--- /dev/null
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package transform provides reader and writer wrappers that transform the
+// bytes passing through as well as various transformations. Example
+// transformations provided by other packages include normalization and
+// conversion between character sets.
+package transform // import "golang.org/x/text/transform"
+
+import (
+ "bytes"
+ "errors"
+ "io"
+ "unicode/utf8"
+)
+
+var (
+ // ErrShortDst means that the destination buffer was too short to
+ // receive all of the transformed bytes.
+ ErrShortDst = errors.New("transform: short destination buffer")
+
+ // ErrShortSrc means that the source buffer has insufficient data to
+ // complete the transformation.
+ ErrShortSrc = errors.New("transform: short source buffer")
+
+ // ErrEndOfSpan means that the input and output (the transformed input)
+ // are not identical.
+ ErrEndOfSpan = errors.New("transform: input and output are not identical")
+
+ // errInconsistentByteCount means that Transform returned success (nil
+ // error) but also returned nSrc inconsistent with the src argument.
+ errInconsistentByteCount = errors.New("transform: inconsistent byte count returned")
+
+ // errShortInternal means that an internal buffer is not large enough
+ // to make progress and the Transform operation must be aborted.
+ errShortInternal = errors.New("transform: short internal buffer")
+)
+
+// Transformer transforms bytes.
+type Transformer interface {
+ // Transform writes to dst the transformed bytes read from src, and
+ // returns the number of dst bytes written and src bytes read. The
+ // atEOF argument tells whether src represents the last bytes of the
+ // input.
+ //
+ // Callers should always process the nDst bytes produced and account
+ // for the nSrc bytes consumed before considering the error err.
+ //
+ // A nil error means that all of the transformed bytes (whether freshly
+ // transformed from src or left over from previous Transform calls)
+ // were written to dst. A nil error can be returned regardless of
+ // whether atEOF is true. If err is nil then nSrc must equal len(src);
+ // the converse is not necessarily true.
+ //
+ // ErrShortDst means that dst was too short to receive all of the
+ // transformed bytes. ErrShortSrc means that src had insufficient data
+ // to complete the transformation. If both conditions apply, then
+ // either error may be returned. Other than the error conditions listed
+ // here, implementations are free to report other errors that arise.
+ Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error)
+
+ // Reset resets the state and allows a Transformer to be reused.
+ Reset()
+}
+
+// SpanningTransformer extends the Transformer interface with a Span method
+// that determines how much of the input already conforms to the Transformer.
+type SpanningTransformer interface {
+ Transformer
+
+ // Span returns a position in src such that transforming src[:n] results in
+ // identical output src[:n] for these bytes. It does not necessarily return
+ // the largest such n. The atEOF argument tells whether src represents the
+ // last bytes of the input.
+ //
+ // Callers should always account for the n bytes consumed before
+ // considering the error err.
+ //
+ // A nil error means that all input bytes are known to be identical to the
+ // output produced by the Transformer. A nil error can be returned
+ // regardless of whether atEOF is true. If err is nil, then n must
+ // equal len(src); the converse is not necessarily true.
+ //
+ // ErrEndOfSpan means that the Transformer output may differ from the
+ // input after n bytes. Note that n may be len(src), meaning that the output
+ // would contain additional bytes after otherwise identical output.
+ // ErrShortSrc means that src had insufficient data to determine whether the
+ // remaining bytes would change. Other than the error conditions listed
+ // here, implementations are free to report other errors that arise.
+ //
+ // Calling Span can modify the Transformer state as a side effect. In
+ // effect, it does the transformation just as calling Transform would, only
+ // without copying to a destination buffer and only up to a point it can
+ // determine the input and output bytes are the same. This is obviously more
+ // limited than calling Transform, but can be more efficient in terms of
+ // copying and allocating buffers. Calls to Span and Transform may be
+ // interleaved.
+ Span(src []byte, atEOF bool) (n int, err error)
+}
+
+// NopResetter can be embedded by implementations of Transformer to add a nop
+// Reset method.
+type NopResetter struct{}
+
+// Reset implements the Reset method of the Transformer interface.
+func (NopResetter) Reset() {}
+
+// Reader wraps another io.Reader by transforming the bytes read.
