Blaze.ByteString.Builder.Internal

blaze-builder-0.2.1.4: Efficient buffered output.

Portability | tested on GHC only
Stability | experimental
Maintainer | Simon Meier <iridcode@gmail.com>
Safe Haskell | None

Blaze.ByteString.Builder.Internal

Contents

- Build Steps
- Builder
- Put
- Writes
- Execution
- Deafult Sizes

Description

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

Synopsis

- data BufRange = BufRange !(Ptr Word8) !(Ptr Word8)
- data BuildSignal a
- data BuildStep a
- done :: Ptr Word8 -> a -> BuildSignal a
- bufferFull :: Int -> Ptr Word8 -> (BufRange -> IO (BuildSignal a)) -> BuildSignal a
- insertByteString :: Ptr Word8 -> ByteString -> (BufRange -> IO (BuildSignal a)) -> BuildSignal a
- data Builder
- fromBuildStepCont :: (forall r. (BufRange -> IO (BuildSignal r)) -> BufRange -> IO (BuildSignal r)) -> Builder
- fromPut :: Put a -> Builder
- flush :: Builder
- data Put a
- putBuilder :: Builder -> Put ()
- putBuildStepCont :: (forall r. (a -> BufRange -> IO (BuildSignal r)) -> BufRange -> IO (BuildSignal r)) -> Put a
- module Blaze.ByteString.Builder.Internal.Write
- toLazyByteString :: Builder -> ByteString
- toLazyByteStringWith :: Int -> Int -> Int -> Builder -> ByteString -> ByteString
- toByteString :: Builder -> ByteString
- toByteStringIO :: (ByteString -> IO ()) -> Builder -> IO ()
- toByteStringIOWith :: Int -> (ByteString -> IO ()) -> Builder -> IO ()
- defaultFirstBufferSize :: Int
- defaultMinimalBufferSize :: Int
- defaultBufferSize :: Int
- defaultMaximalCopySize :: Int

# Build Steps

data BufRange

Constructors

BufRange !(Ptr Word8) !(Ptr Word8) |

data BuildSignal a

data BuildStep a

done :: Ptr Word8 -> a -> BuildSignal a

bufferFull :: Int -> Ptr Word8 -> (BufRange -> IO (BuildSignal a)) -> BuildSignal a

insertByteString :: Ptr Word8 -> ByteString -> (BufRange -> IO (BuildSignal a)) -> BuildSignal a

# Builder

data Builder

Instances

Monoid Builder |

fromBuildStepCont :: (forall r. (BufRange -> IO (BuildSignal r)) -> BufRange -> IO (BuildSignal r)) -> Builder

fromPut :: Put a -> Builder

Ignore the value of a put and only exploit its output side effect.

flush :: Builder

Output all data written in the current buffer and start a new chunk.

The use uf this function depends on how the resulting bytestrings are consumed. `flush` is possibly not very useful in non-interactive scenarios. However, it is kept for compatibility with the builder provided by Data.Binary.Builder.

When using `toLazyByteString` to extract a lazy `ByteString` from a `Builder`, this means that a new chunk will be started in the resulting lazy `ByteString`. The remaining part of the buffer is spilled, if the reamining free space is smaller than the minimal desired buffer size.

# Put

data Put a

Instances

Monad Put |
Functor Put |

putBuilder :: Builder -> Put ()

Put the given builder.

putBuildStepCont :: (forall r. (a -> BufRange -> IO (BuildSignal r)) -> BufRange -> IO (BuildSignal r)) -> Put a

# Writes

module Blaze.ByteString.Builder.Internal.Write

# Execution

toLazyByteString :: Builder -> ByteString

Extract the lazy `ByteString` from the builder by running it with default buffer sizes. Use this function, if you do not have any special considerations with respect to buffer sizes.

     toLazyByteString b = toLazyByteStringWith defaultBufferSize defaultMinimalBufferSize defaultFirstBufferSize b L.empty

Note that ``toLazyByteString`` is a `Monoid` homomorphism.

     toLazyByteString mempty          == mempty
     toLazyByteString (x `mappend` y) == toLazyByteString x `mappend` toLazyByteString y

However, in the second equation, the left-hand-side is generally faster to execute.

toLazyByteStringWith

Arguments

:: Int | Buffer size (upper-bounds the resulting chunk size).
-> Int | Minimal free buffer space for continuing filling the same buffer after a `flush` or a direct bytestring insertion. This corresponds to the minimal desired chunk size.
-> Int | Size of the first buffer to be used and copied for larger resulting sequences
-> Builder | Builder to run.
-> ByteString | Lazy bytestring to output after the builder is finished.
-> ByteString | Resulting lazy bytestring

Run a `Builder` with the given buffer sizes.

