be more forgiving of IPv4-mapped addresses in json (#1404)

Currently Zipkin checks that all IPv6 addresses are 16 bytes long.
However, if an IPv4-mapped addresses such as `::ffff:192.168.1.128` is
given then InetAddress.getByName will return an Inet4Address and the
assertion will fail.

Instead accept the address, but store it as ipv4 to maintain all
existing assertions.  This absolves clients of reconciling the nuances
of IPv4-mapped addresses in their environments (for example, in node
`net.isIPv6('::ffff:192.168.1.128')` is true) with Java's.

zipkin/src/main/java/zipkin/internal/JsonCodec.java

@@ -19,6 +19,7 @@
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.io.InputStreamReader;
+import java.net.InetAddress;
 import java.net.Inet6Address;
 import java.nio.ByteBuffer;
 import java.util.Collections;
@@ -73,16 +74,18 @@ public Endpoint fromJson(JsonReader reader) throws IOException {
         if (nextName.equals("serviceName")) {
           result.serviceName(reader.nextString());
         } else if (nextName.equals("ipv4")) {
-          String[] ipv4String = reader.nextString().split("\\.", 5);
-          int ipv4 = 0;
-          for (String part : ipv4String) {
-            ipv4 = ipv4 << 8 | (Integer.parseInt(part) & 0xff);
-          }
-          result.ipv4(ipv4);
+          result.ipv4(parseIPv4Address(reader.nextString()));
         } else if (nextName.equals("ipv6")) {
           String input = reader.nextString();
           // Shouldn't hit DNS, because it's an IP string literal.
-          result.ipv6(Inet6Address.getByName(input).getAddress());
+          InetAddress addr = Inet6Address.getByName(input);
+          //  InetAddress.getByName returns an Inet4Address for
+          //  IPv4-mapped IPv6 addresses such as ::ffff:192.0.2.128
+          if (addr instanceof Inet6Address) {
+            result.ipv6(addr.getAddress());
+          } else {
+            result.ipv4(parseIPv4Address(addr.getHostAddress()));
+          }
         } else if (nextName.equals("port")) {
           result.port(reader.nextInt());
         } else {
@@ -93,6 +96,15 @@ public Endpoint fromJson(JsonReader reader) throws IOException {
       return result.build();
     }
 
+    private int parseIPv4Address(String input) {
+      String[] ipv4String = input.split("\\.", 5);
+      int ipv4 = 0;
+      for (String part : ipv4String) {
+          ipv4 = ipv4 << 8 | (Integer.parseInt(part) & 0xff);
+      }
+      return ipv4;
+    }
+
     @Override public int sizeInBytes(Endpoint value) {
       int sizeInBytes = 0;
       sizeInBytes += asciiSizeInBytes("{\"serviceName\":\"");

zipkin/src/test/java/zipkin/internal/JsonCodecTest.java

@@ -292,6 +292,32 @@ public void endpointHighPort() {
         .isEqualTo(span);
   }
 
+  @Test
+  public void mappedIPv6toIPv4() {
+    String json = "{\n"
+        + "  \"traceId\": \"6b221d5bc9e6496c\",\n"
+        + "  \"name\": \"get-traces\",\n"
+        + "  \"id\": \"6b221d5bc9e6496c\",\n"
+        + "  \"binaryAnnotations\": [\n"
+        + "    {\n"
+        + "      \"key\": \"foo\",\n"
+        + "      \"value\": \"bar\",\n"
+        + "      \"endpoint\": {\n"
+        + "        \"serviceName\": \"service\",\n"
+        + "        \"port\": 65535,\n"
+        + "        \"ipv6\": \"::ffff:192.0.2.128\"\n"
+        + "      }\n"
+        + "    }\n"
+        + "  ]\n"
+        + "}";
+
+    Span span = Codec.JSON.readSpan(json.getBytes(UTF_8));
+    assertThat(span.binaryAnnotations.get(0).endpoint.ipv6)
+        .isNull();
+    assertThat(span.binaryAnnotations.get(0).endpoint.ipv4)
+        .isEqualTo((192 << 24) | (0 << 16) | (2 << 8) | 128); // 192.0.2.128
+  }
+
   @Test
   public void sizeInBytes_span() throws IOException {
     Span span = TestObjects.LOTS_OF_SPANS[0];