include module type of struct include Cstruct end
Base types
Type of a buffer. A cstruct is composed of an underlying buffer and position/length within this buffer.
byte v convert v to a single byte.
8-bit unsigned integer. The representation is currently an unboxed OCaml integer.
16-bit unsigned integer. The representation is currently an unboxed OCaml integer.
32-bit unsigned integer. The representation is currently a boxed OCaml int32.
64-bit unsigned integer. The representation is currently a boxed OCaml int64.
Creation and conversion
empty is the cstruct of length 0.
of_bigarray ~off ~len b is the cstruct contained in b starting at offset off (default 0) of length len (default Bigarray.Array1.dim b - off).
to_bigarray t converts a t into a buffer Bigarray, using the Bigarray slicing to allocate a fresh array that preserves sharing of the underlying buffer.
create len is a fresh cstruct of size len with an offset of 0, filled with zero bytes.
create_unsafe len is a cstruct of size len with an offset of 0.
Note that the returned cstruct will contain arbitrary data, likely including the contents of previously-deallocated cstructs.
Beware!
Forgetting to replace this data could cause your application to leak sensitive information.
Sourceval of_string : ?allocator:(int -> t) -> ?off:int -> ?len:int -> string -> t of_string ~allocator ~off ~len str is the cstruct representation of str slice located at offset off (default 0) and of length len (default String.length str - off), with the underlying buffer allocated by alloc. If allocator is not provided, create is used.
Sourceval of_bytes : ?allocator:(int -> t) -> ?off:int -> ?len:int -> bytes -> t of_bytes ~allocator byt is the cstruct representation of byt slice located at offset off (default 0) and of length len (default Bytes.length byt - off), with the underlying buffer allocated by alloc. If allocator is not provided, create is used.
Sourceval of_hex : ?off:int -> ?len:int -> string -> t of_hex ~off ~len str is the cstruct cs. Every pair of hex-encoded characters in str starting at offset off (default 0) of length len (default String.length str - off) are converted to one byte in cs. Whitespaces (space, newline, tab, carriage return) in str are skipped.
Comparison
equal t1 t2 is true iff t1 and t2 correspond to the same sequence of bytes.
compare t1 t2 gives an unspecified total ordering over t.
Getters and Setters
Convert a byte to an integer
Sourceval check_bounds : t -> int -> bool check_bounds cstr len is true if len is a non-negative integer and cstr.buffer's size is greater or equal than len false otherwise.
Sourceval check_alignment : t -> int -> bool check_alignment cstr alignment is true if the first byte stored within cstr is at a memory address where address mod alignment = 0, false otherwise. Typical uses are to check a buffer is aligned to a page or disk sector boundary.
Sourceval get_char : t -> int -> char get_char t off returns the character contained in the cstruct at offset off.
get_uint8 t off returns the byte contained in the cstruct at offset off.
Sourceval set_char : t -> int -> char -> unit set_char t off c sets the byte contained in the cstruct at offset off to character c.
set_uint8 t off c sets the byte contained in the cstruct at offset off to byte c.
sub cstr off len is { t with off = t.off + off; len }
Sourceval sub_copy : t -> int -> int -> t sub_copy cstr off len is a new copy of sub cstr off len, that does not share the underlying buffer of cstr.
shift cstr len is { cstr with off=t.off+len; len=t.len-len }
Sourceval copy : t -> int -> int -> string copy cstr off len is the string representation of the segment of t starting at off of size len. It is equivalent to Cstruct.to_string cstr ~off ~len.
Sourceval blit : t -> int -> t -> int -> int -> unit blit src srcoff dst dstoff len copies len characters from cstruct src, starting at index srcoff, to cstruct dst, starting at index dstoff. It works correctly even if src and dst are the same string, and the source and destination intervals overlap.
Sourceval blit_from_string : string -> int -> t -> int -> int -> unit blit_from_string src srcoff dst dstoff len copies len characters from string src, starting at index srcoff, to cstruct dst, starting at index dstoff.
