1 (** Bitmatch library. *)
2 (* Copyright (C) 2008 Red Hat Inc., Richard W.M. Jones
4 * This library is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU Lesser General Public
6 * License as published by the Free Software Foundation; either
7 * version 2 of the License, or (at your option) any later version.
9 * This library is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * Lesser General Public License for more details.
14 * You should have received a copy of the GNU Lesser General Public
15 * License along with this library; if not, write to the Free Software
16 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
22 {{:#reference}Jump straight to the reference section for
23 documentation on types and functions}.
27 Bitmatch adds Erlang-style bitstrings and matching over bitstrings
28 as a syntax extension and library for OCaml. You can use
29 this module to both parse and generate binary formats, for
30 example, communications protocols, disk formats and binary files.
32 {{:http://code.google.com/p/bitmatch/}OCaml bitmatch website}
36 A function which can parse IPv4 packets:
43 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
44 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
45 | 4 | IHL |Type of Service| Total Length |
46 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
47 | Identification |Flags| Fragment Offset |
48 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
49 | Time to Live | Protocol | Header Checksum |
50 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
52 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
53 | Destination Address |
54 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
56 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
58 | { 4 : 4; hdrlen : 4; tos : 8; length : 16;
59 identification : 16; flags : 3; fragoffset : 13;
60 ttl : 8; protocol : 8; checksum : 16;
63 options : (hdrlen-5)*32 : bitstring;
64 payload : -1 : bitstring } ->
67 printf " header length: %d * 32 bit words\n" hdrlen;
68 printf " type of service: %d\n" tos;
69 printf " packet length: %d bytes\n" length;
70 printf " identification: %d\n" identification;
71 printf " flags: %d\n" flags;
72 printf " fragment offset: %d\n" fragoffset;
73 printf " ttl: %d\n" ttl;
74 printf " protocol: %d\n" protocol;
75 printf " checksum: %d\n" checksum;
76 printf " source: %lx dest: %lx\n" source dest;
77 printf " header options + padding:\n";
78 Bitmatch.hexdump_bitstring stdout options;
79 printf " packet payload:\n";
80 Bitmatch.hexdump_bitstring stdout payload
83 eprintf "unknown IP version %d\n" version;
87 eprintf "data is smaller than one nibble:\n";
88 Bitmatch.hexdump_bitstring stderr pkt;
92 A program which can parse
93 {{:http://lxr.linux.no/linux/include/linux/ext3_fs.h}Linux EXT3 filesystem superblocks}:
96 let bits = Bitmatch.bitstring_of_file "tests/ext3_sb"
100 | { s_inodes_count : 32 : littleendian; (* Inodes count *)
101 s_blocks_count : 32 : littleendian; (* Blocks count *)
102 s_r_blocks_count : 32 : littleendian; (* Reserved blocks count *)
103 s_free_blocks_count : 32 : littleendian; (* Free blocks count *)
104 s_free_inodes_count : 32 : littleendian; (* Free inodes count *)
105 s_first_data_block : 32 : littleendian; (* First Data Block *)
106 s_log_block_size : 32 : littleendian; (* Block size *)
107 s_log_frag_size : 32 : littleendian; (* Fragment size *)
108 s_blocks_per_group : 32 : littleendian; (* # Blocks per group *)
109 s_frags_per_group : 32 : littleendian; (* # Fragments per group *)
110 s_inodes_per_group : 32 : littleendian; (* # Inodes per group *)
111 s_mtime : 32 : littleendian; (* Mount time *)
112 s_wtime : 32 : littleendian; (* Write time *)
113 s_mnt_count : 16 : littleendian; (* Mount count *)
114 s_max_mnt_count : 16 : littleendian; (* Maximal mount count *)
115 0xef53 : 16 : littleendian } -> (* Magic signature *)
117 printf "ext3 superblock:\n";
118 printf " s_inodes_count = %ld\n" s_inodes_count;
119 printf " s_blocks_count = %ld\n" s_blocks_count;
120 printf " s_free_inodes_count = %ld\n" s_free_inodes_count;
121 printf " s_free_blocks_count = %ld\n" s_free_blocks_count
124 eprintf "not an ext3 superblock!\n%!";
