--- /dev/null
+INTERNET-DRAFT Adam M. Costello
+draft-ietf-idn-punycode-02.txt 2002-May-23
+Expires 2002-Nov-23
+
+ Punycode: An encoding of Unicode for use with IDNA
+
+Status of this Memo
+
+ This document is an Internet-Draft and is in full conformance with
+ all provisions of Section 10 of RFC2026.
+
+ Internet-Drafts are working documents of the Internet Engineering
+ Task Force (IETF), its areas, and its working groups. Note
+ that other groups may also distribute working documents as
+ Internet-Drafts.
+
+ Internet-Drafts are draft documents valid for a maximum of six
+ months and may be updated, replaced, or obsoleted by other documents
+ at any time. It is inappropriate to use Internet-Drafts as
+ reference material or to cite them other than as "work in progress."
+
+ The list of current Internet-Drafts can be accessed at
+ http://www.ietf.org/ietf/1id-abstracts.txt
+
+ The list of Internet-Draft Shadow Directories can be accessed at
+ http://www.ietf.org/shadow.html
+
+ Distribution of this document is unlimited.
+
+Abstract
+
+ Punycode is a simple and efficient transfer encoding syntax designed
+ for use with Internationalized Domain Names in Applications [IDNA].
+ It uniquely and reversibly transforms a Unicode string [UNICODE]
+ into an ASCII string [ASCII]. ASCII characters in the Unicode
+ string are represented literally, and non-ASCII characters are
+ represented by ASCII characters that are allowed in host name labels
+ (letters, digits, and hyphens). This document defines a general
+ algorithm called Bootstring that allows a string of basic code
+ points to uniquely represent any string of code points drawn from
+ a larger set. Punycode is an instance of Bootstring that uses
+ particular parameter values specified by this document, appropriate
+ for IDNA.
+\f
+Contents
+
+ 1. Introduction
+ 1.1 Features
+ 1.2 Interaction of protocol parts
+ 2. Terminology
+ 3. Bootstring description
+ 3.1 Basic code point segregation
+ 3.2 Insertion unsort coding
+ 3.3 Generalized variable-length integers
+ 3.4 Bias adaptation
+ 4. Bootstring parameters
+ 5. Parameter values for Punycode
+ 6. Bootstring algorithms
+ 6.1 Bias adaptation function
+ 6.2 Decoding procedure
+ 6.3 Encoding procedure
+ 6.4 Overflow handling
+ 7. Punycode examples
+ 7.1 Sample strings
+ 7.2 Decoding traces
+ 7.3 Encoding traces
+ 8. Security considerations
+ 9. References (non-normative)
+ A. Author contact information
+ B. Mixed-case annotation
+ C. Disclaimer and license
+ D. Punycode sample implementation
+
+1. Introduction
+
+ [IDNA] describes an architecture for supporting internationalized
+ domain names. Labels containing non-ASCII characters can be
+ represented by ACE labels, which begin with a special ACE prefix and
+ contain only ASCII characters. The remainder of the label after the
+ prefix is a Punycode encoding of a Unicode string satisfying certain
+ constraints. For the details of the prefix and constraints, see
+ [IDNA] and [NAMEPREP].
+
+1.1 Features
+
+ Bootstring has been designed to have the following features:
+
+ * Completeness: Every extended string (sequence of arbitrary code
+ points) can be represented by a basic string (sequence of basic
+ code points). Restrictions on what strings are allowed, and on
+ length, can be imposed by higher layers.
+
+ * Uniqueness: There is at most one basic string that represents a
+ given extended string.
+
+ * Reversibility: Any extended string mapped to a basic string can
+ be recovered from that basic string.
+
+ * Efficient encoding: The ratio of basic string length to
+ extended string length is small. This is important in the
+ context of domain names because RFC 1034 [RFC1034] restricts the
+ length of a domain label to 63 characters.
+\f
+ * Simplicity: The encoding and decoding algorithms are reasonably
+ simple to implement. The goals of efficiency and simplicity are
+ at odds; Bootstring aims at a good balance between them.
+
+ * Readability: Basic code points appearing in the extended string
+ are represented as themselves in the basic string (although the
+ main purpose is to improve efficiency, not readability).
+
+ Punycode can also support an additional feature that is not used
+ by the ToASCII and ToUnicode operations of [IDNA]. When extended
+ strings are case-folded prior to encoding, the basic string can
+ use mixed case to tell how to convert the folded string into a
+ mixed-case string. See appendix B "Mixed-case annotation".
+
+1.2 Interaction of protocol parts
+
+ Punycode is used by the IDNA protocol [IDNA] for converting domain
+ labels into ASCII; it is not designed for any other purpose. It is
+ explicitly not designed for processing arbitrary free text.
+
+2. Terminology
+
+ The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
+ "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
+ document are to be interpreted as described in RFC 2119 [RFC2119].
+
+ A code point is an integral value associated with a character in a
+ coded character set.
+
+ As in the Unicode Standard [UNICODE], Unicode code points are
+ denoted by "U+" followed by four to six hexadecimal digits, while a
+ range of code points is denoted by two hexadecimal numbers separated
+ by "..", with no prefixes.
+
+ The operators div and mod perform integer division; (x div y) is the
+ quotient of x divided by y, discarding the remainder, and (x mod y)
+ is the remainder, so (x div y) * y + (x mod y) == x. Bootstring
+ uses these operators only with nonnegative operands, so the quotient
+ and remainder are always nonnegative.
+
+ The break statement jumps out of the innermost loop (as in C).
+
+ An overflow is an attempt to compute a value that exceeds the
+ maximum value of an integer variable.
+
+3. Bootstring description
+
+ Bootstring represents an arbitrary sequence of code points (the
+ "extended string") as a sequence of basic code points (the "basic
+ string"). This section describes the representation. Section 6
+ "Bootstring algorithms" presents the algorithms as pseudocode.
+ Sections 7.1 "Decoding traces" and 7.2 "Encoding traces" trace the
+ algorithms for sample inputs.
+\f
+ The following sections describe the four techniques used in
+ Bootstring. "Basic code point segregation" is a very simple
+ and efficient encoding for basic code points occurring in the
+ extended string: they are simply copied all at once. "Insertion
+ unsort coding" encodes the non-basic code points as deltas, and
+ processes the code points in numerical order rather than in order of
+ appearance, which typically results in smaller deltas. The deltas
+ are represented as "generalized variable-length integers", which use
+ basic code points to represent nonnegative integers. The parameters
+ of this integer representation are dynamically adjusted using "bias
+ adaptation", to improve efficiency when consecutive deltas have
+ similar magnitudes.
+
+3.1 Basic code point segregation
+
+ All basic code points appearing in the extended string are
+ represented literally at the beginning of the basic string, in their
+ original order, followed by a delimiter if (and only if) the number
+ of basic code points is nonzero. The delimiter is a particular
+ basic code point, which never appears in the remainder of the basic
+ string. The decoder can therefore find the end of the literal
+ portion (if there is one) by scanning for the last delimiter.
+
+3.2 Insertion unsort coding
+
+ The remainder of the basic string (after the last delimiter if there
+ is one) represents a sequence of nonnegative integral deltas as
+ generalized variable-length integers, described in section 3.3. The
+ meaning of the deltas is best understood in terms of the decoder.
+
+ The decoder builds the extended string incrementally. Initially,
+ the extended string is a copy of the literal portion of the basic
+ string (excluding the last delimiter). The decoder inserts
+ non-basic code points, one for each delta, into the extended string,
+ ultimately arriving at the final decoded string.