Sourceval blit_from_bytes : bytes -> int -> t -> int -> int -> unit blit_from_bytes src srcoff dst dstoff len copies len characters from bytes src, starting at index srcoff, to cstruct dst, starting at index dstoff.
Sourceval blit_to_bytes : t -> int -> bytes -> int -> int -> unit blit_to_bytes src srcoff dst dstoff len copies len characters from cstruct src, starting at index srcoff, to the dst buffer, starting at index dstoff.
Sourceval memset : t -> int -> unit memset t x sets all the bytes of t to x land 0xff.
Sourceval split : ?start:int -> t -> int -> t * t split ~start cstr len is a tuple containing the cstruct extracted from cstr at offset start (default: 0) of length len as first element, and the rest of cstr as second element.
Sourceval to_string : ?off:int -> ?len:int -> t -> string to_string ~off ~len t will allocate a fresh OCaml string and copy the contents of the cstruct starting at offset off (default 0) of length len (default Cstruct.length t - off) into it, and return that string.
Sourceval to_hex_string : ?off:int -> ?len:int -> t -> string to_hex_string ~off ~len t is a fresh OCaml string containing the hex representation of sub t off len. It is therefore of length 2 * len. This string can be read back into a Cstruct using of_hex.
Sourceval to_bytes : ?off:int -> ?len:int -> t -> bytes to_bytes ~off ~len t will allocate a fresh OCaml bytes and copy the contents of the cstruct starting at offset off (default 0) of length len (default Cstruct.length t - off) into it, and return that bytes.
Debugging
When the going gets tough, the tough hexdump their cstructs and peer at it until the bug disappears. This will directly prettyprint the contents of the cstruct to the standard output.
hexdump_to_buffer buf c will append the pretty-printed hexdump of the cstruct c to the buffer buf.
hexdump_pp f c pretty-prints a hexdump of c to f.
debug t will print out the internal details of a cstruct such as its base offset and the length, and raise an assertion failure if invariants have been violated. Not intended for casual use.
List of buffers
lenv cstrs is the combined length of all cstructs in cstrs.
copyv cstrs is the string representation of the concatenation of all cstructs in cstrs.
Sourceval fillv : src:t list -> dst:t -> int * t list fillv ~src ~dst copies from src to dst until src is exhausted or dst is full. Returns the number of bytes copied and the remaining data from src, if any. This is useful if you want buffer data into fixed-sized chunks.
Sourceval shiftv : t list -> int -> t list shiftv ts n is ts without the first n bytes. It has the property that equal (concat (shiftv ts n)) (shift (concat ts) n). This operation is fairly fast, as it will share the tail of the list. The first item in the returned list is never an empty cstruct, so you'll get [] if and only if lenv ts = n.
Iterations
Sourcetype 'a iter = unit -> 'a option iter lenf of_cstr cstr is an iterator over cstr that returns elements of size lenf cstr and type of_cstr cstr.
Sourceval fold : ('b -> 'a -> 'b) -> 'a iter -> 'b -> 'b fold f iter acc is (f iterN accN ... (f iter acc)...).
append t1 t2 is the concatenation t1 || t2.
concat ts is the concatenation of all the ts. It is not guaranteed that * the result is a newly created t in the zero- and one-element cases.
rev t is t in reverse order. The return value is a freshly allocated cstruct, and the argument is not modified.
Helpers to parse.
Cstruct is used to manipulate payloads which can be formatted according an RFC or an user-defined format. In such context, this module provides utilities to be able to easily parse payloads.
Due to the type Cstruct.t, no copy are done when you use these utilities and you are able to extract your information without a big performance cost.
More precisely, each values returned by these utilities will be located into the minor-heap where the base buffer will never be copied or relocated.
For instance, to parse a Git tree object:
entry := perm ' ' name '\000' 20byte
tree := entry *
open Cstruct
let ( >>= ) = Option.bind
let rec hash_of_name ~name payload =
if is_empty payload then raise Not_found
else
cut ~sep:(v " ") payload >>= fun (_, payload) ->
cut ~sep:(v "\000") payload >>= fun (name', payload) ->
if name = name' then with_range ~len:20 payload
else hash_of_name ~name (shift payload 20)
A Cstruct defines a possibly empty subsequence of bytes in a base buffer (a Bigarray.Array1.t).
