Non-blocking streaming Unicode codec.
Uutf
is a non-blocking streaming codec to decode and
encode the UTF-8, UTF-16, UTF-16LE
and UTF-16BE encoding schemes. It can efficiently work character by
character without blocking on IO. Decoders perform
character position tracking and support newline normalization.
Functions are also provided to fold over the characters of UTF encoded OCaml string values and to directly encode characters in OCaml Buffer.t values.
See examples of use.
Release 0.9.3 - Daniel Bünzli <daniel.buenzl i@erratique.ch>
Uutf
uses the term character for a Unicode
scalar
value which is an integer value in the ranges 0x0000
... 0xD7FF
and 0xE000
... 0x10FFFF
. This should not be
confused with a Unicode
code point, which is
a scalar value or a (textually meaningless)
surrogate
code point.
The type for Unicode characters. Any value of this type returned
by Uutf
is a Unicode
scalar value.
cp_to_string cp
represents the
code point cp
in
ASCII according to the Unicode notational convention
(see Appendix A in Unicode 6.1.0).
If cp
is not a valid code point "U+Invalid(X)"
is
returned where X
is the hexadecimal integer value.
Warning. Not thread safe. Use pp_cp for thread safety.
The type for encoding schemes decoded by Uutf
. Unicode encoding
schemes plus US-ASCII and
ISO/IEC 8859-1 (latin-1).
encoding_of_string s
converts a (case insensitive)
IANA character set name
to an encoding.
The type for newline normalizations. The variant argument is the normalization character.
`ASCII
, normalizes CR (U+000D
), LF (U+000A
) and CRLF
(<U+000D
, U+000A
>).`NLF
, normalizes the Unicode newline function (NLF). This is
NEL (U+0085
) and the normalizations of `ASCII
.`Readline
, normalizes for a Unicode readline function. This is FF
(U+000C
), LS (U+2028
), PS (U+2029
), and the normalizations
of `NLF
.
Used with an appropriate normalization character the `NLF
and
`Readline
normalizations allow to implement all the different
recommendations of Unicode's newline guidelines (section 5.8 in
Unicode 6.1.0).
The type for decoders.
decoder nln encoding src
is a decoder that inputs from src
.
Byte order mark.
Byte order mark
(BOM) constraints are application dependent and prone to
misunderstandings (see the
FAQ). Hence,
Uutf
decoders have a simple rule: an initial BOM is always
removed from the input and not counted in character position
tracking. The function decoder_removed_bom does however return
true
if a BOM was removed so that all the information can be
recovered if needed.
For UTF-16BE and UTF-16LE the above rule is a violation of
conformance D96 and D97 of the standard. Uutf
favors the idea
that if there's a BOM, decoding with `UTF_16
or the `UTF_16XX
corresponding to the BOM should decode the same character sequence
(this is not the case if you stick to the standard). The client
can however regain conformance by consulting the result of
decoder_removed_bom and take appropriate action.
Encoding. encoding
specifies the decoded encoding
scheme. If `UTF_16
is used the endianness is determined
according to the standard: from a
BOM
if there is one, `UTF_16BE
otherwise.
If encoding
is unspecified it is guessed. The result of a guess
can only be `UTF_8
, `UTF_16BE
or `UTF_16LE
. The heuristic
looks at the first three bytes of input (or less if impossible)
and takes the first matching byte pattern in the table below.
xx = any byte
.. = any byte or no byte (input too small)
pp = positive byte
uu = valid UTF-8 first byte
Bytes | Guess | Rationale
---------+-----------+-----------------------------------------------
EF BB BF | `UTF_8 | UTF-8 BOM
FE FF .. | `UTF_16BE | UTF-16BE BOM
FF FE .. | `UTF_16LE | UTF-16LE BOM
00 pp .. | `UTF_16BE | ASCII UTF-16BE and U+0000 is often forbidden
pp 00 .. | `UTF_16LE | ASCII UTF-16LE and U+0000 is often forbidden
uu .. .. | `UTF_8 | ASCII UTF-8 or valid UTF-8 first byte.
xx xx .. | `UTF_16BE | Not UTF-8 => UTF-16, no BOM => UTF-16BE
.. .. .. | `UTF_8 | Single malformed UTF-8 byte or no input.
This heuristic is compatible both with BOM based recognitition and JSON-like encoding recognition that relies on ASCII being present at the beginning of the stream. Also, decoder_removed_bom will tell the client if the guess was BOM based.
