1Bytes(3) OCamldoc 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 Since 4.02.0
42 val length : bytes -> int
49 Return the length (number of bytes) of the argument.
51 val get : bytes -> int -> char
55 get s n returns the byte at index n in argument s .
58 Raise Invalid_argument if n is not a valid index in s .
60 val set : bytes -> int -> char -> unit
64 set s n c modifies s in place, replacing the byte at index n with c .
67 Raise Invalid_argument if n is not a valid index in s .
69 val create : int -> bytes
73 create n returns a new byte sequence of length n . The sequence is
76 uninitialized and contains arbitrary bytes.
77 Raise Invalid_argument if n < 0 or n > Sys.max_string_length .
79 val make : int -> char -> bytes
83 make n c returns a new byte sequence of length n , filled with the byte
86 c .
87 Raise Invalid_argument if n < 0 or n > Sys.max_string_length .
89 val init : int -> (int -> char) -> bytes
93 Bytes.init n f returns a fresh byte sequence of length n , with charac‐
96 ter i initialized to the result of f i (in increasing index order).
97 Raise Invalid_argument if n < 0 or n > Sys.max_string_length .
99 val empty : bytes
103 A byte sequence of size 0.
105 val copy : bytes -> bytes
109 Return a new byte sequence that contains the same bytes as the argu‐
111 ment.
112 val of_string : string -> bytes
116 Return a new byte sequence that contains the same bytes as the given
118 string.
119 val to_string : bytes -> string
123 Return a new string that contains the same bytes as the given byte
125 sequence.
126 val sub : bytes -> int -> int -> bytes
130 sub s start len returns a new byte sequence of length len , containing
133 the subsequence of s that starts at position start and has length len .
134 Raise Invalid_argument if start and len do not designate a valid range
136 of s .
137 val sub_string : bytes -> int -> int -> string
141 Same as sub but return a string instead of a byte sequence.
143 val extend : bytes -> int -> int -> bytes
147 extend s left right returns a new byte sequence that contains the bytes
150 of s , with left uninitialized bytes prepended and right uninitialized
151 bytes appended to it. If left or right is negative, then bytes are
152 removed (instead of appended) from the corresponding side of s .
153 Raise Invalid_argument if the result length is negative or longer than
155 Sys.max_string_length bytes.
156 val fill : bytes -> int -> int -> char -> unit
160 fill s start len c modifies s in place, replacing len characters with c
163 , starting at start .
164 Raise Invalid_argument if start and len do not designate a valid range
166 of s .
167 val blit : bytes -> int -> bytes -> int -> int -> unit
171 blit src srcoff dst dstoff len copies len bytes from sequence src ,
174 starting at index srcoff , to sequence dst , starting at index dstoff .
175 It works correctly even if src and dst are the same byte sequence, and
176 the source and destination intervals overlap.
177 Raise Invalid_argument if srcoff and len do not designate a valid range
179 of src , or if dstoff and len do not designate a valid range of dst .
180 val blit_string : string -> int -> bytes -> int -> int -> unit
184 blit src srcoff dst dstoff len copies len bytes from string src ,
187 starting at index srcoff , to byte sequence dst , starting at index
188 dstoff .
189 Raise Invalid_argument if srcoff and len do not designate a valid range
191 of src , or if dstoff and len do not designate a valid range of dst .
192 val concat : bytes -> bytes list -> bytes
196 concat sep sl concatenates the list of byte sequences sl , inserting
199 the separator byte sequence sep between each, and returns the result as
200 a new byte sequence.
201 Raise Invalid_argument if the result is longer than
203 Sys.max_string_length bytes.
204 val cat : bytes -> bytes -> bytes
208 cat s1 s2 concatenates s1 and s2 and returns the result as new byte
211 sequence.
212 Raise Invalid_argument if the result is longer than
214 Sys.max_string_length bytes.
215 val iter : (char -> unit) -> bytes -> unit
219 iter f s applies function f in turn to all the bytes of s . It is
222 equivalent to f (get s 0); f (get s 1); ...; f (get s (length s - 1));
223 () .
224 val iteri : (int -> char -> unit) -> bytes -> unit
228 Same as Bytes.iter , but the function is applied to the index of the
230 byte as first argument and the byte itself as second argument.
231 val map : (char -> char) -> bytes -> bytes
235 map f s applies function f in turn to all the bytes of s (in increasing
238 index order) and stores the resulting bytes in a new sequence that is
239 returned as the result.
240 val mapi : (int -> char -> char) -> bytes -> bytes
244 mapi f s calls f with each character of s and its index (in increasing
247 index order) and stores the resulting bytes in a new sequence that is
248 returned as the result.
249 val trim : bytes -> bytes
253 Return a copy of the argument, without leading and trailing whitespace.
255 The bytes regarded as whitespace are the ASCII characters ' ' , '\012'
256 , '\n' , '\r' , and '\t' .