+type Reader struct {
+ r io.Reader
+ t Transformer
+ err error
+
+ // dst[dst0:dst1] contains bytes that have been transformed by t but
+ // not yet copied out via Read.
+ dst []byte
+ dst0, dst1 int
+
+ // src[src0:src1] contains bytes that have been read from r but not
+ // yet transformed through t.
+ src []byte
+ src0, src1 int
+
+ // transformComplete is whether the transformation is complete,
+ // regardless of whether or not it was successful.
+ transformComplete bool
+}
+
+const defaultBufSize = 4096
+
+// NewReader returns a new Reader that wraps r by transforming the bytes read
+// via t. It calls Reset on t.
+func NewReader(r io.Reader, t Transformer) *Reader {
+ t.Reset()
+ return &Reader{
+ r: r,
+ t: t,
+ dst: make([]byte, defaultBufSize),
+ src: make([]byte, defaultBufSize),
+ }
+}
+
+// Read implements the io.Reader interface.
+func (r *Reader) Read(p []byte) (int, error) {
+ n, err := 0, error(nil)
+ for {
+ // Copy out any transformed bytes and return the final error if we are done.
+ if r.dst0 != r.dst1 {
+ n = copy(p, r.dst[r.dst0:r.dst1])
+ r.dst0 += n
+ if r.dst0 == r.dst1 && r.transformComplete {
+ return n, r.err
+ }
+ return n, nil
+ } else if r.transformComplete {
+ return 0, r.err
+ }
+
+ // Try to transform some source bytes, or to flush the transformer if we
+ // are out of source bytes. We do this even if r.r.Read returned an error.
+ // As the io.Reader documentation says, "process the n > 0 bytes returned
+ // before considering the error".
+ if r.src0 != r.src1 || r.err != nil {
+ r.dst0 = 0
+ r.dst1, n, err = r.t.Transform(r.dst, r.src[r.src0:r.src1], r.err == io.EOF)
+ r.src0 += n
+
+ switch {
+ case err == nil:
+ if r.src0 != r.src1 {
+ r.err = errInconsistentByteCount
+ }
+ // The Transform call was successful; we are complete if we
+ // cannot read more bytes into src.
+ r.transformComplete = r.err != nil
+ continue
+ case err == ErrShortDst && (r.dst1 != 0 || n != 0):
+ // Make room in dst by copying out, and try again.
+ continue
+ case err == ErrShortSrc && r.src1-r.src0 != len(r.src) && r.err == nil:
+ // Read more bytes into src via the code below, and try again.
+ default:
+ r.transformComplete = true
+ // The reader error (r.err) takes precedence over the
+ // transformer error (err) unless r.err is nil or io.EOF.
+ if r.err == nil || r.err == io.EOF {
+ r.err = err
+ }
+ continue
+ }
+ }
+
+ // Move any untransformed source bytes to the start of the buffer
+ // and read more bytes.
+ if r.src0 != 0 {
+ r.src0, r.src1 = 0, copy(r.src, r.src[r.src0:r.src1])
+ }
+ n, r.err = r.r.Read(r.src[r.src1:])
+ r.src1 += n
+ }
+}
+
+// TODO: implement ReadByte (and ReadRune??).
+
+// Writer wraps another io.Writer by transforming the bytes read.
+// The user needs to call Close to flush unwritten bytes that may
+// be buffered.
+type Writer struct {
+ w io.Writer
+ t Transformer
+ dst []byte
+
+ // src[:n] contains bytes that have not yet passed through t.
+ src []byte
+ n int
+}
+
+// NewWriter returns a new Writer that wraps w by transforming the bytes written
+// via t. It calls Reset on t.
+func NewWriter(w io.Writer, t Transformer) *Writer {
+ t.Reset()
+ return &Writer{
+ w: w,
+ t: t,
+ dst: make([]byte, defaultBufSize),
+ src: make([]byte, defaultBufSize),
+ }
+}
+
+// Write implements the io.Writer interface. If there are not enough
+// bytes available to complete a Transform, the bytes will be buffered
+// for the next write. Call Close to convert the remaining bytes.