+
+ At the heart of this process is a state machine with two state
+ variables: an index i and a counter n. The index i refers to
+ a position in the extended string; it ranges from 0 (the first
+ position) to the current length of the extended string (which refers
+ to a potential position beyond the current end). If the current
+ state is <n,i>, the next state is <n,i+1> if i is less than the
+ length of the extended string, or <n+1,0> if i equals the length of
+ the extended string. In other words, each state change causes i to
+ increment, wrapping around to zero if necessary, and n counts the
+ number of wrap-arounds.
+\f
+ Notice that the state always advances monotonically (there is no
+ way for the decoder to return to an earlier state). At each state,
+ an insertion is either performed or not performed. At most one
+ insertion is performed in a given state. An insertion inserts the
+ value of n at position i in the extended string. The deltas are
+ a run-length encoding of this sequence of events: they are the
+ lengths of the runs of non-insertion states preceeding the insertion
+ states. Hence, for each delta, the decoder performs delta state
+ changes, then an insertion, and then one more state change. (An
+ implementation need not perform each state change individually, but
+ can instead use division and remainder calculations to compute the
+ next insertion state directly.) It is an error if the inserted code
+ point is a basic code point (because basic code points were supposed
+ to be segregated as described in section 3.1).
+
+ The encoder's main task is to derive the sequence of deltas that
+ will cause the decoder to construct the desired string. It can do
+ this by repeatedly scanning the extended string for the next code
+ point that the decoder would need to insert, and counting the number
+ of state changes the decoder would need to perform, mindful of the
+ fact that the decoder's extended string will include only those
+ code points that have already been inserted. Section 6.3 "Encoding
+ procedure" gives a precise algorithm.
+
+3.3 Generalized variable-length integers
+
+ In a conventional integer representation the base is the number of
+ distinct symbols for digits, whose values are 0 through base-1. Let
+ digit_0 denote the least significant digit, digit_1 the next least
+ significant, and so on. The value represented is the sum over j of
+ digit_j * w(j), where w(j) = base^j is the weight (scale factor)
+ for position j. For example, in the base 8 integer 437, the digits
+ are 7, 3, and 4, and the weights are 1, 8, and 64, so the value is
+ 7 + 3*8 + 4*64 = 287. This representation has two disadvantages:
+ First, there are multiple encodings of each value (because there
+ can be extra zeros in the most significant positions), which is
+ inconvenient when unique encodings are needed. Second, the integer
+ is not self-delimiting, so if multiple integers are concatenated the
+ boundaries between them are lost.
+
+ The generalized variable-length representation solves these two
+ problems. The digit values are still 0 through base-1, but now
+ the integer is self-delimiting by means of thresholds t(j), each
+ of which is in the range 0 through base-1. Exactly one digit, the
+ most significant, satisfies digit_j < t(j). Therefore, if several
+ integers are concatenated, it is easy to separate them, starting
+ with the first if they are little-endian (least significant digit
+ first), or starting with the last if they are big-endian (most
+ significant digit first). As before, the value is the sum over j of
+ digit_j * w(j), but the weights are different:
+
+ w(0) = 1
+ w(j) = w(j-1) * (base - t(j-1)) for j > 0
+\f
+ For example, consider the little-endian sequence of base 8 digits
+ 734251... Suppose the thresholds are 2, 3, 5, 5, 5, 5... This
+ implies that the weights are 1, 1*(8-2) = 6, 6*(8-3) = 30, 30*(8-5)
+ = 90, 90*(8-5) = 270, and so on. 7 is not less than 2, and 3 is
+ not less than 3, but 4 is less than 5, so 4 is the last digit. The
+ value of 734 is 7*1 + 3*6 + 4*30 = 145. The next integer is 251,
+ with value 2*1 + 5*6 + 1*30 = 62. Decoding this representation
+ is very similar to decoding a conventional integer: Start with a
+ current value of N = 0 and a weight w = 1. Fetch the next digit d
+ and increase N by d * w. If d is less than the current threshold
+ (t) then stop, otherwise increase w by a factor of (base - t),
+ update t for the next position, and repeat.
+
+ Encoding this representation is similar to encoding a conventional
+ integer: If N < t then output one digit for N and stop, otherwise
+ output the digit for t + ((N - t) mod (base - t)), then replace N
+ with (N - t) div (base - t), update t for the next position, and
+ repeat.
+
+ For any particular set of values of t(j), there is exactly one
+ generalized variable-length representation of each nonnegative
+ integral value.
+
+ Bootstring uses little-endian ordering so that the deltas can be
+ separated starting with the first. The t(j) values are defined in
+ terms of the constants base, tmin, and tmax, and a state variable
+ called bias:
+
+ t(j) = base * (j + 1) - bias,
+ clamped to the range tmin through tmax
+
+ The clamping means that if the formula yields a value less than tmin
+ or greater than tmax, then t(j) = tmin or tmax, respectively. (In
+ the pseudocode in section 6 "Bootstring algorithms", the expression
+ base * (j + 1) is denoted by k for performance reasons.) These
+ t(j) values cause the representation to favor integers within a
+ particular range determined by the bias.
+
+3.4 Bias adaptation
+
+ After each delta is encoded or decoded, bias is set for the next
+ delta as follows:
+
+ 1. Delta is scaled in order to avoid overflow in the next step:
+
+ let delta = delta div 2
+
+ But when this is the very first delta, the divisor is not 2, but
+ instead a constant called damp. This compensates for the fact
+ that the second delta is usually much smaller than the first.
+
+ 2. Delta is increased to compensate for the fact that the next
+ delta will be inserting into a longer string:
+\f
+ let delta = delta + (delta div numpoints)
+
+ numpoints is the total number of code points encoded/decoded so
+ far (including the one corresponding to this delta itself, and
+ including the basic code points).
+
+ 3. Delta is repeatedly divided until it falls within a threshold,
+ to predict the minimum number of digits needed to represent the
+ next delta:
+
+ while delta > ((base - tmin) * tmax) div 2
+ do let delta = delta div (base - tmin)
+
+ 4. The bias is set:
+
+ let bias =
+ (base * the number of divisions performed in step 3) +
+ (((base - tmin + 1) * delta) div (delta + skew))
+
+ The motivation for this procedure is that the current delta provides
+ a hint about the likely size of the next delta, and so t(j) is
+ set to tmax for the more significant digits starting with the one
+ expected to be last, tmin for the less significant digits up through
+ the one expected to be third-last, and somewhere between tmin and
+ tmax for the digit expected to be second-last (balancing the hope of
+ the expected-last digit being unnecessary against the danger of it
+ being insufficient).
+
+4. Bootstring parameters
+
+ Given a set of basic code points, one needs to be designated as
+ the delimiter. The base cannot be greater than the number of
+ distinguishable basic code points remaining. The digit-values in
+ the range 0 through base-1 need to be associated with distinct
+ non-delimiter basic code points. In some cases multiple code points
+ need to have the same digit-value; for example, uppercase and
+ lowercase versions of the same letter need to be equivalent if basic
+ strings are case-insensitive.
+
+ The initial value of n cannot be greater than the minimum non-basic
+ code point that could appear in extended strings.
+
+ The remaining five parameters (tmin, tmax, skew, damp, and the
+ initial value of bias) need to satisfy the following constraints:
+
+ 0 <= tmin <= tmax <= base-1
+ skew >= 1
+ damp >= 2
+ initial_bias mod base <= base - tmin
+
+ Provided the constraints are satisfied, these five parameters affect
+ efficiency but not correctness. They are best chosen empirically.
+
+ If support for mixed-case annotation is desired (see appendix B),
+ make sure that the code points corresponding to 0 through tmax-1 all
+ have both uppercase and lowercase forms.
