h2

A high-performance, memory-efficient, and scalable HTTP/2 library for for OCaml
Library h2
type t
type error = [
| `Malformed_response of string
| `Invalid_response_body_length of Response.t
| `Protocol_error
| `Exn of exn
]
type response_handler = Response.t -> [ `read ] Body.t -> unit
type error_handler = error -> unit
val create : ?config:Config.t -> ?push_handler:( Request.t -> ( response_handler, unit ) result ) -> error_handler:error_handler -> t

create ?config ?push_handler ~error_handler creates a connection that can be used to interact with servers over the HTTP/2 protocol.

error_handler will be called for connection-level errors. HTTP/2 is multiplexed over a single TCP connection and distinguishes connection-level errors from stream-level errors. See See RFC7540§5.4 for more details.

If present, push_handler will be called upon the receipt of PUSH_PROMISE frames with the request promised by the server. This function should return Ok response_handler if the client wishes to accept the pushed request. In this case, response_handler will be called once the server respondes to the pushed request. Returning Error () will signal to h2 that the client is choosing to reject the request that the server is pushing, and its stream will be closed, as per the following excerpt from the HTTP/2 specification:

From RFC7540§6.6: Recipients of PUSH_PROMISE frames can choose to reject promised streams by returning a RST_STREAM referencing the promised stream identifier back to the sender of the PUSH_PROMISE.

val request : t -> Request.t -> error_handler:error_handler -> response_handler:response_handler -> [ `write ] Body.t

request connection req ~error_handler ~response_handler opens a new HTTP/2 stream with req and returns a request body that can be written to. Once a response arrives, response_handler will be called with its headers and body. error_handler will be called for stream-level errors.

HTTP/2 is multiplexed over a single TCP connection and distinguishes connection-level errors from stream-level errors. See RFC7540§5.4 for more details.

val ping : t -> ?payload:Bigstringaf.t -> ?off:int -> ( unit -> unit ) -> unit

ping connection ?payload ?off f sends an HTTP/2 PING frame and registers f to be called when the server has sent an acknowledgement for it. A custom payload (and offset into that payload) for the PING frame may also be provided. If not, a payload with all bytes set to zero will be used. Note that a PING frame's payload must be 8 octets in length.

In HTTP/2, the PING frame is a mechanism for measuring a minimal round-trip time from the sender, as well as determining whether an idle connection is still functional. See RFC7540§5.4 for more details.

val shutdown : t -> unit

shutdown connection initiates the graceful shutdown of connection, and sends an HTTP/2 GOAWAY frame with NO_ERROR on the output channel (See RFC7540§6.8 for more details).

val next_read_operation : t -> [ `Read | `Close ]

next_read_operation t returns a value describing the next operation that the caller should conduct on behalf of the connection.

val read : t -> Bigstringaf.t -> off:int -> len:int -> int

read t bigstring ~off ~len reads bytes of input from the provided range of bigstring and returns the number of bytes consumed by the connection. read should be called after next_read_operation returns a `Read value and additional input is available for the connection to consume.

val read_eof : t -> Bigstringaf.t -> off:int -> len:int -> int

read t bigstring ~off ~len reads bytes of input from the provided range of bigstring and returns the number of bytes consumed by the connection. read should be called after next_read_operation returns a `Read and an EOF has been received from the communication channel. The connection will attempt to consume any buffered input and then shutdown the HTTP parser for the connection.

val next_write_operation : t -> [ `Write of Bigstringaf.t IOVec.t list | `Yield | `Close of int ]

next_write_operation t returns a value describing the next operation that the caller should conduct on behalf of the connection.

val report_write_result : t -> [ `Ok of int | `Closed ] -> unit

report_write_result t result reports the result of the latest write attempt to the connection. report_write_result should be called after a call to next_write_operation that returns a `Write buffer value.

  • `Ok n indicates that the caller successfully wrote n bytes of output from the buffer that the caller was provided by next_write_operation.
  • `Closed indicates that the output destination will no longer accept bytes from the write processor.
val yield_writer : t -> ( unit -> unit ) -> unit

yield_writer t continue registers with the connection to call continue when writing should resume. yield_writer should be called after next_write_operation returns a `Yield value.

val report_exn : t -> exn -> unit

report_exn t exn reports that an error exn has been caught and that it has been attributed to t. Calling this function will switch t into an error state. Depending on the state t is transitioning from, it may call its (connection-level) error handler before terminating the connection.

val is_closed : t -> bool

is_closed t is true if both the read and write processors have been shutdown. When this is the case next_read_operation will return `Close _ and next_write_operation will do the same will return a `Write _ until all buffered output has been flushed, at which point it will return `Close.