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: 14 Dec 2017

README

Cstruct -- access C-like structures directly from OCaml

v3.2.1

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 jbuilder, using make or jbuilder build directly. Since everything is built via jbuilder, you can also place this repository within a wider jbuilder 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. jbuilder >= "1.0+beta10"
  3. ocaml >= "4.03.0"

Dev Dependencies (1)

  1. ounit 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. conduit >= "0.6.0" & < "0.15.2"
  26. conduit-async = "3.0.0"
  27. conduit-lwt = "3.0.0"
  28. conduit-mirage != "3.0.0"
  29. conex < "0.10.0"
  30. conex-mirage-crypto
  31. conex-nocrypto
  32. cowabloga >= "0.0.5"
  33. crc
  34. crunch >= "2.0.0" & < "3.0.0"
  35. cstruct-async >= "3.2.0" & != "3.4.0" & < "4.0.0"
  36. cstruct-lwt >= "3.1.0" & != "3.4.0" & < "4.0.0"
  37. cstruct-unix >= "3.1.0" & != "3.4.0" & < "4.0.0"
  38. datakit
  39. datakit-ci >= "0.10.0" & < "0.12.4"
  40. datakit-client
  41. datakit-client-9p
  42. datakit-server
  43. depyt
  44. dns >= "0.20.0" & < "6.0.0"
  45. dns-forward >= "0.9.0"
  46. dnssd
  47. dream < "1.0.0~alpha2"
  48. duff < "0.3"
  49. eqaf >= "0.8"
  50. ethernet < "2.2.1"
  51. fat-filesystem >= "0.11.0" & < "0.15.1"
  52. frenetic < "2.0.0" | >= "3.2.0" & < "5.0.0"
  53. git >= "2.0.0" & < "3.0.0"
  54. git-http < "1.11.0"
  55. github-hooks >= "0.2.0"
  56. gluten-mirage < "0.3.0"
  57. gpt
  58. h2-mirage
  59. hacl-star >= "0.7.0"
  60. hex >= "0.2.0"
  61. hkdf
  62. hvsock < "3.0.0"
  63. io-page
  64. io-page-unix
  65. io-page-xen
  66. ipaddr-cstruct < "5.2.0"
  67. ipv6-multicast >= "0.9"
  68. irmin >= "0.9.0" & < "2.0.0"
  69. irmin-git >= "2.3.0"
  70. irmin-indexeddb >= "0.3"
  71. key-parsers >= "0.5.0" & < "1.2.1"
  72. launchd
  73. letsencrypt = "0.2.5"
  74. letsencrypt-app < "0.4.0"
  75. macaddr-cstruct < "5.2.0"
  76. metrics-mirage
  77. mirage >= "0.7.2" & < "0.9.0" | >= "0.10.0" & < "2.4.0"
  78. mirage-block < "1.0.0"
  79. mirage-block-ccm < "1.1.0"
  80. mirage-block-combinators < "3.0.0"
  81. mirage-block-lwt
  82. mirage-block-ramdisk
  83. mirage-block-solo5 < "0.6.2"
  84. mirage-block-unix >= "2.0.0" & < "2.13.0"
  85. mirage-block-xen >= "1.4.0" & < "2.1.1"
  86. mirage-btrees
  87. mirage-channel-lwt
  88. mirage-clock-unix < "1.0.0"
  89. mirage-clock-xen < "1.0.0"
  90. mirage-conduit < "2.0.0" | >= "2.3.1"
  91. mirage-console-lwt
  92. mirage-console-solo5 >= "0.2.0"
  93. mirage-console-unix >= "2.2.1" & < "3.0.0"
  94. mirage-console-xen = "4.0.0"
  95. mirage-console-xen-backend >= "2.3.2" & < "2.3.4" | = "4.0.0"
  96. mirage-crypto < "0.10.4"
  97. mirage-crypto-pk < "0.10.4"