128 Constructing packets for a simple binary message
133 +---------------+---------------+--------------------------+
134 | type | subtype | parameter |
135 +---------------+---------------+--------------------------+
136 <-- 16 bits --> <-- 16 bits --> <------- 32 bits -------->
138 All fields are in network byte order.
141 let make_message typ subtype param =
149 {2 Loading, creating bitstrings}
151 The basic data type is the {!bitstring}, a string of bits of
152 arbitrary length. Bitstrings can be any length in bits and
153 operations do not need to be byte-aligned (although they will
154 generally be more efficient if they are byte-aligned).
156 Internally a bitstring is stored as a normal OCaml [string]
157 together with an offset and length, where the offset and length are
158 measured in bits. Thus one can efficiently form substrings of
159 bitstrings, overlay a bitstring on existing data, and load and save
160 bitstrings from files or other external sources.
162 To load a bitstring from a file use {!bitstring_of_file} or
163 {!bitstring_of_chan}.
165 There are also functions to create bitstrings from arbitrary data.
166 See the {{:#reference}reference} below.
168 {2 Matching bitstrings with patterns}
170 Use the [bitmatch] operator (part of the syntax extension) to break
171 apart a bitstring into its fields. [bitmatch] works a lot like the
172 OCaml [match] operator.
174 The general form of [bitmatch] is:
176 [bitmatch] {i bitstring-expression} [with]
178 [| {] {i pattern} [} ->] {i code}
180 [| {] {i pattern} [} ->] {i code}
184 As with normal match, the statement attempts to match the
185 bitstring against each pattern in turn. If none of the patterns
186 match then the standard library [Match_failure] exception is
189 Patterns look a bit different from normal match patterns. They
190 consist of a list of bitfields separated by [;] where each bitfield
191 contains a bind variable, the width (in bits) of the field, and
192 other information. Some example patterns:
197 | { version : 8; name : 8; param : 8 } -> ...
199 (* Bitstring of at least 3 bytes. First byte is the version
200 number, second byte is a field called name, third byte is
201 a field called parameter. *)
204 printf "flag is %b\n" flag
206 (* A single flag bit (mapped into an OCaml boolean). *)
208 | { len : 4; data : 1+len } ->
209 printf "len = %d, data = 0x%Lx\n" len data
211 (* A 4-bit length, followed by 1-16 bits of data, where the
212 length of the data is computed from len. *)
214 | { ipv6_source : 128 : bitstring;
215 ipv6_dest : 128 : bitstring } -> ...
217 (* IPv6 source and destination addresses. Each is 128 bits
218 and is mapped into a bitstring type which will be a substring
219 of the main bitstring expression. *)
222 You can also add conditional when-clauses:
226 when version = 4 || version = 6 -> ...
228 (* Only match and run the code when version is 4 or 6. If
229 it isn't we will drop through to the next case. *)
232 Note that the pattern is only compared against the first part of
233 the bitstring (there may be more data in the bitstring following
234 the pattern, which is not matched). In terms of regular
235 expressions you might say that the pattern matches [^pattern], not
236 [^pattern$]. To ensure that the bitstring contains only the
237 pattern, add a length -1 bitstring to the end and test that its
238 length is zero in the when-clause:
242 rest : -1 : bitstring }
243 when Bitmatch.bitstring_length rest = 0 -> ...
245 (* Only matches exactly 4 bits. *)
248 Normally the first part of each field is a binding variable,
249 but you can also match a constant, as in:
252 | { (4|6) : 4 } -> ...
254 (* Only matches if the first 4 bits contain either
255 the integer 4 or the integer 6. *)
258 One may also match on strings:
261 | { "MAGIC" : 5*8 : string } -> ...
263 (* Only matches if the string "MAGIC" appears at the start
267 {3:patternfieldreference Pattern field reference}
269 The exact format of each pattern field is:
271 [pattern : length [: qualifier [,qualifier ...]]]
