package cstruct

  1. Overview
  2. Docs

Description

Cstruct is a library and syntax extension to make it easier to access C-like structures directly from OCaml. It supports both reading and writing to these structures, and they are accessed via the Bigarray module.

Tags

org:mirage org:ocamllabs

Published: 23 Jan 2019

README

Cstruct -- access C-like structures directly from OCaml

v3.3.0

Cstruct is a library and syntax extension to make it easier to access C-like structures directly from OCaml. It supports both reading and writing to these structures, and they are accessed via the Bigarray module.

Installation

This repository provides several packages that can be installed via the OPAM package manager:

  • cstruct: the core Cstruct library

  • cstruct-async: provide Async Pipe and Bigstring support

  • cstruct-lwt: provide Lwt variants of read/write functions

  • ppx_cstruct: a PPX syntax extension (see below)

The libraries depend on OCaml version 4.02.3 and later, since it provides a ppx extension point. The old camlp4 syntax extension is nolonger available; the last version which contained it was v1.9.0.

Local development

You can build the library via dune, using make or dune build directly. Since everything is built via dune, you can also place this repository within a wider dune workspace in order to make local modifications across repositories.

Usage

PPX

The PPX processor is used by passing the OCaml source code through the ppx_cstruct binary. An example pcap description is:

[%%cstruct
type pcap_header = {
  magic_number: uint32_t;   (* magic number *)
  version_major: uint16_t;  (* major version number *)
  version_minor: uint16_t;  (* minor version number *)
  thiszone: uint32_t;       (* GMT to local correction *)
  sigfigs: uint32_t;        (* accuracy of timestamps *)
  snaplen: uint32_t;        (* max length of captured packets, in octets *)
  network: uint32_t;        (* data link type *)
} [@@little_endian]]

[%%cstruct
type pcap_packet = {
  ts_sec: uint32_t;         (* timestamp seconds *)
  ts_usec: uint32_t;        (* timestamp microseconds *)
  incl_len: uint32_t;       (* number of octets of packet saved in file *)
  orig_len: uint32_t;       (* actual length of packet *)
} [@@little_endian]]

[%%cstruct
type ethernet = {
  dst: uint8_t [@len 6];
  src: uint8_t [@len 6];
  ethertype: uint16_t;
} [@@big_endian]]

[%%cstruct
type ipv4 = {
  hlen_version: uint8_t;
  tos: uint8_t;
  len: uint16_t;
  id: uint16_t;
  off: uint16_t;
  ttl: uint8_t;
  proto: uint8_t;
  csum: uint16_t;
  src: uint8_t [@len 4];
  dst: uint8_t [@len 4];
} [@@big_endian]]

This auto-generates generates functions of the form below in the ml file:

let sizeof_pcap_packet = 16
let get_pcap_packet_ts_sec v = Cstruct.LE.get_uint32 v 0
let set_pcap_packet_ts_sec v x = Cstruct.LE.set_uint32 v 0 x
let get_pcap_packet_ts_usec v = Cstruct.LE.get_uint32 v 4
let set_pcap_packet_ts_usec v x = Cstruct.LE.set_uint32 v 4 x
let get_pcap_packet_incl_len v = Cstruct.LE.get_uint32 v 8
let set_pcap_packet_incl_len v x = Cstruct.LE.set_uint32 v 8 x
let get_pcap_packet_orig_len v = Cstruct.LE.get_uint32 v 12
let set_pcap_packet_orig_len v x = Cstruct.LE.set_uint32 v 12 x

let sizeof_ethernet = 14
let get_ethernet_dst src = Cstruct.sub src 0 6
let copy_ethernet_dst src = Cstruct.copy src 0 6
let set_ethernet_dst src srcoff dst =
  Cstruct.blit_from_string src srcoff dst 0 6
let blit_ethernet_dst src srcoff dst = Cstruct.blit src srcoff dst 0 6
let get_ethernet_src src = Cstruct.sub src 6 6
let copy_ethernet_src src = Cstruct.copy src 6 6
let set_ethernet_src src srcoff dst =
  Cstruct.blit_from_string src srcoff dst 6 6
let blit_ethernet_src src srcoff dst = Cstruct.blit src srcoff dst 6 6
let get_ethernet_ethertype v = Cstruct.BE.get_uint16 v 12
let set_ethernet_ethertype v x = Cstruct.BE.set_uint16 v 12 x

