Linux: Fix Ethernet client and server (#836)

- Fix documentation.
- Add function close() to client class.
- Function connected() now return true if the connection is in
  stablished state or there is still unread data.
- Update hasClient() to check if any client has disconnected.
- Fix _accept() to better handle the case of maximum clients reached.
- Fix peek() to return the next byte of the read queue.
- Simplifies write() of the server class.
- Implements flush().
- Updates read() to non-blocking type, the same way as in Arduino.

drivers/Linux/EthernetClient.cpp

@@ -19,9 +19,11 @@
  * Based on Arduino ethernet library, Copyright (c) 2010 Arduino LLC. All right reserved.
  */
 
+#include "EthernetClient.h"
 #include <cstdio>
 #include <sys/socket.h>
 #include <sys/ioctl.h>
+#include <linux/sockios.h>
 #include <netdb.h>
 #include <arpa/inet.h>
 #include <cstring>
@@ -30,7 +32,6 @@
 #include <netinet/tcp.h>
 #include <errno.h>
 #include "log.h"
-#include "EthernetClient.h"
 
 EthernetClient::EthernetClient() : _sock(-1)
 {
@@ -67,7 +68,7 @@ int EthernetClient::connect(const char* host, uint16_t port)
 		}
 
 		if (::connect(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
-			close(sockfd);
+			::close(sockfd);
 			logError("connect: %s\n", strerror(errno));
 			continue;
 		}
@@ -113,8 +114,7 @@ size_t EthernetClient::write(const uint8_t *buf, size_t size)
 		int rc = send(_sock, buf + bytes, size, MSG_NOSIGNAL | MSG_DONTWAIT);
 		if (rc == -1) {
 			logError("send: %s\n", strerror(errno));
-			close(_sock);
-			_sock = -1;
+			close();
 			break;
 		}
 		bytes += rc;
@@ -141,16 +141,16 @@ int EthernetClient::available()
 	int count = 0;
 
 	if (_sock != -1) {
-		ioctl(_sock, FIONREAD, &count);
-		return count;
+		ioctl(_sock, SIOCINQ, &count);
 	}
-	return 0;
+
+	return count;
 }
 
 int EthernetClient::read()
 {
 	uint8_t b;
-	if ( recv(_sock, &b, 1, 0) > 0 ) {
+	if ( recv(_sock, &b, 1, MSG_DONTWAIT) > 0 ) {
 		// recv worked
 		return b;
 	} else {
@@ -159,22 +159,35 @@ int EthernetClient::read()
 	}
 }
 
-int EthernetClient::read(uint8_t *buf, size_t size)
+int EthernetClient::read(uint8_t *buf, size_t bytes)
 {
-	return recv(_sock, buf, size, 0);
+	return recv(_sock, buf, bytes, MSG_DONTWAIT);
 }
 
 int EthernetClient::peek()
 {
 	uint8_t b;
 
-	return recv(_sock, &b, 1, MSG_PEEK | MSG_DONTWAIT);
+	if (recv(_sock, &b, 1, MSG_PEEK | MSG_DONTWAIT) > 0) {
+		return b;
+	} else {
+		return -1;
+	}
 }
 
 void EthernetClient::flush()
 {
-	// There isn't much we can do here
-	return;
+	int count = 0;
+
+	if (_sock != -1) {
+		while (true) {
+			ioctl(_sock, SIOCOUTQ, &count);
+			if (count == 0) {
+				return;
+			}
+			usleep(1000);
+		}
+	}
 }
 
 void EthernetClient::stop()
@@ -203,7 +216,7 @@ void EthernetClient::stop()
 
 	// if it hasn't closed, close it forcefully
 	if (s != ETHERNETCLIENT_W5100_CLOSED) {
-		close(_sock);
+		::close(_sock);
 	}
 	_sock = -1;
 }
@@ -249,17 +262,15 @@ uint8_t EthernetClient::status()
 
 uint8_t EthernetClient::connected()
 {
-	if (_sock == -1) {
-		return 0;
-	}
+	return status() == ETHERNETCLIENT_W5100_ESTABLISHED || available();
+}
 
-	if (peek() < 0) {
-		if (errno == EAGAIN) {
-			return 1;
-		}
-		return 0;
+void EthernetClient::close()
+{
+	if (_sock != -1) {
+		::close(_sock);
+		_sock = -1;
 	}
-	return 1;
 }
 
 int EthernetClient::getSocketNumber()