  98. mirage-crypto-rng < "0.7.0"
  99. mirage-dns != "2.6.0" & < "2.7.0"
  100. mirage-entropy < "0.5.0"
  101. mirage-entropy-xen < "0.3.0"
  102. mirage-flow < "1.2.0"
  103. mirage-flow-lwt
  104. mirage-flow-rawlink
  105. mirage-flow-unix < "2.0.0"
  106. mirage-fs >= "0.4.0" & < "1.0.0"
  107. mirage-fs-lwt
  108. mirage-fs-mem
  109. mirage-fs-unix
  110. mirage-kv-lwt
  111. mirage-kv-unix
  112. mirage-nat < "2.2.4"
  113. mirage-net = "0.5.2"
  114. mirage-net-fd
  115. mirage-net-lwt
  116. mirage-net-macosx
  117. mirage-net-solo5
  118. mirage-net-unix < "2.1.0" | >= "2.2.1"
  119. mirage-net-xen != "1.4.2" & < "2.1.0"
  120. mirage-profile >= "0.8.2"
  121. mirage-protocols-lwt
  122. mirage-qubes != "0.2" & < "0.9.2"
  123. mirage-qubes-ipv4 < "0.9.3"
  124. mirage-random < "2.0.0"
  125. mirage-random-stdlib
  126. mirage-random-test
  127. mirage-solo5
  128. mirage-stack-lwt
  129. mirage-tc
  130. mirage-tcpip-unix
  131. mirage-tcpip-xen
  132. mirage-types-lwt < "3.7.1"
  133. mirage-unix < "0.9.4" | >= "2.5.0" & < "3.0.8"
  134. mirage-vnetif < "0.6.0"
  135. mirage-www < "0.4.0" | >= "1.1.0"
  136. mirage-xen < "2.0.0" | >= "2.6.0"
  137. monorobot
  138. mrt-format
  139. mstruct
  140. nbd >= "3.0.0" & < "6.0.0"
  141. netchannel < "2.1.0"
  142. nocrypto < "0.4.0" | >= "0.5.4"
  143. noise
  144. openflow < "0.2.0"
  145. otr >= "0.3.1" & < "0.3.9"
  146. ox < "1.1.1"
  147. pbkdf < "0.3.0" | = "1.1.0"
  148. pcap-format >= "0.4.0"
  149. ppx_cstruct = "3.2.1"
  150. protocol-9p < "0.5.1" | >= "0.10.0" & < "2.0.1"
  151. protocol-9p-tool = "0.12.0" | >= "2.0.0" & < "2.0.2"
  152. protocol-9p-unix < "2.0.2"
  153. qcow < "0.11.0"
  154. qcow-format >= "0.4.1"
  155. qcow-tool
  156. randomconv < "0.2.0"
  157. rawlink >= "0.6" & < "1.2"
  158. resp-mirage = "0.10.0"
  159. rfc6287 >= "1.0.2"
  160. salsa20 < "1.2.0"
  161. salsa20-core >= "0.3.0" & < "1.1.0"
  162. scrypt-kdf >= "0.2.0" & < "1.2.0"
  163. secp256k1-internal < "0.3.0"
  164. sendmail >= "0.4.1" & < "0.5.0"
  165. shared-block-ring < "3.0.1"
  166. shared-memory-ring >= "1.2.0" & < "3.1.1"
  167. shared-memory-ring-lwt
  168. slack
  169. ssh-agent
  170. tar < "2.0.0"
  171. tar-mirage
  172. tar-unix < "2.0.0"
  173. tcpip < "2.3.0" | >= "2.7.0" & < "6.3.0"
  174. tezos-lmdb
  175. tls >= "0.9.0" & < "0.10.2"
  176. u2f = "0.1.1"
  177. uecc
  178. vchan >= "2.1.0" & < "6.0.1"
  179. vchan-unix
  180. vchan-xen
  181. vhd-format >= "0.8.0"
  182. vhd-format-lwt
  183. vhd-tool < "0.12.0"
  184. vmnet >= "1.1.0"
  185. x509 < "0.6.3"
  186. xe
  187. xen-api-client >= "0.9.6" & < "0.9.14"
  188. xen-block-driver >= "0.2.5"
  189. xen-gnt
  190. xenstore >= "1.3.0"

Conflicts

None