[webnfc] Implement watch method for Android nfc mojo service.

device/nfc/android/java/src/org/chromium/device/nfc/NfcTypeConverter.java

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.device.nfc;
 
 import android.nfc.NdefMessage;
 import android.nfc.NdefRecord;
 import android.os.Build;
 
 import org.chromium.base.Log;
 import org.chromium.mojom.device.nfc.NfcMessage;
 import org.chromium.mojom.device.nfc.NfcRecord;
 import org.chromium.mojom.device.nfc.NfcRecordType;
 
 import java.io.UnsupportedEncodingException;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 
 /**
  * Utility class that provides convesion between Android NdefMessage
  * and mojo NfcMessage data structures.
  */
 public final class NfcTypeConverter {
     private static final String TAG = "NfcTypeConverter";
     private static final String DOMAIN = "w3.org";
     private static final String TYPE = "webnfc";
@@ skipping 18 matching lines @@
             NdefRecord[] ndefRecords = new NdefRecord[records.size()];
             records.toArray(ndefRecords);
             return new NdefMessage(ndefRecords);
         } catch (UnsupportedEncodingException | InvalidNfcMessageException
                 | IllegalArgumentException e) {
             throw new InvalidNfcMessageException();
         }
     }
 
     /**
+     * Converts android.nfc.NdefMessage to mojo NfcMessage
+     */
+    public static NfcMessage toNfcMessage(NdefMessage ndefMessage)
+            throws UnsupportedEncodingException {

[dcheng, 2016/09/08 05:02:32]

If we're going to enforce max message size, we should be enforcing it in the
browser side (and ultimately triggering the promise rejection from here)

[shalamov, 2016/09/22 13:38:40]

Yes, it is done in another CL.

+        NdefRecord[] ndefRecords = ndefMessage.getRecords();
+        NfcMessage nfcMessage = new NfcMessage();
+        List<NfcRecord> nfcRecords = new ArrayList<NfcRecord>();
+
+        for (int i = 0; i < ndefRecords.length; i++) {
+            if ((ndefRecords[i].getTnf() == NdefRecord.TNF_EXTERNAL_TYPE)
+                    && (Arrays.equals(ndefRecords[i].getType(), WEBNFC_URN.getBytes("UTF-8")))) {
+                nfcMessage.url = new String(ndefRecords[i].getPayload(), "UTF-8");
+                continue;
+            }
+
+            NfcRecord nfcRecord = toNfcRecord(ndefRecords[i]);
+            if (nfcRecord != null) nfcRecords.add(nfcRecord);

[dcheng, 2016/09/08 05:02:32]

What does it mean for toNfcRecord() to return null? Shouldn't that be considered
an error of sorts?

[shalamov, 2016/09/22 13:38:40]

According to the spec, records that are not supported are skipped.
https://w3c.github.io/web-nfc/#steps-receiving
10. Otherwise, skip to the next NDEF record in input.

+        }
+
+        nfcMessage.data = new NfcRecord[nfcRecords.size()];
+        nfcRecords.toArray(nfcMessage.data);
+        return nfcMessage;
+    }
+
+    /**
      * Returns charset of mojo NfcRecord. Only applicable for URL and TEXT records.
      * If charset cannot be determined, UTF-8 charset is used by default.
      */
     private static String getCharset(NfcRecord record) {
         if (record.mediaType.endsWith(CHARSET_UTF8)) return "UTF-8";
 
         // When 16bit WTF::String data is converted to bytearray, it is in LE byte order, without
         // BOM. By default, Android interprets UTF-16 charset without BOM as UTF-16BE, thus, use
         // UTF-16LE as encoding for text data.
 
