Portability | tested on GHC only |
---|---|
Stability | experimental |
Maintainer | Simon Meier <iridcode@gmail.com> |
Safe Haskell | Safe-Infered |
Blaze.ByteString.Builder is the main module, which you should import as a user
of the blaze-builder
library.
import Blaze.ByteString.Builder
It provides you with a type Builder
that allows to efficiently construct
lazy bytestrings with a large average chunk size.
Intuitively, a Builder
denotes the construction of a part of a lazy
bytestring. Builders can either be created using one of the primitive
combinators in Blaze.ByteString.Builder.Write or by using one of the predefined
combinators for standard Haskell values (see the exposed modules of this
package). Concatenation of builders is done using mappend
from the
Monoid
typeclass.
Here is a small example that serializes a list of strings using the UTF-8 encoding.
import Blaze.ByteString.Builder.Char.Utf8
strings :: [String] strings = replicate 10000 "Hello there!"
The function
creates a fromString
Builder
denoting the UTF-8 encoded
argument. Hence, UTF-8 encoding and concatenating all strings
can be done
follows.
concatenation :: Builder concatenation = mconcat $ map fromString strings
The function toLazyByteString
can be used to execute a Builder
and
obtain the resulting lazy bytestring.
result :: L.ByteString result = toLazyByteString concatenation
The result
is a lazy bytestring containing 10000 repetitions of the string
"Hello there!"
encoded using UTF-8. The corresponding 120000 bytes are
distributed among three chunks of 32kb and a last chunk of 6kb.
A note on history. This serialization library was inspired by the
Data.Binary.Builder
module provided by the binary
package. It was
originally developed with the specific needs of the blaze-html
package in
mind. Since then it has been restructured to serve as a drop-in replacement
for Data.Binary.Builder
, which it improves upon both in speed as well as
expressivity.
- data Builder
- module Blaze.ByteString.Builder.Int
- module Blaze.ByteString.Builder.Word
- module Blaze.ByteString.Builder.ByteString
- flush :: Builder
- toLazyByteString :: Builder -> ByteString
- toLazyByteStringWith :: Int -> Int -> Int -> Builder -> ByteString -> ByteString
- toByteString :: Builder -> ByteString
- toByteStringIO :: (ByteString -> IO ()) -> Builder -> IO ()
- toByteStringIOWith :: Int -> (ByteString -> IO ()) -> Builder -> IO ()
- data Write
- fromWrite :: Write -> Builder
- fromWriteSingleton :: (a -> Write) -> a -> Builder
- fromWriteList :: (a -> Write) -> [a] -> Builder
- writeStorable :: Storable a => a -> Write
- fromStorable :: Storable a => a -> Builder
- fromStorables :: Storable a => [a] -> Builder
The Builder
type
Creating builders
module Blaze.ByteString.Builder.Int
Output all data written in the current buffer and start a new chunk.
The use of 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.
Executing builders
toLazyByteString :: Builder -> ByteStringSource
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
is a toLazyByteString
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.
:: Int | Buffer size (upper-bounds the resulting chunk size). |
-> Int | Minimal free buffer space for continuing filling
the same buffer after a |
-> 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 -> ByteStringSource
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
is a toByteString
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 ()Source
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
:: Int | Buffer size (upper bounds
the number of bytes forced
per call to the |
-> (ByteString -> IO ()) |
|
-> Builder |
|
-> IO () | Resulting |
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.
Write
s
A write of a bounded number of bytes.
When defining a function write :: a -> Write
for some a
, then it is
important to ensure that the bound on the number of bytes written is
data-independent. Formally,
forall x y. getBound (write x) = getBound (write y)
The idea is that this data-independent bound is specified such that the compiler can optimize the check, if there are enough free bytes in the buffer, to a single subtraction between the pointer to the next free byte and the pointer to the end of the buffer with this constant bound of the maximal number of bytes to be written.
fromWriteSingleton :: (a -> Write) -> a -> BuilderSource
fromWriteList :: (a -> Write) -> [a] -> BuilderSource
Construct a Builder
writing a list of data one element at a time.
Writing Storable
s
writeStorable :: Storable a => a -> WriteSource
Write a storable value.
fromStorable :: Storable a => a -> BuilderSource
A builder that serializes a storable value. No alignment is done.
fromStorables :: Storable a => [a] -> BuilderSource
A builder that serializes a list of storable values by writing them consecutively. No alignment is done. Parsing information needs to be provided externally.