257 val escaped : bytes -> bytes
261 Return a copy of the argument, with special characters represented by
263 escape sequences, following the lexical conventions of OCaml. All
264 characters outside the ASCII printable range (32..126) are escaped, as
265 well as backslash and double-quote.
266 Raise Invalid_argument if the result is longer than
268 Sys.max_string_length bytes.
269 val index : bytes -> char -> int
273 index s c returns the index of the first occurrence of byte c in s .
276 Raise Not_found if c does not occur in s .
278 val index_opt : bytes -> char -> int option
282 index_opt s c returns the index of the first occurrence of byte c in s
285 or None if c does not occur in s .
286 Since 4.05
289 val rindex : bytes -> char -> int
293 rindex s c returns the index of the last occurrence of byte c in s .
296 Raise Not_found if c does not occur in s .
298 val rindex_opt : bytes -> char -> int option
302 rindex_opt s c returns the index of the last occurrence of byte c in s
305 or None if c does not occur in s .
306 Since 4.05
309 val index_from : bytes -> int -> char -> int
313 index_from s i c returns the index of the first occurrence of byte c in
316 s after position i . Bytes.index s c is equivalent to Bytes.index_from
317 s 0 c .
318 Raise Invalid_argument if i is not a valid position in s . Raise
320 Not_found if c does not occur in s after position i .
321 val index_from_opt : bytes -> int -> char -> int option
325 index_from _opts i c returns the index of the first occurrence of byte
328 c in s after position i or None if c does not occur in s after position
329 i . Bytes.index_opt s c is equivalent to Bytes.index_from_opt s 0 c .
330 Raise Invalid_argument if i is not a valid position in s .
332 Since 4.05
335 val rindex_from : bytes -> int -> char -> int
339 rindex_from s i c returns the index of the last occurrence of byte c in
342 s before position i+1 . rindex s c is equivalent to rindex_from s
343 (Bytes.length s - 1) c .
344 Raise Invalid_argument if i+1 is not a valid position in s . Raise
346 Not_found if c does not occur in s before position i+1 .
347 val rindex_from_opt : bytes -> int -> char -> int option
351 rindex_from_opt s i c returns the index of the last occurrence of byte
354 c in s before position i+1 or None if c does not occur in s before
355 position i+1 . rindex_opt s c is equivalent to rindex_from s
356 (Bytes.length s - 1) c .
357 Raise Invalid_argument if i+1 is not a valid position in s .
359 Since 4.05
362 val contains : bytes -> char -> bool
366 contains s c tests if byte c appears in s .
369 val contains_from : bytes -> int -> char -> bool
373 contains_from s start c tests if byte c appears in s after position
376 start . contains s c is equivalent to contains_from s 0 c .
377 Raise Invalid_argument if start is not a valid position in s .
379 val rcontains_from : bytes -> int -> char -> bool
383 rcontains_from s stop c tests if byte c appears in s before position
386 stop+1 .
387 Raise Invalid_argument if stop < 0 or stop+1 is not a valid position in
389 s .
390 val uppercase : bytes -> bytes
394 Deprecated. Functions operating on Latin-1 character set are depre‐
396 cated.
397 Return a copy of the argument, with all lowercase letters translated to
400 uppercase, including accented letters of the ISO Latin-1 (8859-1) char‐
401 acter set.
402 val lowercase : bytes -> bytes
406 Deprecated. Functions operating on Latin-1 character set are depre‐
408 cated.
409 Return a copy of the argument, with all uppercase letters translated to
412 lowercase, including accented letters of the ISO Latin-1 (8859-1) char‐
413 acter set.
414 val capitalize : bytes -> bytes
418 Deprecated. Functions operating on Latin-1 character set are depre‐
420 cated.
421 Return a copy of the argument, with the first character set to upper‐
424 case, using the ISO Latin-1 (8859-1) character set..
425 val uncapitalize : bytes -> bytes
429 Deprecated. Functions operating on Latin-1 character set are depre‐
431 cated.
432 Return a copy of the argument, with the first character set to lower‐
435 case, using the ISO Latin-1 (8859-1) character set..
436 val uppercase_ascii : bytes -> bytes
440 Return a copy of the argument, with all lowercase letters translated to
442 uppercase, using the US-ASCII character set.
443 Since 4.03.0
446 val lowercase_ascii : bytes -> bytes
450 Return a copy of the argument, with all uppercase letters translated to
452 lowercase, using the US-ASCII character set.
453 Since 4.03.0
456 val capitalize_ascii : bytes -> bytes
460 Return a copy of the argument, with the first character set to upper‐
462 case, using the US-ASCII character set.
463 Since 4.03.0
466 val uncapitalize_ascii : bytes -> bytes
470 Return a copy of the argument, with the first character set to lower‐
472 case, using the US-ASCII character set.
