module BatBytes: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]
(inclusive). 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
.
typet =
bytes
An alias for the type of byte sequences.
val length : t -> int
Return the length (number of t) of the argument.
val get : t -> int -> char
get s n
returns the byte at index n
in argument s
.
Raise Invalid_argument
if n
not a valid index in s
.
val set : t -> int -> char -> unit
set s n c
modifies s
in place, replacing the byte at index n
with c
.
Raise Invalid_argument
if n
is not a valid index in s
.
val create : int -> t
create n
returns a new byte sequence of length n
. The
sequence is uninitialized and contains arbitrary bytes.
Raise Invalid_argument
if n < 0
or n >
Sys.max_string_length
.
val make : int -> char -> t
make n c
returns a new byte sequence of length n
, filled with
the byte c
.
Raise Invalid_argument
if n < 0
or n >
Sys.max_string_length
.
val init : int -> (int -> char) -> t
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).
Raise Invalid_argument
if n < 0
or n >
Sys.max_string_length
.
val empty : t
A byte sequence of size 0.
val copy : t -> t
Return a new byte sequence that contains the same bytes as the argument.
val of_string : string -> t
Return a new byte sequence that contains the same bytes as the given string.
val to_string : t -> string
Return a new string that contains the same bytes as the given byte sequence.
val sub : t -> int -> int -> t
sub s start len
returns a new byte sequence of length len
,
containing the subsequence of s
that starts at position start
and has length len
.
Raise Invalid_argument
if start
and len
do not designate a
valid range of s
.
val sub_string : t -> int -> int -> string
Same as sub
but return a string instead of a byte sequence.
val extend : t -> int -> int -> t
extend s left right
returns a new byte sequence that contains
the bytes of s
, with left
uninitialized bytes prepended and
right
uninitialized bytes appended to it. If left
or right
is negative, then bytes are removed (instead of appended) from
the corresponding side of s
.
Raise Invalid_argument
if the result length is negative or
longer than Sys.max_string_length
bytes.
val fill : t -> int -> int -> char -> unit
fill s start len c
modifies s
in place, replacing len
characters with c
, starting at start
.
Raise Invalid_argument
if start
and len
do not designate a
valid range of s
.
val blit : t -> int -> t -> int -> int -> unit
blit src srcoff dst dstoff len
copies len
bytes from sequence
src
, starting at index srcoff
, to sequence dst
, starting at
index dstoff
. It works correctly even if src
and dst
are the
same byte sequence, and the source and destination intervals
overlap.
Raise Invalid_argument
if srcoff
and len
do not
designate a valid range of src
, or if dstoff
and len
do not designate a valid range of dst
.
val blit_string : string -> int -> t -> int -> int -> unit
blit_string src srcoff dst dstoff len
copies len
bytes from string
src
, starting at index srcoff
, to byte sequence dst
,
starting at index dstoff
.
Raise Invalid_argument
if srcoff
and len
do not
designate a valid range of src
, or if dstoff
and len
do not designate a valid range of dst
.
val concat : t -> t list -> t
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.
Raise Invalid_argument
if the result is longer than
Sys.max_string_length
bytes.
val cat : t -> t -> t
cat s1 s2
concatenates s1
and s2
and returns the result
as new byte sequence.
Raise Invalid_argument
if the result is longer than
Sys.max_string_length
bytes.
val iter : (char -> unit) -> t -> 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 : (int -> char -> unit) -> t -> unit
Same as Bytes.iter
, but the function is applied to the index of
the byte as first argument and the byte itself as second
argument.
val map : (char -> char) -> t -> t
map f s
applies function f
in turn to all the bytes of s
(in increasing index order) and stores the resulting bytes in
a new sequence that is returned as the result.
val mapi : (int -> char -> char) -> t -> t
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 trim : t -> t
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 : t -> t
Return a copy of the argument, with special characters represented by escape sequences, following the lexical conventions of OCaml.
Raise Invalid_argument
if the result is longer than
Sys.max_string_length
bytes.
val index : t -> char -> int
index s c
returns the index of the first occurrence of byte c
in s
.
Raise Not_found
if c
does not occur in s
.
val index_opt : t -> 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
.
val rindex : t -> char -> int
rindex s c
returns the index of the last occurrence of byte c
in s
.
Raise Not_found
if c
does not occur in s
.
val rindex_opt : t -> 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
.
val index_from : t -> int -> char -> int
index_from s i c
returns the index of the first occurrence of
byte c
in s
after position i
. Bytes.index s c
is
equivalent to Bytes.index_from s 0 c
.
Raise Invalid_argument
if i
is not a valid position in s
.
Raise Not_found
if c
does not occur in s
after position i
.
val index_from_opt : t -> int -> char -> int option
index_from _opts 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
.
