1Bytes(3) OCaml library Bytes(3)
2
6 Bytes - Byte sequence operations.
7
9 Module Bytes
10
12 Module Bytes
13 : sig end
14 Byte sequence operations.
17 A byte sequence is a mutable data structure that contains a
19 fixed-length sequence of bytes. Each byte can be indexed in constant
20 time for reading or writing.
21 Given a byte sequence s of length l , we can access each of the l bytes
23 of s via its index in the sequence. Indexes start at 0 , and we will
24 call an index valid in s if it falls within the range [0...l-1] (inclu‐
25 sive). A position is the point between two bytes or at the beginning or
26 end of the sequence. We call a position valid in s if it falls within
27 the range [0...l] (inclusive). Note that the byte at index n is between
28 positions n and n+1 .
29 Two parameters start and len are said to designate a valid range of s
31 if len >= 0 and start and start+len are valid positions in s .
32 Byte sequences can be modified in place, for instance via the set and
34 blit functions described below. See also strings (module String ),
35 which are almost the same data structure, but cannot be modified in
36 place.
37 Bytes are represented by the OCaml type char .
39 The labeled version of this module can be used as described in the Std‐
41 Labels module.
42 Since 4.02.0
45 val length : bytes -> int
52 Return the length (number of bytes) of the argument.
54 val get : bytes -> int -> char
58 get s n returns the byte at index n in argument s .
61 Raises Invalid_argument if n is not a valid index in s .
64 val set : bytes -> int -> char -> unit
68 set s n c modifies s in place, replacing the byte at index n with c .
71 Raises Invalid_argument if n is not a valid index in s .
74 val create : int -> bytes
78 create n returns a new byte sequence of length n . The sequence is
81 uninitialized and contains arbitrary bytes.
82 Raises Invalid_argument if n < 0 or n > Sys.max_string_length .
85 val make : int -> char -> bytes
89 make n c returns a new byte sequence of length n , filled with the byte
92 c .
93 Raises Invalid_argument if n < 0 or n > Sys.max_string_length .
96 val init : int -> (int -> char) -> bytes
100 init n f returns a fresh byte sequence of length n , with character i
103 initialized to the result of f i (in increasing index order).
104 Raises Invalid_argument if n < 0 or n > Sys.max_string_length .
107 val empty : bytes
111 A byte sequence of size 0.
113 val copy : bytes -> bytes
117 Return a new byte sequence that contains the same bytes as the argu‐
119 ment.
120 val of_string : string -> bytes
124 Return a new byte sequence that contains the same bytes as the given
126 string.
127 val to_string : bytes -> string
131 Return a new string that contains the same bytes as the given byte se‐
133 quence.
134 val sub : bytes -> int -> int -> bytes
138 sub s pos len returns a new byte sequence of length len , containing
141 the subsequence of s that starts at position pos and has length len .
142 Raises Invalid_argument if pos and len do not designate a valid range
145 of s .
146 val sub_string : bytes -> int -> int -> string
150 Same as Bytes.sub but return a string instead of a byte sequence.
152 val extend : bytes -> int -> int -> bytes
156 extend s left right returns a new byte sequence that contains the bytes
159 of s , with left uninitialized bytes prepended and right uninitialized
160 bytes appended to it. If left or right is negative, then bytes are re‐
161 moved (instead of appended) from the corresponding side of s .
162 Since 4.05.0 in BytesLabels
165 Raises Invalid_argument if the result length is negative or longer than
168 Sys.max_string_length bytes.
169 val fill : bytes -> int -> int -> char -> unit
173 fill s pos len c modifies s in place, replacing len characters with c ,
176 starting at pos .
177 Raises Invalid_argument if pos and len do not designate a valid range
180 of s .
181 val blit : bytes -> int -> bytes -> int -> int -> unit
185 blit src src_pos dst dst_pos len copies len bytes from sequence src ,
188 starting at index src_pos , to sequence dst , starting at index dst_pos
189 . It works correctly even if src and dst are the same byte sequence,
190 and the source and destination intervals overlap.
191 Raises Invalid_argument if src_pos and len do not designate a valid
194 range of src , or if dst_pos and len do not designate a valid range of
195 dst .
