Extend and rework WiFi interface

General refactoring of the API and new methods added:
  * get_rssi() - measures radio signal strenght
  * get_state() - returns current state (not connected,
   		 connecting, connected, error)
  * scan() - scans for available networks sync and async versions
  * connect_async() - connect to a network without blocking

Author: bulislaw

features/net/network-socket/NetworkInterface.h

@@ -36,6 +36,12 @@ class NetworkInterface {
      */
     virtual const char *get_ip_address() = 0;
 
+    /** Get the local MAC address
+     *
+     *  @return         Null-terminated representation of the local MAC address
+     */
+    virtual const char *get_mac_address() = 0;
+
 protected:
     friend class Socket;
     friend class UDPSocket;

features/net/network-socket/WiFiInterface.h

@@ -1,5 +1,5 @@
 /* WiFiInterface
- * Copyright (c) 2015 ARM Limited
+ * Copyright (c) 2015 - 2016 ARM Limited
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,22 +17,19 @@
 #ifndef WIFI_INTERFACE_H
 #define WIFI_INTERFACE_H
 
+#include <string.h>
 #include "network-socket/NetworkInterface.h"
 
+typedef struct wifi_ap {
+    char ssid[33]; /* 32 is what 802.11 defines as longest possible name; +1 for the \0 */
+    uint8_t bssid[6];
+    nsapi_security_t security;
+    int8_t rssi;
+    uint8_t channel;
+} wifi_ap_t;
 
-/** Enum of WiFi encryption types
- *
- *  The security type specifies a particular security to use when
- *  connected to a WiFi network
- *
- *  @enum nsapi_protocol_t
- */
-enum nsapi_security_t {
-    NSAPI_SECURITY_NONE = 0,   /*!< open access point */
-    NSAPI_SECURITY_WEP,        /*!< phrase conforms to WEP */
-    NSAPI_SECURITY_WPA,        /*!< phrase conforms to WPA */
-    NSAPI_SECURITY_WPA2,       /*!< phrase conforms to WPA2 */
-};
+typedef void (*wifi_ap_scan_cb_t)(wifi_ap_t *ap, void *data);
+typedef void (*wifi_connect_cb_t)(nsapi_error_t res, void *data);
 
 /** WiFiInterface class
  *
@@ -43,28 +40,81 @@ class WiFiInterface: public NetworkInterface
 public:
     /** Start the interface
      *
-     *  Attempts to connect to a WiFi network. If passphrase is invalid,
-     *  NSAPI_ERROR_AUTH_ERROR is returned.
+     *  Attempts to connect to a WiFi network.
+     *
+     *  @param ssid      Name of the network to connect to
+     *  @param pass      Security passphrase to connect to the network
+     *  @param security  Type of encryption for connection
+     *  @param timeout   Timeout in milliseconds; 0 for no timeout
+     *  @return          0 on success, or error code on failure
+     */
+    virtual nsapi_error_t connect(const char *ssid, const char *pass, nsapi_security_t security = NSAPI_SECURITY_NONE,
+                                  unsigned timeout = 0) = 0;
+
+    /** Start the interface
+     *
+     *  Attempts to connect to a WiFi network asynchronously, the call will return straight away. If the @a cb was NULL
+     *  you'll need to query @a get_state until it's in NSAPI_IF_STATE_CONNECTED state, otherwise the @a cb will be
+     *  called with connection results.
+     *
+     *  Note: @a ssid and @a pass must be kept until the connection is made, that is the callback has been called or the
+     *        state changed to @a NSAPI_IF_STATE_CONNECTED as they are passed by value.
      *
      *  @param ssid      Name of the network to connect to
      *  @param pass      Security passphrase to connect to the network
      *  @param security  Type of encryption for connection
-     *  @return          0 on success, negative error code on failure
+     *  @param cb        Function to be called when the connect finishes
+     *  @param data      Arbitrary user data to pass to @a cb function
      */
-    virtual int connect(const char *ssid, const char *pass, nsapi_security_t security = NSAPI_SECURITY_NONE) = 0;
+    virtual void connect_async(const char *ssid, const char *pass,nsapi_security_t security = NSAPI_SECURITY_NONE,
+                               wifi_connect_cb_t cb = NULL, void *data = NULL) = 0;
 
     /** Stop the interface
      *
-     *  @return          0 on success, negative error code on failure
+     *  @return          0 on success, or error code on failure
      */
-    virtual int disconnect() = 0;
+    virtual nsapi_error_t disconnect() = 0;
 
     /** Get the local MAC address
      *
      *  @return         Null-terminated representation of the local MAC address
      */
     virtual const char *get_mac_address() = 0;
-};
 