+\f
+5. Parameter values for Punycode
+
+ Punycode uses the following Bootstring parameter values:
+
+ base = 36
+ tmin = 1
+ tmax = 26
+ skew = 38
+ damp = 700
+ initial_bias = 72
+ initial_n = 128 = 0x80
+
+ Although the only restriction Punycode imposes on the input integers
+ is that they be nonnegative, these parameters are especially
+ designed to work well with Unicode [UNICODE] code points, which
+ are integers in the range 0..10FFFF (but not D800..DFFF, which are
+ reserved for use by the UTF-16 encoding of Unicode). The basic code
+ points are the ASCII [ASCII] code points (0..7F), of which U+002D
+ (-) is the delimiter, and some of the others have digit-values as
+ follows:
+
+ code points digit-values
+ ------------ ----------------------
+ 41..5A (A-Z) = 0 to 25, respectively
+ 61..7A (a-z) = 0 to 25, respectively
+ 30..39 (0-9) = 26 to 35, respectively
+
+ Using hyphen-minus as the delimiter implies that the encoded string
+ can end with a hyphen-minus only if the Unicode string consists
+ entirely of basic code points, but IDNA forbids such strings from
+ being encoded. The encoded string can begin with a hyphen-minus,
+ but IDNA prepends a prefix. Therefore IDNA using Punycode conforms
+ to the RFC 952 rule that host name labels neither begin nor end with
+ a hyphen-minus [RFC952].
+
+ A decoder MUST recognize the letters in both uppercase and lowercase
+ forms (including mixtures of both forms). An encoder SHOULD output
+ only uppercase forms or only lowercase forms, unless it uses
+ mixed-case annotation (see appendix B).
+
+ Presumably most users will not manually write or type encoded
+ strings (as opposed to cutting and pasting them), but those who do
+ will need to be alert to the potential visual ambiguity between the
+ following sets of characters:
+
+ G 6
+ I l 1
+ O 0
+ S 5
+ U V
+ Z 2
+
+ Such ambiguities are usually resolved by context, but in a Punycode
+ encoded string there is no context apparent to humans.
+\f
+6. Bootstring algorithms
+
+ Some parts of the pseudocode can be omitted if the parameters
+ satisfy certain conditions (for which Punycode qualifies). These
+ parts are enclosed in {braces}, and notes immediately following the
+ pseudocode explain the conditions under which they can be omitted.
+
+ Formally, code points are integers, and hence the pseudocode assumes
+ that arithmetic operations can be performed directly on code points.
+ In some programming languages, explicit conversion between code
+ points and integers might be necessary.
+
+6.1 Bias adaptation function
+
+ function adapt(delta,numpoints,firsttime):
+ if firsttime then let delta = delta div damp
+ else let delta = delta div 2
+ let delta = delta + (delta div numpoints)
+ let k = 0
+ while delta > ((base - tmin) * tmax) div 2 do begin
+ let delta = delta div (base - tmin)
+ let k = k + base
+ end
+ return k + (((base - tmin + 1) * delta) div (delta + skew))
+
+ It does not matter whether the modifications to delta and k
+ inside adapt() affect variables of the same name inside the
+ encoding/decoding procedures, because after calling adapt() the
+ caller does not read those variables before overwriting them.
+\f
+6.2 Decoding procedure
+
+ let n = initial_n
+ let i = 0
+ let bias = initial_bias
+ let output = an empty string indexed from 0
+ consume all code points before the last delimiter (if there is one)
+ and copy them to output, fail on any non-basic code point
+ if more than zero code points were consumed then consume one more
+ (which will be the last delimiter)
+ while the input is not exhausted do begin
+ let oldi = i
+ let w = 1
+ for k = base to infinity in steps of base do begin
+ consume a code point, or fail if there was none to consume
+ let digit = the code point's digit-value, fail if it has none
+ let i = i + digit * w, fail on overflow
+ let t = tmin if k <= bias {+ tmin}, or
+ tmax if k >= bias + tmax, or k - bias otherwise
+ if digit < t then break
+ let w = w * (base - t), fail on overflow
+ end
+ let bias = adapt(i - oldi, length(output) + 1, test oldi is 0?)
+ let n = n + i div (length(output) + 1), fail on overflow
+ let i = i mod (length(output) + 1)
+ {if n is a basic code point then fail}
+ insert n into output at position i
+ increment i
+ end
+
+ The full statement enclosed in braces (checking whether n is a basic
+ code point) can be omitted if initial_n exceeds all basic code
+ points (which is true for Punycode), because n is never less than
+ initial_n.
+
+ In the assignment of t, where t is clamped to the range tmin through
+ tmax, "+ tmin" can always be omitted. This makes the clamping
+ calculation incorrect when bias < k < bias + tmin, but that cannot
+ happen because of the way bias is computed and because of the
+ constraints on the parameters.
+
+ Because the decoder state can only advance monotonically, and there
+ is only one representation of any delta, there is therefore only
+ one encoded string that can represent a given sequence of integers.
+ The only error conditions are invalid code points, unexpected
+ end-of-input, overflow, and basic code points encoded using deltas
+ instead of appearing literally. If the decoder fails on these
+ errors as shown above, then it cannot produce the same output for
+ two distinct inputs. Without this property it would have been
+ necessary to re-encode the output and verify that it matches the
+ input in order to guarantee the uniqueness of the encoding.
+\f
+6.3 Encoding procedure
+
+ let n = initial_n
+ let delta = 0
+ let bias = initial_bias
+ let h = b = the number of basic code points in the input
+ copy them to the output in order, followed by a delimiter if b > 0
+ {if the input contains a non-basic code point < n then fail}
+ while h < length(input) do begin
+ let m = the minimum {non-basic} code point >= n in the input
+ let delta = delta + (m - n) * (h + 1), fail on overflow
+ let n = m
+ for each code point c in the input (in order) do begin
+ if c < n {or c is basic} then increment delta, fail on overflow
+ if c == n then begin
+ let q = delta
+ for k = base to infinity in steps of base do begin
+ let t = tmin if k <= bias {+ tmin}, or
+ tmax if k >= bias + tmax, or k - bias otherwise
+ if q < t then break
+ output the code point for digit t + ((q - t) mod (base - t))
+ let q = (q - t) div (base - t)
+ end
+ output the code point for digit q
+ let bias = adapt(delta, h + 1, test h equals b?)
+ let delta = 0
+ increment h
+ end
+ end
+ increment delta and n
+ end
+
+ The full statement enclosed in braces (checking whether the input
+ contains a non-basic code point less than n) can be omitted if all
+ code points less than initial_n are basic code points (which is true
+ for Punycode if code points are unsigned).
+
+ The brace-enclosed conditions "non-basic" and "or m is basic" can be
+ omitted if initial_n exceeds all basic code points (which is true
+ for Punycode), because the code point being tested is never less
+ than initial_n.
+
+ In the assignment of t, where t is clamped to the range tmin through
+ tmax, "+ tmin" can always be omitted. This makes the clamping
+ calculation incorrect when bias < k < bias + tmin, but that cannot
+ happen because of the way bias is computed and because of the
+ constraints on the parameters.
+
+ The checks for overflow are necessary to avoid producing invalid
+ output when the input contains very large values or is very long.
+
+ The increment of delta at the bottom of the outer loop cannot
+ overflow because delta < length(input) before the increment, and
+ length(input) is already assumed to be representable. The increment
+ of n could overflow, but only if h == length(input), in which case
+ the procedure is finished anyway.
