module BytesLabels: sig .. endByte 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.
The labeled version of this module can be used as described in the
StdLabels module.
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.
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.
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.
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.
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).
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 argument.
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 sequence.
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.
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 uninitialized bytes appended to it. If left or right
is negative, then bytes are removed (instead of appended) from
the corresponding side of s.
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.
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 sequence, and the source and destination intervals
overlap.
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.
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.
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.
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
increasing 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 -> 'afold_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.
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.
val for_all : f:(char -> bool) -> bytes -> bool
for_all p s checks if all characters in s satisfy the predicate p.
val exists : f:(char -> bool) -> bytes -> bool
exists p s checks if at least one character of s satisfies the predicate
p.
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.
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.
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.
val rindex : bytes -> char -> int
rindex s c returns the index of the last occurrence of byte c
in s.
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.
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.
Invalid_argument if i is not a valid position in s.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.
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.
Invalid_argument if i+1 is not a valid position in s.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 position i+1. rindex_opt s c is equivalent to
rindex_from s (length s - 1) c.
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.
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.
Invalid_argument if stop < 0 or stop+1 is not a valid
position in s.val uppercase_ascii : bytes -> bytes
Return a copy of the argument, with all lowercase letters translated to uppercase, using the US-ASCII character set.
val lowercase_ascii : bytes -> bytes
Return a copy of the argument, with all uppercase letters translated to lowercase, using the US-ASCII character set.
val capitalize_ascii : bytes -> bytes
Return a copy of the argument, with the first character set to uppercase, using the US-ASCII character set.
val uncapitalize_ascii : bytes -> bytes
Return a copy of the argument, with the first character set to lowercase, using the US-ASCII character set.
type t = bytes
An alias for the type of byte sequences.
val compare : t -> t -> int
val equal : t -> t -> bool
The equality function for byte sequences.
val starts_with : prefix:bytes -> bytes -> bool
starts_with ~prefix s is true if and only if s starts with
prefix.
val ends_with : suffix:bytes -> bytes -> bool
ends_with ~suffix s is true if and only if s ends with suffix.
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 BytesLabels.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
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 -> 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 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 split_on_char : sep:char -> bytes -> bytes list
split_on_char sep s returns the list of all (possibly empty)
subsequences of s that are delimited by the sep character.
The function's output is specified by the following invariants:
sep as a separator returns a
byte sequence equal to the input (Bytes.concat (Bytes.make 1 sep)
(Bytes.split_on_char sep s) = s).sep character.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.
val to_seqi : t -> (int * char) Seq.t
Iterate on the string, in increasing order, yielding indices along chars
val of_seq : char Seq.t -> t
Create a string from the generator
val get_utf_8_uchar : t -> int -> Uchar.utf_decode
get_utf_8_uchar b i decodes an UTF-8 character at index i in
b.
val set_utf_8_uchar : t -> int -> Uchar.t -> int
set_utf_8_uchar b i u UTF-8 encodes u at index i in b
and returns the number of bytes n that were written starting
at i. If n is 0 there was not enough space to encode u
at i and b was left untouched. Otherwise a new character can
be encoded at i + n.
val is_valid_utf_8 : t -> bool
is_valid_utf_8 b is true if and only if b contains valid
UTF-8 data.
val get_utf_16be_uchar : t -> int -> Uchar.utf_decode
get_utf_16be_uchar b i decodes an UTF-16BE character at index
i in b.
val set_utf_16be_uchar : t -> int -> Uchar.t -> int
set_utf_16be_uchar b i u UTF-16BE encodes u at index i in b
and returns the number of bytes n that were written starting
at i. If n is 0 there was not enough space to encode u
at i and b was left untouched. Otherwise a new character can
be encoded at i + n.
val is_valid_utf_16be : t -> bool
is_valid_utf_16be b is true if and only if b contains valid
UTF-16BE data.
val get_utf_16le_uchar : t -> int -> Uchar.utf_decode
get_utf_16le_uchar b i decodes an UTF-16LE character at index
i in b.
val set_utf_16le_uchar : t -> int -> Uchar.t -> int
set_utf_16le_uchar b i u UTF-16LE encodes u at index i in b
and returns the number of bytes n that were written starting
at i. If n is 0 there was not enough space to encode u
at i and b was left untouched. Otherwise a new character can
be encoded at i + n.
val is_valid_utf_16le : t -> bool
is_valid_utf_16le b is true if and only if b contains valid
UTF-16LE data.
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.
Care must be taken when concurrently accessing byte sequences from multiple domains: accessing a byte sequence will never crash a program, but unsynchronized accesses might yield surprising (non-sequentially-consistent) results.
Every byte sequence operation that accesses more than one byte is not atomic. This includes iteration and scanning.
For example, consider the following program:
let size = 100_000_000
let b = Bytes.make size ' '
let update b f () =
Bytes.iteri (fun i x -> Bytes.set b i (Char.chr (f (Char.code x)))) b
let d1 = Domain.spawn (update b (fun x -> x + 1))
let d2 = Domain.spawn (update b (fun x -> 2 * x + 1))
let () = Domain.join d1; Domain.join d2
the bytes sequence b may contain a non-deterministic mixture
of '!', 'A', 'B', and 'C' values.
After executing this code, each byte of the sequence b is either '!',
'A', 'B', or 'C'. If atomicity is required, then the user must
implement their own synchronization (for example, using Mutex.t).
If two domains only access disjoint parts of a byte sequence, then the observed behaviour is the equivalent to some sequential interleaving of the operations from the two domains.
A data race is said to occur when two domains access the same byte without synchronization and at least one of the accesses is a write. In the absence of data races, the observed behaviour is equivalent to some sequential interleaving of the operations from different domains.
Whenever possible, data races should be avoided by using synchronization to mediate the accesses to the elements of the sequence.
Indeed, in the presence of data races, programs will not crash but the observed behaviour may not be equivalent to any sequential interleaving of operations from different domains. Nevertheless, even in the presence of data races, a read operation will return the value of some prior write to that location.
Another subtle point is that if a data race involves mixed-size writes and
reads to the same location, the order in which those writes and reads
are observed by domains is not specified.
For instance, the following code write sequentially a 32-bit integer and a
char to the same index
let b = Bytes.make 10 '\000'
let d1 = Domain.spawn (fun () -> Bytes.set_int32_ne b 0 100; b.[0] <- 'd' )
In this situation, a domain that observes the write of 'd' to b.0 is not
guaranteed to also observe the write to indices 1, 2, or 3.