sockets: add readv() implementation (task #14610)

Adds an implementation of readv() that calls recvmsg()

See http://pubs.opengroup.org/onlinepubs/009695399/functions/readv.html

CHANGELOG

@@ -6,6 +6,9 @@ HISTORY
 
   ++ New features:
 
+  2017-09-10: Joel Cunningham
+  * sockets: add readv() implementation (task #14610)
+
   2017-08-04: Simon Goldschmidt
   * Clean up DHCP a bit: no need keep msg_out and msg_in as members in struct
     dhcp - they are used in a call stack only (p_out and options_out_len as well)

src/api/sockets.c

@@ -1204,6 +1204,23 @@ lwip_read(int s, void *mem, size_t len)
   return lwip_recvfrom(s, mem, len, 0, NULL, NULL);
 }
 
+ssize_t
+lwip_readv(int s, const struct iovec *iov, int iovcnt)
+{
+  struct msghdr msg;
+
+  msg.msg_name = NULL;
+  msg.msg_namelen = 0;
+  /* Hack: we have to cast via number to cast from 'const' pointer to non-const.
+     Blame the opengroup standard for this inconsistency. */
+  msg.msg_iov = LWIP_CONST_CAST(struct iovec *, iov);
+  msg.msg_iovlen = iovcnt;
+  msg.msg_control = NULL;
+  msg.msg_controllen = 0;
+  msg.msg_flags = 0;
+  return lwip_recvmsg(s, &msg, 0);
+}
+
 ssize_t
 lwip_recv(int s, void *mem, size_t len, int flags)
 {

src/include/lwip/sockets.h

@@ -529,6 +529,7 @@ void lwip_socket_thread_cleanup(void); /* LWIP_NETCONN_SEM_PER_THREAD==1: destro
 
 #if LWIP_POSIX_SOCKETS_IO_NAMES
 #define lwip_read         read
+#define lwip_readv        readv
 #define lwip_write        write
 #define lwip_writev       writev
 #undef lwip_close
@@ -551,6 +552,7 @@ int lwip_connect(int s, const struct sockaddr *name, socklen_t namelen);
 int lwip_listen(int s, int backlog);
 ssize_t lwip_recv(int s, void *mem, size_t len, int flags);
 ssize_t lwip_read(int s, void *mem, size_t len);
+ssize_t lwip_readv(int s, const struct iovec *iov, int iovcnt);
 ssize_t lwip_recvfrom(int s, void *mem, size_t len, int flags,
       struct sockaddr *from, socklen_t *fromlen);
 ssize_t lwip_recvmsg(int s, struct msghdr *message, int flags);
@@ -619,6 +621,8 @@ int lwip_inet_pton(int af, const char *src, void *dst);
 /** @ingroup socket */
 #define read(s,mem,len)                           lwip_read(s,mem,len)
 /** @ingroup socket */
+#define readv(s,iov,iovcnt)                       lwip_readv(s,iov,iovcnt)
+/** @ingroup socket */
 #define write(s,dataptr,len)                      lwip_write(s,dataptr,len)
 /** @ingroup socket */
 #define writev(s,iov,iovcnt)                      lwip_writev(s,iov,iovcnt)