The mli file will have signatures of this form:

val sizeof_pcap_packet : int
val get_pcap_packet_ts_sec : Cstruct.t -> Cstruct.uint32
val set_pcap_packet_ts_sec : Cstruct.t -> Cstruct.uint32 -> unit
val get_pcap_packet_ts_usec : Cstruct.t -> Cstruct.uint32
val set_pcap_packet_ts_usec : Cstruct.t -> Cstruct.uint32 -> unit
val get_pcap_packet_incl_len : Cstruct.t -> Cstruct.uint32
val set_pcap_packet_incl_len : Cstruct.t -> Cstruct.uint32 -> unit
val get_pcap_packet_orig_len : Cstruct.t -> Cstruct.uint32
val set_pcap_packet_orig_len : Cstruct.t -> Cstruct.uint32 -> unit
val hexdump_pcap_packet_to_buffer : Buffer.t -> pcap_packet -> unit
val hexdump_pcap_packet : Cstruct.t -> unit

val sizeof_ethernet : int
val get_ethernet_dst : Cstruct.t -> Cstruct.t
val copy_ethernet_dst : Cstruct.t -> string
val set_ethernet_dst : string -> int -> Cstruct.t -> unit
val blit_ethernet_dst : Cstruct.t -> int -> Cstruct.t -> unit
val get_ethernet_src : Cstruct.t -> Cstruct.t
val copy_ethernet_src : Cstruct.t -> string
val set_ethernet_src : string -> int -> Cstruct.t -> unit
val blit_ethernet_src : Cstruct.t -> int -> Cstruct.t -> unit
val get_ethernet_ethertype : Cstruct.t -> Cstruct.uint16
val set_ethernet_ethertype : Cstruct.t -> Cstruct.uint16 -> unit
val hexdump_ethernet_to_buffer : Buffer.t -> Cstruct.t -> unit
val hexdump_ethernet : Cstruct.t -> unit

The hexdump functions above are convenient pretty-printing functions to help you debug, and aren't intended to be high performance.

You can also declare C-like enums:

[%%cenum
type foo32 =
  | ONE32
  | TWO32 [@id 0xfffffffel]
  | THREE32
  [@@uint32_t]
]

[%%cenum
type bar16 =
  | ONE [@id 1]
  | TWO
  | FOUR [@id 4]
  | FIVE
  [@@uint16_t]
]

This generates signatures of the form:

type foo32 = | ONE32 | TWO32 | THREE32
val int_to_foo32 : int32 -> foo32 option
val foo32_to_int : foo32 -> int32
val foo32_to_string : foo32 -> string
val string_to_foo32 : string -> foo32 option
type bar16 = | ONE | TWO | FOUR | FIVE
val int_to_bar16 : int -> bar16 option
val bar16_to_int : bar16 -> int
val bar16_to_string : bar16 -> string
val string_to_bar16 : string -> bar16 option

You can also add a (sexp) decorator to output s-expression convertors for use with the sexplib library.

[%%cenum
type foo64 =
  | ONE64
  | TWO64
  | THREE64
  [@@uint64_t] [@@sexp]
]

And sexp_of_foo64 and foo64_of_sexp functions will also be available. The representation of the Sexp is the string representation of the enum.

Please see the ppx_test/ directory for more in-depth examples.

Dependencies (3)

  1. sexplib
  2. dune >= "1.0"
  3. ocaml >= "4.03.0"

Dev Dependencies (1)

