add small explanation to iob.h

CHANGES

@@ -8,6 +8,7 @@
   add buffer functions to write strerror(errno)
   add io API supporting poll, epoll and kqueue
   remove obsolete "extern" from header files
+  add iob API to send several buffers and files in one batch
 
 0.15:
   man page update (document stralloc return values)

GNUmakefile

@@ -62,6 +62,9 @@ $(ARRAY_OBJS): uint64.h array.h
 $(MULT_OBJS): uint64.h uint32.h uint16.h safemult.h
 $(IO_OBJS): uint64.h array.h io.h io_internal.h taia.h tai.h haveepoll.h havekqueue.h
 
+
+iob_addbuf.o iob_addfile.o iob_new.o iob_reset.o iob_send.o: iob_internal.h iob.h
+
 iopause.o: select.h
 openreadclose.o readclose.o: readclose.h
 dns_rcip.o dns_rcrw.o openreadclose.o: openreadclose.h

iob.h

@@ -1,6 +1,17 @@
 #ifndef _IOB_H
 #define _IOB_H
 
+/* These functions can be used to create a queue of small (or large)
+ * buffers and parts of files to be sent out over a socket.  It is meant
+ * for writing HTTP servers or the like. */
+
+/* This API works with non-blocking I/O.  Simply call iob_send until it
+ * returns 0 (or -1).  The implementation uses sendfile for zero-copy
+ * TCP and it will employ writev (or the built-in sendfile writev on
+ * BSD) to make sure the output fragments are coalesced into as few TCP
+ * frames as possible.  On Linux it will also use the TCP_CORK socket
+ * option. */
+
 #include "io.h"
 
 typedef struct io_batch io_batch;