BytesLabels(3o) OCaml library BytesLabels(3o)
NAME
BytesLabels - Byte sequence operations.
Module
Module BytesLabels
Documentation
Module BytesLabels
: sig end
Byte sequence operations.
A byte sequence is a mutable data structure that contains a
fixed-length sequence of bytes. Each byte can be indexed in constant
time for reading or writing.
Given a byte sequence s of length l , we can access each of the l bytes
of s via its index in the sequence. Indexes start at 0 , and we will
call an index valid in s if it falls within the range [0...l-1] (inclu-
sive). A position is the point between two bytes or at the beginning or
end of the sequence. We call a position valid in s if it falls within
the range [0...l] (inclusive). Note that the byte at index n is between
positions n and n+1 .
Two parameters start and len are said to designate a valid range of s
if len >= 0 and start and start+len are valid positions in s .
Byte sequences can be modified in place, for instance via the set and
blit functions described below. See also strings (module String ),
which are almost the same data structure, but cannot be modified in
place.
Bytes are represented by the OCaml type char .
The labeled version of this module can be used as described in the Std-
Labels module.
Since 4.02.0
val length : bytes -> int
Return the length (number of bytes) of the argument.
val get : bytes -> int -> char
get s n returns the byte at index n in argument s .
Raises Invalid_argument if n is not a valid index in s .
val set : bytes -> int -> char -> unit
set s n c modifies s in place, replacing the byte at index n with c .
Raises Invalid_argument if n is not a valid index in s .
val create : int -> bytes
create n returns a new byte sequence of length n . The sequence is
uninitialized and contains arbitrary bytes.
Raises Invalid_argument if n < 0 or n > Sys.max_string_length .
val make : int -> char -> bytes
make n c returns a new byte sequence of length n , filled with the byte
c .
Raises Invalid_argument if n < 0 or n > Sys.max_string_length .
val init : int -> f:(int -> char) -> bytes
init n f returns a fresh byte sequence of length n , with character i
initialized to the result of f i (in increasing index order).
Raises Invalid_argument if n < 0 or n > Sys.max_string_length .
val empty : bytes
A byte sequence of size 0.
val copy : bytes -> bytes
Return a new byte sequence that contains the same bytes as the argu-
ment.
val of_string : string -> bytes
Return a new byte sequence that contains the same bytes as the given
string.
val to_string : bytes -> string
Return a new string that contains the same bytes as the given byte se-
quence.
val sub : bytes -> pos:int -> len:int -> bytes
sub s ~pos ~len returns a new byte sequence of length len , containing
the subsequence of s that starts at position pos and has length len .
Raises Invalid_argument if pos and len do not designate a valid range
of s .
val sub_string : bytes -> pos:int -> len:int -> string
Same as BytesLabels.sub but return a string instead of a byte sequence.
val extend : bytes -> left:int -> right:int -> bytes
extend s ~left ~right returns a new byte sequence that contains the
bytes of s , with left uninitialized bytes prepended and right unini-
tialized bytes appended to it. If left or right is negative, then bytes
are removed (instead of appended) from the corresponding side of s .
Since 4.05.0 in BytesLabels
Raises Invalid_argument if the result length is negative or longer than
Sys.max_string_length bytes.
val fill : bytes -> pos:int -> len:int -> char -> unit
fill s ~pos ~len c modifies s in place, replacing len characters with c
, starting at pos .
Raises Invalid_argument if pos and len do not designate a valid range
of s .
val blit : src:bytes -> src_pos:int -> dst:bytes -> dst_pos:int ->
len:int -> unit
blit ~src ~src_pos ~dst ~dst_pos ~len copies len bytes from sequence
src , starting at index src_pos , to sequence dst , starting at index
dst_pos . It works correctly even if src and dst are the same byte se-
quence, and the source and destination intervals overlap.
Raises Invalid_argument if src_pos and len do not designate a valid
range of src , or if dst_pos and len do not designate a valid range of
dst .
val blit_string : src:string -> src_pos:int -> dst:bytes -> dst_pos:int
-> len:int -> unit
blit ~src ~src_pos ~dst ~dst_pos ~len copies len bytes from string src
, starting at index src_pos , to byte sequence dst , starting at index
dst_pos .
Since 4.05.0 in BytesLabels
Raises Invalid_argument if src_pos and len do not designate a valid
range of src , or if dst_pos and len do not designate a valid range of
dst .
val concat : sep:bytes -> bytes list -> bytes
concat ~sep sl concatenates the list of byte sequences sl , inserting
the separator byte sequence sep between each, and returns the result as
a new byte sequence.