+    /** Get the current WiFi interface state
+     *
+     * @returns         Interface state enum
+     */
+    virtual nsapi_if_state_t get_state() = 0;
+
+    /** Gets the current radio signal strength for active connection
+     *
+     * @return Connection strength in dBm (negative value), or 0 if measurement impossible
+     */
+    virtual int8_t get_rssi() = 0;
+
+    /** Scan for available networks
+     *
+     * This function will block.
+     *
+     * @param  ap       Pointer to allocated array to store discovered AP
+     * @param  count    Size of allocated @a res array, or 0 to only count available AP
+     * @param  timeout  Timeout in milliseconds; 0 for no timeout
+     * @return          Number of entries in @a, or if @a count was 0 number of available networks, negative on error
+     *                  see @a nsapi_error
+     */
+    virtual int scan(wifi_ap_t *res, unsigned count, unsigned timeout = 0) = 0;
+
+    /** Scan for available networks
+     *
+     * This function won't block, it'll return immediately and call provided callback for each discovered network with
+     * AP data and user @a data. After the last discovered network @a cb will be called with NULL as @a ap, so it
+     * will be always called at least once.
+     *
+     * @param  cb    Function to be called for every discovered network
+     * @param  data  A user handle that will be passed to @a cb along with the AP data
+     */
+    virtual void scan_async(wifi_ap_scan_cb_t cb, void *data = NULL) = 0;
+};
 
 #endif

features/net/network-socket/nsapi_types.h

@@ -24,14 +24,15 @@ extern "C" {
 #endif
 
 
-/** Enum of standardized error codes 
+/** Enum of standardized error codes
  *
  *  Valid error codes have negative values and may
  *  be returned by any network operation.
  *
  *  @enum nsapi_error_t
  */
 typedef enum nsapi_error {
+    NSAPI_ERROR_OK            =  0,        /*!< no error */
     NSAPI_ERROR_WOULD_BLOCK   = -3001,     /*!< no data is not available but call is non-blocking */
     NSAPI_ERROR_UNSUPPORTED   = -3002,     /*!< unsupported functionality */
     NSAPI_ERROR_PARAMETER     = -3003,     /*!< invalid configuration */
@@ -41,10 +42,36 @@ typedef enum nsapi_error {
     NSAPI_ERROR_NO_MEMORY     = -3007,     /*!< memory resource not available */
     NSAPI_ERROR_DNS_FAILURE   = -3008,     /*!< DNS failed to complete successfully */
     NSAPI_ERROR_DHCP_FAILURE  = -3009,     /*!< DHCP failed to complete successfully */
-    NSAPI_ERROR_AUTH_FAILURE  = -3010,     /*!< connection to access point faield */
-    NSAPI_ERROR_DEVICE_ERROR  = -3011,     /*!< failure interfacing with the network procesor */
+    NSAPI_ERROR_AUTH_FAILURE  = -3010,     /*!< connection to access point failed */
+    NSAPI_ERROR_DEVICE_ERROR  = -3011,     /*!< failure interfacing with the network processor */
+    NSAPI_ERROR_TIMEOUT       = -3012,     /*!< operation timed out */
+    NSAPI_ERROR_BAD_SSID      = -3013,     /*!< ssid not found */
 } nsapi_error_t;
 
+/** Enum of encryption types
+ *
+ *  The security type specifies a particular security to use when
+ *  connected to a WiFi network
+ */
+typedef enum nsapi_security {
+    NSAPI_SECURITY_NONE         = 0x0,      /*!< open access point */
+    NSAPI_SECURITY_WEP          = 0x1,      /*!< phrase conforms to WEP */
+    NSAPI_SECURITY_WPA          = 0x2,      /*!< phrase conforms to WPA */
+    NSAPI_SECURITY_WPA2         = 0x3,      /*!< phrase conforms to WPA2 */
+    NSAPI_SECURITY_WPA_WPA2     = 0x4,      /*!< phrase conforms to WPA/WPA2 */
+    NSAPI_SECURITY_UNSSUPPORTED = 0xFF,     /*!< unknown/unsupported security in scan results */
+} nsapi_security_t;
+
+/** Enum of interface states
+ *
+ * List of all possible states a WiFi network interface can be in
+ */
+typedef enum nsapi_if_state {
+    NSAPI_IF_STATE_NOT_CONNECTED = 0x0,
+    NSAPI_IF_STATE_CONNECTING    = 0x01,
+    NSAPI_IF_STATE_CONNECTED     = 0x02,
+    NSAPI_IF_STATE_ERROR         = 0xFF
+} nsapi_if_state_t;
 
 /** Maximum size of IP address representation
  */