Newline normalization. If nln
is specified, the given
newline normalization is performed, see nln. Otherwise
all newlines are returned as found in the input.
Character position. The line number, column number and
character count of the last decoded character (including
`Malformed
ones) are respectively returned by decoder_line,
decoder_col and decoder_count. Before the first call to
decode the line number is 1
and the column is 0
. Each
decode returning `Uchar
or `Malformed
increments the column
until a newline. On a newline, the line number is incremented and
the column set to zero. For example the line is 2
and column 0
after the first newline was decoded. This can be understood as if decode
was moving an insertion point to the right in the data. A newline is anything normalized by `Readline
, see nln.
Uutf
assumes that each Unicode scalar value has a column width
of 1. The same assumption may not be made by the display program
(e.g. for emacs
' compilation mode you need to set
compilation-error-screen-columns
to nil
). For implementing
more involved column width increments yourself, look into
wcwidth
and
grapheme cluster boundaries.
decode d
is:
`Await
if d
has a `Manual
input source and awaits
for more input. The client must use Manual.src to provide it.`Uchar u
if a Unicode scalar value u
was decoded.`End
if the end of input was reached.`Malformed bytes
if the bytes
sequence is malformed according to
the decoded encoding scheme. If you are interested in a best-effort
decoding you can still continue to decode after an error until the
decoder synchronizes again on valid bytes. It may however be a good
idea to signal the malformed characters by adding an u_rep
character to the parsed data, see the examples.Note. Repeated invocation always eventually returns `End
, even
in case of errors.
decoder_encoding d
is d
's the decoded encoding scheme of d
.
Warning. If the decoder guesses the encoding or uses `UTF_16
,
rely on this value only after the first `Uchar
was decoded.
The type for Unicode encoders.
encode e v
is :
`Partial
iff e
has a `Manual
destination and needs more output
storage. The client must use Manual.dst to provide a new buffer
and then call encode with `Await
until `Ok
is returned.`Ok
when the encoder is ready to encode a new `Uchar
or `End
For `Manual
destination, encoding `End
always returns
`Partial
, the client should continue as usual with `Await
until `Ok
is returned at which point Manual.dst_rem e
is
guaranteed to be the size of the last provided buffer (i.e. nothing
was written).
Warning. The function assumes that u
is a Unicode
scalar value.
If you are handling foreign data you can use is_uchar to assert that.
Raises. Invalid_argument
if an `Uchar
or `End
is encoded
after a `Partial
encode.
Fold over the characters of UTF encoded OCaml string
values.
encoding_guess s
is the encoding guessed for s
coupled with
true
iff there's an initial
BOM.
Note. Initial BOMs are also folded over.
The type for character folders. The integer is the index in the
string where the `Uchar
or `Malformed
starts.
fold_utf_8 f a s
is
f (
... (f (f a 0 u
0) j
1u
1)
... )
... )
j
nu
n
where u
i, j
i are the Unicode
scalar value
and the starting position of the characters in the
UTF-8 encoded string s
.
fold_utf_16be f a s
is
f (
... (f (f a 0 u
0) j
1u
1)
... )
... )
j
nu
n
where u
i, j
i are the Unicode
scalar value
and the starting position of the characters in the
UTF-16BE encoded string s
.
fold_utf_16le f a s
is
f (
... (f (f a 0 u
0) j
1u
1)
... )
... )
j
nu
n
where u
i, j
i are the Unicode
scalar value
and the starting position of the characters in the
UTF-16LE encoded string s
.
UTF encode characters in OCaml Buffer.t values.
Warning. All the functions below assumes that u
is a
unicode
scalar value. If you are handling foreign data you
can use is_uchar to assert that.
add_utf_8 b u
adds the UTF-8 encoding of the
unicode
scalar value u
to b
.
add_utf_16be b u
adds the UTF-16BE encoding of the
unicode
scalar value u
to b
.
add_utf_16le b u
adds the UTF-16LE encoding of the
unicode
scalar value u
to b
.
