] #
Show Builder Source # | Since: bytestring-0.11.1.0
Instance details Defined in Data.ByteString.Builder Methods showsPrec :: Int -> Builder -> ShowS # show :: Builder -> String # showList :: [Builder] -> ShowS #
type Item Builder Source # |
Instance details Defined in Data.ByteString.Builder.Internal type Item Builder = Word8

builder Source #

Arguments

:: (forall r. BuildStep r -> BuildStep r) | A function that fills a `BufferRange`, calls the continuation with the updated `BufferRange` once its done, and signals its caller how to proceed using `done`, `bufferFull`, or `insertChunk`. This function must be referentially transparent; i.e., calling it multiple times with equally sized `BufferRange`s must result in the same sequence of bytes being written. If you need mutable state, then you must allocate it anew upon each call of this function. Moreover, this function must call the continuation once its done. Otherwise, concatenation of `Builder`s does not work. Finally, this function must write to all bytes that it claims it has written. Otherwise, the resulting `Builder` is not guaranteed to be referentially transparent and sensitive data might leak.
-> Builder |

Construct a `Builder`. In contrast to `BuildStep`s, `Builder`s are referentially transparent.

runBuilder Source #

Arguments

:: Builder | `Builder` to run
-> BuildStep () | `BuildStep` that writes the byte stream of this `Builder` and signals `done` upon completion.

Run a `Builder` with the `finalBuildStep`.

runBuilderWith Source #

Arguments

:: Builder | `Builder` to run
-> BuildStep a | Continuation `BuildStep`
-> BuildStep a |

Run a `Builder`.

## Primitive combinators

empty :: Builder Source #

The `Builder` denoting a zero-length sequence of bytes. This function is only exported for use in rewriting rules. Use `mempty` otherwise.

append :: Builder -> Builder -> Builder Source #

Concatenate two `Builder`s. This function is only exported for use in rewriting rules. Use `mappend` otherwise.

flush :: Builder Source #

Flush the current buffer. This introduces a chunk boundary.

ensureFree :: Int -> Builder Source #

``ensureFree` n` ensures that there are at least `n` free bytes for the following `Builder`.

byteStringCopy :: StrictByteString -> Builder Source #

Construct a `Builder` that copies the `StrictByteString`.

Use this function to create `Builder`s from smallish (`<= 4kb`) `StrictByteString`s or if you need to guarantee that the `StrictByteString` is not shared with the chunks generated by the `Builder`.

byteStringInsert :: StrictByteString -> Builder Source #

Construct a `Builder` that always inserts the `StrictByteString` directly as a chunk.

This implies flushing the output buffer, even if it contains just a single byte. You should therefore use `byteStringInsert` only for large (`> 8kb`) `StrictByteString`s. Otherwise, the generated chunks are too fragmented to be processed efficiently afterwards.

byteStringThreshold :: Int -> StrictByteString -> Builder Source #

Construct a `Builder` that copies the `StrictByteString`s, if it is smaller than the treshold, and inserts it directly otherwise.

For example, `byteStringThreshold 1024` copies `StrictByteString`s whose size is less or equal to 1kb, and inserts them directly otherwise. This implies that the average chunk-size of the generated `LazyByteString` may be as low as 513 bytes, as there could always be just a single byte between the directly inserted 1025 byte, `StrictByteString`s.

lazyByteStringCopy :: LazyByteString -> Builder Source #

Construct a `Builder` that copies the `LazyByteString`.

lazyByteStringInsert :: LazyByteString -> Builder Source #

Construct a `Builder` that inserts all chunks of the `LazyByteString` directly.

lazyByteStringThreshold :: Int -> LazyByteString -> Builder Source #

Construct a `Builder` that uses the thresholding strategy of `byteStringThreshold` for each chunk of the `LazyByteString`.

shortByteString :: ShortByteString -> Builder Source #

Construct a `Builder` that copies the `ShortByteString`.

maximalCopySize :: Int Source #

The maximal size of a `StrictByteString` that is copied. `2 * `smallChunkSize`` to guarantee that on average a chunk is of `smallChunkSize`.

byteString :: StrictByteString -> Builder Source #

Create a `Builder` denoting the same sequence of bytes as a `StrictByteString`. The `Builder` inserts large `StrictByteString`s directly, but copies small ones to ensure that the generated chunks are large on average.

lazyByteString :: LazyByteString -> Builder Source #

Create a `Builder` denoting the same sequence of bytes as a lazy `LazyByteString`. The `Builder` inserts large chunks of the `LazyByteString` directly, but copies small ones to ensure that the generated chunks are large on average.

