Fix handling of hidden access points

We now get raw hex data from the supplicant and we convert it into
printable format.

For hidden access point, we always used to return a single empty string.
We need to make sure we maintain that behavior for apps to not start
displaying empty strings.

Bug: 7310749
Change-Id: I2599b9b5e15be91fc34e9af629ad893b1a0357fc

Author: isheriff

wifi/java/android/net/wifi/WifiSsid.java

@@ -156,22 +156,33 @@ private void convertToBytes(String asciiEncoded) {
 
     @Override
     public String toString() {
-        if (octets.size() <= 0) return "";
+        byte[] ssidBytes = octets.toByteArray();
+        // Supplicant returns \x00\x00\x00\x00\x00\x00\x00\x00 hex string
+        // for a hidden access point. Make sure we maintain the previous
+        // behavior of returning empty string for this case.
+        if (octets.size() <= 0 || isArrayAllZeroes(ssidBytes)) return "";
         // TODO: Handle conversion to other charsets upon failure
         Charset charset = Charset.forName("UTF-8");
         CharsetDecoder decoder = charset.newDecoder()
                 .onMalformedInput(CodingErrorAction.REPLACE)
                 .onUnmappableCharacter(CodingErrorAction.REPLACE);
         CharBuffer out = CharBuffer.allocate(32);
 
-        CoderResult result = decoder.decode(ByteBuffer.wrap(octets.toByteArray()), out, true);
+        CoderResult result = decoder.decode(ByteBuffer.wrap(ssidBytes), out, true);
         out.flip();
         if (result.isError()) {
             return NONE;
         }
         return out.toString();
     }
 
+    private boolean isArrayAllZeroes(byte[] ssidBytes) {
+        for (int i = 0; i< ssidBytes.length; i++) {
+            if (ssidBytes[i] != 0) return false;
+        }
+        return true;
+    }
+
     /** @hide */
     public byte[] getOctets() {
         return  octets.toByteArray();