Bytesrw adapter for Eio
ocaml
codec
Merge branch 'main' of https://git.recoil.org/gazagnaire.org/ocaml-bytesrw-eio
# Conflicts:
# .ocamlformat
# README.md
# bytesrw-eio.opam
# dune-project
# test/dune
# test/test_bytesrw_eio.ml
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README.md
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README.md
···
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```ocaml
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(* Specify custom slice length for reading *)
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let reader = Bytesrw_eio.bytes_reader_of_flow ~slice_length:4096 flow in
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let reader flow = Bytesrw_eio.bytes_reader_of_flow ~slice_length:4096 flow
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(* Specify custom slice length for writing *)
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let writer = Bytesrw_eio.bytes_writer_of_flow ~slice_length:4096 flow in
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()
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let writer flow = Bytesrw_eio.bytes_writer_of_flow ~slice_length:4096 flow
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```
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For random-access file reading:
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```ocaml
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(* Read from a specific offset in a file *)
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let reader file = Bytesrw_eio.pread_reader ~offset:1024 file
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```
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## Installation
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Install with opam:
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```sh
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$ opam install bytesrw-eio
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```
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opam install bytesrw-eio
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If opam cannot find the package, it may not yet be released in the public
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`opam-repository`. Add the overlay repository, then install it:
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```sh
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$ opam repo add samoht https://tangled.org/gazagnaire.org/opam-overlay.git
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$ opam update
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$ opam install bytesrw-eio
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```
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## Documentation
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odig doc bytesrw-eio
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```
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## License
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## Licence
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ISC
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bytesrw-eio.opam
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bytesrw-eio.opam
···
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maintainer: ["Anil Madhavapeddy <anil@recoil.org>"]
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authors: ["Anil Madhavapeddy"]
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license: "ISC"
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tags: ["org:blacksun" "eio"]
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homepage: "https://tangled.org/anil.recoil.org/ocaml-bytesrw-eio"
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bug-reports: "https://tangled.org/anil.recoil.org/ocaml-bytesrw-eio/issues"
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depends: [
···
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"eio" {>= "1.0"}
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"odoc" {with-doc}
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"alcotest" {with-test & >= "1.7.0"}
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"mdx" {with-test}
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"eio_main" {with-test}
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]
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build: [
···
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]
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dev-repo: "git+https://tangled.org/anil.recoil.org/ocaml-bytesrw-eio"
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x-maintenance-intent: ["(latest)"]
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x-quality-test: "2026-04-15"
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bytesrw-eio.opam.template
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bytesrw-eio.opam.template
···
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x-quality-test: "2026-04-15"
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dune
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dune
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dune-project
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dune-project
···
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(lang dune 3.21)
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(using mdx 0.4)
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(name bytesrw-eio)
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(generate_opam_files true)
···
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(package
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(name bytesrw-eio)
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(synopsis "Bytesrw readers and writers for Eio")
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(tags (org:blacksun eio))
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(description "Provides Bytesrw.Bytes.Reader and Writer adapters for Eio Flows")
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(depends
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(ocaml (>= 5.0))
···
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(eio (>= 1.0))
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(odoc :with-doc)
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(alcotest (and :with-test (>= 1.7.0)))
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(mdx :with-test)
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(eio_main :with-test)))
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lib/bytesrw_eio.ml
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lib/bytesrw_eio.ml
···
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(*---------------------------------------------------------------------------
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Copyright (c) 2025 Anil Madhavapeddy <anil@recoil.org>. All rights reserved.
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SPDX-License-Identifier: ISC
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---------------------------------------------------------------------------*)
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(** Bytesrw adapters for Eio
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This module provides adapters to create {!Bytesrw.Bytes.Reader.t} and
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{!Bytesrw.Bytes.Writer.t} from Eio flows, mirroring the API of
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{!Bytesrw_unix} for Eio's effect-based I/O. *)
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open Bytesrw
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(** Create a [Bytes.Reader.t] from an Eio source flow.
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Reads directly from the flow without intermediate buffering.
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@param slice_length
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Maximum bytes per slice (default: 65536, which is
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{!Bytes.Slice.unix_io_buffer_size}) *)
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let bytes_reader_of_flow ?(slice_length = Bytes.Slice.unix_io_buffer_size)
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(flow : _ Eio.Flow.source) : Bytes.Reader.t =
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let buf_size = Bytes.Slice.check_length slice_length in
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let read () =
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let cstruct = Cstruct.create buf_size in
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match Eio.Flow.single_read flow cstruct with
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| 0 -> Bytes.Slice.eod
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| count ->
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let data_cs = Cstruct.sub cstruct 0 count in
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let buf = Cstruct.to_bytes data_cs in
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Bytes.Slice.make buf ~first:0 ~length:count
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| exception End_of_file -> Bytes.Slice.eod
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in
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Bytes.Reader.make ~slice_length read
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(** Create a [Bytes.Reader.t] from an Eio file at [offset].
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Uses pread for random-access reading without loading the whole file.
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@param slice_length Maximum bytes per slice (default: 65536).
