[webnfc] Implement push 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.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";
+    private static final String WEBNFC_URN = DOMAIN + ":" + TYPE;
+    private static final String TEXT_MIME = "text/plain";
+    private static final String JSON_MIME = "application/json";
+    private static final String CHARSET_UTF8 = ";charset=UTF-8";
+    private static final String CHARSET_UTF16 = ";charset=UTF-16";
+
+    /**
+     * Converts mojo NfcMessage to android.nfc.NdefMessage
+     */
+    public static NdefMessage toNdefMessage(NfcMessage message) throws InvalidNfcMessageException {
+        if (message == null || message.data.length == 0) throw new InvalidNfcMessageException();

[dcheng, 2016/08/16 06:27:20]

Should this be <= 0?

[shalamov, 2016/08/16 12:47:15]

According to java specification, array length guaranteed to be non-negative.

[dcheng, 2016/08/16 20:50:08]

OK, the Java types aren't clear to me. Is there some doc that covers how mojom
map to java?

+
+        try {
+            List<NdefRecord> records = new ArrayList<NdefRecord>();
+            for (int i = 0; i < message.data.length; ++i) {
+                records.add(toNdefRecord(message.data[i]));
+            }
+            records.add(NdefRecord.createExternal(DOMAIN, TYPE, message.url.getBytes("UTF-8")));
+            NdefRecord[] ndefRecords = new NdefRecord[records.size()];
+            records.toArray(ndefRecords);
+            return new NdefMessage(ndefRecords);
+        } catch (UnsupportedEncodingException | InvalidNfcMessageException
+                | IllegalArgumentException e) {
+            throw new InvalidNfcMessageException();
+        }
+    }
+
+    /**
+     * 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";

[dcheng, 2016/08/16 06:27:20]

Can we add some comments to the mojom? What is a mediaType? What can it look
like? Is it anything like a MIME type? It's not clear at all from the mojom
definition.

(It also appears the mojom doesn't follow naming conventions: I would expect
things in the mojom to be named_with_underscores, and let the mojom compiler
handle the underscore -> camel case conversion)

[shalamov, 2016/08/16 12:47:15]

Added comment to mojom.
Would it be fine if I do it in a separate CL? Otherwise this patch would be too
big. I would need to change blink part, mock JS service implementation, etc.

[dcheng, 2016/08/16 20:50:08]

OK, I think similar comments would help for some other fields as well (for
example, are there any length limits on data? Is it ever freeform binary data or
is it always a string? etc)
Yes, that's fine.

+
+        // 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.
+
+        if (record.mediaType.endsWith(CHARSET_UTF16)) return "UTF-16LE";
+
+        Log.w(TAG, "Unknown charset, defaulting to UTF-8.");
+        return "UTF-8";
+    }
+
+    /**
+     * Converts mojo NfcRecord to android.nfc.NdefRecord
+     */
+    private static NdefRecord toNdefRecord(NfcRecord record) throws InvalidNfcMessageException,
+                                                                    IllegalArgumentException,
+                                                                    UnsupportedEncodingException {
+        switch (record.recordType) {
+            case NfcRecordType.URL:
+                return NdefRecord.createUri(new String(record.data, getCharset(record)));
+            case NfcRecordType.TEXT:
+                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
+                    return NdefRecord.createTextRecord(
+                            "en-US", new String(record.data, getCharset(record)));
+                } 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();
+        }
+    }
+}