add io_sendfile with BSD support

io.h

@@ -63,4 +63,8 @@ void io_closeonexec(int64 d);
 
 void io_close(int64 d);
 
+/* send n bytes from file fd starting at offset off to socket s */
+/* return number of bytes written */
+int64 io_sendfile(int64 s,int64 fd,uint64 off,uint64 n);
+
 #endif

io/io_sendfile.c

@@ -0,0 +1,58 @@
+#define _FILE_OFFSET_BITS 64
+#include "io_internal.h"
+
+#if defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__NetBSD__)
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/uio.h>
+
+int64 io_sendfile(int64 s,int64 fd,uint64 off,uint64 n) {
+  off_t sbytes;
+  int r=sendfile(fd,s,off,n,0,&sbytes,0);
+  if (r==0) return n;
+  if (r==-1)
+    return (errno==EAGAIN?sbytes:-1);
+}
+#elif defined(__linux__)
+
+#if defined(__GLIBC__)
+#include <sys/sendfile.h>
+#elif defined(__dietlibc__)
+#include <sys/sendfile.h>
+#else
+#include <linux/unistd.h>
+_syscall4(int,sendfile,int,out,int,in,long *,offset,unsigned long,count)
+#endif
+
+int64 io_sendfile(int64 s,int64 fd,uint64 off,uint64 n) {
+  off_t o=off;
+  return sendfile(s,fd,&o,n);
+}
+
+#else
+
+#define BUFSIZE 16384
+
+int64 io_sendfile(int64 out,int64 in,uint64 off,uint64 bytes) {
+  char buf[BUFSIZE];
+  int n,m;
+  uint64 sent=0;
+  if (lseek(in,off,SEEK_SET) != off)
+    return -1;
+  while (bytes>0) {
+    char* tmp=buf;
+    if ((n=read(in,tmp,(bytes<BUFSIZE)?bytes:BUFSIZE))<=0)
+      return (sent?sent:-1);
+    while (n>0) {
+      if ((m=write(out,tmp,n))<0)
+	goto abort;
+      sent+=m;
+      n-=m;
+      tmp+=m;
+    }
+  }
+abort:
+  return sent;
+}
+
+#endif