327 lines
7.3 KiB
Go
327 lines
7.3 KiB
Go
package fastpath
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import (
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"unsafe"
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)
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// Clean: see Builder.Clean(). Analogous to path.Clean().
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func Clean(path string) string {
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return (&Builder{}).Clean(path)
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}
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// Join: see Builder.Join(). Analogous to path.Join().
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func Join(elems ...string) string {
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return (&Builder{}).Join(elems...)
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}
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// Builder provides a means of cleaning and joining system paths,
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// while retaining a singular underlying byte buffer for performance.
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type Builder struct {
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// B is the underlying byte buffer
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B []byte
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dd int // pos of last '..' appended to builder
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abs bool // abs stores whether path passed to first .Append() is absolute
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set bool // set stores whether b.abs has been set i.e. not first call to .Append()
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}
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// Reset resets the Builder object
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func (b *Builder) Reset() {
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b.B = b.B[:0]
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b.dd = 0
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b.abs = false
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b.set = false
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}
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// Len returns the number of accumulated bytes in the Builder
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func (b Builder) Len() int {
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return len(b.B)
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}
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// Cap returns the capacity of the underlying Builder buffer
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func (b Builder) Cap() int {
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return cap(b.B)
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}
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// Bytes returns the accumulated path bytes.
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func (b Builder) Bytes() []byte {
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return b.B
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}
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// String returns the accumulated path string.
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func (b Builder) String() string {
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return *(*string)(unsafe.Pointer(&b.B))
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}
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// Absolute returns whether current path is absolute (not relative).
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func (b Builder) Absolute() bool {
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return b.abs
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}
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// SetAbsolute converts the current path to-or-from absolute.
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func (b *Builder) SetAbsolute(enabled bool) {
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if !b.set {
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// Ensure 1B avail
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b.Guarantee(1)
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if enabled {
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// Set empty 'abs'
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b.appendByte('/')
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b.abs = true
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} else {
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// Set empty 'rel'
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b.appendByte('.')
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b.abs = false
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}
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b.set = true
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return
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}
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if !enabled && b.abs {
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// set && absolute
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// -> update
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b.abs = false
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// If empty, set to '.' (empty rel path)
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if len(b.B) == 0 || (len(b.B) == 1 && b.B[0] == '/') {
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b.Guarantee(1)
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b.B = b.B[:1]
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b.B[0] = '.'
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return
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}
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if b.B[0] != '/' {
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// No need to change
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return
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}
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if len(b.B) > 1 {
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// Shift bytes 1 left
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copy(b.B, b.B[1:])
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}
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// and drop the '/' prefix'
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b.B = b.B[:len(b.B)-1]
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} else if enabled && !b.abs {
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// set && !absolute
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// -> update
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b.abs = true
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// Ensure 1B avail
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b.Guarantee(1)
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// If empty, set to '/' (empty abs path)
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if len(b.B) == 0 || (len(b.B) == 1 && b.B[0] == '.') {
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b.Guarantee(1)
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b.B = b.B[:1]
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b.B[0] = '/'
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return
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}
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// Increase length
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l := len(b.B)
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b.B = b.B[:l+1]
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// Shift bytes 1 right
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copy(b.B[1:], b.B[:l])
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// Set first byte '/'
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b.B[0] = '/'
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}
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}
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// AppendBytes adds and cleans the supplied path bytes to the
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// builder's internal buffer, growing the buffer if necessary
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// to accomodate the extra path length.
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func (b *Builder) AppendBytes(path []byte) {
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if len(path) == 0 {
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return
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}
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b.Guarantee(len(path) + 1)
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b.append(*(*string)(unsafe.Pointer(&b)))
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}
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// Append adds and cleans the supplied path string to the
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// builder's internal buffer, growing the buffer if necessary
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// to accomodate the extra path length.
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func (b *Builder) Append(path string) {
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if len(path) == 0 {
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return
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}
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b.Guarantee(len(path) + 1)
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b.append(path)
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}
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// Clean creates the shortest possible functional equivalent
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// to the supplied path, resetting the builder before performing
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// this operation. The builder object is NOT reset after return.
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func (b *Builder) Clean(path string) string {
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if path == "" {
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return "."
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}
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b.Reset()
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b.Guarantee(len(path) + 1)
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b.append(path)
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return string(b.B)
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}
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// Join connects and cleans multiple paths, resetting the builder before
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// performing this operation and returning the shortest possible combination
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// of all the supplied paths. The builder object is NOT reset after return.