Raises Invalid_argument if the result is longer than
Sys.max_string_length bytes.
val cat : bytes -> bytes -> bytes
cat s1 s2 concatenates s1 and s2 and returns the result as a new byte
sequence.
Since 4.05.0 in BytesLabels
Raises Invalid_argument if the result is longer than
Sys.max_string_length bytes.
val iter : f:(char -> unit) -> bytes -> unit
iter ~f s applies function f in turn to all the bytes of s . It is
equivalent to f (get s 0); f (get s 1); ...; f (get s
(length s - 1)); () .
val iteri : f:(int -> char -> unit) -> bytes -> unit
Same as BytesLabels.iter , but the function is applied to the index of
the byte as first argument and the byte itself as second argument.
val map : f:(char -> char) -> bytes -> bytes
map ~f s applies function f in turn to all the bytes of s (in increas-
ing index order) and stores the resulting bytes in a new sequence that
is returned as the result.
val mapi : f:(int -> char -> char) -> bytes -> bytes
mapi ~f s calls f with each character of s and its index (in increasing
index order) and stores the resulting bytes in a new sequence that is
returned as the result.
val fold_left : f:('a -> char -> 'a) -> init:'a -> bytes -> 'a
fold_left f x s computes f (... (f (f x (get s 0)) (get s 1)) ...) (get
s (n-1)) , where n is the length of s .
Since 4.13.0
val fold_right : f:(char -> 'a -> 'a) -> bytes -> init:'a -> 'a
fold_right f s x computes f (get s 0) (f (get s 1) ( ... (f (get s
(n-1)) x) ...)) , where n is the length of s .
Since 4.13.0
val for_all : f:(char -> bool) -> bytes -> bool
for_all p s checks if all characters in s satisfy the predicate p .
Since 4.13.0
val exists : f:(char -> bool) -> bytes -> bool
exists p s checks if at least one character of s satisfies the predi-
cate p .
Since 4.13.0
val trim : bytes -> bytes
Return a copy of the argument, without leading and trailing whitespace.
The bytes regarded as whitespace are the ASCII characters ' ' , '\012'
, '\n' , '\r' , and '\t' .
val escaped : bytes -> bytes
Return a copy of the argument, with special characters represented by
escape sequences, following the lexical conventions of OCaml. All
characters outside the ASCII printable range (32..126) are escaped, as
well as backslash and double-quote.
Raises Invalid_argument if the result is longer than
Sys.max_string_length bytes.
val index : bytes -> char -> int
index s c returns the index of the first occurrence of byte c in s .
Raises Not_found if c does not occur in s .
val index_opt : bytes -> char -> int option
index_opt s c returns the index of the first occurrence of byte c in s
or None if c does not occur in s .
Since 4.05
val rindex : bytes -> char -> int
rindex s c returns the index of the last occurrence of byte c in s .
Raises Not_found if c does not occur in s .
val rindex_opt : bytes -> char -> int option
rindex_opt s c returns the index of the last occurrence of byte c in s
or None if c does not occur in s .
Since 4.05
val index_from : bytes -> int -> char -> int
index_from s i c returns the index of the first occurrence of byte c in
s after position i . index s c is equivalent to index_from s 0 c .
Raises Invalid_argument if i is not a valid position in s .
Raises Not_found if c does not occur in s after position i .
val index_from_opt : bytes -> int -> char -> int option
index_from_opt s i c returns the index of the first occurrence of byte
c in s after position i or None if c does not occur in s after position
i . index_opt s c is equivalent to index_from_opt s 0 c .
Since 4.05
Raises Invalid_argument if i is not a valid position in s .
val rindex_from : bytes -> int -> char -> int
rindex_from s i c returns the index of the last occurrence of byte c in
s before position i+1 . rindex s c is equivalent to rindex_from s
(length s - 1) c .
Raises Invalid_argument if i+1 is not a valid position in s .
Raises Not_found if c does not occur in s before position i+1 .
val rindex_from_opt : bytes -> int -> char -> int option
rindex_from_opt s i c returns the index of the last occurrence of byte
c in s before position i+1 or None if c does not occur in s before po-
sition i+1 . rindex_opt s c is equivalent to rindex_from s (length s -
1) c .