The positions of a buffer b of length l are the slits found before each byte and after the last byte of the buffer. They are labelled from left to right by increasing number in the range [0;l].
positions 0 1 2 3 4 l-1 l
+---+---+---+---+ +-----+
indices | 0 | 1 | 2 | 3 | ... | l-1 |
+---+---+---+---+ +-----+The ith byte index is between positions i and i+1.
Formally we define a subbuffer of b as being a subsequence of bytes defined by a off position and a len number. When len is 0 the subbuffer is empty. Note that for a given base buffer there are as many empty subbuffers as there are positions in the buffer.
Like in strings, we index the bytes of a subbuffer using zero-based indices.
get cs zidx is the byte of cs at its zero-based index zidx. It's an alias of get_char.
Sourceval get_byte : t -> int -> int get_byte cs zidx is Char.code (get cs zidx). It's an alias of get_uint8.
Sourceval string : ?off:int -> ?len:int -> string -> t string ~off ~len str is the subbuffer of str that starts at position off (defaults to 0) and stops at position off + len (defaults to String.length str). str is fully-replaced by an fresh allocated buffer.
buffer ~off ~len buffer is the sub-part of buffer that starts at position off (default to 0) and stops at position off + len (default to Bigarray.Array1.dim buffer). buffer is used as the base buffer of the returned value (no major-heap allocation are performed).
start_pos cs is cs's start position in the base buffer.
stop_pos cs is cs's stop position in the base buffer.
Returns the length of the current cstruct view. Note that this length is potentially smaller than the actual size of the underlying buffer, as the sub function can construct a smaller view.
Sourceval head : ?rev:bool -> t -> char option head cs is Some (get cs h) with h = 0 if rev = false (default) or h = length cs - 1 if rev = true. None is returned if cs is empty.
tail cs is cs without its first (rev is false, default) or last (rev is true) byte or cs is empty.
is_empty cs is length cs = 0.
Sourceval is_prefix : affix:t -> t -> bool is_prefix ~affix cs is true iff affix.[zidx] = cs.[zidx] for all indices zidx of affix.
Sourceval is_suffix : affix:t -> t -> bool is_suffix ~affix cs is true iff affix.[n - zidx] = cs.[m - zidx] for all indices zidx of affix with n = length affix - 1 and m = length cs - 1.
Sourceval is_infix : affix:t -> t -> bool is_infix ~affix cs is true iff there exists an index z in cs such that for all indices zidx of affix we have affix.[zidx] = cs.[z + zidx].
Sourceval for_all : (char -> bool) -> t -> bool for_all p cs is true iff for all indices zidx of cs, p cs.[zidx] = true.
Sourceval exists : (char -> bool) -> t -> bool exists p cs is true iff there exists an index zidx of cs with p cs.[zidx] = true.
start cs is the empty sub-part at the start position of cs.
stop cs is the empty sub-part at the stop position of cs.
Sourceval trim : ?drop:(char -> bool) -> t -> t trim ~drop cs is cs with prefix and suffix bytes satisfying drop in cs removed. drop defaults to function ' ' | '\r' .. '\t' -> true | _ -> false.
Sourceval span :
?rev:bool ->
?min:int ->
?max:int ->
?sat:(char -> bool) ->
t ->
t * t span ~rev ~min ~max ~sat cs is (l, r) where:
- if
rev is false (default), l is at least min and at most max consecutive sat satisfying initial bytes of cs or empty if there are no such bytes. r are the remaining bytes of cs. - if
rev is true, r is at least min and at most max consecutive sat satisfying final bytes of cs or empty if there are no such bytes. l are the remaining bytes of cs.
If max is unspecified the span is unlimited. If min is unspecified it defaults to 0. If min > max the condition can't be satisfied and the left or right span, depending on rev, is always empty. sat defaults to (fun _ -> true).