+func (w *Writer) Write(data []byte) (n int, err error) {
+ src := data
+ if w.n > 0 {
+ // Append bytes from data to the last remainder.
+ // TODO: limit the amount copied on first try.
+ n = copy(w.src[w.n:], data)
+ w.n += n
+ src = w.src[:w.n]
+ }
+ for {
+ nDst, nSrc, err := w.t.Transform(w.dst, src, false)
+ if _, werr := w.w.Write(w.dst[:nDst]); werr != nil {
+ return n, werr
+ }
+ src = src[nSrc:]
+ if w.n == 0 {
+ n += nSrc
+ } else if len(src) <= n {
+ // Enough bytes from w.src have been consumed. We make src point
+ // to data instead to reduce the copying.
+ w.n = 0
+ n -= len(src)
+ src = data[n:]
+ if n < len(data) && (err == nil || err == ErrShortSrc) {
+ continue
+ }
+ }
+ switch err {
+ case ErrShortDst:
+ // This error is okay as long as we are making progress.
+ if nDst > 0 || nSrc > 0 {
+ continue
+ }
+ case ErrShortSrc:
+ if len(src) < len(w.src) {
+ m := copy(w.src, src)
+ // If w.n > 0, bytes from data were already copied to w.src and n
+ // was already set to the number of bytes consumed.
+ if w.n == 0 {
+ n += m
+ }
+ w.n = m
+ err = nil
+ } else if nDst > 0 || nSrc > 0 {
+ // Not enough buffer to store the remainder. Keep processing as
+ // long as there is progress. Without this case, transforms that
+ // require a lookahead larger than the buffer may result in an
+ // error. This is not something one may expect to be common in
+ // practice, but it may occur when buffers are set to small
+ // sizes during testing.
+ continue
+ }
+ case nil:
+ if w.n > 0 {
+ err = errInconsistentByteCount
+ }
+ }
+ return n, err
+ }
+}
+
+// Close implements the io.Closer interface.
+func (w *Writer) Close() error {
+ src := w.src[:w.n]
+ for {
+ nDst, nSrc, err := w.t.Transform(w.dst, src, true)
+ if _, werr := w.w.Write(w.dst[:nDst]); werr != nil {
+ return werr
+ }
+ if err != ErrShortDst {
+ return err
+ }
+ src = src[nSrc:]
+ }
+}
+
+type nop struct{ NopResetter }
+
+func (nop) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
+ n := copy(dst, src)
+ if n < len(src) {
+ err = ErrShortDst
+ }
+ return n, n, err
+}
+
+func (nop) Span(src []byte, atEOF bool) (n int, err error) {
+ return len(src), nil
+}
+
+type discard struct{ NopResetter }
+
+func (discard) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
+ return 0, len(src), nil
+}
+
+var (
+ // Discard is a Transformer for which all Transform calls succeed
+ // by consuming all bytes and writing nothing.
+ Discard Transformer = discard{}
+
+ // Nop is a SpanningTransformer that copies src to dst.
+ Nop SpanningTransformer = nop{}
+)
+
+// chain is a sequence of links. A chain with N Transformers has N+1 links and
+// N+1 buffers. Of those N+1 buffers, the first and last are the src and dst
+// buffers given to chain.Transform and the middle N-1 buffers are intermediate
+// buffers owned by the chain. The i'th link transforms bytes from the i'th
+// buffer chain.link[i].b at read offset chain.link[i].p to the i+1'th buffer
+// chain.link[i+1].b at write offset chain.link[i+1].n, for i in [0, N).
+type chain struct {
+ link []link
+ err error
+ // errStart is the index at which the error occurred plus 1. Processing
+ // errStart at this level at the next call to Transform. As long as
+ // errStart > 0, chain will not consume any more source bytes.
+ errStart int
+}
+
+func (c *chain) fatalError(errIndex int, err error) {
+ if i := errIndex + 1; i > c.errStart {
+ c.errStart = i
+ c.err = err
+ }
+}
+
+type link struct {
+ t Transformer
+ // b[p:n] holds the bytes to be transformed by t.