196 val blit_string : string -> int -> bytes -> int -> int -> unit
200 blit src src_pos dst dst_pos len copies len bytes from string src ,
203 starting at index src_pos , to byte sequence dst , starting at index
204 dst_pos .
205 Since 4.05.0 in BytesLabels
208 Raises Invalid_argument if src_pos and len do not designate a valid
211 range of src , or if dst_pos and len do not designate a valid range of
212 dst .
213 val concat : bytes -> bytes list -> bytes
217 concat sep sl concatenates the list of byte sequences sl , inserting
220 the separator byte sequence sep between each, and returns the result as
221 a new byte sequence.
222 Raises Invalid_argument if the result is longer than
225 Sys.max_string_length bytes.
226 val cat : bytes -> bytes -> bytes
230 cat s1 s2 concatenates s1 and s2 and returns the result as a new byte
233 sequence.
234 Since 4.05.0 in BytesLabels
237 Raises Invalid_argument if the result is longer than
240 Sys.max_string_length bytes.
241 val iter : (char -> unit) -> bytes -> unit
245 iter f s applies function f in turn to all the bytes of s . It is
248 equivalent to f (get s 0); f (get s 1); ...; f (get s
249 (length s - 1)); () .
250 val iteri : (int -> char -> unit) -> bytes -> unit
254 Same as Bytes.iter , but the function is applied to the index of the
256 byte as first argument and the byte itself as second argument.
257 val map : (char -> char) -> bytes -> bytes
261 map f s applies function f in turn to all the bytes of s (in increasing
264 index order) and stores the resulting bytes in a new sequence that is
265 returned as the result.
266 val mapi : (int -> char -> char) -> bytes -> bytes
270 mapi f s calls f with each character of s and its index (in increasing
273 index order) and stores the resulting bytes in a new sequence that is
274 returned as the result.
275 val fold_left : ('a -> char -> 'a) -> 'a -> bytes -> 'a
279 fold_left f x s computes f (... (f (f x (get s 0)) (get s 1)) ...) (get
282 s (n-1)) , where n is the length of s .
283 Since 4.13.0
286 val fold_right : (char -> 'a -> 'a) -> bytes -> 'a -> 'a
290 fold_right f s x computes f (get s 0) (f (get s 1) ( ... (f (get s
293 (n-1)) x) ...)) , where n is the length of s .
294 Since 4.13.0
297 val for_all : (char -> bool) -> bytes -> bool
301 for_all p s checks if all characters in s satisfy the predicate p .
304 Since 4.13.0
307 val exists : (char -> bool) -> bytes -> bool
311 exists p s checks if at least one character of s satisfies the predi‐
314 cate p .
315 Since 4.13.0
318 val trim : bytes -> bytes
322 Return a copy of the argument, without leading and trailing whitespace.
324 The bytes regarded as whitespace are the ASCII characters ' ' , '\012'
325 , '\n' , '\r' , and '\t' .
326 val escaped : bytes -> bytes
330 Return a copy of the argument, with special characters represented by
332 escape sequences, following the lexical conventions of OCaml. All
333 characters outside the ASCII printable range (32..126) are escaped, as
334 well as backslash and double-quote.
335 Raises Invalid_argument if the result is longer than
338 Sys.max_string_length bytes.
339 val index : bytes -> char -> int
343 index s c returns the index of the first occurrence of byte c in s .
346 Raises Not_found if c does not occur in s .
349 val index_opt : bytes -> char -> int option
353 index_opt s c returns the index of the first occurrence of byte c in s
356 or None if c does not occur in s .
357 Since 4.05
360 val rindex : bytes -> char -> int
364 rindex s c returns the index of the last occurrence of byte c in s .
367 Raises Not_found if c does not occur in s .
370 val rindex_opt : bytes -> char -> int option
374 rindex_opt s c returns the index of the last occurrence of byte c in s
377 or None if c does not occur in s .
378 Since 4.05
381 val index_from : bytes -> int -> char -> int
385 index_from s i c returns the index of the first occurrence of byte c in
388 s after position i . index s c is equivalent to index_from s 0 c .