Since 4.05
Raises Invalid_argument if i+1 is not a valid position in s .
val contains : bytes -> char -> bool
contains s c tests if byte c appears in s .
val contains_from : bytes -> int -> char -> bool
contains_from s start c tests if byte c appears in s after position
start . contains s c is equivalent to contains_from
s 0 c .
Raises Invalid_argument if start is not a valid position in s .
val rcontains_from : bytes -> int -> char -> bool
rcontains_from s stop c tests if byte c appears in s before position
stop+1 .
Raises Invalid_argument if stop < 0 or stop+1 is not a valid position
in s .
val uppercase : bytes -> bytes
Deprecated. Functions operating on Latin-1 character set are depre-
cated.
Return a copy of the argument, with all lowercase letters translated to
uppercase, including accented letters of the ISO Latin-1 (8859-1) char-
acter set.
val lowercase : bytes -> bytes
Deprecated. Functions operating on Latin-1 character set are depre-
cated.
Return a copy of the argument, with all uppercase letters translated to
lowercase, including accented letters of the ISO Latin-1 (8859-1) char-
acter set.
val capitalize : bytes -> bytes
Deprecated. Functions operating on Latin-1 character set are depre-
cated.
Return a copy of the argument, with the first character set to upper-
case, using the ISO Latin-1 (8859-1) character set.
val uncapitalize : bytes -> bytes
Deprecated. Functions operating on Latin-1 character set are depre-
cated.
Return a copy of the argument, with the first character set to lower-
case, using the ISO Latin-1 (8859-1) character set.
val uppercase_ascii : bytes -> bytes
Return a copy of the argument, with all lowercase letters translated to
uppercase, using the US-ASCII character set.
Since 4.05.0
val lowercase_ascii : bytes -> bytes
Return a copy of the argument, with all uppercase letters translated to
lowercase, using the US-ASCII character set.
Since 4.05.0
val capitalize_ascii : bytes -> bytes
Return a copy of the argument, with the first character set to upper-
case, using the US-ASCII character set.
Since 4.05.0
val uncapitalize_ascii : bytes -> bytes
Return a copy of the argument, with the first character set to lower-
case, using the US-ASCII character set.
Since 4.05.0
type t = bytes
An alias for the type of byte sequences.
val compare : t -> t -> int
The comparison function for byte sequences, with the same specification
as compare . Along with the type t , this function compare allows the
module Bytes to be passed as argument to the functors Set.Make and
Map.Make .
val equal : t -> t -> bool
The equality function for byte sequences.
Since 4.05.0
val starts_with : prefix:bytes -> bytes -> bool
starts_with ~ prefix s is true if and only if s starts with prefix .
Since 4.13.0
val ends_with : suffix:bytes -> bytes -> bool
ends_with suffix s is true if and only if s ends with suffix .
Since 4.13.0
Unsafe conversions (for advanced users)
This section describes unsafe, low-level conversion functions between
bytes and string . They do not copy the internal data; used improperly,
they can break the immutability invariant on strings provided by the
-safe-string option. They are available for expert library authors, but
for most purposes you should use the always-correct BytesLa-
bels.to_string and BytesLabels.of_string instead.
val unsafe_to_string : bytes -> string
Unsafely convert a byte sequence into a string.
To reason about the use of unsafe_to_string , it is convenient to con-
sider an "ownership" discipline. A piece of code that manipulates some
data "owns" it; there are several disjoint ownership modes, including:
-Unique ownership: the data may be accessed and mutated
-Shared ownership: the data has several owners, that may only access
it, not mutate it.
Unique ownership is linear: passing the data to another piece of code
means giving up ownership (we cannot write the data again). A unique
owner may decide to make the data shared (giving up mutation rights on
it), but shared data may not become uniquely-owned again.
unsafe_to_string s can only be used when the caller owns the byte se-
quence s -- either uniquely or as shared immutable data. The caller
gives up ownership of s , and gains ownership of the returned string.
There are two valid use-cases that respect this ownership discipline:
1. Creating a string by initializing and mutating a byte sequence that
is never changed after initialization is performed.
let string_init len f : string =
let s = Bytes.create len in
for i = 0 to len - 1 do Bytes.set s i (f i) done;
Bytes.unsafe_to_string s
This function is safe because the byte sequence s will never be ac-
cessed or mutated after unsafe_to_string is called. The string_init
code gives up ownership of s , and returns the ownership of the result-
ing string to its caller.
Note that it would be unsafe if s was passed as an additional parameter
to the function f as it could escape this way and be mutated in the fu-
ture -- string_init would give up ownership of s to pass it to f , and
could not call unsafe_to_string safely.