+ b []byte
+ p int
+ n int
+}
+
+func (l *link) src() []byte {
+ return l.b[l.p:l.n]
+}
+
+func (l *link) dst() []byte {
+ return l.b[l.n:]
+}
+
+// Chain returns a Transformer that applies t in sequence.
+func Chain(t ...Transformer) Transformer {
+ if len(t) == 0 {
+ return nop{}
+ }
+ c := &chain{link: make([]link, len(t)+1)}
+ for i, tt := range t {
+ c.link[i].t = tt
+ }
+ // Allocate intermediate buffers.
+ b := make([][defaultBufSize]byte, len(t)-1)
+ for i := range b {
+ c.link[i+1].b = b[i][:]
+ }
+ return c
+}
+
+// Reset resets the state of Chain. It calls Reset on all the Transformers.
+func (c *chain) Reset() {
+ for i, l := range c.link {
+ if l.t != nil {
+ l.t.Reset()
+ }
+ c.link[i].p, c.link[i].n = 0, 0
+ }
+}
+
+// TODO: make chain use Span (is going to be fun to implement!)
+
+// Transform applies the transformers of c in sequence.
+func (c *chain) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
+ // Set up src and dst in the chain.
+ srcL := &c.link[0]
+ dstL := &c.link[len(c.link)-1]
+ srcL.b, srcL.p, srcL.n = src, 0, len(src)
+ dstL.b, dstL.n = dst, 0
+ var lastFull, needProgress bool // for detecting progress
+
+ // i is the index of the next Transformer to apply, for i in [low, high].
+ // low is the lowest index for which c.link[low] may still produce bytes.
+ // high is the highest index for which c.link[high] has a Transformer.
+ // The error returned by Transform determines whether to increase or
+ // decrease i. We try to completely fill a buffer before converting it.
+ for low, i, high := c.errStart, c.errStart, len(c.link)-2; low <= i && i <= high; {
+ in, out := &c.link[i], &c.link[i+1]
+ nDst, nSrc, err0 := in.t.Transform(out.dst(), in.src(), atEOF && low == i)
+ out.n += nDst
+ in.p += nSrc
+ if i > 0 && in.p == in.n {
+ in.p, in.n = 0, 0
+ }
+ needProgress, lastFull = lastFull, false
+ switch err0 {
+ case ErrShortDst:
+ // Process the destination buffer next. Return if we are already
+ // at the high index.
+ if i == high {
+ return dstL.n, srcL.p, ErrShortDst
+ }
+ if out.n != 0 {
+ i++
+ // If the Transformer at the next index is not able to process any
+ // source bytes there is nothing that can be done to make progress
+ // and the bytes will remain unprocessed. lastFull is used to
+ // detect this and break out of the loop with a fatal error.
+ lastFull = true
+ continue
+ }
+ // The destination buffer was too small, but is completely empty.
+ // Return a fatal error as this transformation can never complete.
+ c.fatalError(i, errShortInternal)
+ case ErrShortSrc:
+ if i == 0 {
+ // Save ErrShortSrc in err. All other errors take precedence.
+ err = ErrShortSrc
+ break
+ }
+ // Source bytes were depleted before filling up the destination buffer.
+ // Verify we made some progress, move the remaining bytes to the errStart
+ // and try to get more source bytes.
+ if needProgress && nSrc == 0 || in.n-in.p == len(in.b) {
+ // There were not enough source bytes to proceed while the source
+ // buffer cannot hold any more bytes. Return a fatal error as this
+ // transformation can never complete.
+ c.fatalError(i, errShortInternal)
+ break
+ }
+ // in.b is an internal buffer and we can make progress.
+ in.p, in.n = 0, copy(in.b, in.src())
+ fallthrough
+ case nil:
+ // if i == low, we have depleted the bytes at index i or any lower levels.
+ // In that case we increase low and i. In all other cases we decrease i to
+ // fetch more bytes before proceeding to the next index.
+ if i > low {
+ i--
+ continue
+ }
+ default:
+ c.fatalError(i, err0)
+ }
+ // Exhausted level low or fatal error: increase low and continue
+ // to process the bytes accepted so far.