The invariant l ^ r = s holds.
For instance, the ABNF expression:
time := 1*10DIGIT
can be translated to:
let (time, _) = span ~min:1 ~max:10 is_digit cs in
Sourceval take : ?rev:bool -> ?min:int -> ?max:int -> ?sat:(char -> bool) -> t -> t take ~rev ~min ~max ~sat cs is the matching span of span without the remaining one. In other words:
(if rev then snd else fst) @@ span ~rev ~min ~max ~sat cs
Sourceval drop : ?rev:bool -> ?min:int -> ?max:int -> ?sat:(char -> bool) -> t -> t drop ~rev ~min ~max ~sat cs is the remaining span of span without the matching one. In other words:
(if rev then fst else snd) @@ span ~rev ~min ~max ~sat cs
Sourceval cut : ?rev:bool -> sep:t -> t -> (t * t) option cut ~sep cs is either the pair Some (l, r) of the two (possibly empty) sub-buffers of cs that are delimited by the first match of the non empty separator string sep or None if sep can't be matched in cs. Matching starts from the beginning of cs (rev is false, default) or the end (rev is true).
The invariant l ^ sep ^ r = s holds.
For instance, the ABNF expression:
field_name := *PRINT
field_value := *ASCII
field := field_name ":" field_value
can be translated to:
match cut ~sep:":" value with
| Some (field_name, field_value) -> ...
| None -> invalid_arg "invalid field"
Sourceval cuts : ?rev:bool -> ?empty:bool -> sep:t -> t -> t list cuts ~sep cs is the list of all sub-buffers of cs that are delimited by matches of the non empty separator sep. Empty sub-buffers are omitted in the list if empty is false (default to true).
Matching separators in cs starts from the beginning of cs (rev is false, default) or the end (rev is true). Once one is found, the separator is skipped and matching starts again, that is separator matches can't overlap. If there is no separator match in cs, the list [cs] is returned.
The following invariants hold:
concat ~sep (cuts ~empty:true ~sep cs) = cscuts ~empty:true ~sep cs <> []
For instance, the ABNF expression:
arg := *(ASCII / ",") ; any characters exclude ","
args := arg *("," arg)can be translated to:
let args = cuts ~sep:"," buffer in
Sourceval fields : ?empty:bool -> ?is_sep:(char -> bool) -> t -> t list fields ~empty ~is_sep cs is the list of (possibly empty) sub-buffers that are delimited by bytes for which is_sep is true. Empty sub-buffers are omitted in the list if empty is false (defaults to true). is_sep c if it's not define by the user is true iff c is an US-ASCII white space character, that is one of space ' ' (0x20), tab '\t' (0x09), newline '\n' (0x0a), vertical tab (0x0b), form feed (0x0c), carriage return '\r' (0x0d).
Sourceval find : ?rev:bool -> (char -> bool) -> t -> t option find ~rev sat cs is the sub-buffer of cs (if any) that spans the first byte that satisfies sat in cs after position start cs (rev is false, default) or before stop cs (rev is true). None is returned if there is no matching byte in s.
Sourceval find_sub : ?rev:bool -> sub:t -> t -> t option find_sub ~rev ~sub cs is the sub-buffer of cs (if any) that spans the first match of sub in cs after position start cs (rev is false, default) or before stop cs (rev is true). Only bytes are compared and sub can be on a different base buffer. None is returned if there is no match of sub in s.
Sourceval filter : (char -> bool) -> t -> t filter sat cs is the buffer made of the bytes of cs that satisfy sat, in the same order.
Sourceval filter_map : (char -> char option) -> t -> t filter_map f cs is the buffer made of the bytes of cs as mapped by f, in the same order.
Sourceval map : (char -> char) -> t -> t map f cs is cs' with cs'.[i] = f cs.[i] for all indices i of cs. f is invoked in increasing index order.
Sourceval mapi : (int -> char -> char) -> t -> t map f cs is cs' with cs'.[i] = f i cs.[i] for all indices i of cs. f is invoked in increasing index order.