Bytes.index_opt s c
is equivalent to Bytes.index_from_opt s 0 c
.
Raise Invalid_argument
if i
is not a valid position in s
.
val rindex_from : t -> 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 (Bytes.length s - 1) c
.
Raise Invalid_argument
if i+1
is not a valid position in s
.
Raise Not_found
if c
does not occur in s
before position i+1
.
val rindex_from_opt : t -> 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 position i+1
. rindex_opt s c
is equivalent to
rindex_from s (Bytes.length s - 1) c
.
Raise Invalid_argument
if i+1
is not a valid position in s
.
val contains : t -> char -> bool
contains s c
tests if byte c
appears in s
.
val contains_from : t -> 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
Raise Invalid_argument
if start
is not a valid position in s
.
val rcontains_from : t -> int -> char -> bool
rcontains_from s stop c
tests if byte c
appears in s
before
position stop+1
.
Raise Invalid_argument
if stop < 0
or stop+1
is not a valid
position in s
.
val uppercase : t -> t
Return a copy of the argument, with all lowercase letters translated to uppercase, including accented letters of the ISO Latin-1 (8859-1) character set.
val lowercase : t -> t
Return a copy of the argument, with all uppercase letters translated to lowercase, including accented letters of the ISO Latin-1 (8859-1) character set.
val capitalize : t -> t
Return a copy of the argument, with the first byte set to uppercase.
val uncapitalize : t -> t
Return a copy of the argument, with the first byte set to lowercase.
val uppercase_ascii : t -> t
Return a copy of the argument, with all lowercase letters translated to uppercase, using the US-ASCII character set.
val lowercase_ascii : t -> t
Return a copy of the argument, with all uppercase letters translated to lowercase, using the US-ASCII character set.
val capitalize_ascii : t -> t
Return a copy of the argument, with the first character set to uppercase, using the US-ASCII character set.
val uncapitalize_ascii : t -> t
Return a copy of the argument, with the first character set to lowercase, using the US-ASCII character set.
val compare : t -> t -> int
The comparison function for byte sequences, with the same
specification as Pervasives.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.
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 Bytes.to_string
and Bytes.of_string
instead.
val unsafe_to_string : t -> string
Unsafely convert a byte sequence into a string.
To reason about the use of unsafe_to_string
, it is convenient to
consider an "ownership" discipline. A piece of code that
manipulates some data "owns" it; there are several disjoint ownership
modes, including:
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
sequence 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
accessed or mutated after unsafe_to_string
is called. The
string_init
code gives up ownership of s
, and returns the
ownership of the resulting 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 future -- 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 argument -- it could
escape by a side-channel such as a memoization combinator.
The caller may not mutate s
while the string is borrowed (it has
temporarily 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 applied and returns ownership.
val unsafe_of_string : string -> t
Unsafely convert a shared string to a byte sequence that should not be mutated.
The same ownership discipline that makes unsafe_to_string
correct applies 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 example, 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 previously used the
string
type for this purpose.
val to_seq : t -> char Stdlib.Seq.t
Iterate on the string, in increasing index order. Modifications of the string during iteration will be reflected in the iterator.
val to_seqi : t -> (int * char) Stdlib.Seq.t
Iterate on the string, in increasing order, yielding indices along chars
val of_seq : char Stdlib.Seq.t -> t
Create a string from the generator
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 network 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:
int
values sign-extend
(resp. zero-extend) their result.int
values 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
.
val get_int8 : bytes -> int -> int
get_int8 b i
is b
's signed 8-bit integer starting at byte index i
.
val get_uint16_ne : bytes -> int -> int
get_uint16_ne b i
is b
's native-endian unsigned 16-bit integer
starting at byte index i
.
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
.
val get_uint16_le : bytes -> int -> int
get_uint16_le b i
is b
's little-endian unsigned 16-bit integer
starting at byte index i
.
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
.
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
.
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
.
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
.
val get_int32_be : bytes -> int -> int32
get_int32_be b i
is b
's big-endian 32-bit integer
starting at byte index i
.
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
.
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
.
val get_int64_be : bytes -> int -> int64
get_int64_be b i
is b
's big-endian 64-bit integer
starting at byte index i
.
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
.
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
.
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
.
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
.
val set_uint16_be : bytes -> int -> int -> unit
set_uint16_be b i v
sets b
's big-endian unsigned 16-bit integer
starting at byte index i
to v
.
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
.
val set_int16_ne : bytes -> int -> int -> unit
set_int16_ne b i v
sets b
's native-endian signed 16-bit integer
starting at byte index i
to v
.
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
.
val set_int16_le : bytes -> int -> int -> unit
set_int16_le b i v
sets b
's little-endian signed 16-bit integer
starting at byte index i
to v
.
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
.
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
.
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
.
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
.
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
.
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
.