389 Raises Invalid_argument if i is not a valid position in s .
392 Raises Not_found if c does not occur in s after position i .
395 val index_from_opt : bytes -> int -> char -> int option
399 index_from_opt s i c returns the index of the first occurrence of byte
402 c in s after position i or None if c does not occur in s after position
403 i . index_opt s c is equivalent to index_from_opt s 0 c .
404 Since 4.05
407 Raises Invalid_argument if i is not a valid position in s .
410 val rindex_from : bytes -> int -> char -> int
414 rindex_from s i c returns the index of the last occurrence of byte c in
417 s before position i+1 . rindex s c is equivalent to rindex_from s
418 (length s - 1) c .
419 Raises Invalid_argument if i+1 is not a valid position in s .
422 Raises Not_found if c does not occur in s before position i+1 .
425 val rindex_from_opt : bytes -> int -> char -> int option
429 rindex_from_opt s i c returns the index of the last occurrence of byte
432 c in s before position i+1 or None if c does not occur in s before po‐
433 sition i+1 . rindex_opt s c is equivalent to rindex_from s (length s -
434 1) c .
435 Since 4.05
438 Raises Invalid_argument if i+1 is not a valid position in s .
441 val contains : bytes -> char -> bool
445 contains s c tests if byte c appears in s .
448 val contains_from : bytes -> int -> char -> bool
452 contains_from s start c tests if byte c appears in s after position
455 start . contains s c is equivalent to contains_from
456 s 0 c .
457 Raises Invalid_argument if start is not a valid position in s .
460 val rcontains_from : bytes -> int -> char -> bool
464 rcontains_from s stop c tests if byte c appears in s before position
467 stop+1 .
468 Raises Invalid_argument if stop < 0 or stop+1 is not a valid position
471 in s .
472 val uppercase : bytes -> bytes
476 Deprecated. Functions operating on Latin-1 character set are depre‐
478 cated.
479 Return a copy of the argument, with all lowercase letters translated to
482 uppercase, including accented letters of the ISO Latin-1 (8859-1) char‐
483 acter set.
484 val lowercase : bytes -> bytes
488 Deprecated. Functions operating on Latin-1 character set are depre‐
490 cated.
491 Return a copy of the argument, with all uppercase letters translated to
494 lowercase, including accented letters of the ISO Latin-1 (8859-1) char‐
495 acter set.
496 val capitalize : bytes -> bytes
500 Deprecated. Functions operating on Latin-1 character set are depre‐
502 cated.
503 Return a copy of the argument, with the first character set to upper‐
506 case, using the ISO Latin-1 (8859-1) character set.
507 val uncapitalize : bytes -> bytes
511 Deprecated. Functions operating on Latin-1 character set are depre‐
513 cated.
514 Return a copy of the argument, with the first character set to lower‐
517 case, using the ISO Latin-1 (8859-1) character set.
518 val uppercase_ascii : bytes -> bytes
522 Return a copy of the argument, with all lowercase letters translated to
524 uppercase, using the US-ASCII character set.
525 Since 4.03.0 (4.05.0 in BytesLabels)
528 val lowercase_ascii : bytes -> bytes
532 Return a copy of the argument, with all uppercase letters translated to
534 lowercase, using the US-ASCII character set.
535 Since 4.03.0 (4.05.0 in BytesLabels)
538 val capitalize_ascii : bytes -> bytes
542 Return a copy of the argument, with the first character set to upper‐
544 case, using the US-ASCII character set.
545 Since 4.03.0 (4.05.0 in BytesLabels)
548 val uncapitalize_ascii : bytes -> bytes
552 Return a copy of the argument, with the first character set to lower‐
554 case, using the US-ASCII character set.
555 Since 4.03.0 (4.05.0 in BytesLabels)
558 type t = bytes
561 An alias for the type of byte sequences.
564 val compare : t -> t -> int
568 The comparison function for byte sequences, with the same specification
570 as compare . Along with the type t , this function compare allows the
571 module Bytes to be passed as argument to the functors Set.Make and
572 Map.Make .
573 val equal : t -> t -> bool
577 The equality function for byte sequences.
579 Since 4.03.0 (4.05.0 in BytesLabels)
582 val starts_with : prefix:bytes -> bytes -> bool
586 starts_with ~ prefix s is true if and only if s starts with prefix .