  1. alcotest with-test

  1. albatross < "1.3.0"
  2. angstrom >= "0.2.0" & < "0.7.0"
  3. arakoon >= "1.8.6" & < "1.8.12"
  4. arp < "3.0.0"
  5. arp-mirage
  6. asn1-combinators >= "0.1.2" & != "0.2.0-1" & < "0.2.6"
  7. awa < "0.0.4"
  8. awa-lwt < "0.0.4"
  9. awa-mirage < "0.0.4"
  10. balancer
  11. bip32
  12. buffer-pool
  13. capnp-rpc-net >= "1.1" & < "1.2.1"
  14. certify >= "0.2"
  15. chacha < "1.1.0"
  16. channel
  17. charrua < "1.4.1"
  18. charrua-client < "1.4.1"
  19. charrua-client-lwt
  20. charrua-client-mirage < "0.12.0"
  21. charrua-core >= "0.8"
  22. charrua-server < "1.4.1"
  23. charrua-unix = "0.6"
  24. cohttp >= "0.9.7" & < "0.10.0"
  25. colombe < "0.2.0"
  26. conduit >= "0.6.0" & < "0.15.2"
  27. conduit-async = "3.0.0"
  28. conduit-lwt = "3.0.0"
  29. conduit-mirage != "3.0.0"
  30. conex < "0.10.0"
  31. conex-mirage-crypto
  32. conex-nocrypto
  33. cowabloga >= "0.0.5"
  34. crc
  35. crunch >= "2.0.0" & < "3.0.0"
  36. cstruct-async = "3.3.0" | >= "3.5.0" & < "4.0.0"
  37. cstruct-lwt >= "3.2.0" & != "3.4.0" & < "4.0.0"
  38. cstruct-unix >= "3.1.0" & != "3.4.0" & < "4.0.0"
  39. datakit
  40. datakit-ci >= "0.10.0" & < "0.12.4"
  41. datakit-client
  42. datakit-client-9p
  43. datakit-server
  44. depyt
  45. dns >= "0.20.0" & < "6.0.0"
  46. dns-forward >= "0.9.0"
  47. dnssd
  48. dream < "1.0.0~alpha2"
  49. duff < "0.3"
  50. eqaf >= "0.8"
  51. ethernet < "2.2.1"
  52. fat-filesystem >= "0.11.0" & < "0.15.1"
  53. frenetic < "2.0.0" | >= "3.2.0" & < "5.0.0"
  54. git >= "2.0.0" & < "3.0.0"
  55. git-http < "1.11.0"
  56. github-hooks >= "0.2.0"
  57. gluten-mirage < "0.3.0"
  58. gpt
  59. h2-mirage
  60. hacl-star >= "0.7.0"
  61. hex >= "0.2.0"
  62. hkdf
  63. hvsock < "3.0.0"
  64. io-page
  65. io-page-unix
  66. io-page-xen
  67. ipaddr-cstruct < "5.2.0"
  68. ipv6-multicast >= "0.9"
  69. irmin >= "0.9.0" & < "1.0.0" | >= "1.1.0" & < "2.0.0"
  70. irmin-git >= "2.3.0"
  71. irmin-indexeddb >= "0.3"
  72. key-parsers >= "0.5.0" & < "1.2.1"
  73. launchd
  74. learn-ocaml-client
  75. letsencrypt = "0.2.5"
  76. letsencrypt-app < "0.4.0"
  77. macaddr-cstruct < "5.2.0"
  78. metrics-mirage
  79. mirage >= "0.7.2" & < "0.9.0" | >= "0.10.0" & < "2.4.0"
  80. mirage-block < "1.0.0"
  81. mirage-block-ccm < "1.1.0"
  82. mirage-block-combinators < "3.0.0"
  83. mirage-block-lwt
  84. mirage-block-ramdisk
  85. mirage-block-solo5 < "0.6.2"
  86. mirage-block-unix >= "2.0.0" & < "2.13.0"
  87. mirage-block-xen >= "1.4.0" & < "2.1.1"
  88. mirage-btrees
  89. mirage-channel-lwt
  90. mirage-clock-unix < "1.0.0"
  91. mirage-clock-xen < "1.0.0"
  92. mirage-conduit < "2.0.0" | >= "2.3.1"
  93. mirage-console-lwt
  94. mirage-console-solo5 >= "0.2.0"
  95. mirage-console-unix >= "2.2.1" & < "3.0.0"
  96. mirage-console-xen = "4.0.0"
  97. mirage-console-xen-backend >= "2.3.2" & < "2.3.4" | = "4.0.0"