+ i++
+ low = i
+ }
+
+ // If c.errStart > 0, this means we found a fatal error. We will clear
+ // all upstream buffers. At this point, no more progress can be made
+ // downstream, as Transform would have bailed while handling ErrShortDst.
+ if c.errStart > 0 {
+ for i := 1; i < c.errStart; i++ {
+ c.link[i].p, c.link[i].n = 0, 0
+ }
+ err, c.errStart, c.err = c.err, 0, nil
+ }
+ return dstL.n, srcL.p, err
+}
+
+// Deprecated: Use runes.Remove instead.
+func RemoveFunc(f func(r rune) bool) Transformer {
+ return removeF(f)
+}
+
+type removeF func(r rune) bool
+
+func (removeF) Reset() {}
+
+// Transform implements the Transformer interface.
+func (t removeF) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
+ for r, sz := rune(0), 0; len(src) > 0; src = src[sz:] {
+
+ if r = rune(src[0]); r < utf8.RuneSelf {
+ sz = 1
+ } else {
+ r, sz = utf8.DecodeRune(src)
+
+ if sz == 1 {
+ // Invalid rune.
+ if !atEOF && !utf8.FullRune(src) {
+ err = ErrShortSrc
+ break
+ }
+ // We replace illegal bytes with RuneError. Not doing so might
+ // otherwise turn a sequence of invalid UTF-8 into valid UTF-8.
+ // The resulting byte sequence may subsequently contain runes
+ // for which t(r) is true that were passed unnoticed.
+ if !t(r) {
+ if nDst+3 > len(dst) {
+ err = ErrShortDst
+ break
+ }
+ nDst += copy(dst[nDst:], "\uFFFD")
+ }
+ nSrc++
+ continue
+ }
+ }
+
+ if !t(r) {
+ if nDst+sz > len(dst) {
+ err = ErrShortDst
+ break
+ }
+ nDst += copy(dst[nDst:], src[:sz])
+ }
+ nSrc += sz
+ }
+ return
+}
+
+// grow returns a new []byte that is longer than b, and copies the first n bytes
+// of b to the start of the new slice.
+func grow(b []byte, n int) []byte {
+ m := len(b)
+ if m <= 32 {
+ m = 64
+ } else if m <= 256 {
+ m *= 2
+ } else {
+ m += m >> 1
+ }
+ buf := make([]byte, m)
+ copy(buf, b[:n])
+ return buf
+}
+
+const initialBufSize = 128
+
+// String returns a string with the result of converting s[:n] using t, where
+// n <= len(s). If err == nil, n will be len(s). It calls Reset on t.
+func String(t Transformer, s string) (result string, n int, err error) {
+ t.Reset()
+ if s == "" {
+ // Fast path for the common case for empty input. Results in about a
+ // 86% reduction of running time for BenchmarkStringLowerEmpty.
+ if _, _, err := t.Transform(nil, nil, true); err == nil {
+ return "", 0, nil
+ }
+ }
+
+ // Allocate only once. Note that both dst and src escape when passed to
+ // Transform.
+ buf := [2 * initialBufSize]byte{}
+ dst := buf[:initialBufSize:initialBufSize]
+ src := buf[initialBufSize : 2*initialBufSize]
+
+ // The input string s is transformed in multiple chunks (starting with a
+ // chunk size of initialBufSize). nDst and nSrc are per-chunk (or
+ // per-Transform-call) indexes, pDst and pSrc are overall indexes.
+ nDst, nSrc := 0, 0
+ pDst, pSrc := 0, 0
+
+ // pPrefix is the length of a common prefix: the first pPrefix bytes of the
+ // result will equal the first pPrefix bytes of s. It is not guaranteed to
+ // be the largest such value, but if pPrefix, len(result) and len(s) are
+ // all equal after the final transform (i.e. calling Transform with atEOF
+ // being true returned nil error) then we don't need to allocate a new
+ // result string.
+ pPrefix := 0
+ for {
+ // Invariant: pDst == pPrefix && pSrc == pPrefix.
+
+ n := copy(src, s[pSrc:])
+ nDst, nSrc, err = t.Transform(dst, src[:n], pSrc+n == len(s))
+ pDst += nDst
+ pSrc += nSrc
+
+ // TODO: let transformers implement an optional Spanner interface, akin
+ // to norm's QuickSpan. This would even allow us to avoid any allocation.