+\f
+6.4 Overflow handling
+
+ For IDNA, 26-bit unsigned integers are sufficient to handle all
+ valid IDNA labels without overflow, because any string that
+ needed a 27-bit delta would have to exceed either the code point
+ limit (0..10FFFF) or the label length limit (63 characters).
+ However, overflow handling is necessary because the inputs are not
+ necessarily valid IDNA labels.
+
+ If the programming language does not provide overflow detection,
+ the following technique can be used. Suppose A, B, and C are
+ representable nonnegative integers and C is nonzero. Then A + B
+ overflows if and only if B > maxint - A, and A + (B * C) overflows
+ if and only if B > (maxint - A) div C, where maxint is the greatest
+ integer for which maxint + 1 cannot be represented. Refer to
+ appendix D "Punycode sample implementation" for demonstrations of
+ this technique in the C language.
+
+ The decoding and encoding algorithms shown in sections 6.2 and
+ 6.3 handle overflow by detecting it whenever it happens. Another
+ approach is to enforce limits on the inputs that prevent overflow
+ from happening. For example, if the encoder were to verify that
+ no input code points exceed M and that the input length does not
+ exceed L, then no delta could ever exceed (M - initial_n) * (L + 1),
+ and hence no overflow could occur if integer variables were capable
+ of representing values that large. This prevention approach would
+ impose more restrictions on the input than the detection approach
+ does, but might be considered simpler in some programming languages.
+
+ In theory, the decoder could use an analogous approach, limiting the
+ number of digits in a variable-length integer (that is, limiting the
+ number of iterations in the innermost loop). However, the number
+ of digits that suffice to represent a given delta can sometimes
+ represent much larger deltas (because of the adaptation), and hence
+ this approach would probably need integers wider than 32 bits.
+
+ Yet another approach for the decoder is to allow overflow to occur,
+ but to check the final output string by re-encoding it and comparing
+ to the decoder input. If and only if they do not match (using a
+ case-insensitive ASCII comparison) overflow has occurred. This
+ delayed-detection approach would not impose any more restrictions on
+ the input than the immediate-detection approach does, and might be
+ considered simpler in some programming languages.
+
+ In fact, if the decoder is used only inside the IDNA ToUnicode
+ operation [IDNA], then it need not check for overflow at all,
+ because ToUnicode performs a higher level re-encoding and
+ comparison, and a mismatch has the same consequence as if the
+ Punycode decoder had failed.
+
+7. Punycode examples
+
+7.1 Sample strings
+
+ In the Punycode encodings below, the ACE prefix is not shown.
+ Backslashes show where line breaks have been inserted in strings too
+ long for one line.
+\f
+ The first several examples are all translations of the sentence "Why
+ can't they just speak in <language>?" (courtesy of Michael Kaplan's
+ "provincial" page [PROVINCIAL]). Word breaks and punctuation have
+ been removed, as is often done in domain names.
+
+ (A) Arabic (Egyptian):
+ u+0644 u+064A u+0647 u+0645 u+0627 u+0628 u+062A u+0643 u+0644
+ u+0645 u+0648 u+0634 u+0639 u+0631 u+0628 u+064A u+061F
+ Punycode: egbpdaj6bu4bxfgehfvwxn
+
+ (B) Chinese (simplified):
+ u+4ED6 u+4EEC u+4E3A u+4EC0 u+4E48 u+4E0D u+8BF4 u+4E2D u+6587
+ Punycode: ihqwcrb4cv8a8dqg056pqjye
+
+ (C) Chinese (traditional):
+ u+4ED6 u+5011 u+7232 u+4EC0 u+9EBD u+4E0D u+8AAA u+4E2D u+6587
+ Punycode: ihqwctvzc91f659drss3x8bo0yb
+
+ (D) Czech: Pro<ccaron>prost<ecaron>nemluv<iacute><ccaron>esky
+ U+0050 u+0072 u+006F u+010D u+0070 u+0072 u+006F u+0073 u+0074
+ u+011B u+006E u+0065 u+006D u+006C u+0075 u+0076 u+00ED u+010D
+ u+0065 u+0073 u+006B u+0079
+ Punycode: Proprostnemluvesky-uyb24dma41a
+
+ (E) Hebrew:
+ u+05DC u+05DE u+05D4 u+05D4 u+05DD u+05E4 u+05E9 u+05D5 u+05D8
+ u+05DC u+05D0 u+05DE u+05D3 u+05D1 u+05E8 u+05D9 u+05DD u+05E2
+ u+05D1 u+05E8 u+05D9 u+05EA
+ Punycode: 4dbcagdahymbxekheh6e0a7fei0b
+
+ (F) Hindi (Devanagari):
+ u+092F u+0939 u+0932 u+094B u+0917 u+0939 u+093F u+0928 u+094D
+ u+0926 u+0940 u+0915 u+094D u+092F u+094B u+0902 u+0928 u+0939
+ u+0940 u+0902 u+092C u+094B u+0932 u+0938 u+0915 u+0924 u+0947
+ u+0939 u+0948 u+0902
+ Punycode: i1baa7eci9glrd9b2ae1bj0hfcgg6iyaf8o0a1dig0cd
+
+ (G) Japanese (kanji and hiragana):
+ u+306A u+305C u+307F u+3093 u+306A u+65E5 u+672C u+8A9E u+3092
+ u+8A71 u+3057 u+3066 u+304F u+308C u+306A u+3044 u+306E u+304B
+ Punycode: n8jok5ay5dzabd5bym9f0cm5685rrjetr6pdxa
+
+ (H) Korean (Hangul syllables):
+ u+C138 u+ACC4 u+C758 u+BAA8 u+B4E0 u+C0AC u+B78C u+B4E4 u+C774
+ u+D55C u+AD6D u+C5B4 u+B97C u+C774 u+D574 u+D55C u+B2E4 u+BA74
+ u+C5BC u+B9C8 u+B098 u+C88B u+C744 u+AE4C
+ Punycode: 989aomsvi5e83db1d2a355cv1e0vak1dwrv93d5xbh15a0dt30a5j\
+ psd879ccm6fea98c
+
+ (I) Russian (Cyrillic):
+ U+043F u+043E u+0447 u+0435 u+043C u+0443 u+0436 u+0435 u+043E
+ u+043D u+0438 u+043D u+0435 u+0433 u+043E u+0432 u+043E u+0440
+ u+044F u+0442 u+043F u+043E u+0440 u+0443 u+0441 u+0441 u+043A
+ u+0438
+ Punycode: b1abfaaepdrnnbgefbaDotcwatmq2g4l
+\f
+ (J) Spanish: Porqu<eacute>nopuedensimplementehablarenEspa<ntilde>ol
+ U+0050 u+006F u+0072 u+0071 u+0075 u+00E9 u+006E u+006F u+0070
+ u+0075 u+0065 u+0064 u+0065 u+006E u+0073 u+0069 u+006D u+0070
+ u+006C u+0065 u+006D u+0065 u+006E u+0074 u+0065 u+0068 u+0061
+ u+0062 u+006C u+0061 u+0072 u+0065 u+006E U+0045 u+0073 u+0070
+ u+0061 u+00F1 u+006F u+006C
+ Punycode: PorqunopuedensimplementehablarenEspaol-fmd56a
+
+ (K) Vietnamese:
+ T<adotbelow>isaoh<odotbelow>kh<ocirc>ngth<ecirchookabove>ch\
+ <ihookabove>n<oacute>iti<ecircacute>ngVi<ecircdotbelow>t
+ U+0054 u+1EA1 u+0069 u+0073 u+0061 u+006F u+0068 u+1ECD u+006B
+ u+0068 u+00F4 u+006E u+0067 u+0074 u+0068 u+1EC3 u+0063 u+0068
+ u+1EC9 u+006E u+00F3 u+0069 u+0074 u+0069 u+1EBF u+006E u+0067
+ U+0056 u+0069 u+1EC7 u+0074
+ Punycode: TisaohkhngthchnitingVit-kjcr8268qyxafd2f1b9g
+
+ The next several examples are all names of Japanese music artists,
+ song titles, and TV programs, just because the author happens to
+ have them handy (but Japanese is useful for providing examples
+ of single-row text, two-row text, ideographic text, and various
+ mixtures thereof).