589 Since 4.13.0
592 val ends_with : suffix:bytes -> bytes -> bool
596 ends_with suffix s is true if and only if s ends with suffix .
599 Since 4.13.0
602 Unsafe conversions (for advanced users)
607 This section describes unsafe, low-level conversion functions between
608 bytes and string . They do not copy the internal data; used improperly,
609 they can break the immutability invariant on strings provided by the
610 -safe-string option. They are available for expert library authors, but
611 for most purposes you should use the always-correct Bytes.to_string and
612 Bytes.of_string instead.
613 val unsafe_to_string : bytes -> string
615 Unsafely convert a byte sequence into a string.
617 To reason about the use of unsafe_to_string , it is convenient to con‐
619 sider an "ownership" discipline. A piece of code that manipulates some
620 data "owns" it; there are several disjoint ownership modes, including:
621 -Unique ownership: the data may be accessed and mutated
623 -Shared ownership: the data has several owners, that may only access
625 it, not mutate it.
626 Unique ownership is linear: passing the data to another piece of code
628 means giving up ownership (we cannot write the data again). A unique
629 owner may decide to make the data shared (giving up mutation rights on
630 it), but shared data may not become uniquely-owned again.
631 unsafe_to_string s can only be used when the caller owns the byte se‐
634 quence s -- either uniquely or as shared immutable data. The caller
635 gives up ownership of s , and gains ownership of the returned string.
636 There are two valid use-cases that respect this ownership discipline:
638 1. Creating a string by initializing and mutating a byte sequence that
640 is never changed after initialization is performed.
641 let string_init len f : string =
644 let s = Bytes.create len in
645 for i = 0 to len - 1 do Bytes.set s i (f i) done;
646 Bytes.unsafe_to_string s
647 This function is safe because the byte sequence s will never be ac‐
650 cessed or mutated after unsafe_to_string is called. The string_init
651 code gives up ownership of s , and returns the ownership of the result‐
652 ing string to its caller.
653 Note that it would be unsafe if s was passed as an additional parameter
655 to the function f as it could escape this way and be mutated in the fu‐
656 ture -- string_init would give up ownership of s to pass it to f , and
657 could not call unsafe_to_string safely.
658 We have provided the String.init , String.map and String.mapi functions
660 to cover most cases of building new strings. You should prefer those
661 over to_string or unsafe_to_string whenever applicable.
662 2. Temporarily giving ownership of a byte sequence to a function that
664 expects a uniquely owned string and returns ownership back, so that we
665 can mutate the sequence again after the call ended.
666 let bytes_length (s : bytes) =
669 String.length (Bytes.unsafe_to_string s)
670 In this use-case, we do not promise that s will never be mutated after
673 the call to bytes_length s . The String.length function temporarily
674 borrows unique ownership of the byte sequence (and sees it as a string
675 ), but returns this ownership back to the caller, which may assume that
676 s is still a valid byte sequence after the call. Note that this is only
677 correct because we know that String.length does not capture its argu‐
678 ment -- it could escape by a side-channel such as a memoization combi‐
679 nator.
680 The caller may not mutate s while the string is borrowed (it has tempo‐
682 rarily given up ownership). This affects concurrent programs, but also
683 higher-order functions: if String.length returned a closure to be
684 called later, s should not be mutated until this closure is fully ap‐
685 plied and returns ownership.
686 val unsafe_of_string : string -> bytes
690 Unsafely convert a shared string to a byte sequence that should not be
692 mutated.
693 The same ownership discipline that makes unsafe_to_string correct ap‐
695 plies to unsafe_of_string : you may use it if you were the owner of the
696 string value, and you will own the return bytes in the same mode.
697 In practice, unique ownership of string values is extremely difficult
699 to reason about correctly. You should always assume strings are shared,
700 never uniquely owned.
701 For example, string literals are implicitly shared by the compiler, so
703 you never uniquely own them.
