Add a new evbuffer_write_atmost() functino to write no more than a given number of bytes to an fd.

svn:r993

ChangeLog

@@ -135,6 +135,7 @@ Changes in current version:
  o Restructure the event backends so that they do not need to keep track of events themselves, as a side effect multiple events can use the same fd or signal.
  o Add generic implementations for parsing and emiting IPv6 addresses on platforms that do not have inet_ntop and/or inet_pton.
  o Allow DNS servers that have IPv6 addresses.
+ o Add an evbuffer_write_atmost() function to write a limited number of bytes to an fd.
 
 Changes in 1.4.0:
  o allow \r or \n individually to separate HTTP headers instead of the standard "\r\n"; from Charles Kerr.

buffer.c

@@ -889,10 +889,15 @@ evbuffer_read(struct evbuffer *buf, evutil_socket_t fd, int howmuch)
 }
 
 int
-evbuffer_write(struct evbuffer *buffer, evutil_socket_t fd)
+evbuffer_write_atmost(struct evbuffer *buffer, evutil_socket_t fd,
+					  ssize_t howmuch)
 {
 	int n;
 
+	if (howmuch < 0)
+		howmuch = buffer->total_len;
+
+	{
 #ifndef WIN32
   #ifdef HAVE_SYS_UIO_H
 	struct iovec iov[NUM_IOVEC];
@@ -901,21 +906,29 @@ evbuffer_write(struct evbuffer *buffer, evutil_socket_t fd)
 	/* XXX make this top out at some maximal data length? if the buffer has
 	 * (say) 1MB in it, split over 128 chains, there's no way it all gets
 	 * written in one go. */
-	while (chain != NULL && i < NUM_IOVEC) {
+	while (chain != NULL && i < NUM_IOVEC && howmuch) {
 		iov[i].iov_base = chain->buffer + chain->misalign;
-		iov[i++].iov_len = chain->off;
+		if (howmuch >= chain->off) {
+			iov[i++].iov_len = chain->off;
+			howmuch -= chain->off;
+		} else {
+			iov[i++].iov_len = howmuch;
+			break;
+		}
 		chain = chain->next;
 	}
 	n = writev(fd, iov, i);
   #else /* !HAVE_SYS_UIO_H */
-	void *p = evbuffer_pullup(buffer, -1);
-	n = write(fd, p, buffer->total_len, 0);
+	void *p = evbuffer_pullup(buffer, howmuch);
+	n = write(fd, p, howmuch, 0);
   #endif
 #else
 	/* XXX(niels): investigate if windows has writev */
-	void *p = evbuffer_pullup(buffer, -1);
-	n = send(fd, p, buffer->total_len, 0);
+	void *p = evbuffer_pullup(buffer, howmuch);
+	n = send(fd, p, howmuch, 0);
 #endif
+	}
+
 	if (n == -1)
 		return (-1);
 	if (n == 0)
@@ -925,6 +938,12 @@ evbuffer_write(struct evbuffer *buffer, evutil_socket_t fd)
 	return (n);
 }
 
+int
+evbuffer_write(struct evbuffer *buffer, evutil_socket_t fd)
+{
+	return evbuffer_write_atmost(buffer, fd, -1);
+}
+
 unsigned char *
 evbuffer_find(struct evbuffer *buffer, const unsigned char *what, size_t len)
 {

include/event2/buffer.h

@@ -289,6 +289,21 @@ void evbuffer_drain(struct evbuffer *buf, size_t len);
  */
 int evbuffer_write(struct evbuffer *buffer, evutil_socket_t fd);
 
+/**
+  Write some of the contents of an evbuffer to a file descriptor.
+
+  The evbuffer will be drained after the bytes have been successfully written.
+
+  @param buffer the evbuffer to be written and drained
+  @param fd the file descriptor to be written to
+  @param howmuch the largest allowable number of bytes to write, or -1
+        to write as many bytes as we can.
+  @return the number of bytes written, or -1 if an error occurred
+  @see evbuffer_read()
+ */
+int evbuffer_write_atmost(struct evbuffer *buffer, evutil_socket_t fd,
+						  ssize_t howmuch);
+
 /**
   Read from a file descriptor and store the result in an evbuffer.
 
@@ -365,9 +380,6 @@ void evbuffer_prepend_buffer(struct evbuffer *dst, struct evbuffer* src);
     A better find-string that returns a smart offset structure rather than a
     pointer. It should also be able to start searching _at_ an offset.
 
-	A variant of evbuffer_write() that takes a maximum number of bytes to
-	write.
-
 	A check-representation functions for testing, so we can assert() that
 	nothing has gone screwy inside an evbuffer.
 */