+
+ (L) 3<nen>B<gumi><kinpachi><sensei>
+ u+0033 u+5E74 U+0042 u+7D44 u+91D1 u+516B u+5148 u+751F
+ Punycode: 3B-ww4c5e180e575a65lsy2b
+
+ (M) <amuro><namie>-with-SUPER-MONKEYS
+ u+5B89 u+5BA4 u+5948 u+7F8E u+6075 u+002D u+0077 u+0069 u+0074
+ u+0068 u+002D U+0053 U+0055 U+0050 U+0045 U+0052 u+002D U+004D
+ U+004F U+004E U+004B U+0045 U+0059 U+0053
+ Punycode: -with-SUPER-MONKEYS-pc58ag80a8qai00g7n9n
+
+ (N) Hello-Another-Way-<sorezore><no><basho>
+ U+0048 u+0065 u+006C u+006C u+006F u+002D U+0041 u+006E u+006F
+ u+0074 u+0068 u+0065 u+0072 u+002D U+0057 u+0061 u+0079 u+002D
+ u+305D u+308C u+305E u+308C u+306E u+5834 u+6240
+ Punycode: Hello-Another-Way--fc4qua05auwb3674vfr0b
+
+ (O) <hitotsu><yane><no><shita>2
+ u+3072 u+3068 u+3064 u+5C4B u+6839 u+306E u+4E0B u+0032
+ Punycode: 2-u9tlzr9756bt3uc0v
+
+ (P) Maji<de>Koi<suru>5<byou><mae>
+ U+004D u+0061 u+006A u+0069 u+3067 U+004B u+006F u+0069 u+3059
+ u+308B u+0035 u+79D2 u+524D
+ Punycode: MajiKoi5-783gue6qz075azm5e
+
+ (Q) <pafii>de<runba>
+ u+30D1 u+30D5 u+30A3 u+30FC u+0064 u+0065 u+30EB u+30F3 u+30D0
+ Punycode: de-jg4avhby1noc0d
+
+ (R) <sono><supiido><de>
+ u+305D u+306E u+30B9 u+30D4 u+30FC u+30C9 u+3067
+ Punycode: d9juau41awczczp
+\f
+ The last example is an ASCII string that breaks the existing rules
+ for host name labels. (It is not a realistic example for IDNA,
+ because IDNA never encodes pure ASCII labels.)
+
+ (S) -> $1.00 <-
+ u+002D u+003E u+0020 u+0024 u+0031 u+002E u+0030 u+0030 u+0020
+ u+003C u+002D
+ Punycode: -> $1.00 <--
+
+7.2 Decoding traces
+
+ In the following traces, the evolving state of the decoder is
+ shown as a sequence of hexadecimal values, representing the code
+ points in the extended string. An asterisk appears just after the
+ most recently inserted code point, indicating both n (the value
+ preceeding the asterisk) and i (the position of the value just after
+ the asterisk). Other numerical values are decimal.
+
+ Decoding trace of example B from section 7.1:
+
+ n is 128, i is 0, bias is 72
+ input is "ihqwcrb4cv8a8dqg056pqjye"
+ there is no delimiter, so extended string starts empty
+ delta "ihq" decodes to 19853
+ bias becomes 21
+ 4E0D *
+ delta "wc" decodes to 64
+ bias becomes 20
+ 4E0D 4E2D *
+ delta "rb" decodes to 37
+ bias becomes 13
+ 4E3A * 4E0D 4E2D
+ delta "4c" decodes to 56
+ bias becomes 17
+ 4E3A 4E48 * 4E0D 4E2D
+ delta "v8a" decodes to 599
+ bias becomes 32
+ 4E3A 4EC0 * 4E48 4E0D 4E2D
+ delta "8d" decodes to 130
+ bias becomes 23
+ 4ED6 * 4E3A 4EC0 4E48 4E0D 4E2D
+ delta "qg" decodes to 154
+ bias becomes 25
+ 4ED6 4EEC * 4E3A 4EC0 4E48 4E0D 4E2D
+ delta "056p" decodes to 46301
+ bias becomes 84
+ 4ED6 4EEC 4E3A 4EC0 4E48 4E0D 4E2D 6587 *
+ delta "qjye" decodes to 88531
+ bias becomes 90
+ 4ED6 4EEC 4E3A 4EC0 4E48 4E0D 8BF4 * 4E2D 6587
+\f
+ Decoding trace of example L from section 7.1:
+
+ n is 128, i is 0, bias is 72
+ input is "3B-ww4c5e180e575a65lsy2b"
+ literal portion is "3B-", so extended string starts as:
+ 0033 0042
+ delta "ww4c" decodes to 62042
+ bias becomes 27
+ 0033 0042 5148 *
+ delta "5e" decodes to 139
+ bias becomes 24
+ 0033 0042 516B * 5148
+ delta "180e" decodes to 16683
+ bias becomes 67
+ 0033 5E74 * 0042 516B 5148
+ delta "575a" decodes to 34821
+ bias becomes 82
+ 0033 5E74 0042 516B 5148 751F *
+ delta "65l" decodes to 14592
+ bias becomes 67
+ 0033 5E74 0042 7D44 * 516B 5148 751F
+ delta "sy2b" decodes to 42088
+ bias becomes 84
+ 0033 5E74 0042 7D44 91D1 * 516B 5148 751F
+
+7.3 Encoding traces
+
+ In the following traces, code point values are hexadecimal, while
+ other numerical values are decimal.
+\f
+ Encoding trace of example B from section 7.1:
+
+ bias is 72
+ input is:
+ 4ED6 4EEC 4E3A 4EC0 4E48 4E0D 8BF4 4E2D 6587
+ there are no basic code points, so no literal portion
+ next code point to insert is 4E0D
+ needed delta is 19853, encodes as "ihq"
+ bias becomes 21
+ next code point to insert is 4E2D
+ needed delta is 64, encodes as "wc"
+ bias becomes 20
+ next code point to insert is 4E3A
+ needed delta is 37, encodes as "rb"
+ bias becomes 13
+ next code point to insert is 4E48
+ needed delta is 56, encodes as "4c"
+ bias becomes 17
+ next code point to insert is 4EC0
+ needed delta is 599, encodes as "v8a"
+ bias becomes 32
+ next code point to insert is 4ED6
+ needed delta is 130, encodes as "8d"
+ bias becomes 23
+ next code point to insert is 4EEC
+ needed delta is 154, encodes as "qg"
+ bias becomes 25
+ next code point to insert is 6587
+ needed delta is 46301, encodes as "056p"
+ bias becomes 84
+ next code point to insert is 8BF4
+ needed delta is 88531, encodes as "qjye"
+ bias becomes 90
+ output is "ihqwcrb4cv8a8dqg056pqjye"
+\f
+ Encoding trace of example L from section 7.1:
+
+ bias is 72
+ input is:
+ 0033 5E74 0042 7D44 91D1 516B 5148 751F
+ basic code points (0033, 0042) are copied to literal portion: "3B-"
+ next code point to insert is 5148
+ needed delta is 62042, encodes as "ww4c"
+ bias becomes 27
+ next code point to insert is 516B
+ needed delta is 139, encodes as "5e"
+ bias becomes 24
+ next code point to insert is 5E74
+ needed delta is 16683, encodes as "180e"
+ bias becomes 67
+ next code point to insert is 751F
+ needed delta is 34821, encodes as "575a"
+ bias becomes 82
+ next code point to insert is 7D44
+ needed delta is 14592, encodes as "65l"
+ bias becomes 67
+ next code point to insert is 91D1
+ needed delta is 42088, encodes as "sy2b"
+ bias becomes 84
+ output is "3B-ww4c5e180e575a65lsy2b"
+
+8. Security considerations
+
+ Users expect each domain name in DNS to be controlled by a single
+ authority. If a Unicode string intended for use as a domain label
+ could map to multiple ACE labels, then an internationalized domain
+ name could map to multiple ASCII domain names, each controlled by
+ a different authority, some of which could be spoofs that hijack
+ service requests intended for another. Therefore Punycode is
+ designed so that each Unicode string has a unique encoding.