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func (b *Builder) Join(elems ...string) string {
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var size int
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for _, elem := range elems {
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size += len(elem)
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}
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if size == 0 {
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return ""
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}
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b.Reset()
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b.Guarantee(size + 1)
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for _, elem := range elems {
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if elem == "" {
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continue
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}
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b.append(elem)
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}
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return string(b.B)
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}
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// append performs the main logic of 'Append()' but without an empty path check or preallocation.
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func (b *Builder) append(path string) {
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if !b.set {
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// Set if absolute or not
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b.abs = path[0] == '/'
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b.set = true
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} else if !b.abs && len(b.B) == 1 && b.B[0] == '.' {
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// Empty non-abs path segment, drop
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// the period so not prefixed './'
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b.B = b.B[:0]
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}
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for i := 0; i < len(path); {
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switch {
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// Empty path segment
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case path[i] == '/':
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i++
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// Singular '.' path segment, treat as empty
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case path[i] == '.' && (i+1 == len(path) || path[i+1] == '/'):
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i++
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// Backtrack segment
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case path[i] == '.' && path[i+1] == '.' && (i+2 == len(path) || path[i+2] == '/'):
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i += 2
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switch {
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// Check if it's possible to backtrack with
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// our current state of the buffer. i.e. is
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// our buffer length longer than the last
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// '..' we placed?
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case len(b.B) > b.dd:
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b.backtrack()
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// If we reached here, need to check if
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// we can append '..' to the path buffer,
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// which is ONLY when path is NOT absolute
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case !b.abs:
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if len(b.B) > 0 {
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b.appendByte('/')
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}
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b.appendByte('.')
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b.appendByte('.')
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b.dd = len(b.B)
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}
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default:
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if (b.abs && len(b.B) != 1) || (!b.abs && len(b.B) > 0) {
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// Append path separator
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b.appendByte('/')
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}
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// Append slice up to next '/'
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i += b.appendSlice(path[i:])
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}
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}
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if len(b.B) > 0 {
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return
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}
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if b.abs {
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// Empty absolute path => /
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b.appendByte('/')
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} else {
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// Empty relative path => .
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b.appendByte('.')
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}
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}
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// Guarantee ensures there is at least the requested size
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// free bytes available in the buffer, reallocating if necessary
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func (b *Builder) Guarantee(size int) {
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if size > cap(b.B)-len(b.B) {
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nb := make([]byte, 2*cap(b.B)+size)
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copy(nb, b.B)
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b.B = nb[:len(b.B)]
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}
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}
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// Truncate reduces the length of the buffer by the requested
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// number of bytes. If the byte slice is *effectively* empty,
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// i.e. absolute and "/" or relative and ".", it won't be truncated.
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func (b *Builder) Truncate(size int) {
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if len(b.B) == 0 {
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return
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}
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if len(b.B) == 1 && ((b.abs && b.B[0] == '/') ||
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(!b.abs && b.B[0] == '.')) {
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// *effectively* empty
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return
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}
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// Truncate requested bytes
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b.B = b.B[:len(b.B)-size]
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}
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// appendByte appends the supplied byte to the end of
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// the buffer. appending is achieved by continually reslicing the
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// buffer and setting the next byte-at-index, this is safe as guarantee()
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// will have been called beforehand
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func (b *Builder) appendByte(c byte) {
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b.B = b.B[:len(b.B)+1]
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b.B[len(b.B)-1] = c
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}
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// appendSlice appends the supplied string slice to
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// the end of the buffer and returns the number of indices
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// we were able to iterate before hitting a path separator '/'.
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// appending is achieved by continually reslicing the buffer
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// and setting the next byte-at-index, this is safe as guarantee()
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// will have been called beforehand
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func (b *Builder) appendSlice(slice string) int {
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i := 0
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for i < len(slice) && slice[i] != '/' {
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b.B = b.B[:len(b.B)+1]
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b.B[len(b.B)-1] = slice[i]
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i++
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}
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return i
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}
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// backtrack reduces the end of the buffer back to the last
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// separating '/', or end of buffer
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func (b *Builder) backtrack() {
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b.B = b.B[:len(b.B)-1]
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for len(b.B)-1 > b.dd && b.B[len(b.B)-1] != '/' {
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b.B = b.B[:len(b.B)-1]
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}
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if len(b.B) > 0 {
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b.B = b.B[:len(b.B)-1]
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}
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}
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