## Execution

toLazyByteString :: Builder -> LazyByteString Source #

Execute a `Builder` and return the generated chunks as a `LazyByteString`. The work is performed lazy, i.e., only when a chunk of the `LazyByteString` is forced.

toLazyByteStringWith Source #

Arguments

:: AllocationStrategy | Buffer allocation strategy to use
-> LazyByteString | `LazyByteString` to use as the tail of the generated lazy `LazyByteString`
-> Builder | `Builder` to execute
-> LazyByteString | Resulting `LazyByteString`

Heavy inlining. Execute a `Builder` with custom execution parameters.

This function is inlined despite its heavy code-size to allow fusing with the allocation strategy. For example, the default `Builder` execution function `toLazyByteString` is defined as follows.

    {-# NOINLINE toLazyByteString #-}
    toLazyByteString =
      toLazyByteStringWith (safeStrategy smallChunkSize defaultChunkSize) L.Empty

where `L.Empty` is the zero-length `LazyByteString`.

In most cases, the parameters used by `toLazyByteString` give good performance. A sub-performing case of `toLazyByteString` is executing short (<128 bytes) `Builder`s. In this case, the allocation overhead for the first 4kb buffer and the trimming cost dominate the cost of executing the `Builder`. You can avoid this problem using

    toLazyByteStringWith (safeStrategy 128 smallChunkSize) L.Empty

This reduces the allocation and trimming overhead, as all generated `LazyByteString`s fit into the first buffer and there is no trimming required, if more than 64 bytes and less than 128 bytes are written.

data AllocationStrategy Source #

A buffer allocation strategy for executing `Builder`s.

safeStrategy Source #

Arguments

:: Int | Size of first buffer
-> Int | Size of successive buffers
-> AllocationStrategy | An allocation strategy that guarantees that at least half of the allocated memory is used for live data

Use this strategy for generating `LazyByteString`s whose chunks are likely to survive one garbage collection. This strategy trims buffers that are filled less than half in order to avoid spilling too much memory.

untrimmedStrategy Source #

Arguments

:: Int | Size of the first buffer
-> Int | Size of successive buffers
-> AllocationStrategy | An allocation strategy that does not trim any of the filled buffers before converting it to a chunk

Use this strategy for generating `LazyByteString`s whose chunks are discarded right after they are generated. For example, if you just generate them to write them to a network socket.

customStrategy Source #

Arguments

:: (Maybe (Buffer, Int) -> IO Buffer) | Buffer allocation function. If `Nothing` is given, then a new first buffer should be allocated. If ``Just` (oldBuf, minSize)` is given, then a buffer with minimal size `minSize` must be returned. The strategy may reuse `oldBuf` only if `oldBuf` is large enough and the consumer can guarantee that this will not result in a violation of referential transparency. Warning: for multithreaded programs, it is generally unsafe to reuse buffers when using the consumers of `Builder` in this package. For example, if `toLazyByteStringWith` is called with an `AllocationStrategy` that reuses buffers, evaluating the result by multiple threads simultaneously may lead to corrupted output.
-> Int | Default buffer size.
-> (Int -> Int -> Bool) | A predicate `trim used allocated` returning `True`, if the buffer should be trimmed before it is returned.
-> AllocationStrategy |

Create a custom allocation strategy. See the code for `safeStrategy` and `untrimmedStrategy` for examples.

smallChunkSize :: Int Source #

The recommended chunk size. Currently set to 4k, less the memory management overhead

defaultChunkSize :: Int Source #

The chunk size used for I/O. Currently set to 32k, less the memory management overhead

chunkOverhead :: Int Source #

The memory management overhead. Currently this is tuned for GHC only.

# The Put monad

data Put a Source #

A `Put` action denotes a computation of a value that writes a stream of bytes as a side-effect. `Put`s are strict in their side-effect; i.e., the stream of bytes will always be written before the computed value is returned.

`Put`s are a generalization of `Builder`s. The typical use case is the implementation of an encoding that might fail (e.g., an interface to the zlib compression library or the conversion from Base64 encoded data to 8-bit data). For a `Builder`, the only way to handle and report such a failure is ignore it or call `error`. In contrast, `Put` actions are expressive enough to allow reporting and handling such a failure in a pure fashion.

``Put` ()` actions are isomorphic to `Builder`s. The functions `putBuilder` and `fromPut` convert between these two types. Where possible, you should use `Builder`s, as sequencing them is slightly cheaper than sequencing `Put`s because they do not carry around a computed value.