+
+ However, there can still be multiple Unicode representations of the
+ "same" text, for various definitions of "same". This problem is
+ addressed to some extent by the Unicode standard under the topic of
+ canonicalization, and this work is leveraged for domain names by
+ Nameprep [NAMEPREP].
+
+9. References (non-normative)
+
+ [ASCII] Vint Cerf, "ASCII format for Network Interchange",
+ 1969-Oct-16, RFC 20.
+
+ [IDNA] Patrik Faltstrom, Paul Hoffman, Adam M. Costello,
+ "Internationalizing Domain Names In Applications (IDNA)",
+ draft-ietf-idn-idna.
+
+ [NAMEPREP] Paul Hoffman, Marc Blanchet, "Nameprep: A
+ Stringprep Profile for Internationalized Domain Names",
+ draft-ietf-idn-nameprep.
+
+ [PROVINCIAL] Michael Kaplan, "The 'anyone can be provincial!' page",
+ http://www.trigeminal.com/samples/provincial.html.
+\f
+ [RFC952] K. Harrenstien, M. Stahl, E. Feinler, "DOD Internet Host
+ Table Specification", 1985-Oct, RFC 952.
+
+ [RFC1034] P. Mockapetris, "Domain Names - Concepts and Facilities",
+ 1987-Nov, RFC 1034.
+
+ [UNICODE] The Unicode Consortium, "The Unicode Standard",
+ http://www.unicode.org/unicode/standard/standard.html.
+
+A. Author contact information
+
+ Adam M. Costello
+ University of California, Berkeley
+ http://www.nicemice.net/amc/
+
+B. Mixed-case annotation
+
+ In order to use Punycode to represent case-insensitive strings,
+ higher layers need to case-fold the strings prior to Punycode
+ encoding. The encoded string can use mixed case as an annotation
+ telling how to convert the folded string into a mixed-case string
+ for display purposes. Note, however, that mixed-case annotation
+ is not used by the ToASCII and ToUnicode operations specified in
+ [IDNA], and therefore implementors of IDNA can disregard this
+ appendix.
+
+ Basic code points can use mixed case directly, because the decoder
+ copies them verbatim, leaving lowercase code points lowercase, and
+ leaving uppercase code points uppercase. Each non-basic code point
+ is represented by a delta, which is represented by a sequence of
+ basic code points, the last of which provides the annotation. If it
+ is uppercase, it is a suggestion to map the non-basic code point to
+ uppercase (if possible); if it is lowercase, it is a suggestion to
+ map the non-basic code point to lowercase (if possible).
+
+ These annotations do not alter the code points returned by decoders;
+ the annotations are returned separately, for the caller to use or
+ ignore. Encoders can accept annotations in addition to code points,
+ but the annotations do not alter the output, except to influence the
+ uppercase/lowercase form of ASCII letters.
+
+ Punycode encoders and decoders need not support these annotations,
+ and higher layers need not use them.
+
+C. Disclaimer and license
+
+ Regarding this entire document or any portion of it (including
+ the pseudocode and C code), the author makes no guarantees and
+ is not responsible for any damage resulting from its use. The
+ author grants irrevocable permission to anyone to use, modify,
+ and distribute it in any way that does not diminish the rights
+ of anyone else to use, modify, and distribute it, provided that
+ redistributed derivative works do not contain misleading author or
+ version information. Derivative works need not be licensed under
+ similar terms.
+
+
+D. Punycode sample implementation
+\f
+/*
+punycode.c from draft-ietf-idn-punycode-02
+http://www.nicemice.net/idn/
+Adam M. Costello
+http://www.nicemice.net/amc/
+
+This is ANSI C code (C89) implementing
+Punycode (draft-ietf-idn-punycode-02).
+
+*/
+
+
+/************************************************************/
+/* Public interface (would normally go in its own .h file): */
+
+#include <limits.h>
+
+enum punycode_status {
+ punycode_success,
+ punycode_bad_input, /* Input is invalid. */
+ punycode_big_output, /* Output would exceed the space provided. */
+ punycode_overflow /* Input needs wider integers to process. */
+};
+
+#if UINT_MAX >= (1 << 26) - 1
+typedef unsigned int punycode_uint;
+#else
+typedef unsigned long punycode_uint;
+#endif
+
+enum punycode_status punycode_encode(
+ punycode_uint input_length,
+ const punycode_uint input[],
+ const unsigned char case_flags[],
+ punycode_uint *output_length,
+ char output[] );
+\f
+ /* punycode_encode() converts Unicode to Punycode. The input */
+ /* is represented as an array of Unicode code points (not code */
+ /* units; surrogate pairs are not allowed), and the output */
+ /* will be represented as an array of ASCII code points. The */
+ /* output string is *not* null-terminated; it will contain */
+ /* zeros if and only if the input contains zeros. (Of course */
+ /* the caller can leave room for a terminator and add one if */
+ /* needed.) The input_length is the number of code points in */
+ /* the input. The output_length is an in/out argument: the */
+ /* caller passes in the maximum number of code points that it */
+ /* can receive, and on successful return it will contain the */
+ /* number of code points actually output. The case_flags array */
+ /* holds input_length boolean values, where nonzero suggests that */
+ /* the corresponding Unicode character be forced to uppercase */
+ /* after being decoded (if possible), and zero suggests that */
+ /* it be forced to lowercase (if possible). ASCII code points */
+ /* are encoded literally, except that ASCII letters are forced */
+ /* to uppercase or lowercase according to the corresponding */
+ /* uppercase flags. If case_flags is a null pointer then ASCII */
+ /* letters are left as they are, and other code points are */
+ /* treated as if their uppercase flags were zero. The return */
+ /* value can be any of the punycode_status values defined above */
+ /* except punycode_bad_input; if not punycode_success, then */
+ /* output_size and output might contain garbage. */
+
+enum punycode_status punycode_decode(
+ punycode_uint input_length,
+ const char input[],
+ punycode_uint *output_length,
+ punycode_uint output[],
+ unsigned char case_flags[] );
+
+ /* punycode_decode() converts Punycode to Unicode. The input is */
+ /* represented as an array of ASCII code points, and the output */
+ /* will be represented as an array of Unicode code points. The */
+ /* input_length is the number of code points in the input. The */
+ /* output_length is an in/out argument: the caller passes in */
+ /* the maximum number of code points that it can receive, and */
+ /* on successful return it will contain the actual number of */
+ /* code points output. The case_flags array needs room for at */
+ /* least output_length values, or it can be a null pointer if the */