704 let incorrect = Bytes.unsafe_of_string "hello"
707 let s = Bytes.of_string "hello"
708 The first declaration is incorrect, because the string literal "hello"
711 could be shared by the compiler with other parts of the program, and
712 mutating incorrect is a bug. You must always use the second version,
713 which performs a copy and is thus correct.
714 Assuming unique ownership of strings that are not string literals, but
716 are (partly) built from string literals, is also incorrect. For exam‐
717 ple, mutating unsafe_of_string ("foo" ^ s) could mutate the shared
718 string "foo" -- assuming a rope-like representation of strings. More
719 generally, functions operating on strings will assume shared ownership,
720 they do not preserve unique ownership. It is thus incorrect to assume
721 unique ownership of the result of unsafe_of_string .
722 The only case we have reasonable confidence is safe is if the produced
724 bytes is shared -- used as an immutable byte sequence. This is possibly
725 useful for incremental migration of low-level programs that manipulate
726 immutable sequences of bytes (for example Marshal.from_bytes ) and pre‐
727 viously used the string type for this purpose.
728 val split_on_char : char -> bytes -> bytes list
732 split_on_char sep s returns the list of all (possibly empty) subse‐
735 quences of s that are delimited by the sep character.
736 The function's output is specified by the following invariants:
738 -The list is not empty.
741 -Concatenating its elements using sep as a separator returns a byte se‐
743 quence equal to the input ( Bytes.concat (Bytes.make 1 sep)
744 (Bytes.split_on_char sep s) = s ).
745 -No byte sequence in the result contains the sep character.
747 Since 4.13.0
751 Iterators
756 val to_seq : t -> char Seq.t
757 Iterate on the string, in increasing index order. Modifications of the
759 string during iteration will be reflected in the sequence.
760 Since 4.07
763 val to_seqi : t -> (int * char) Seq.t
767 Iterate on the string, in increasing order, yielding indices along
769 chars
770 Since 4.07
773 val of_seq : char Seq.t -> t
777 Create a string from the generator
779 Since 4.07
782 Binary encoding/decoding of integers
787 The functions in this section binary encode and decode integers to and
788 from byte sequences.
789 All following functions raise Invalid_argument if the space needed at
791 index i to decode or encode the integer is not available.
792 Little-endian (resp. big-endian) encoding means that least (resp. most)
794 significant bytes are stored first. Big-endian is also known as net‐
795 work byte order. Native-endian encoding is either little-endian or
796 big-endian depending on Sys.big_endian .
797 32-bit and 64-bit integers are represented by the int32 and int64
799 types, which can be interpreted either as signed or unsigned numbers.
800 8-bit and 16-bit integers are represented by the int type, which has
802 more bits than the binary encoding. These extra bits are handled as
803 follows:
804 -Functions that decode signed (resp. unsigned) 8-bit or 16-bit integers
806 represented by int values sign-extend (resp. zero-extend) their result.
807 -Functions that encode 8-bit or 16-bit integers represented by int val‐
809 ues truncate their input to their least significant bytes.
810 val get_uint8 : bytes -> int -> int
813 get_uint8 b i is b 's unsigned 8-bit integer starting at byte index i .
816 Since 4.08
819 val get_int8 : bytes -> int -> int
823 get_int8 b i is b 's signed 8-bit integer starting at byte index i .
826 Since 4.08
829 val get_uint16_ne : bytes -> int -> int
833 get_uint16_ne b i is b 's native-endian unsigned 16-bit integer start‐
836 ing at byte index i .
837 Since 4.08
840 val get_uint16_be : bytes -> int -> int
844 get_uint16_be b i is b 's big-endian unsigned 16-bit integer starting
847 at byte index i .
848 Since 4.08
851 val get_uint16_le : bytes -> int -> int
855 get_uint16_le b i is b 's little-endian unsigned 16-bit integer start‐
858 ing at byte index i .
859 Since 4.08
862 val get_int16_ne : bytes -> int -> int
866 get_int16_ne b i is b 's native-endian signed 16-bit integer starting
869 at byte index i .
870 Since 4.08
873 val get_int16_be : bytes -> int -> int
877 get_int16_be b i is b 's big-endian signed 16-bit integer starting at
880 byte index i .
