Network.Wai.Enumerator

A collection of utility functions for dealing with Enumerators.

Utilities

mapE :: (ByteString -> ByteString) -> Enumerator -> Enumerator

Performs a specified conversion on each ByteString output by an enumerator.

Conversions

Lazy byte strings

toLBS :: Enumerator -> IO ByteString

This uses unsafeInterleaveIO to lazily read from an enumerator. All normal lazy I/O warnings apply. In addition, since it is based on toSource, please observe all precautions for that function.

fromLBS :: ByteString -> Enumerator

This function safely converts a lazy bytestring into an enumerator.

fromLBS' :: IO ByteString -> Enumerator

Same as fromLBS, but the lazy bytestring is in the IO monad. This allows you to lazily read a file into memory, perform some mapping on the data and convert it into an enumerator.

Source

toSource :: Enumerator -> IO Source

This function uses another thread to convert an Enumerator to a Source. In essence, this allows you to write code which "pulls" instead of code which is pushed to. While this can be a useful technique, some caveats apply:

• It will be more resource heavy than using the Enumerator directly.
• You *must* consume all input. If you do not, then the other thread will be deadlocked.

Handle

fromHandle :: Handle -> Enumerator

Read a chunk of data from the given Handle at a time. We use defaultChunkSize from the bytestring package to determine the largest chunk to take.

FilePath

fromFile :: FilePath -> Enumerator

A little wrapper around fromHandle which first opens a file for reading.

fromEitherFile :: Either FilePath Enumerator -> Enumerator

Since the response body is defined as an Either FilePath Enumerator, this function simply reduces the whole operator to an enumerator. This can be convenient for server implementations not optimizing file sending.