+ /* case information is not needed. A nonzero flag suggests that */
+ /* the corresponding Unicode character be forced to uppercase */
+ /* by the caller (if possible), while zero suggests that it be */
+ /* forced to lowercase (if possible). ASCII code points are */
+ /* output already in the proper case, but their flags will be set */
+ /* appropriately so that applying the flags would be harmless. */
+ /* The return value can be any of the punycode_status values */
+ /* defined above; if not punycode_success, then output_length, */
+ /* output, and case_flags might contain garbage. On success, the */
+ /* decoder will never need to write an output_length greater than */
+ /* input_length, because of how the encoding is defined. */
+\f
+/**********************************************************/
+/* Implementation (would normally go in its own .c file): */
+
+#include <string.h>
+
+/*** Bootstring parameters for Punycode ***/
+
+enum { base = 36, tmin = 1, tmax = 26, skew = 38, damp = 700,
+ initial_bias = 72, initial_n = 0x80, delimiter = 0x2D };
+
+/* basic(cp) tests whether cp is a basic code point: */
+#define basic(cp) ((punycode_uint)(cp) < 0x80)
+
+/* delim(cp) tests whether cp is a delimiter: */
+#define delim(cp) ((cp) == delimiter)
+
+/* decode_digit(cp) returns the numeric value of a basic code */
+/* point (for use in representing integers) in the range 0 to */
+/* base-1, or base if cp is does not represent a value. */
+
+static punycode_uint decode_digit(punycode_uint cp)
+{
+ return cp - 48 < 10 ? cp - 22 : cp - 65 < 26 ? cp - 65 :
+ cp - 97 < 26 ? cp - 97 : base;
+}
+
+/* encode_digit(d,flag) returns the basic code point whose value */
+/* (when used for representing integers) is d, which needs to be in */
+/* the range 0 to base-1. The lowercase form is used unless flag is */
+/* nonzero, in which case the uppercase form is used. The behavior */
+/* is undefined if flag is nonzero and digit d has no uppercase form. */
+
+static char encode_digit(punycode_uint d, int flag)
+{
+ return d + 22 + 75 * (d < 26) - ((flag != 0) << 5);
+ /* 0..25 map to ASCII a..z or A..Z */
+ /* 26..35 map to ASCII 0..9 */
+}
+
+/* flagged(bcp) tests whether a basic code point is flagged */
+/* (uppercase). The behavior is undefined if bcp is not a */
+/* basic code point. */
+
+#define flagged(bcp) ((punycode_uint)(bcp) - 65 < 26)
+
+/* encode_basic(bcp,flag) forces a basic code point to lowercase */
+/* if flag is zero, uppercase if flag is nonzero, and returns */
+/* the resulting code point. The code point is unchanged if it */
+/* is caseless. The behavior is undefined if bcp is not a basic */
+/* code point. */
+
+static char encode_basic(punycode_uint bcp, int flag)
+{
+ bcp -= (bcp - 97 < 26) << 5;
+ return bcp + ((!flag && (bcp - 65 < 26)) << 5);
+}
+\f
+/*** Platform-specific constants ***/
+
+/* maxint is the maximum value of a punycode_uint variable: */
+static const punycode_uint maxint = -1;
+/* Because maxint is unsigned, -1 becomes the maximum value. */
+
+/*** Bias adaptation function ***/
+
+static punycode_uint adapt(
+ punycode_uint delta, punycode_uint numpoints, int firsttime )
+{
+ punycode_uint k;
+
+ delta = firsttime ? delta / damp : delta >> 1;
+ /* delta >> 1 is a faster way of doing delta / 2 */
+ delta += delta / numpoints;
+
+ for (k = 0; delta > ((base - tmin) * tmax) / 2; k += base) {
+ delta /= base - tmin;
+ }
+
+ return k + (base - tmin + 1) * delta / (delta + skew);
+}
+
+/*** Main encode function ***/
+
+enum punycode_status punycode_encode(
+ punycode_uint input_length,
+ const punycode_uint input[],
+ const unsigned char case_flags[],
+ punycode_uint *output_length,
+ char output[] )
+{
+ punycode_uint n, delta, h, b, out, max_out, bias, j, m, q, k, t;
+
+ /* Initialize the state: */
+
+ n = initial_n;
+ delta = out = 0;
+ max_out = *output_length;
+ bias = initial_bias;
+
+ /* Handle the basic code points: */
+
+ for (j = 0; j < input_length; ++j) {
+ if (basic(input[j])) {
+ if (max_out - out < 2) return punycode_big_output;
+ output[out++] =
+ case_flags ? encode_basic(input[j], case_flags[j]) : input[j];
+ }
+ /* else if (input[j] < n) return punycode_bad_input; */
+ /* (not needed for Punycode with unsigned code points) */
+ }
+\f
+ h = b = out;
+
+ /* h is the number of code points that have been handled, b is the */
+ /* number of basic code points, and out is the number of characters */
+ /* that have been output. */
+
+ if (b > 0) output[out++] = delimiter;
+
+ /* Main encoding loop: */
+
+ while (h < input_length) {
+ /* All non-basic code points < n have been */
+ /* handled already. Find the next larger one: */
+
+ for (m = maxint, j = 0; j < input_length; ++j) {
+ /* if (basic(input[j])) continue; */
+ /* (not needed for Punycode) */
+ if (input[j] >= n && input[j] < m) m = input[j];
+ }
+
+ /* Increase delta enough to advance the decoder's */
+ /* <n,i> state to <m,0>, but guard against overflow: */
+
+ if (m - n > (maxint - delta) / (h + 1)) return punycode_overflow;
+ delta += (m - n) * (h + 1);
+ n = m;
+
+ for (j = 0; j < input_length; ++j) {
+ /* Punycode does not need to check whether input[j] is basic: */
+ if (input[j] < n /* || basic(input[j]) */ ) {
+ if (++delta == 0) return punycode_overflow;
+ }
+
+ if (input[j] == n) {
+ /* Represent delta as a generalized variable-length integer: */
+
+ for (q = delta, k = base; ; k += base) {
+ if (out >= max_out) return punycode_big_output;
+ t = k <= bias /* + tmin */ ? tmin : /* +tmin not needed */
+ k >= bias + tmax ? tmax : k - bias;
+ if (q < t) break;
+ output[out++] = encode_digit(t + (q - t) % (base - t), 0);
+ q = (q - t) / (base - t);
+ }
+
+ output[out++] = encode_digit(q, case_flags && case_flags[j]);
+ bias = adapt(delta, h + 1, h == b);
+ delta = 0;
+ ++h;
+ }
+ }
+
+ ++delta, ++n;
+ }
+
+ *output_length = out;
+ return punycode_success;
+}
+\f
+/*** Main decode function ***/
+
+enum punycode_status punycode_decode(
+ punycode_uint input_length,
+ const char input[],
+ punycode_uint *output_length,
+ punycode_uint output[],
+ unsigned char case_flags[] )
+{
+ punycode_uint n, out, i, max_out, bias,
+ b, j, in, oldi, w, k, digit, t;
+
+ /* Initialize the state: */
+
+ n = initial_n;
+ out = i = 0;
+ max_out = *output_length;
+ bias = initial_bias;
+
+ /* Handle the basic code points: Let b be the number of input code */
+ /* points before the last delimiter, or 0 if there is none, then */
+ /* copy the first b code points to the output. */
+
+ for (b = j = 0; j < input_length; ++j) if (delim(input[j])) b = j;
+ if (b > max_out) return punycode_big_output;
+
+ for (j = 0; j < b; ++j) {
+ if (case_flags) case_flags[out] = flagged(input[j]);