@@ skipping 19 matching lines @@
                 } else {
                     return NdefRecord.createMime(TEXT_MIME, record.data);
                 }
             case NfcRecordType.JSON:
             case NfcRecordType.OPAQUE_RECORD:
                 return NdefRecord.createMime(record.mediaType, record.data);
             default:
                 throw new InvalidNfcMessageException();
         }
     }
-}
+
+    /**
+     * Converts android.nfc.NdefRecord to mojo NfcRecord
+     */
+    private static NfcRecord toNfcRecord(NdefRecord ndefRecord)
+            throws UnsupportedEncodingException {
+        switch (ndefRecord.getTnf()) {
+            case NdefRecord.TNF_EMPTY:
+                return createEmptyRecord();
+            case NdefRecord.TNF_MIME_MEDIA:
+                return createMIMERecord(
+                        new String(ndefRecord.getType(), "UTF-8"), ndefRecord.getPayload());
+            case NdefRecord.TNF_ABSOLUTE_URI:
+                return createURLRecord(ndefRecord.getPayload());
+            case NdefRecord.TNF_WELL_KNOWN:
+                return createWellKnownRecord(ndefRecord.getType(), ndefRecord.getPayload());
+        }
+        return null;
+    }
+
+    /**
+     * Constructs empty NdefMessage
+     */
+    public static NdefMessage emptyNdefMessage() {
+        return new NdefMessage(new NdefRecord(NdefRecord.TNF_EMPTY, null, null, null));

[dcheng, 2016/09/08 05:02:32]

I'm not sure how common this is in Chromium code, but I feel like having a
builder pattern here would be really nice... (here and below as well)

[shalamov, 2016/09/22 13:38:40]

NfcRecord and NfcMessage are final, I can't add static builder methods to them
and new NdefRecord(NdefRecord.TNF_EMPTY, null, null, null), it is from Android
APIs and there are builder methods, but for some reason
NdefRecord.createEmpty(); is missing.

+    }
+
+    /**
+     * Constructs empty NfcRecord
+     */
+    private static NfcRecord createEmptyRecord() {
+        NfcRecord nfcRecord = new NfcRecord();
+        nfcRecord.recordType = NfcRecordType.EMPTY;
+        return nfcRecord;
+    }
+
+    /**
+     * Constructs URL NfcRecord
+     */
+    private static NfcRecord createURLRecord(byte[] payload) {
+        NfcRecord nfcRecord = new NfcRecord();
+        nfcRecord.recordType = NfcRecordType.URL;
+        nfcRecord.data = payload;
+        return nfcRecord;
+    }
+
+    /**
+     * Constructs MIME or JSON NfcRecord
+     */
+    private static NfcRecord createMIMERecord(String mediaType, byte[] payload) {
+        NfcRecord nfcRecord = new NfcRecord();
+        if (mediaType.equals(JSON_MIME)) {
+            nfcRecord.recordType = NfcRecordType.JSON;
+        } else {
+            nfcRecord.recordType = NfcRecordType.OPAQUE_RECORD;
+        }
+        nfcRecord.mediaType = mediaType;
+        nfcRecord.data = payload;
+        return nfcRecord;
+    }
+
+    /**
+     * Constructs TEXT NfcRecord
+     */
+    private static NfcRecord createTextRecord(byte[] text) {
+        NfcRecord nfcRecord = new NfcRecord();
+        nfcRecord.recordType = NfcRecordType.TEXT;
+        nfcRecord.mediaType = TEXT_MIME;
+        int langCodeLength = (text[0] & (byte) 0xFF);
+        nfcRecord.data = Arrays.copyOfRange(text, langCodeLength + 1, text.length);
+        return nfcRecord;
+    }
+
+    /**
+     * Constructs well known type (TEXT or URI) NfcRecord
+     */
+    private static NfcRecord createWellKnownRecord(byte[] type, byte[] payload) {
+        if (Arrays.equals(type, NdefRecord.RTD_URI)) return createURLRecord(payload);
+
+        if (Arrays.equals(type, NdefRecord.RTD_TEXT)) return createTextRecord(payload);
+
+        return null;
+    }
+}