We have provided the String.init , String.map and String.mapi functions
to cover most cases of building new strings. You should prefer those
over to_string or unsafe_to_string whenever applicable.
2. Temporarily giving ownership of a byte sequence to a function that
expects a uniquely owned string and returns ownership back, so that we
can mutate the sequence again after the call ended.
let bytes_length (s : bytes) =
String.length (Bytes.unsafe_to_string s)
In this use-case, we do not promise that s will never be mutated after
the call to bytes_length s . The String.length function temporarily
borrows unique ownership of the byte sequence (and sees it as a string
), but returns this ownership back to the caller, which may assume that
s is still a valid byte sequence after the call. Note that this is only
correct because we know that String.length does not capture its argu-
ment -- it could escape by a side-channel such as a memoization combi-
nator.
The caller may not mutate s while the string is borrowed (it has tempo-
rarily given up ownership). This affects concurrent programs, but also
higher-order functions: if String.length returned a closure to be
called later, s should not be mutated until this closure is fully ap-
plied and returns ownership.
val unsafe_of_string : string -> bytes
Unsafely convert a shared string to a byte sequence that should not be
mutated.
The same ownership discipline that makes unsafe_to_string correct ap-
plies to unsafe_of_string : you may use it if you were the owner of the
string value, and you will own the return bytes in the same mode.
In practice, unique ownership of string values is extremely difficult
to reason about correctly. You should always assume strings are shared,
never uniquely owned.
For example, string literals are implicitly shared by the compiler, so
you never uniquely own them.
let incorrect = Bytes.unsafe_of_string "hello"
let s = Bytes.of_string "hello"
The first declaration is incorrect, because the string literal "hello"
could be shared by the compiler with other parts of the program, and
mutating incorrect is a bug. You must always use the second version,
which performs a copy and is thus correct.
Assuming unique ownership of strings that are not string literals, but
are (partly) built from string literals, is also incorrect. For exam-
ple, mutating unsafe_of_string ("foo" ^ s) could mutate the shared
string "foo" -- assuming a rope-like representation of strings. More
generally, functions operating on strings will assume shared ownership,
they do not preserve unique ownership. It is thus incorrect to assume
unique ownership of the result of unsafe_of_string .
The only case we have reasonable confidence is safe is if the produced
bytes is shared -- used as an immutable byte sequence. This is possibly
useful for incremental migration of low-level programs that manipulate
immutable sequences of bytes (for example Marshal.from_bytes ) and pre-
viously used the string type for this purpose.
val split_on_char : sep:char -> bytes -> bytes list
split_on_char sep s returns the list of all (possibly empty) subse-
quences of s that are delimited by the sep character.
The function's output is specified by the following invariants:
-The list is not empty.
-Concatenating its elements using sep as a separator returns a byte se-
quence equal to the input ( Bytes.concat (Bytes.make 1 sep)
(Bytes.split_on_char sep s) = s ).
-No byte sequence in the result contains the sep character.
Since 4.13.0
Iterators
val to_seq : t -> char Seq.t
Iterate on the string, in increasing index order. Modifications of the
string during iteration will be reflected in the sequence.
Since 4.07
val to_seqi : t -> (int * char) Seq.t
Iterate on the string, in increasing order, yielding indices along
chars
Since 4.07
val of_seq : char Seq.t -> t
Create a string from the generator
Since 4.07
Binary encoding/decoding of integers
The functions in this section binary encode and decode integers to and
from byte sequences.
All following functions raise Invalid_argument if the space needed at
index i to decode or encode the integer is not available.
Little-endian (resp. big-endian) encoding means that least (resp. most)
significant bytes are stored first. Big-endian is also known as net-
work byte order. Native-endian encoding is either little-endian or
big-endian depending on Sys.big_endian .
32-bit and 64-bit integers are represented by the int32 and int64
types, which can be interpreted either as signed or unsigned numbers.
8-bit and 16-bit integers are represented by the int type, which has
more bits than the binary encoding. These extra bits are handled as
follows:
-Functions that decode signed (resp. unsigned) 8-bit or 16-bit integers
represented by int values sign-extend (resp. zero-extend) their result.
-Functions that encode 8-bit or 16-bit integers represented by int val-
ues truncate their input to their least significant bytes.
val get_uint8 : bytes -> int -> int
get_uint8 b i is b 's unsigned 8-bit integer starting at byte index i .
