mirror of
https://github.com/zrepl/zrepl.git
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134 lines
3.5 KiB
Go
134 lines
3.5 KiB
Go
// +build !illumos
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// +build !solaris
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package timeoutconn
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import (
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"io"
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"net"
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"syscall"
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"unsafe"
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)
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func buildIovecs(buffers net.Buffers) (totalLen int64, vecs []syscall.Iovec) {
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vecs = make([]syscall.Iovec, 0, len(buffers))
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for i := range buffers {
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totalLen += int64(len(buffers[i]))
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if len(buffers[i]) == 0 {
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continue
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}
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v := syscall.Iovec{
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Base: &buffers[i][0],
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}
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// syscall.Iovec.Len has platform-dependent size, thus use SetLen
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v.SetLen(len(buffers[i]))
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vecs = append(vecs, v)
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}
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return totalLen, vecs
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}
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func (c Conn) readv(buffers net.Buffers) (n int64, err error) {
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scc, ok := c.Wire.(SyscallConner)
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if !ok {
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return c.readvFallback(buffers)
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}
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rawConn, err := scc.SyscallConn()
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if err == SyscallConnNotSupported {
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return c.readvFallback(buffers)
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}
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if err != nil {
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return 0, err
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}
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_, iovecs := buildIovecs(buffers)
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for len(iovecs) > 0 {
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if err := c.renewReadDeadline(); err != nil {
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return n, err
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}
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oneN, oneErr := c.doOneReadv(rawConn, &iovecs)
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n += oneN
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if netErr, ok := oneErr.(net.Error); ok && netErr.Timeout() && oneN > 0 { // TODO likely not working
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continue
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} else if oneErr == nil && oneN > 0 {
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continue
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} else {
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return n, oneErr
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}
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}
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return n, nil
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}
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func (c Conn) doOneReadv(rawConn syscall.RawConn, iovecs *[]syscall.Iovec) (n int64, err error) {
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rawReadErr := rawConn.Read(func(fd uintptr) (done bool) {
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// iovecs, n and err must not be shadowed!
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// NOTE: unsafe.Pointer safety rules
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// https://tip.golang.org/pkg/unsafe/#Pointer
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//
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// (4) Conversion of a Pointer to a uintptr when calling syscall.Syscall.
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// ...
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// uintptr() conversions must appear within the syscall.Syscall argument list.
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// (even though we are not the escape analysis Likely not )
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thisReadN, _, errno := syscall.Syscall(
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syscall.SYS_READV,
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fd,
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uintptr(unsafe.Pointer(&(*iovecs)[0])),
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uintptr(len(*iovecs)),
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)
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if thisReadN == ^uintptr(0) {
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if errno == syscall.EAGAIN {
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return false
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}
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err = syscall.Errno(errno)
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return true
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}
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if int(thisReadN) < 0 {
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panic("unexpected return value")
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}
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n += int64(thisReadN) // TODO check overflow
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// shift iovecs forward
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for left := int(thisReadN); left > 0; {
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// conversion to uint does not change value, see TestIovecLenFieldIsMachineUint, and left > 0
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thisIovecConsumedCompletely := uint((*iovecs)[0].Len) <= uint(left)
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if thisIovecConsumedCompletely {
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// Update left, cannot go below 0 due to
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// a) definition of thisIovecConsumedCompletely
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// b) left > 0 due to loop invariant
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// Converting .Len to int64 is thus also safe now, because it is < left < INT_MAX
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left -= int((*iovecs)[0].Len)
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*iovecs = (*iovecs)[1:]
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} else {
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// trim this iovec to remaining length
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// NOTE: unsafe.Pointer safety rules
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// https://tip.golang.org/pkg/unsafe/#Pointer
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// (3) Conversion of a Pointer to a uintptr and back, with arithmetic.
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// ...
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// Note that both conversions must appear in the same expression,
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// with only the intervening arithmetic between them:
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(*iovecs)[0].Base = (*byte)(unsafe.Pointer(uintptr(unsafe.Pointer((*iovecs)[0].Base)) + uintptr(left)))
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curVecNewLength := uint((*iovecs)[0].Len) - uint(left) // casts to uint do not change value
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(*iovecs)[0].SetLen(int(curVecNewLength)) // int and uint have the same size, no change of value
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break // inner
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}
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}
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if thisReadN == 0 {
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err = io.EOF
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return true
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}
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return true
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})
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if rawReadErr != nil {
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err = rawReadErr
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}
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return n, err
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}
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