mirror of
https://gitea.com/Lydanne/buildx.git
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133 lines
3.4 KiB
Go
133 lines
3.4 KiB
Go
package stringbuffer
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import (
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"sync"
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"unicode/utf16"
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)
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// TODO: worth exporting and using in mkwinsyscall?
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// Uint16BufferSize is the buffer size in the pool, chosen somewhat arbitrarily to accommodate
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// large path strings:
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// MAX_PATH (260) + size of volume GUID prefix (49) + null terminator = 310.
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const MinWStringCap = 310
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// use *[]uint16 since []uint16 creates an extra allocation where the slice header
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// is copied to heap and then referenced via pointer in the interface header that sync.Pool
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// stores.
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var pathPool = sync.Pool{ // if go1.18+ adds Pool[T], use that to store []uint16 directly
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New: func() interface{} {
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b := make([]uint16, MinWStringCap)
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return &b
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},
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}
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func newBuffer() []uint16 { return *(pathPool.Get().(*[]uint16)) }
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// freeBuffer copies the slice header data, and puts a pointer to that in the pool.
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// This avoids taking a pointer to the slice header in WString, which can be set to nil.
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func freeBuffer(b []uint16) { pathPool.Put(&b) }
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// WString is a wide string buffer ([]uint16) meant for storing UTF-16 encoded strings
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// for interacting with Win32 APIs.
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// Sizes are specified as uint32 and not int.
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//
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// It is not thread safe.
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type WString struct {
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// type-def allows casting to []uint16 directly, use struct to prevent that and allow adding fields in the future.
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// raw buffer
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b []uint16
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}
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// NewWString returns a [WString] allocated from a shared pool with an
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// initial capacity of at least [MinWStringCap].
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// Since the buffer may have been previously used, its contents are not guaranteed to be empty.
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//
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// The buffer should be freed via [WString.Free]
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func NewWString() *WString {
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return &WString{
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b: newBuffer(),
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}
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}
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func (b *WString) Free() {
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if b.empty() {
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return
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}
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freeBuffer(b.b)
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b.b = nil
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}
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// ResizeTo grows the buffer to at least c and returns the new capacity, freeing the
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// previous buffer back into pool.
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func (b *WString) ResizeTo(c uint32) uint32 {
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// allready sufficient (or n is 0)
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if c <= b.Cap() {
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return b.Cap()
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}
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if c <= MinWStringCap {
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c = MinWStringCap
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}
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// allocate at-least double buffer size, as is done in [bytes.Buffer] and other places
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if c <= 2*b.Cap() {
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c = 2 * b.Cap()
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}
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b2 := make([]uint16, c)
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if !b.empty() {
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copy(b2, b.b)
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freeBuffer(b.b)
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}
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b.b = b2
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return c
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}
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// Buffer returns the underlying []uint16 buffer.
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func (b *WString) Buffer() []uint16 {
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if b.empty() {
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return nil
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}
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return b.b
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}
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// Pointer returns a pointer to the first uint16 in the buffer.
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// If the [WString.Free] has already been called, the pointer will be nil.
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func (b *WString) Pointer() *uint16 {
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if b.empty() {
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return nil
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}
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return &b.b[0]
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}
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// String returns the returns the UTF-8 encoding of the UTF-16 string in the buffer.
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//
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// It assumes that the data is null-terminated.
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func (b *WString) String() string {
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// Using [windows.UTF16ToString] would require importing "golang.org/x/sys/windows"
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// and would make this code Windows-only, which makes no sense.
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// So copy UTF16ToString code into here.
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// If other windows-specific code is added, switch to [windows.UTF16ToString]
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s := b.b
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for i, v := range s {
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if v == 0 {
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s = s[:i]
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break
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}
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}
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return string(utf16.Decode(s))
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}
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// Cap returns the underlying buffer capacity.
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func (b *WString) Cap() uint32 {
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if b.empty() {
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return 0
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}
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return b.cap()
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}
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func (b *WString) cap() uint32 { return uint32(cap(b.b)) }
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func (b *WString) empty() bool { return b == nil || b.cap() == 0 }
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