881 Since 4.08
884 val get_int16_le : bytes -> int -> int
888 get_int16_le b i is b 's little-endian signed 16-bit integer starting
891 at byte index i .
892 Since 4.08
895 val get_int32_ne : bytes -> int -> int32
899 get_int32_ne b i is b 's native-endian 32-bit integer starting at byte
902 index i .
903 Since 4.08
906 val get_int32_be : bytes -> int -> int32
910 get_int32_be b i is b 's big-endian 32-bit integer starting at byte in‐
913 dex i .
914 Since 4.08
917 val get_int32_le : bytes -> int -> int32
921 get_int32_le b i is b 's little-endian 32-bit integer starting at byte
924 index i .
925 Since 4.08
928 val get_int64_ne : bytes -> int -> int64
932 get_int64_ne b i is b 's native-endian 64-bit integer starting at byte
935 index i .
936 Since 4.08
939 val get_int64_be : bytes -> int -> int64
943 get_int64_be b i is b 's big-endian 64-bit integer starting at byte in‐
946 dex i .
947 Since 4.08
950 val get_int64_le : bytes -> int -> int64
954 get_int64_le b i is b 's little-endian 64-bit integer starting at byte
957 index i .
958 Since 4.08
961 val set_uint8 : bytes -> int -> int -> unit
965 set_uint8 b i v sets b 's unsigned 8-bit integer starting at byte index
968 i to v .
969 Since 4.08
972 val set_int8 : bytes -> int -> int -> unit
976 set_int8 b i v sets b 's signed 8-bit integer starting at byte index i
979 to v .
980 Since 4.08
983 val set_uint16_ne : bytes -> int -> int -> unit
987 set_uint16_ne b i v sets b 's native-endian unsigned 16-bit integer
990 starting at byte index i to v .
991 Since 4.08
994 val set_uint16_be : bytes -> int -> int -> unit
998 set_uint16_be b i v sets b 's big-endian unsigned 16-bit integer start‐
1001 ing at byte index i to v .
1002 Since 4.08
1005 val set_uint16_le : bytes -> int -> int -> unit
1009 set_uint16_le b i v sets b 's little-endian unsigned 16-bit integer
1012 starting at byte index i to v .
1013 Since 4.08
1016 val set_int16_ne : bytes -> int -> int -> unit
1020 set_int16_ne b i v sets b 's native-endian signed 16-bit integer start‐
1023 ing at byte index i to v .
1024 Since 4.08
1027 val set_int16_be : bytes -> int -> int -> unit
1031 set_int16_be b i v sets b 's big-endian signed 16-bit integer starting
1034 at byte index i to v .
1035 Since 4.08
1038 val set_int16_le : bytes -> int -> int -> unit
1042 set_int16_le b i v sets b 's little-endian signed 16-bit integer start‐
1045 ing at byte index i to v .
1046 Since 4.08
1049 val set_int32_ne : bytes -> int -> int32 -> unit
1053 set_int32_ne b i v sets b 's native-endian 32-bit integer starting at
1056 byte index i to v .
1057 Since 4.08
1060 val set_int32_be : bytes -> int -> int32 -> unit
1064 set_int32_be b i v sets b 's big-endian 32-bit integer starting at byte
1067 index i to v .
1068 Since 4.08
1071 val set_int32_le : bytes -> int -> int32 -> unit
1075 set_int32_le b i v sets b 's little-endian 32-bit integer starting at
1078 byte index i to v .
1079 Since 4.08
1082 val set_int64_ne : bytes -> int -> int64 -> unit
1086 set_int64_ne b i v sets b 's native-endian 64-bit integer starting at
1089 byte index i to v .
1090 Since 4.08
1093 val set_int64_be : bytes -> int -> int64 -> unit
1097 set_int64_be b i v sets b 's big-endian 64-bit integer starting at byte
1100 index i to v .
1101 Since 4.08
1104 val set_int64_le : bytes -> int -> int64 -> unit
1108 set_int64_le b i v sets b 's little-endian 64-bit integer starting at
1111 byte index i to v .
1112 Since 4.08
1115OCamldoc 2022-02-04 Bytes(3)