#### Instances

Instances details

Applicative Put Source # |
Instance details Defined in Data.ByteString.Builder.Internal Methods pure :: a -> Put a # (<*>) :: Put (a -> b) -> Put a -> Put b # liftA2 :: (a -> b -> c) -> Put a -> Put b -> Put c # (*>) :: Put a -> Put b -> Put b # (<*) :: Put a -> Put b -> Put a #
Functor Put Source # |
Instance details Defined in Data.ByteString.Builder.Internal Methods fmap :: (a -> b) -> Put a -> Put b # (<$) :: a -> Put b -> Put a #
Monad Put Source # |
Instance details Defined in Data.ByteString.Builder.Internal Methods (>>=) :: Put a -> (a -> Put b) -> Put b # (>>) :: Put a -> Put b -> Put b # return :: a -> Put a #

put Source #

Arguments

:: (forall r. (a -> BuildStep r) -> BuildStep r) | A function that fills a `BufferRange`, calls the continuation with the updated `BufferRange` and its computed value once its done, and signals its caller how to proceed using `done`, `bufferFull`, or `insertChunk` signals. This function must be referentially transparent; i.e., calling it multiple times with equally sized `BufferRange`s must result in the same sequence of bytes being written and the same value being computed. If you need mutable state, then you must allocate it anew upon each call of this function. Moreover, this function must call the continuation once its done. Otherwise, monadic sequencing of `Put`s does not work. Finally, this function must write to all bytes that it claims it has written. Otherwise, the resulting `Put` is not guaranteed to be referentially transparent and sensitive data might leak.
-> Put a |

Construct a `Put` action. In contrast to `BuildStep`s, `Put`s are referentially transparent in the sense that sequencing the same `Put` multiple times yields every time the same value with the same side-effect.

runPut Source #

Arguments

:: Put a | Put to run
-> BuildStep a | `BuildStep` that first writes the byte stream of this `Put` and then yields the computed value using the `done` signal.

Run a `Put`.

## Execution

putToLazyByteString Source #

Arguments

:: Put a | `Put` to execute
-> (a, LazyByteString) | Result and `LazyByteString` written as its side-effect

Execute a `Put` and return the computed result and the bytes written during the computation as a `LazyByteString`.

This function is strict in the computed result and lazy in the writing of the bytes. For example, given

    infinitePut = sequence_ (repeat (putBuilder (word8 1))) >> return 0

evaluating the expression

    fst $ putToLazyByteString infinitePut

does not terminate, while evaluating the expression

    L.head $ snd $ putToLazyByteString infinitePut

does terminate and yields the value `1 :: Word8`.

An illustrative example for these strictness properties is the implementation of Base64 decoding (http://en.wikipedia.org/wiki/Base64).

    type DecodingState = ...

    decodeBase64 :: StrictByteString -> DecodingState -> Put (Maybe DecodingState)
    decodeBase64 = ...

The above function takes a `StrictByteString` supposed to represent Base64 encoded data and the current decoding state. It writes the decoded bytes as the side-effect of the `Put` and returns the new decoding state, if the decoding of all data in the `StrictByteString` was successful. The checking if the `StrictByteString` represents Base64 encoded data and the actual decoding are fused. This makes the common case, where all data represents Base64 encoded data, more efficient. It also implies that all data must be decoded before the final decoding state can be returned. `Put`s are intended for implementing such fused checking and decoding/encoding, which is reflected in their strictness properties.

putToLazyByteStringWith Source #

Arguments

:: AllocationStrategy | Buffer allocation strategy to use
-> (a -> (b, LazyByteString)) | Continuation to use for computing the final result and the tail of its side-effect (the written bytes).
-> Put a | `Put` to execute
-> (b, LazyByteString) | Resulting `LazyByteString`

Execute a `Put` with a buffer-allocation strategy and a continuation. For example, `putToLazyByteString` is implemented as follows.

    putToLazyByteString = putToLazyByteStringWith
        (safeStrategy smallChunkSize defaultChunkSize) (x -> (x, L.empty))

hPut :: Handle -> Put a -> IO a Source #

Run a `Put` action redirecting the produced output to a `Handle`.

The output is buffered using the `Handle`s associated buffer. If this buffer is too small to execute one step of the `Put` action, then it is replaced with a large enough buffer.

## Conversion to and from Builders

putBuilder :: Builder -> Put () Source #

Run a `Builder` as a side-effect of a ``Put` ()` action.

fromPut :: Put () -> Builder Source #

Convert a ``Put` ()` action to a `Builder`.