273 [pattern] is the pattern, binding variable name, or constant to
274 match. [length] is the length in bits which may be either a
275 constant or an expression. The length expression is just an OCaml
276 expression and can use any values defined in the program, and refer
277 back to earlier fields (but not to later fields).
279 Integers can only have lengths in the range \[1..64\] bits. See the
280 {{:#integertypes}integer types} section below for how these are
281 mapped to the OCaml int/int32/int64 types. This is checked
282 at compile time if the length expression is constant, otherwise it is
283 checked at runtime and you will get a runtime exception eg. in
284 the case of a computed length expression.
286 A bitstring field of length -1 matches all the rest of the
287 bitstring (thus this is only useful as the last field in a
290 A bitstring field of length 0 matches an empty bitstring
291 (occasionally useful when matching optional subfields).
293 Qualifiers are a list of identifiers/expressions which control the type,
294 signedness and endianness of the field. Permissible qualifiers are:
296 - [int]: field has an integer type
297 - [string]: field is a string type
298 - [bitstring]: field is a bitstring type
299 - [signed]: field is signed
300 - [unsigned]: field is unsigned
301 - [bigendian]: field is big endian - a.k.a network byte order
302 - [littleendian]: field is little endian - a.k.a Intel byte order
303 - [nativeendian]: field is same endianness as the machine
304 - [endian (expr)]: [expr] should be an expression which evaluates to
305 a {!endian} type, ie. [LittleEndian], [BigEndian] or [NativeEndian].
306 The expression is an arbitrary OCaml expression and can use the
307 value of earlier fields in the bitmatch.
309 The default settings are [int], [unsigned], [bigendian].
311 Note that many of these qualifiers cannot be used together,
312 eg. bitstrings do not have endianness. The syntax extension should
313 give you a compile-time error if you use incompatible qualifiers.
315 {3 Other cases in bitmatch}
317 As well as a list of fields, it is possible to name the
318 bitstring and/or have a default match case:
323 (* Default match case. *)
325 | { _ } as pkt -> ...
327 (* Default match case, with 'pkt' bound to the whole bitstring. *)
330 {2 Constructing bitstrings}
332 Bitstrings may be constructed using the [BITSTRING] operator (as an
333 expression). The [BITSTRING] operator takes a list of fields,
334 similar to the list of fields for matching:
345 (* Constructs a 16-bit bitstring with the first four bits containing
346 the integer 1, and the following 12 bits containing the integer 10,
347 arranged in network byte order. *)
349 Bitmatch.hexdump_bitstring stdout bits ;;
357 The format of each field is the same as for pattern fields (see
358 {{:#patternfieldreference}Pattern field reference section}), and
359 things like computed length fields, fixed value fields, insertion
360 of bitstrings within bitstrings, etc. are all supported.
362 {3 Construction exception}
364 The [BITSTRING] operator may throw a {!Construct_failure}
365 exception at runtime.
367 Runtime errors include:
369 - int field length not in the range \[1..64\]
370 - a bitstring with a length declared which doesn't have the
371 same length at runtime
372 - trying to insert an out of range value into an int field
373 (eg. an unsigned int field which is 2 bits wide can only
374 take values in the range \[0..3\]).
376 {2:integertypes Integer types}
378 Integer types are mapped to OCaml types [bool], [int], [int32] or
379 [int64] using a system which tries to ensure that (a) the types are
380 reasonably predictable and (b) the most efficient type is
383 The rules are slightly different depending on whether the bit
384 length expression in the field is a compile-time constant or a
387 Detection of compile-time constants is quite simplistic so only
388 simple integer literals and simple expressions (eg. [5*8]) are
389 recognized as constants.
391 In any case the bit size of an integer is limited to the range
392 \[1..64\]. This is detected as a compile-time error if that is
393 possible, otherwise a runtime check is added which can throw an
394 [Invalid_argument] exception.
399 Bit size ---- OCaml type ----
400 Constant Computed expression
408 A possible future extension may allow people with 64 bit computers
409 to specify a more optimal [int] type for bit sizes in the range
410 [32..63]. If this was implemented then such code {i could not even
411 be compiled} on 32 bit platforms, so it would limit portability.
