# Module Netulex.ULB

    module ULB: sig .. end

This module provides the `unicode_lexbuf` record with access functions. In this record, the data is available in two forms: As an array of Unicode code points `ulb_chars`, and as string of encoded chars `ulb_rawbuf`. Both buffers are synchronised by `ulb_chars_pos`. This array stores where every character of `ulb_chars` can be found in `ulb_rawbuf`.

    type unicode_lexbuf = private {

`` | `mutable ulb_encoding :`Netconversion.encoding`;` | `(*` | The character encoding of `ulb_rawbuf` | `*)`
`` | `mutable ulb_encoding_start :`int`;` | `(*` | The first character position to which `ulb_encoding` applies (the encoding of earlier positions is lost) | `*)`
`` | `mutable ulb_rawbuf :`string`;` | `(*` | The encoded string to analyse | `*)`
`` | `mutable ulb_rawbuf_len :`int`;` | `(*` | The filled part of `ulb_rawbuf` | `*)`
`` | `mutable ulb_rawbuf_end :`int`;` | `(*` | The analysed part of `ulb_rawbuf`. We have always `ulb_rawbuf_end <= ulb_rawbuf_len`. The analysed part may be shorter than the filled part because there is not enough space in `ulb_chars`, or because the filled part ends with an incomplete multi-byte character | `*)`
`` | `mutable ulb_rawbuf_const :`bool`;` | `(*` | Whether `ulb_rawbuf` is considered as a constant. If `true`, it is never blitted. | `*)`
`` | `mutable ulb_chars :`int array`;` | `(*` | The analysed part of `ulb_rawbuf` as array of Unicode code points. Only the positions 0 to `ulb_chars_len-1` of the array are filled. | `*)`
`` | `mutable ulb_chars_pos :`int array`;` | `(*` | For every analysed character this array stores the byte position where the character begins in `ulb_rawbuf`. In addition, the array contains at `ulb_chars_len` the value of `ulb_rawbuf_end`. This array is one element longer than `ulb_chars`. | `*)`
`` | `mutable ulb_chars_len :`int`;` | `(*` | The filled part of `ulb_chars` | `*)`
`` | `mutable ulb_eof :`bool`;` | `(*` | Whether EOF has been seen | `*)`
`` | `mutable ulb_refill :`string -> int -> int -> int`;` | `(*` | The refill function | `*)`
`` | `mutable ulb_enc_change_hook :`unicode_lexbuf -> unit`;` | `(*` | This function is called when the encoding changes | `*)`
`` | `mutable ulb_cursor :`Netconversion.cursor`;` | `(*` | Internally used by the implementation | `*)`

}

    val from_function : ?raw_size:int ->
           ?char_size:int ->
           ?enc_change_hook:(unicode_lexbuf -> unit) ->
           refill:(string -> int -> int -> int) ->
           Netconversion.encoding -> unicode_lexbuf

Creates a `unicode_lexbuf` to analyse strings of the passed `encoding` coming from the `refill` function.

`raw_size` : The initial size for `ulb_rawbuf`. Defaults to 512
`char_size` : The initial size for `ulb_chars`. Defaults to 256
`enc_change_hook` : This function is called when the encoding is changed, either by this module, or by the user calling `set_encoding`.
`refill` : This function is called with arguments `ulb_rawbuf`, `ulb_rawbuf_len`, and `l`, where `l = String.length ulb_rawbuf - ulb_rawbuf_len` is the free space in the buffer. The function should fill new bytes into this substring, and return the number of added bytes. The return value 0 signals EOF.

    val from_in_obj_channel : ?raw_size:int ->
           ?char_size:int ->
           ?enc_change_hook:(unicode_lexbuf -> unit) ->
           Netconversion.encoding ->
           Netchannels.in_obj_channel -> unicode_lexbuf

Creates a `unicode_lexbuf` to analyse strings of the passed `encoding` coming from the object channel.

`raw_size` : The initial size for `ulb_rawbuf`. Defaults to 512
`char_size` : The initial size for `ulb_chars`. Defaults to 256
`enc_change_hook` : This function is called when the encoding is changed, either by this module, or by the user calling `set_encoding`.

    val from_string : ?enc_change_hook:(unicode_lexbuf -> unit) ->
           Netconversion.encoding -> string -> unicode_lexbuf

Creates a `unicode_lexbuf` analysing the passed string encoded in the passed encoding. This function copies the input string.

`enc_change_hook` : This function is called when the encoding is changed, either by this module, or by the user calling `set_encoding`

    val from_string_inplace : ?enc_change_hook:(unicode_lexbuf -> unit) ->
           Netconversion.encoding -> string -> unicode_lexbuf

Creates a `unicode_lexbuf` analysing the passed string encoded in the passed encoding. This function does not copy the input string, but uses it directly as `ulb_rawbuf`. The string is not modified by `ULB`, but the caller must ensure that other program parts do not modify it either.

`enc_change_hook` : This function is called when the encoding is changed, either by this module, or by the user calling `set_encoding`

    val delete : int -> unicode_lexbuf -> unit

Deletes the number of characters from `unicode_lexbuf`. These characters are removed from the beginning of the buffer, i.e. `ulb_chars.(n)` becomes the new first character of the buffer. All three buffers `ulb_rawbuf`, `ulb_chars`, and `ulb_chars_pos` are blitted as necessary.

When the buffer is already at EOF, the function fails.

For efficiency, it should be tried to call `delete` as seldom as possible. Its speed is linear to the number of characters to move.

    val refill : unicode_lexbuf -> unit

Tries to add characters to the `unicode_lexbuf` by calling the `ulb_refill` function. When the buffer is already at EOF, the exception `End_of_file` is raised, and the buffer is not modified. Otherwise, the `ulb_refill` function is called to add new characters. If necessary, `ulb_rawbuf`, `ulb_chars`, and `ulb_chars_pos` are enlarged such that it is ensured that either at least one new character is added, or that EOF is found for the first time In the latter case, `ulb_eof` is set to `true` (and the next call of `refill_unicode_lexbuf` will raise `End_of_file`).

    val set_encoding : Netconversion.encoding -> unicode_lexbuf -> unit

Sets the `encoding` to the passed value. This only affects future `refill` calls. The hook `enc_change_hook` is invoked when defined.

    val close : unicode_lexbuf -> unit

Sets `ulb_eof` of the `unicode_lexbuf`. The rest of the buffer is not modified

    val utf8_sub_string : int -> int -> unicode_lexbuf -> string

The two `int` arguments are the position and length of a sub string of the lexbuf that is returned as UTF8 string. Position and length are given as character multiples, not byte multiples.

    val utf8_sub_string_length : int -> int -> unicode_lexbuf -> int

Returns `String.length(utf8_sub_string args)`. Tries not to allocate the UTF-8 string.