Read Receipts (#101)

* add api client with grpc kotlin

* add read receipt content type to kotlin

library/src/androidTest/java/org/xmtp/android/library/ReadReceiptTest.kt

@@ -0,0 +1,39 @@
+package org.xmtp.android.library
+
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import org.junit.Assert.assertEquals
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.xmtp.android.library.codecs.ContentTypeReadReceipt
+import org.xmtp.android.library.codecs.ReadReceipt
+import org.xmtp.android.library.codecs.ReadReceiptCodec
+import org.xmtp.android.library.messages.walletAddress
+
+@RunWith(AndroidJUnit4::class)
+class ReadReceiptTest {
+
+    @Test
+    fun testCanUseReadReceiptCodec() {
+        Client.register(codec = ReadReceiptCodec())
+
+        val fixtures = fixtures()
+        val aliceClient = fixtures.aliceClient
+        val aliceConversation =
+            aliceClient.conversations.newConversation(fixtures.bob.walletAddress)
+
+        aliceConversation.send(text = "hey alice 2 bob")
+
+        val readReceipt = ReadReceipt(timestamp = "2019-09-26T07:58:30.996+0200")
+
+        aliceConversation.send(
+            content = readReceipt,
+            options = SendOptions(contentType = ContentTypeReadReceipt),
+        )
+        val messages = aliceConversation.messages()
+        assertEquals(messages.size, 2)
+        if (messages.size == 2) {
+            val content: ReadReceipt? = messages.first().content()
+            assertEquals("2019-09-26T07:58:30.996+0200", content?.timestamp)
+        }
+    }
+}

library/src/main/java/org/xmtp/android/library/codecs/ReadReceiptCodec.kt

@@ -0,0 +1,34 @@
+package org.xmtp.android.library.codecs
+
+import com.google.protobuf.ByteString
+import org.xmtp.android.library.XMTPException
+
+val ContentTypeReadReceipt = ContentTypeIdBuilder.builderFromAuthorityId(
+    "xmtp.org",
+    "readReceipt",
+    versionMajor = 1,
+    versionMinor = 0
+)
+
+data class ReadReceipt(
+    // The timestamp the read receipt was sent, in ISO 8601 format
+    val timestamp: String,
+)
+
+data class ReadReceiptCodec(override var contentType: ContentTypeId = ContentTypeReadReceipt) :
+    ContentCodec<ReadReceipt> {
+
+    override fun encode(content: ReadReceipt): EncodedContent {
+        return EncodedContent.newBuilder().also {
+            it.type = ContentTypeReadReceipt
+            it.putParameters("timestamp", content.timestamp)
+            it.content = ByteString.EMPTY
+        }.build()
+    }
+
+    override fun decode(content: EncodedContent): ReadReceipt {
+        val timestamp = content.parametersMap["timestamp"] ?: throw XMTPException("Invalid Content")
+
+        return ReadReceipt(timestamp = timestamp)
+    }
+}