|Copyright||(c) 2013 Leon P Smith|
|Maintainer||Leon P Smith <firstname.lastname@example.org>|
Blaze.ByteString.Builder is the main module, which you should import as a user
It provides you with a type
Builder that allows to efficiently construct
lazy bytestrings with a large average chunk size.
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
Here is a small example that serializes a list of strings using the UTF-8 encoding.
strings :: [String] strings = replicate 10000 "Hello there!"
Builder denoting the UTF-8 encoded
argument. Hence, UTF-8 encoding and concatenating all
strings can be done
concatenation :: Builder concatenation = mconcat $ map fromString strings
toLazyByteString can be used to execute a
obtain the resulting lazy bytestring.
result :: L.ByteString result = toLazyByteString concatenation
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
Data.Binary.Builder, which it improves upon both in speed as well as
- 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
- writeToByteString :: Write -> ByteString
- writeStorable :: Storable a => a -> Write
- fromStorable :: Storable a => a -> Builder
- fromStorables :: Storable a => [a] -> Builder
data Builder :: *
Buffer size (upper-bounds the resulting chunk size).
This parameter is ignored as of blaze-builder-0.4
Size of the first buffer to be used and copied for larger resulting sequences
Builder to run.
Lazy bytestring to output after the builder is finished.
Resulting lazy bytestring
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.
FIXME: Note that the following paragraphs are not entirely correct as of blaze-builder-0.4:
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
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
bufSize. This is recommended, if you know that you always output
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
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.
toByteStringIOWith bufSize io b runs the builder
b with a buffer of
at least the size
bufSize and executes the
io whenever the
buffer is full.
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.
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
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.
Builder writing a list of data one element at a time.
A builder that serializes a storable value. No alignment is done.