Use this function for integrating the `Builder` type with other libraries that generate lazy bytestrings.

Note that the builders should guarantee that on average the desired chunk size is attained. Builders may decide to start a new buffer and not completely fill the existing buffer, if this is faster. However, they should not spill too much of the buffer, if they cannot compensate for it.

A call `toLazyByteStringWith bufSize minBufSize firstBufSize` will generate a lazy bytestring according to the following strategy. First, we allocate a buffer of size `firstBufSize` and start filling it. If it overflows, we allocate a buffer of size `minBufSize` and copy the first buffer to it in order to avoid generating a too small chunk. Finally, every next buffer will be of size `bufSize`. This, slow startup strategy is required to achieve good speed for short (<200 bytes) resulting bytestrings, as for them the allocation cost is of a large buffer cannot be compensated. Moreover, this strategy also allows us to avoid spilling too much memory for short resulting bytestrings.

Note that setting `firstBufSize >= minBufSize` implies that the first buffer is no longer copied but allocated and filled directly. Hence, setting `firstBufSize = bufSize` means that all chunks will use an underlying buffer of size `bufSize`. This is recommended, if you know that you always output more than `minBufSize` bytes.

toByteString :: Builder -> ByteString

Run the builder to construct a strict bytestring containing the sequence of bytes denoted by the builder. This is done by first serializing to a lazy bytestring and then packing its chunks to a appropriately sized strict bytestring.

     toByteString = packChunks . toLazyByteString

Note that ``toByteString`` is a `Monoid` homomorphism.

     toByteString mempty          == mempty
     toByteString (x `mappend` y) == toByteString x `mappend` toByteString y

However, in the second equation, the left-hand-side is generally faster to execute.

toByteStringIO :: (ByteString -> IO ()) -> Builder -> IO ()

Run the builder with a `defaultBufferSize`d buffer and execute the given `IO` action whenever the buffer is full or gets flushed.

     toByteStringIO = toByteStringIOWith defaultBufferSize

This is a `Monoid` homomorphism in the following sense.

     toByteStringIO io mempty          == return ()
     toByteStringIO io (x `mappend` y) == toByteStringIO io x >> toByteStringIO io y

toByteStringIOWith

Arguments

:: Int | Buffer size (upper bounds the number of bytes forced per call to the `IO` action).
-> (ByteString -> IO ()) | `IO` action to execute per full buffer, which is referenced by a strict `ByteString`.
-> Builder | `Builder` to run.
-> IO () | Resulting `IO` action.

`toByteStringIOWith bufSize io b` runs the builder `b` with a buffer of at least the size `bufSize` and executes the `IO` action `io` whenever the buffer is full.

Compared to `toLazyByteStringWith` this function requires less allocation, as the output buffer is only allocated once at the start of the serialization and whenever something bigger than the current buffer size has to be copied into the buffer, which should happen very seldomly for the default buffer size of 32kb. Hence, the pressure on the garbage collector is reduced, which can be an advantage when building long sequences of bytes.

# Deafult Sizes

defaultFirstBufferSize :: Int

The default length (64) for the first buffer to be allocated when converting a `Builder` to a lazy bytestring.

See `toLazyByteStringWith` for further explanation.

defaultMinimalBufferSize :: Int

The minimal length (~4kb) a buffer must have before filling it and outputting it as a chunk of the output stream.

This size determines when a buffer is spilled after a `flush` or a direct bytestring insertion. It is also the size of the first chunk generated by `toLazyByteString`.

defaultBufferSize :: Int

Default size (~32kb) for the buffer that becomes a chunk of the output stream once it is filled.

defaultMaximalCopySize :: Int

The maximal number of bytes for that copying is cheaper than direct insertion into the output stream. This takes into account the fragmentation that may occur in the output buffer due to the early `flush` implied by the direct bytestring insertion.

    defaultMaximalCopySize = 2 * defaultMinimalBufferSize