The value of lines src
is the list of lines in src
as UTF-8
encoded OCaml strings. Line breaks are determined according to the
recommendation R4 for a readline
function in section 5.8 of
Unicode 6.1.0. If a decoding error occurs we silently replace the
malformed sequence by the replacement character u_rep and continue.
let lines ?encoding (src : [`Channel of in_channel | `String of string]) =
let rec loop d buf acc = match Uutf.decode d with
| `Uchar 0x000A ->
let line = Buffer.contents buf in
Buffer.clear buf; loop d buf (line :: acc)
| `Uchar u -> Uutf.Buffer.add_utf_8 buf u; loop d buf acc
| `End -> List.rev (Buffer.contents buf :: acc)
| `Malformed _ -> Uutf.Buffer.add_utf_8 buf Uutf.u_rep; loop d buf acc
| `Await -> assert false
in
let nln = `Readline 0x000A in
loop (Uutf.decoder ~nln ?encoding src) (Buffer.create 512) []
Using the `Manual
interface, lines_fd
does the same but on a Unix file
descriptor.
let lines_fd ?encoding (fd : Unix.file_descr) =
let rec loop fd s d buf acc = match Uutf.decode d with
| `Uchar 0x000A ->
let line = Buffer.contents buf in
Buffer.clear buf; loop fd s d buf (line :: acc)
| `Uchar u -> Uutf.Buffer.add_utf_8 buf u; loop fd s d buf acc
| `End -> List.rev (Buffer.contents buf :: acc)
| `Malformed _ -> Uutf.Buffer.add_utf_8 buf Uutf.u_rep; loop fd s d buf acc
| `Await ->
let rec unix_read fd s j l = try Unix.read fd s j l with
| Unix.Unix_error (Unix.EINTR, _, _) -> unix_read fd s j l
in
let rc = unix_read fd s 0 (String.length s) in
Uutf.Manual.src d s 0 rc; loop fd s d buf acc
in
let s = String.create 65536 (* UNIX_BUFFER_SIZE in 4.0.0 *) in
let nln = `Readline 0x000A in
loop fd s (Uutf.decoder ~nln ?encoding `Manual) (Buffer.create 512) []
The result of recode src out_encoding dst
has the characters of
src
written on dst
with encoding out_encoding
. If a
decoding error occurs we silently replace the malformed sequence
by the replacement character u_rep and continue. Note that we
don't add an initial
BOM to dst
,
recoding will thus loose the initial BOM src
may have. Whether
this is a problem or not depends on the context.
let recode ?nln ?encoding out_encoding
(src : [`Channel of in_channel | `String of string])
(dst : [`Channel of out_channel | `Buffer of Buffer.t])
=
let rec loop d e = match Uutf.decode d with
| `Uchar _ as u -> ignore (Uutf.encode e u); loop d e
| `End -> ignore (Uutf.encode e `End)
| `Malformed _ -> ignore (Uutf.encode e (`Uchar Uutf.u_rep)); loop d e
| `Await -> assert false
in
let d = Uutf.decoder ?nln ?encoding src in
let e = Uutf.encoder out_encoding dst in
loop d e
Using the `Manual
interface, recode_fd
does the same but between
Unix file descriptors.
let recode_fd ?nln ?encoding out_encoding
(fdi : Unix.file_descr)
(fdo : Unix.file_descr)
=
let rec encode fd s e v = match Uutf.encode e v with `Ok -> ()
| `Partial ->
let rec unix_write fd s j l =
let rec write fd s j l = try Unix.single_write fd s j l with
| Unix.Unix_error (Unix.EINTR, _, _) -> write fd s j l
in
let wc = write fd s j l in
if wc < l then unix_write fd s (j + wc) (l - wc) else ()
in
unix_write fd s 0 (String.length s - Uutf.Manual.dst_rem e);
Uutf.Manual.dst e s 0 (String.length s);
encode fd s e `Await
in
let rec loop fdi fdo ds es d e = match Uutf.decode d with
| `Uchar _ as u -> encode fdo es e u; loop fdi fdo ds es d e
| `End -> encode fdo es e `End
| `Malformed _ -> encode fdo es e (`Uchar Uutf.u_rep); loop fdi fdo ds es d e
| `Await ->
let rec unix_read fd s j l = try Unix.read fd s j l with
| Unix.Unix_error (Unix.EINTR, _, _) -> unix_read fd s j l
in
let rc = unix_read fdi ds 0 (String.length ds) in
Uutf.Manual.src d ds 0 rc; loop fdi fdo ds es d e
in
let ds = String.create 65536 (* UNIX_BUFFER_SIZE in 4.0.0 *) in
let es = String.create 65536 (* UNIX_BUFFER_SIZE in 4.0.0 *) in
let d = Uutf.decoder ?nln ?encoding `Manual in
let e = Uutf.encoder out_encoding `Manual in
Uutf.Manual.dst e es 0 (String.length es);
loop fdi fdo ds es d e