413 Another future extension may be to allow computed
414 expressions to assert min/max range for the bit size,
415 allowing a more efficient data type than int64 to be
416 used. (Of course under such circumstances there would
417 still need to be a runtime check to enforce the
420 {2 Named patterns and persistent patterns}
422 Please see {!Bitmatch_persistent} for documentation on this subject.
426 Using the compiler directly you can do:
429 ocamlc -I +bitmatch \
430 -pp "camlp4o bitmatch.cma bitmatch_persistent.cma \
431 `ocamlc -where`/bitmatch/pa_bitmatch.cmo" \
432 bitmatch.cma test.ml -o test
435 Simpler method using findlib:
439 -package bitmatch.syntax -syntax bitmatch.syntax \
440 -linkpkg test.ml -o test
443 {2 Security and type safety}
445 {3 Security on input}
447 The main concerns for input are buffer overflows and denial
450 It is believed that this library is robust against attempted buffer
451 overflows. In addition to OCaml's normal bounds checks, we check
452 that field lengths are >= 0, and many additional checks.
454 Denial of service attacks are more problematic. We only work
455 forwards through the bitstring, thus computation will eventually
456 terminate. As for computed lengths, code such as this is thought
462 buffer : Int64.to_int len : bitstring } ->
465 The [len] field can be set arbitrarily large by an attacker, but
466 when pattern-matching against the [buffer] field this merely causes
467 a test such as [if len <= remaining_size] to fail. Even if the
468 length is chosen so that [buffer] bitstring is allocated, the
469 allocation of sub-bitstrings is efficient and doesn't involve an
470 arbitary-sized allocation or any copying.
472 However the above does not necessarily apply to strings used in
473 matching, since they may cause the library to use the
474 {!Bitmatch.string_of_bitstring} function, which allocates a string.
475 So you should take care if you use the [string] type particularly
476 with a computed length that is derived from external input.
478 The main protection against attackers should be to ensure that the
479 main program will only read input bitstrings up to a certain
480 length, which is outside the scope of this library.
482 {3 Security on output}
484 As with the input side, computed lengths are believed to be
488 let len = read_untrusted_source () in
489 let buffer = allocate_bitstring () in
491 buffer : len : bitstring
495 This code merely causes a check that buffer's length is the same as
496 [len]. However the program function [allocate_bitstring] must
497 refuse to allocate an oversized buffer (but that is outside the
498 scope of this library).
500 {3 Order of evaluation}
502 In [bitmatch] statements, fields are evaluated left to right.
504 Note that the when-clause is evaluated {i last}, so if you are
505 relying on the when-clause to filter cases then your code may do a
506 lot of extra and unncessary pattern-matching work on fields which
507 may never be needed just to evaluate the when-clause. You can
508 usually rearrange the code to do only the first part of the match,
509 followed by the when-clause, followed by a second inner bitmatch.
513 The current implementation is believed to be fully type-safe,
514 and makes compile and run-time checks where appropriate. If
515 you find a case where a check is missing please submit a
516 bug report or a patch.
520 These are thought to be the current limits:
522 Integers: \[1..64\] bits.
524 Bitstrings (32 bit platforms): maximum length is limited
525 by the string size, ie. 16 MBytes.
527 Bitstrings (64 bit platforms): maximum length is thought to be
528 limited by the string size, ie. effectively unlimited.
530 Bitstrings must be loaded into memory before we can match against
531 them. Thus available memory may be considered a limit for some
534 {2:reference Reference}
538 type endian = BigEndian | LittleEndian | NativeEndian
540 val string_of_endian : endian -> string
543 type bitstring = string * int * int
544 (** [bitstring] is the basic type used to store bitstrings.
546 The type contains the underlying data (a string),
547 the current bit offset within the string and the
548 current bit length of the string (counting from the
549 bit offset). Note that the offset and length are
550 in {b bits}, not bytes.
552 Normally you don't need to use the bitstring type
553 directly, since there are functions and syntax
554 extensions which hide the details.
