Streamly.FileSystem.Handle

>>> import qualified Streamly.FileSystem.Handle as Handle

Read and write byte streams and array streams to and from file handles (Handle).

The TextEncoding, NewLineMode, and Buffering options of the underlying GHC Handle are ignored by these APIs. Please use Streamly.Unicode.* modules for encoding and decoding a byte stream, use stream splitting operations in Streamly.Prelude to create a stream of lines or to split the input stream on any other type of boundaries.

To set the read or write start position use hSeek on the Handle, the before combinator may be used to do that on a streaming combinator. To restrict the length of read or write use the stream trimming operations like take.

Note that a Handle is inherently stateful, therefore, we cannot use these APIs from multiple threads without serialization; reading or writing in one thread would affect the file position for other threads.

For additional, experimental APIs take a look at Streamly.Internal.FileSystem.Handle module.

Singleton IO

Read or write a single buffer.

getChunk :: MonadIO m => Int -> Handle -> m (Array Word8)

Read a ByteArray consisting of one or more bytes from a file handle. If no data is available on the handle it blocks until at least one byte becomes available. If any data is available then it immediately returns that data without blocking. As a result of this behavior, it may read less than or equal to the size requested.

Since: 0.8.1

putChunk :: (MonadIO m, Storable a) => Handle -> Array a -> m ()

Write an Array to a file handle.

Since: 0.8.1

Streaming IO

Read or write a stream of data to or from a file or device sequentially.

Read requests to the IO device are performed in chunks limited to a maximum size of defaultChunkSize. Note that the size of the actual chunks in the resulting stream may be less than the defaultChunkSize but it can never exceed it. If the whole stream is not consumed, it is possible that we may have read slightly more from the IO device than what the consumer needed.

Unless specified otherwise in the API, writes are collected into chunks of defaultChunkSize before they are written to the IO device.

Reading

TextEncoding, NewLineMode, and Buffering options of the underlying handle are ignored. The read occurs from the current seek position of the file handle. The stream ends as soon as EOF is encountered.

read :: MonadIO m => Unfold m Handle Word8

Unfolds a file handle into a byte stream. IO requests to the device are performed in sizes of defaultChunkSize.

>>> read = Unfold.many Handle.readChunks Array.read

Since: 0.7.0

readWithBufferOf :: MonadIO m => Unfold m (Int, Handle) Word8

Unfolds the tuple (bufsize, handle) into a byte stream, read requests to the IO device are performed using buffers of bufsize.

>>> readWithBufferOf = Unfold.many Handle.readChunksWithBufferOf Array.read

Since: 0.7.0

readChunks :: MonadIO m => Unfold m Handle (Array Word8)

Unfolds a handle into a stream of Word8 arrays. Requests to the IO device are performed using a buffer of size defaultChunkSize. The size of arrays in the resulting stream are therefore less than or equal to defaultChunkSize.

>>> readChunks = Unfold.supplyFirst IO.defaultChunkSize Handle.readChunksWithBufferOf

Since: 0.7.0

readChunksWithBufferOf :: MonadIO m => Unfold m (Int, Handle) (Array Word8)

Unfold the tuple (bufsize, handle) into a stream of Word8 arrays. Read requests to the IO device are performed using a buffer of size bufsize. The size of an array in the resulting stream is always less than or equal to bufsize.

Since: 0.7.0

Writing

TextEncoding, NewLineMode, and Buffering options of the underlying handle are ignored. The write occurs from the current seek position of the file handle. The write behavior depends on the IOMode of the handle.

write :: MonadIO m => Handle -> Fold m Word8 ()

Write a byte stream to a file handle. Accumulates the input in chunks of up to defaultChunkSize before writing to the IO device.

>>> write = Handle.writeWithBufferOf IO.defaultChunkSize

Since: 0.7.0

writeWithBufferOf :: MonadIO m => Int -> Handle -> Fold m Word8 ()

writeWithBufferOf reqSize handle writes the input stream to handle. Bytes in the input stream are collected into a buffer until we have a chunk of reqSize and then written to the IO device.

>>> writeWithBufferOf n h = Fold.chunksOf n (Array.writeNUnsafe n) (Handle.writeChunks h)

Since: 0.7.0

writeChunks :: (MonadIO m, Storable a) => Handle -> Fold m (Array a) ()

Write a stream of arrays to a handle. Each array in the stream is written to the device as a separate IO request.

writeChunks h = Fold.drainBy (Handle.putChunk h)

Since: 0.7.0