Module Activebuffer
type t

val create : int -> t

create n returns a fresh buffer, initially empty. The n parameter is the initial size of the internal string that holds the buffer contents. That string is automatically reallocated when more than n characters are stored in the buffer, but shrinks back to n characters when reset is called. For best performance, n should be of the same order of magnitude as the number of characters that are expected to be stored in the buffer (for instance, 80 for a buffer that holds one output line). Nothing bad will happen if the buffer grows beyond that limit, however. In doubt, take n = 16 for instance. If n is not between 1 and Sys.max_string_length, it will be clipped to that interval.
val contents : t -> string

Return a copy of the current contents of the buffer. The buffer itself is unchanged.
val length : t -> int

Return the number of characters currently contained in the buffer.
val clear : t -> unit

Empty the buffer.
val reset : t -> unit

Empty the buffer and deallocate the internal string holding the buffer contents, replacing it with the initial internal string of length n that was allocated by create n. For long-lived buffers that may have grown a lot, reset allows faster reclaimation of the space used by the buffer.
val add_char : t -> char -> unit

add_char b c appends the character c at the end of the buffer b.
val add_string : t -> string -> unit

add_string b s appends the string s at the end of the buffer b.
val add_substring : t -> string -> int -> int -> unit

add_substring b s ofs len takes len characters from offset ofs in string s and appends them at the end of the buffer b.
val add_buffer : t -> t -> unit

add_buffer b1 b2 appends the current contents of buffer b2 at the end of buffer b1. b2 is not modified.
val add_channel : t -> in_channel -> int -> unit

add_channel b ic n reads exactly n character from the input channel ic and stores them at the end of buffer b. Raise End_of_file if the channel contains fewer than n characters.
val output_buffer : out_channel -> t -> unit

output_buffer oc b writes the current contents of buffer b on the output channel oc.
These functions do not exist in Buffer
val add_subbuffer : t -> t -> int -> int -> unit

add_subbuffer dst src pos len appends the sub_part of buffer src starting at position pos and of length len to the buffer dst. src is not modified. Raise Invalid_argument if pos and len do not designate a valid sub_part of src
val sub : t -> int -> int -> unit

sub b pos len modify the buffer in order its content to designate the substring of the initial content, starting at offset pos and of length len. This function does not copy nor create strings. Raise Invalid_argument if pos and len do not designate a valid sub_part of the buffer
val buffer : t -> string*int

buffer b gives the internal string used by the buffer and the starting active posistion. It can be used in conjunction with sub when doing write in order to avoid unnecessary copy. let len = length b in let str, pos = buffer b in let nb_written = write fds str pos len in sub b nb_written (len - nb_written)
val before_read : t -> int -> string*int

val after_read : t -> int -> unit

before_read b len can be used if you want to do a read directly inside a buffer for avoiding copy. You should use a sequence like this :
let str, pos = before_read b len in
let nb_read = read fds str pos len in
after_read b nb_read
You should always use before_read and after_read together.