556 See also {!bitstring_of_string}, {!bitstring_of_file},
557 {!hexdump_bitstring}, {!bitstring_length}.
560 (** {3 Exceptions} *)
562 exception Construct_failure of string * string * int * int
563 (** [Construct_failure (message, file, line, char)] may be
564 raised by the [BITSTRING] constructor.
566 Common reasons are that values are out of range of
567 the fields that contain them, or that computed lengths
568 are impossible (eg. negative length bitfields).
570 [message] is the error message.
572 [file], [line] and [char] point to the original source
573 location of the [BITSTRING] constructor that failed.
576 (** {3 Bitstrings} *)
578 val empty_bitstring : bitstring
579 (** [empty_bitstring] is the empty, zero-length bitstring. *)
581 val create_bitstring : int -> bitstring
582 (** [create_bitstring n] creates an [n] bit bitstring
583 containing all zeroes. *)
585 val make_bitstring : int -> char -> bitstring
586 (** [make_bitstring n c] creates an [n] bit bitstring
587 containing the repeated 8 bit pattern in [c].
589 For example, [make_bitstring 16 '\x5a'] will create
590 the bitstring [0x5a5a] or in binary [0101 1010 0101 1010].
592 Note that the length is in bits, not bytes. *)
594 val bitstring_of_string : string -> bitstring
595 (** [bitstring_of_string str] creates a bitstring
596 of length [String.length str * 8] (bits) containing the
599 Note that the bitstring uses [str] as the underlying
600 string (see the representation of {!bitstring}) so you
601 should not change [str] after calling this. *)
603 val bitstring_of_file : string -> bitstring
604 (** [bitstring_of_file filename] loads the named file
607 val bitstring_of_chan : in_channel -> bitstring
608 (** [bitstring_of_chan chan] loads the contents of
609 the input channel [chan] as a bitstring.
611 The length of the final bitstring is determined
612 by the remaining input in [chan], but will always
613 be a multiple of 8 bits.
615 See also {!bitstring_of_chan_max}. *)
617 val bitstring_of_chan_max : in_channel -> int -> bitstring
618 (** [bitstring_of_chan_max chan max] works like
619 {!bitstring_of_chan} but will only read up to
620 [max] bytes from the channel (or fewer if the end of input
621 occurs before that). *)
623 val bitstring_of_file_descr : Unix.file_descr -> bitstring
624 (** [bitstring_of_file_descr fd] loads the contents of
625 the file descriptor [fd] as a bitstring.
627 See also {!bitstring_of_chan}, {!bitstring_of_file_descr_max}. *)
629 val bitstring_of_file_descr_max : Unix.file_descr -> int -> bitstring
630 (** [bitstring_of_file_descr_max fd max] works like
631 {!bitstring_of_file_descr} but will only read up to
632 [max] bytes from the channel (or fewer if the end of input
633 occurs before that). *)
635 val bitstring_length : bitstring -> int
636 (** [bitstring_length bitstring] returns the length of
637 the bitstring in bits. *)
639 val string_of_bitstring : bitstring -> string
640 (** [string_of_bitstring bitstring] converts a bitstring to a string
641 (eg. to allow comparison).
643 This function is inefficient. In the best case when the bitstring
644 is nicely byte-aligned we do a [String.sub] operation. If the
645 bitstring isn't aligned then this involves a lot of bit twiddling
646 and is particularly inefficient.
648 If the bitstring is not a multiple of 8 bits wide then the
649 final byte of the string contains the high bits set to the
650 remaining bits and the low bits set to 0. *)
652 val bitstring_to_file : bitstring -> string -> unit
653 (** [bitstring_to_file bits filename] writes the bitstring [bits]
654 to the file [filename]. It overwrites the output file.
656 Some restrictions apply, see {!bitstring_to_chan}. *)
658 val bitstring_to_chan : bitstring -> out_channel -> unit
659 (** [bitstring_to_file bits filename] writes the bitstring [bits]
660 to the channel [chan].