+ if !bytes.Equal(dst[:nDst], src[:nSrc]) {
+ break
+ }
+ pPrefix = pSrc
+ if err == ErrShortDst {
+ // A buffer can only be short if a transformer modifies its input.
+ break
+ } else if err == ErrShortSrc {
+ if nSrc == 0 {
+ // No progress was made.
+ break
+ }
+ // Equal so far and !atEOF, so continue checking.
+ } else if err != nil || pPrefix == len(s) {
+ return string(s[:pPrefix]), pPrefix, err
+ }
+ }
+ // Post-condition: pDst == pPrefix + nDst && pSrc == pPrefix + nSrc.
+
+ // We have transformed the first pSrc bytes of the input s to become pDst
+ // transformed bytes. Those transformed bytes are discontiguous: the first
+ // pPrefix of them equal s[:pPrefix] and the last nDst of them equal
+ // dst[:nDst]. We copy them around, into a new dst buffer if necessary, so
+ // that they become one contiguous slice: dst[:pDst].
+ if pPrefix != 0 {
+ newDst := dst
+ if pDst > len(newDst) {
+ newDst = make([]byte, len(s)+nDst-nSrc)
+ }
+ copy(newDst[pPrefix:pDst], dst[:nDst])
+ copy(newDst[:pPrefix], s[:pPrefix])
+ dst = newDst
+ }
+
+ // Prevent duplicate Transform calls with atEOF being true at the end of
+ // the input. Also return if we have an unrecoverable error.
+ if (err == nil && pSrc == len(s)) ||
+ (err != nil && err != ErrShortDst && err != ErrShortSrc) {
+ return string(dst[:pDst]), pSrc, err
+ }
+
+ // Transform the remaining input, growing dst and src buffers as necessary.
+ for {
+ n := copy(src, s[pSrc:])
+ nDst, nSrc, err := t.Transform(dst[pDst:], src[:n], pSrc+n == len(s))
+ pDst += nDst
+ pSrc += nSrc
+
+ // If we got ErrShortDst or ErrShortSrc, do not grow as long as we can
+ // make progress. This may avoid excessive allocations.
+ if err == ErrShortDst {
+ if nDst == 0 {
+ dst = grow(dst, pDst)
+ }
+ } else if err == ErrShortSrc {
+ if nSrc == 0 {
+ src = grow(src, 0)
+ }
+ } else if err != nil || pSrc == len(s) {
+ return string(dst[:pDst]), pSrc, err
+ }
+ }
+}
+
+// Bytes returns a new byte slice with the result of converting b[:n] using t,
+// where n <= len(b). If err == nil, n will be len(b). It calls Reset on t.
+func Bytes(t Transformer, b []byte) (result []byte, n int, err error) {
+ return doAppend(t, 0, make([]byte, len(b)), b)
+}
+
+// Append appends the result of converting src[:n] using t to dst, where
+// n <= len(src), If err == nil, n will be len(src). It calls Reset on t.
+func Append(t Transformer, dst, src []byte) (result []byte, n int, err error) {
+ if len(dst) == cap(dst) {
+ n := len(src) + len(dst) // It is okay for this to be 0.
+ b := make([]byte, n)
+ dst = b[:copy(b, dst)]
+ }
+ return doAppend(t, len(dst), dst[:cap(dst)], src)
+}
+
+func doAppend(t Transformer, pDst int, dst, src []byte) (result []byte, n int, err error) {
+ t.Reset()
+ pSrc := 0
+ for {
+ nDst, nSrc, err := t.Transform(dst[pDst:], src[pSrc:], true)
+ pDst += nDst
+ pSrc += nSrc
+ if err != ErrShortDst {
+ return dst[:pDst], pSrc, err
+ }
+
+ // Grow the destination buffer, but do not grow as long as we can make
+ // progress. This may avoid excessive allocations.
+ if nDst == 0 {
+ dst = grow(dst, pDst)
+ }
+ }
+}
Code Review / barometer.git / blobdiff