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Source file src/net/writev_unix.go

Documentation: net

  // Copyright 2016 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.
  
  // +build darwin dragonfly freebsd linux netbsd openbsd
  
  package net
  
  import (
  	"io"
  	"os"
  	"syscall"
  	"unsafe"
  )
  
  func (c *conn) writeBuffers(v *Buffers) (int64, error) {
  	if !c.ok() {
  		return 0, syscall.EINVAL
  	}
  	n, err := c.fd.writeBuffers(v)
  	if err != nil {
  		return n, &OpError{Op: "writev", Net: c.fd.net, Source: c.fd.laddr, Addr: c.fd.raddr, Err: err}
  	}
  	return n, nil
  }
  
  func (fd *netFD) writeBuffers(v *Buffers) (n int64, err error) {
  	if err := fd.writeLock(); err != nil {
  		return 0, err
  	}
  	defer fd.writeUnlock()
  	if err := fd.pd.prepareWrite(); err != nil {
  		return 0, err
  	}
  
  	var iovecs []syscall.Iovec
  	if fd.iovecs != nil {
  		iovecs = *fd.iovecs
  	}
  	// TODO: read from sysconf(_SC_IOV_MAX)? The Linux default is
  	// 1024 and this seems conservative enough for now. Darwin's
  	// UIO_MAXIOV also seems to be 1024.
  	maxVec := 1024
  
  	for len(*v) > 0 {
  		iovecs = iovecs[:0]
  		for _, chunk := range *v {
  			if len(chunk) == 0 {
  				continue
  			}
  			iovecs = append(iovecs, syscall.Iovec{Base: &chunk[0]})
  			if fd.isStream && len(chunk) > 1<<30 {
  				iovecs[len(iovecs)-1].SetLen(1 << 30)
  				break // continue chunk on next writev
  			}
  			iovecs[len(iovecs)-1].SetLen(len(chunk))
  			if len(iovecs) == maxVec {
  				break
  			}
  		}
  		if len(iovecs) == 0 {
  			break
  		}
  		fd.iovecs = &iovecs // cache
  
  		wrote, _, e0 := syscall.Syscall(syscall.SYS_WRITEV,
  			uintptr(fd.sysfd),
  			uintptr(unsafe.Pointer(&iovecs[0])),
  			uintptr(len(iovecs)))
  		if wrote == ^uintptr(0) {
  			wrote = 0
  		}
  		testHookDidWritev(int(wrote))
  		n += int64(wrote)
  		v.consume(int64(wrote))
  		if e0 == syscall.EAGAIN {
  			if err = fd.pd.waitWrite(); err == nil {
  				continue
  			}
  		} else if e0 != 0 {
  			err = syscall.Errno(e0)
  		}
  		if err != nil {
  			break
  		}
  		if n == 0 {
  			err = io.ErrUnexpectedEOF
  			break
  		}
  	}
  	if _, ok := err.(syscall.Errno); ok {
  		err = os.NewSyscallError("writev", err)
  	}
  	return n, err
  }
  

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