473 Since 4.03.0
476 type t = bytes
479 An alias for the type of byte sequences.
482 val compare : t -> t -> int
486 The comparison function for byte sequences, with the same specification
488 as Pervasives.compare . Along with the type t , this function compare
489 allows the module Bytes to be passed as argument to the functors
490 Set.Make and Map.Make .
491 val equal : t -> t -> bool
495 The equality function for byte sequences.
497 Since 4.03.0
500 === Unsafe conversions (for advanced users) This section describes
505 unsafe, low-level conversion functions between bytes and string. They
506 do not copy the internal data; used improperly, they can break the
507 immutability invariant on strings provided by the -safe-string option.
508 They are available for expert library authors, but for most purposes
509 you should use the always-correct Bytes.to_string and Bytes.of_string
510 instead. ===
511 val unsafe_to_string : bytes -> string
514 Unsafely convert a byte sequence into a string.
516 To reason about the use of unsafe_to_string , it is convenient to con‐
518 sider an "ownership" discipline. A piece of code that manipulates some
519 data "owns" it; there are several disjoint ownership modes, including:
520 -Unique ownership: the data may be accessed and mutated
522 -Shared ownership: the data has several owners, that may only access
524 it, not mutate it.
525 Unique ownership is linear: passing the data to another piece of code
527 means giving up ownership (we cannot write the data again). A unique
528 owner may decide to make the data shared (giving up mutation rights on
529 it), but shared data may not become uniquely-owned again.
530 unsafe_to_string s can only be used when the caller owns the byte
533 sequence s -- either uniquely or as shared immutable data. The caller
534 gives up ownership of s , and gains ownership of the returned string.
535 There are two valid use-cases that respect this ownership discipline:
537 1. Creating a string by initializing and mutating a byte sequence that
539 is never changed after initialization is performed.
540 let string_init len f : string = let s = Bytes.create len in for i = 0
543 to len - 1 do Bytes.set s i (f i) done; Bytes.unsafe_to_string s
544 This function is safe because the byte sequence s will never be
546 accessed or mutated after unsafe_to_string is called. The string_init
547 code gives up ownership of s , and returns the ownership of the result‐
548 ing string to its caller.
549 Note that it would be unsafe if s was passed as an additional parameter
551 to the function f as it could escape this way and be mutated in the
552 future -- string_init would give up ownership of s to pass it to f ,
553 and could not call unsafe_to_string safely.
554 We have provided the String.init , String.map and String.mapi functions
556 to cover most cases of building new strings. You should prefer those
557 over to_string or unsafe_to_string whenever applicable.
558 2. Temporarily giving ownership of a byte sequence to a function that
560 expects a uniquely owned string and returns ownership back, so that we
561 can mutate the sequence again after the call ended.
562 let bytes_length (s : bytes) = String.length (Bytes.unsafe_to_string s)
565 In this use-case, we do not promise that s will never be mutated after
567 the call to bytes_length s . The String.length function temporarily
568 borrows unique ownership of the byte sequence (and sees it as a string
569 ), but returns this ownership back to the caller, which may assume that
570 s is still a valid byte sequence after the call. Note that this is only
571 correct because we know that String.length does not capture its argu‐
572 ment -- it could escape by a side-channel such as a memoization combi‐
573 nator.
574 The caller may not mutate s while the string is borrowed (it has tempo‐
576 rarily given up ownership). This affects concurrent programs, but also
577 higher-order functions: if String.length returned a closure to be
578 called later, s should not be mutated until this closure is fully
579 applied and returns ownership.
580 val unsafe_of_string : string -> bytes
584 Unsafely convert a shared string to a byte sequence that should not be
586 mutated.
587 The same ownership discipline that makes unsafe_to_string correct
589 applies to unsafe_of_string : you may use it if you were the owner of
590 the string value, and you will own the return bytes in the same mode.
591 In practice, unique ownership of string values is extremely difficult
593 to reason about correctly. You should always assume strings are shared,
594 never uniquely owned.
595 For example, string literals are implicitly shared by the compiler, so
597 you never uniquely own them.
598 let incorrect = Bytes.unsafe_of_string hello let s = Bytes.of_string
601 hello
602 The first declaration is incorrect, because the string literal hello
604 could be shared by the compiler with other parts of the program, and
605 mutating incorrect is a bug. You must always use the second version,
606 which performs a copy and is thus correct.
607 Assuming unique ownership of strings that are not string literals, but
609 are (partly) built from string literals, is also incorrect. For exam‐
610 ple, mutating unsafe_of_string ("foo" ^ s) could mutate the shared
611 string foo -- assuming a rope-like representation of strings. More gen‐
612 erally, functions operating on strings will assume shared ownership,
613 they do not preserve unique ownership. It is thus incorrect to assume
614 unique ownership of the result of unsafe_of_string .
615 The only case we have reasonable confidence is safe is if the produced
617 bytes is shared -- used as an immutable byte sequence. This is possibly
618 useful for incremental migration of low-level programs that manipulate
619 immutable sequences of bytes (for example Marshal.from_bytes ) and pre‐
620 viously used the string type for this purpose.
6212018-04-14 source: Bytes(3)