662 Channels are made up of bytes, bitstrings can be any bit length
663 including fractions of bytes. So this function only works
664 if the length of the bitstring is an exact multiple of 8 bits
665 (otherwise it raises [Invalid_argument "bitstring_to_chan"]).
667 Furthermore the function is efficient only in the case where
668 the bitstring is stored fully aligned, otherwise it has to
669 do inefficient bit twiddling like {!string_of_bitstring}.
671 In the common case where the bitstring was generated by the
672 [BITSTRING] operator and is an exact multiple of 8 bits wide,
673 then this function will always work efficiently.
676 (** {3 Printing bitstrings} *)
678 val hexdump_bitstring : out_channel -> bitstring -> unit
679 (** [hexdump_bitstring chan bitstring] prints the bitstring
680 to the output channel in a format similar to the
681 Unix command [hexdump -C]. *)
683 (** {3 Bitstring buffer} *)
687 val create : unit -> t
688 val contents : t -> bitstring
689 val add_bits : t -> string -> int -> unit
690 val add_bit : t -> bool -> unit
691 val add_byte : t -> int -> unit
693 (** Buffers are mainly used by the [BITSTRING] constructor, but
694 may also be useful for end users. They work much like the
695 standard library [Buffer] module. *)
697 (** {3 Miscellaneous} *)
700 (** The package name, always ["ocaml-bitmatch"] *)
703 (** The package version as a string. *)
706 (** Set this variable to true to enable extended debugging.
707 This only works if debugging was also enabled in the
708 [pa_bitmatch.ml] file at compile time, otherwise it
713 (* Private functions, called from generated code. Do not use
714 * these directly - they are not safe.
717 val extract_bitstring : string -> int -> int -> int -> bitstring * int * int
719 val extract_remainder : string -> int -> int -> bitstring * int * int
721 val extract_bit : string -> int -> int -> int -> bool * int * int
723 val extract_char_unsigned : string -> int -> int -> int -> int * int * int
725 val extract_int_be_unsigned : string -> int -> int -> int -> int * int * int
727 val extract_int_le_unsigned : string -> int -> int -> int -> int * int * int
729 val extract_int_ne_unsigned : string -> int -> int -> int -> int * int * int
731 val extract_int_ee_unsigned : endian -> string -> int -> int -> int -> int * int * int
733 val extract_int32_be_unsigned : string -> int -> int -> int -> int32 * int * int
735 val extract_int32_le_unsigned : string -> int -> int -> int -> int32 * int * int
737 val extract_int32_ne_unsigned : string -> int -> int -> int -> int32 * int * int
739 val extract_int32_ee_unsigned : endian -> string -> int -> int -> int -> int32 * int * int
741 val extract_int64_be_unsigned : string -> int -> int -> int -> int64 * int * int
743 val extract_int64_le_unsigned : string -> int -> int -> int -> int64 * int * int
745 val extract_int64_ne_unsigned : string -> int -> int -> int -> int64 * int * int
747 val extract_int64_ee_unsigned : endian -> string -> int -> int -> int -> int64 * int * int
749 val construct_bit : Buffer.t -> bool -> int -> exn -> unit
751 val construct_char_unsigned : Buffer.t -> int -> int -> exn -> unit
753 val construct_int_be_unsigned : Buffer.t -> int -> int -> exn -> unit
755 val construct_int_ne_unsigned : Buffer.t -> int -> int -> exn -> unit
757 val construct_int_ee_unsigned : endian -> Buffer.t -> int -> int -> exn -> unit
759 val construct_int32_be_unsigned : Buffer.t -> int32 -> int -> exn -> unit
761 val construct_int32_ne_unsigned : Buffer.t -> int32 -> int -> exn -> unit
763 val construct_int32_ee_unsigned : endian -> Buffer.t -> int32 -> int -> exn -> unit
765 val construct_int64_be_unsigned : Buffer.t -> int64 -> int -> exn -> unit
767 val construct_int64_ne_unsigned : Buffer.t -> int64 -> int -> exn -> unit
769 val construct_int64_ee_unsigned : endian -> Buffer.t -> int64 -> int -> exn -> unit
771 val construct_string : Buffer.t -> string -> unit