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@param length Number of bytes to read (default: to end of file). *)
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let pread_reader ?(slice_length = Bytes.Slice.unix_io_buffer_size) ?length
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~offset (file : _ Eio.File.ro) : Bytes.Reader.t =
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let stat = Eio.File.stat file in
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let file_length = Optint.Int63.to_int stat.size in
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let total = match length with Some n -> n | None -> file_length - offset in
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let pos = ref 0 in
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let buf_size = Bytes.Slice.check_length slice_length in
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let buf = Bytes.create buf_size in
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let read () =
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if !pos >= total then Bytes.Slice.eod
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else
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let len = min buf_size (total - !pos) in
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let cs = Cstruct.create len in
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Eio.File.pread_exact file
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~file_offset:(Optint.Int63.of_int (offset + !pos))
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[ cs ];
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Cstruct.blit_to_bytes cs 0 buf 0 len;
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pos := !pos + len;
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Bytes.Slice.make buf ~first:0 ~length:len
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in
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Bytes.Reader.make ~slice_length read
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(** Create a [Bytes.Writer.t] from an Eio sink flow.
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Writes directly to the flow without intermediate buffering.
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@param slice_length
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Suggested slice length for upstream (default: 65536, which is
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{!Bytes.Slice.unix_io_buffer_size}) *)
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let bytes_writer_of_flow ?(slice_length = Bytes.Slice.unix_io_buffer_size)
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(flow : _ Eio.Flow.sink) : Bytes.Writer.t =
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let rec write slice =
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if Bytes.Slice.is_eod slice then ()
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else begin
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let bytes = Bytes.Slice.bytes slice in
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let first = Bytes.Slice.first slice in
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let length = Bytes.Slice.length slice in
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let cstruct = Cstruct.of_bytes ~off:first ~len:length bytes in
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match Eio.Flow.single_write flow [ cstruct ] with
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| count when count = length -> ()
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| count -> write (Option.get (Bytes.Slice.drop count slice))
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end
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in
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Bytes.Writer.make ~slice_length write
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lib/bytesrw_eio.mli
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lib/bytesrw_eio.mli
···
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(*---------------------------------------------------------------------------
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Copyright (c) 2025 Anil Madhavapeddy <anil@recoil.org>. All rights reserved.
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SPDX-License-Identifier: ISC
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---------------------------------------------------------------------------*)
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(** Bytesrw adapters for Eio
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This module provides adapters to create {!Bytesrw.Bytes.Reader.t} and
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{!Bytesrw.Bytes.Writer.t} from Eio flows, mirroring the API of
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[Bytesrw_unix] for Eio's effect-based I/O.
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Unlike the Buf_read/Buf_write wrappers, these adapters read and write
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directly to the flow, allowing bytesrw to handle its own buffering. *)
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(** {1 Readers} *)
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val bytes_reader_of_flow :
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?slice_length:int -> _ Eio.Flow.source -> Bytesrw.Bytes.Reader.t
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(** [bytes_reader_of_flow flow] creates a reader from an Eio source flow.
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Reads directly from the flow without intermediate buffering.
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@param slice_length Maximum bytes per slice (default: 65536). *)
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(** {1 Random-access readers} *)
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val pread_reader :
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?slice_length:int ->
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?length:int ->
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offset:int ->
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_ Eio.File.ro ->
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Bytesrw.Bytes.Reader.t
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(** [pread_reader ~offset file] creates a reader from [file] starting at
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[offset] bytes. Reads via pread on demand — does not load the file into
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memory.
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@param slice_length Maximum bytes per slice (default: 65536).
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@param length Number of bytes to read (default: to end of file). *)
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(** {1 Writers} *)
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val bytes_writer_of_flow :
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?slice_length:int -> _ Eio.Flow.sink -> Bytesrw.Bytes.Writer.t
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(** [bytes_writer_of_flow flow] creates a writer from an Eio sink flow.
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Writes directly to the flow without intermediate buffering.
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@param slice_length Suggested slice length for upstream (default: 65536). *)
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lib/dune
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lib/dune
+1
-1
test/dune
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test/dune
+1
test/test.ml
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test/test.ml
···
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let () = Alcotest.run "bytesrw_eio" [ Test_bytesrw_eio.suite ]
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test/test_bytesrw_eio.ml
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test/test_bytesrw_eio.ml
···
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Alcotest.(check string) "round-trip data matches" test_data read_data
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let () =
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Alcotest.run "Bytesrw_eio"
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let suite =
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( "bytesrw_eio",
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[
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( "reader",
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[
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Alcotest.test_case "basic read" `Quick test_reader_basic;
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Alcotest.test_case "custom slice length" `Quick
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test_reader_custom_slice_length;
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Alcotest.test_case "empty flow" `Quick test_reader_empty;
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Alcotest.test_case "multiple reads data isolation" `Quick
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test_reader_multiple_reads;
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] );
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( "writer",
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[
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Alcotest.test_case "basic write" `Quick test_writer_basic;
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Alcotest.test_case "custom slice length" `Quick
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test_writer_custom_slice_length;
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Alcotest.test_case "eod write" `Quick test_writer_eod;
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Alcotest.test_case "partial slice" `Quick test_writer_partial_slice;
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] );
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("integration", [ Alcotest.test_case "round-trip" `Quick test_roundtrip ]);
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]
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Alcotest.test_case "reader basic read" `Quick test_reader_basic;
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Alcotest.test_case "reader custom slice length" `Quick
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test_reader_custom_slice_length;
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Alcotest.test_case "reader empty flow" `Quick test_reader_empty;
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Alcotest.test_case "reader multiple reads data isolation" `Quick
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test_reader_multiple_reads;
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Alcotest.test_case "writer basic write" `Quick test_writer_basic;
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Alcotest.test_case "writer custom slice length" `Quick
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test_writer_custom_slice_length;
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Alcotest.test_case "writer eod write" `Quick test_writer_eod;
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Alcotest.test_case "writer partial slice" `Quick test_writer_partial_slice;
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Alcotest.test_case "round-trip" `Quick test_roundtrip;
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] )