  98. mirage-crypto < "0.10.4"
  99. mirage-crypto-pk < "0.10.4"
  100. mirage-crypto-rng < "0.7.0"
  101. mirage-dns != "2.6.0" & < "2.7.0"
  102. mirage-entropy < "0.5.0"
  103. mirage-entropy-xen < "0.3.0"
  104. mirage-flow < "1.2.0"
  105. mirage-flow-lwt
  106. mirage-flow-rawlink
  107. mirage-flow-unix < "2.0.0"
  108. mirage-fs >= "0.4.0" & < "1.0.0"
  109. mirage-fs-lwt
  110. mirage-fs-mem
  111. mirage-fs-unix
  112. mirage-kv-lwt
  113. mirage-kv-unix
  114. mirage-nat < "2.2.4"
  115. mirage-net = "0.5.2"
  116. mirage-net-fd
  117. mirage-net-lwt
  118. mirage-net-macosx
  119. mirage-net-solo5
  120. mirage-net-unix < "2.1.0" | >= "2.2.1"
  121. mirage-net-xen != "1.4.2" & < "2.1.0"
  122. mirage-profile >= "0.8.2"
  123. mirage-protocols-lwt
  124. mirage-qubes != "0.2" & < "0.9.2"
  125. mirage-qubes-ipv4 < "0.9.3"
  126. mirage-random < "2.0.0"
  127. mirage-random-stdlib
  128. mirage-random-test
  129. mirage-solo5
  130. mirage-stack-lwt
  131. mirage-tc
  132. mirage-tcpip-unix
  133. mirage-tcpip-xen
  134. mirage-types-lwt < "3.7.1"
  135. mirage-unix < "0.9.4" | >= "2.5.0" & < "3.0.8"
  136. mirage-vnetif < "0.6.0"
  137. mirage-www < "0.4.0" | >= "1.1.0"
  138. mirage-xen < "2.0.0" | >= "2.6.0"
  139. monorobot
  140. mrt-format
  141. mstruct
  142. nbd >= "3.0.0" & < "6.0.0"
  143. netchannel < "2.1.0"
  144. nocrypto < "0.4.0" | >= "0.5.4"
  145. noise
  146. openflow < "0.2.0"
  147. otr >= "0.3.1" & < "0.3.9"
  148. ox < "1.1.1"
  149. pbkdf < "0.3.0" | = "1.1.0"
  150. pcap-format >= "0.4.0"
  151. pf-qubes
  152. ppx_cstruct = "3.3.0"
  153. protocol-9p < "0.5.1" | >= "0.10.0" & < "2.0.1"
  154. protocol-9p-tool = "0.12.0" | >= "2.0.0" & < "2.0.2"
  155. protocol-9p-unix < "2.0.2"
  156. qcow < "0.11.0"
  157. qcow-format >= "0.4.1"
  158. qcow-tool
  159. randomconv < "0.2.0"
  160. rawlink >= "0.6" & < "1.2"
  161. resp-mirage = "0.10.0"
  162. rfc6287 >= "1.0.2"
  163. salsa20 < "1.2.0"
  164. salsa20-core >= "0.3.0" & < "1.1.0"
  165. scrypt-kdf >= "0.2.0" & < "1.2.0"
  166. secp256k1-internal < "0.3.0"
  167. sendmail >= "0.4.1" & < "0.5.0"
  168. shared-block-ring < "3.0.1"
  169. shared-memory-ring >= "1.2.0" & < "3.1.1"
  170. shared-memory-ring-lwt
  171. slack
  172. ssh-agent
  173. tar < "2.0.0"
  174. tar-mirage
  175. tar-unix < "2.0.0"
  176. tcpip < "2.3.0" | >= "2.7.0" & < "6.3.0"
  177. tezos-lmdb
  178. tls >= "0.9.0" & < "0.10.2"
  179. u2f = "0.1.1"
  180. uecc
  181. vchan >= "2.1.0" & < "6.0.1"
  182. vchan-unix
  183. vchan-xen
  184. vhd-format >= "0.8.0"
  185. vhd-format-lwt
  186. vhd-tool < "0.12.0"
  187. vmnet >= "1.1.0"
  188. x509 < "0.6.3"
  189. xe
  190. xen-api-client >= "0.9.6" & < "0.9.14"
  191. xen-block-driver >= "0.2.5"
  192. xen-gnt
  193. xenstore >= "1.3.0" & < "2.3.0"

Conflicts

None

OCaml

Innovation. Community. Security.