Since 4.08
val get_int8 : bytes -> int -> int
get_int8 b i is b 's signed 8-bit integer starting at byte index i .
Since 4.08
val get_uint16_ne : bytes -> int -> int
get_uint16_ne b i is b 's native-endian unsigned 16-bit integer start-
ing at byte index i .
Since 4.08
val get_uint16_be : bytes -> int -> int
get_uint16_be b i is b 's big-endian unsigned 16-bit integer starting
at byte index i .
Since 4.08
val get_uint16_le : bytes -> int -> int
get_uint16_le b i is b 's little-endian unsigned 16-bit integer start-
ing at byte index i .
Since 4.08
val get_int16_ne : bytes -> int -> int
get_int16_ne b i is b 's native-endian signed 16-bit integer starting
at byte index i .
Since 4.08
val get_int16_be : bytes -> int -> int
get_int16_be b i is b 's big-endian signed 16-bit integer starting at
byte index i .
Since 4.08
val get_int16_le : bytes -> int -> int
get_int16_le b i is b 's little-endian signed 16-bit integer starting
at byte index i .
Since 4.08
val get_int32_ne : bytes -> int -> int32
get_int32_ne b i is b 's native-endian 32-bit integer starting at byte
index i .
Since 4.08
val get_int32_be : bytes -> int -> int32
get_int32_be b i is b 's big-endian 32-bit integer starting at byte in-
dex i .
Since 4.08
val get_int32_le : bytes -> int -> int32
get_int32_le b i is b 's little-endian 32-bit integer starting at byte
index i .
Since 4.08
val get_int64_ne : bytes -> int -> int64
get_int64_ne b i is b 's native-endian 64-bit integer starting at byte
index i .
Since 4.08
val get_int64_be : bytes -> int -> int64
get_int64_be b i is b 's big-endian 64-bit integer starting at byte in-
dex i .
Since 4.08
val get_int64_le : bytes -> int -> int64
get_int64_le b i is b 's little-endian 64-bit integer starting at byte
index i .
Since 4.08
val set_uint8 : bytes -> int -> int -> unit
set_uint8 b i v sets b 's unsigned 8-bit integer starting at byte index
i to v .
Since 4.08
val set_int8 : bytes -> int -> int -> unit
set_int8 b i v sets b 's signed 8-bit integer starting at byte index i
to v .
Since 4.08
val set_uint16_ne : bytes -> int -> int -> unit
set_uint16_ne b i v sets b 's native-endian unsigned 16-bit integer
starting at byte index i to v .
Since 4.08
val set_uint16_be : bytes -> int -> int -> unit
set_uint16_be b i v sets b 's big-endian unsigned 16-bit integer start-
ing at byte index i to v .
Since 4.08
val set_uint16_le : bytes -> int -> int -> unit
set_uint16_le b i v sets b 's little-endian unsigned 16-bit integer
starting at byte index i to v .
Since 4.08
val set_int16_ne : bytes -> int -> int -> unit
set_int16_ne b i v sets b 's native-endian signed 16-bit integer start-
ing at byte index i to v .
Since 4.08
val set_int16_be : bytes -> int -> int -> unit
set_int16_be b i v sets b 's big-endian signed 16-bit integer starting
at byte index i to v .
Since 4.08
val set_int16_le : bytes -> int -> int -> unit
set_int16_le b i v sets b 's little-endian signed 16-bit integer start-
ing at byte index i to v .
Since 4.08
val set_int32_ne : bytes -> int -> int32 -> unit
set_int32_ne b i v sets b 's native-endian 32-bit integer starting at
byte index i to v .
Since 4.08
val set_int32_be : bytes -> int -> int32 -> unit
set_int32_be b i v sets b 's big-endian 32-bit integer starting at byte
index i to v .
Since 4.08
val set_int32_le : bytes -> int -> int32 -> unit
set_int32_le b i v sets b 's little-endian 32-bit integer starting at
byte index i to v .
Since 4.08
val set_int64_ne : bytes -> int -> int64 -> unit
set_int64_ne b i v sets b 's native-endian 64-bit integer starting at
byte index i to v .
Since 4.08
val set_int64_be : bytes -> int -> int64 -> unit
set_int64_be b i v sets b 's big-endian 64-bit integer starting at byte
index i to v .
Since 4.08
val set_int64_le : bytes -> int -> int64 -> unit
set_int64_le b i v sets b 's little-endian 64-bit integer starting at
byte index i to v .
Since 4.08
OCamldoc 2023-02-12 BytesLabels(3o)
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