+ if (!basic(input[j])) return punycode_bad_input;
+ output[out++] = input[j];
+ }
+
+ /* Main decoding loop: Start just after the last delimiter if any */
+ /* basic code points were copied; start at the beginning otherwise. */
+
+ for (in = b > 0 ? b + 1 : 0; in < input_length; ++out) {
+
+ /* in is the index of the next character to be consumed, and */
+ /* out is the number of code points in the output array. */
+
+ /* Decode a generalized variable-length integer into delta, */
+ /* which gets added to i. The overflow checking is easier */
+ /* if we increase i as we go, then subtract off its starting */
+ /* value at the end to obtain delta. */
+
+ for (oldi = i, w = 1, k = base; ; k += base) {
+ if (in >= input_length) return punycode_bad_input;
+ digit = decode_digit(input[in++]);
+ if (digit >= base) return punycode_bad_input;
+ if (digit > (maxint - i) / w) return punycode_overflow;
+ i += digit * w;
+ t = k <= bias /* + tmin */ ? tmin : /* +tmin not needed */
+ k >= bias + tmax ? tmax : k - bias;
+ if (digit < t) break;
+ if (w > maxint / (base - t)) return punycode_overflow;
+ w *= (base - t);
+ }
+\f
+ bias = adapt(i - oldi, out + 1, oldi == 0);
+
+ /* i was supposed to wrap around from out+1 to 0, */
+ /* incrementing n each time, so we'll fix that now: */
+
+ if (i / (out + 1) > maxint - n) return punycode_overflow;
+ n += i / (out + 1);
+ i %= (out + 1);
+
+ /* Insert n at position i of the output: */
+
+ /* not needed for Punycode: */
+ /* if (decode_digit(n) <= base) return punycode_invalid_input; */
+ if (out >= max_out) return punycode_big_output;
+
+ if (case_flags) {
+ memmove(case_flags + i + 1, case_flags + i, out - i);
+ /* Case of last character determines uppercase flag: */
+ case_flags[i] = flagged(input[in - 1]);
+ }
+
+ memmove(output + i + 1, output + i, (out - i) * sizeof *output);
+ output[i++] = n;
+ }
+
+ *output_length = out;
+ return punycode_success;
+}
+
+
+/******************************************************************/
+/* Wrapper for testing (would normally go in a separate .c file): */
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+/* For testing, we'll just set some compile-time limits rather than */
+/* use malloc(), and set a compile-time option rather than using a */
+/* command-line option. */
+
+enum {
+ unicode_max_length = 256,
+ ace_max_length = 256
+};
+\f
+static void usage(char **argv)
+{
+ fprintf(stderr,
+ "\n"
+ "%s -e reads code points and writes a Punycode string.\n"
+ "%s -d reads a Punycode string and writes code points.\n"
+ "\n"
+ "Input and output are plain text in the native character set.\n"
+ "Code points are in the form u+hex separated by whitespace.\n"
+ "Although the specification allows Punycode strings to contain\n"
+ "any characters from the ASCII repertoire, this test code\n"
+ "supports only the printable characters, and needs the Punycode\n"
+ "string to be followed by a newline.\n"
+ "The case of the u in u+hex is the force-to-uppercase flag.\n"
+ , argv[0], argv[0]);
+ exit(EXIT_FAILURE);
+}
+
+
+static void fail(const char *msg)
+{
+ fputs(msg,stderr);
+ exit(EXIT_FAILURE);
+}
+
+static const char too_big[] =
+ "input or output is too large, recompile with larger limits\n";
+static const char invalid_input[] = "invalid input\n";
+static const char overflow[] = "arithmetic overflow\n";
+static const char io_error[] = "I/O error\n";
+
+
+/* The following string is used to convert printable */
+/* characters between ASCII and the native charset: */
+
+static const char print_ascii[] =
+ "\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n"
+ "\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n"
+ " !\"#$%&'()*+,-./"
+ "0123456789:;<=>?"
+ "@ABCDEFGHIJKLMNO"
+ "PQRSTUVWXYZ[\\]^_"
+ "`abcdefghijklmno"
+ "pqrstuvwxyz{|}~\n";
+
+
+int main(int argc, char **argv)
+{
+ enum punycode_status status;
+ int r;
+ unsigned int input_length, output_length, j;
+ unsigned char case_flags[unicode_max_length];
+
+ if (argc != 2) usage(argv);
+ if (argv[1][0] != '-') usage(argv);
+ if (argv[1][2] != 0) usage(argv);
+\f
+ if (argv[1][1] == 'e') {
+ punycode_uint input[unicode_max_length];
+ unsigned long codept;
+ char output[ace_max_length+1], uplus[3];
+ int c;
+
+ /* Read the input code points: */
+
+ input_length = 0;
+
+ for (;;) {
+ r = scanf("%2s%lx", uplus, &codept);
+ if (ferror(stdin)) fail(io_error);
+ if (r == EOF || r == 0) break;
+
+ if (r != 2 || uplus[1] != '+' || codept > (punycode_uint)-1) {
+ fail(invalid_input);
+ }
+
+ if (input_length == unicode_max_length) fail(too_big);
+
+ if (uplus[0] == 'u') case_flags[input_length] = 0;
+ else if (uplus[0] == 'U') case_flags[input_length] = 1;
+ else fail(invalid_input);
+
+ input[input_length++] = codept;
+ }
+
+ /* Encode: */
+
+ output_length = ace_max_length;
+ status = punycode_encode(input_length, input, case_flags,
+ &output_length, output);
+ if (status == punycode_bad_input) fail(invalid_input);
+ if (status == punycode_big_output) fail(too_big);
+ if (status == punycode_overflow) fail(overflow);
+ assert(status == punycode_success);
+
+ /* Convert to native charset and output: */
+
+ for (j = 0; j < output_length; ++j) {
+ c = output[j];
+ assert(c >= 0 && c <= 127);
+ if (print_ascii[c] == 0) fail(invalid_input);
+ output[j] = print_ascii[c];
+ }
+
+ output[j] = 0;
+ r = puts(output);
+ if (r == EOF) fail(io_error);
+ return EXIT_SUCCESS;
+ }
+
+ if (argv[1][1] == 'd') {
+ char input[ace_max_length+2], *p, *pp;
+ punycode_uint output[unicode_max_length];
+\f
+ /* Read the Punycode input string and convert to ASCII: */
+
+ fgets(input, ace_max_length+2, stdin);
+ if (ferror(stdin)) fail(io_error);
+ if (feof(stdin)) fail(invalid_input);
+ input_length = strlen(input) - 1;
+ if (input[input_length] != '\n') fail(too_big);
+ input[input_length] = 0;
+
+ for (p = input; *p != 0; ++p) {
+ pp = strchr(print_ascii, *p);
+ if (pp == 0) fail(invalid_input);
+ *p = pp - print_ascii;
+ }
+
+ /* Decode: */
+
+ output_length = unicode_max_length;
+ status = punycode_decode(input_length, input, &output_length,
+ output, case_flags);
+ if (status == punycode_bad_input) fail(invalid_input);
+ if (status == punycode_big_output) fail(too_big);
+ if (status == punycode_overflow) fail(overflow);
+ assert(status == punycode_success);
+
+ /* Output the result: */
+
+ for (j = 0; j < output_length; ++j) {
+ r = printf("%s+%04lX\n",
+ case_flags[j] ? "U" : "u",
+ (unsigned long) output[j] );
+ if (r < 0) fail(io_error);
+ }
+
+ return EXIT_SUCCESS;
+ }
+
+ usage(argv);
+ return EXIT_SUCCESS; /* not reached, but quiets compiler warning */
+}
+
+
+
+ INTERNET-DRAFT expires 2002-Nov-23
projects / thirdparty / bind9.git / commitdiff
