Module Eio.Buf_write

The type of a serializer.

Raised when waiting for a flush to complete if the buffer is destroyed instead.

with_flow flow fn runs fn writer, where writer is a buffer that flushes to flow.

Concurrently with fn, it also runs a fiber that copies from writer to flow. If this fiber runs out of data to copy then it will suspend itself. Writing to writer will automatically schedule it to be resumed. This means that pending data is flushed automatically before the process sleeps.

When fn returns, writer is automatically closed and any remaining data is flushed before with_flow itself returns.

• parameter initial_size

  The initial size of the buffer used to collect writes. New buffers will be allocated as needed, with the same size. If the buffer is too small to contain a write, the size is increased.

string t ?off ?len str copies str into the serializer's internal buffer.

bytes t ?off ?len bytes copies bytes into the serializer's internal buffer. It is safe to modify bytes after this call returns.

cstruct t cs copies cs into the serializer's internal buffer. It is safe to modify cs after this call returns. For large cstructs, it may be more efficient to use schedule_cstruct.

printf t fmt ... formats the arguments according to the format string fmt.

It supports all formatting and pretty-printing features of the Format module. The formatter's internal buffer is flushed to t after the call, without flushing t itself. Explicit flushes (e.g. using @. or %!) perform a full (blocking) flush of t.

make_formatter t creates a new formatter that writes to t.

Flushing the formatter also flushes t itself.

write_gen t ~blit ~off ~len x copies x into the serializer's internal buffer using the provided blit operation. See Bigstring.blit for documentation of the arguments.

char t c copies c into the serializer's internal buffer.

uint8 t n copies the lower 8 bits of n into the serializer's internal buffer.

Big endian serializers

Little endian serializers

schedule_cstruct t cs schedules cs to be written. cs is not copied in this process, so cs should only be modified after t has been flushed.

free_bytes_in_buffer t returns the free space, in bytes, of the serializer's write buffer. If a write call has a length that exceeds this value, the serializer will allocate a new buffer that will replace the serializer's internal buffer for that and subsequent calls.

has_pending_output t is true if t's output queue is non-empty. It may be the case that t's queued output is being serviced by some other thread of control, but has not yet completed.

pending_bytes t is the size of the next write, in bytes, that t will surface to the caller via await_batch.

pause t causes t to stop surfacing writes to the user. This gives the serializer an opportunity to collect additional writes before sending them to the underlying device, which will increase the write batch size.

As one example, code may want to call this function if it's about to release the OCaml lock and perform a blocking system call, but would like to batch output across that system call.

Call unpause to resume writing later. Note that calling flush or close will automatically call unpause too.

unpause t resumes writing data after a previous call to pause.

flush t waits until all prior writes have been successfully completed. If t has no pending writes, flush returns immediately. If t is paused then it is unpaused first.

• raises Flush_aborted

  if abort is called before the data is written.

close t closes t. All subsequent write calls will raise, and any subsequent pause calls will be ignored. If the serializer has any pending writes, user code will have an opportunity to service them before receiving End_of_file. Flush callbacks will continue to be invoked while output is shifted out of t as needed.

is_closed t is true if close has been called on t and false otherwise. A closed t may still have pending output.

create ~sw len creates a serializer with a fixed-length internal buffer of length len. See the Buffered writes section for details about what happens when len is not large enough to support a write.

• parameter sw

  When the switch is finished, abort is called. If you don't pass a switch, you may want to call abort manually on error.

of_buffer ~sw buf creates a serializer, using buf as its internal buffer. The serializer takes ownership of buf until the serializer has been closed and flushed of all output.

abort t is like close followed by drain, except that any pending flush operations fail instead of completing successfully.

await_batch t returns a list of buffers that should be written. If no data is currently available, it waits until some is. After performing a write, call shift with the number of bytes written. You must accurately report the number of bytes written. Failure to do so will result in the same bytes being surfaced multiple times.

• raises End_of_file

  t is closed and there is nothing left to write.

shift t n removes the first n bytes in t's write queue. Any flush operations called within this span of the write queue will be scheduled to resume.

serialize t writev calls writev bufs each time t is ready to write. In the event that writev indicates a partial write, serialize will call Fiber.yield before continuing.

serialize_to_string t runs t, collecting the output into a string and returning it. serializie_to_string t immediately closes t.

serialize_to_cstruct t runs t, collecting the output into a cstruct and returning it. serialize_to_cstruct t immediately closes t.

drain t removes all pending writes from t, returning the number of bytes that were enqueued to be written and freeing any scheduled buffers in the process. Note that this does not close t itself, and does not return until t has been closed.