Support querying & setting transport lists on connections.

The list is specified via a magic request property
"X-Android-Transports" and can be queried via the request
property "X-Android-Selected-Transport".

System wide defaults / switches don't need any changes
to okhttp. They can be set as options on the OkHttpClient
used by the platform UrlStreamHandlers.

.gitignore

@@ -15,6 +15,8 @@ release.properties
 
 .idea
 *.iml
+*.ipr
+*.iws
 classes
 
 obj

okhttp/src/main/java/com/squareup/okhttp/internal/http/HttpEngine.java

@@ -278,7 +278,7 @@ public class HttpEngine {
         hostnameVerifier = policy.hostnameVerifier;
       }
       Address address = new Address(uriHost, getEffectivePort(uri), sslSocketFactory,
-          hostnameVerifier, policy.authenticator, policy.requestedProxy, policy.transports);
+          hostnameVerifier, policy.authenticator, policy.requestedProxy, policy.getTransports());
       routeSelector = new RouteSelector(address, uri, policy.proxySelector, policy.connectionPool,
           Dns.DEFAULT, policy.getFailedRoutes());
     }

okhttp/src/main/java/com/squareup/okhttp/internal/http/HttpTransport.java

@@ -127,10 +127,13 @@ public final class HttpTransport implements Transport {
   }
 
   @Override public ResponseHeaders readResponseHeaders() throws IOException {
-    RawHeaders headers = RawHeaders.fromBytes(socketIn);
-    httpEngine.connection.setHttpMinorVersion(headers.getHttpMinorVersion());
-    httpEngine.receiveHeaders(headers);
-    return new ResponseHeaders(httpEngine.uri, headers);
+    RawHeaders rawHeaders = RawHeaders.fromBytes(socketIn);
+    httpEngine.connection.setHttpMinorVersion(rawHeaders.getHttpMinorVersion());
+    httpEngine.receiveHeaders(rawHeaders);
+
+    ResponseHeaders headers = new ResponseHeaders(httpEngine.uri, rawHeaders);
+    headers.setTransport("http/1.1");
+    return headers;
   }
 
   public boolean makeReusable(boolean streamCancelled, OutputStream requestBodyOut,

okhttp/src/main/java/com/squareup/okhttp/internal/http/HttpURLConnectionImpl.java

@@ -40,6 +40,7 @@ import java.net.SocketPermission;
 import java.net.URL;
 import java.security.Permission;
 import java.security.cert.CertificateException;
+import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -93,7 +94,7 @@ public class HttpURLConnectionImpl extends HttpURLConnection {
   /* SSL configuration; necessary for HTTP requests that get redirected to HTTPS. */
   SSLSocketFactory sslSocketFactory;
   HostnameVerifier hostnameVerifier;
-  List<String> transports;
+  private List<String> transports;
   OkAuthenticator authenticator;
   final Set<Route> failedRoutes;
 
@@ -125,6 +126,10 @@ public class HttpURLConnectionImpl extends HttpURLConnection {
     return failedRoutes;
   }
 
+  List<String> getTransports() {
+    return transports;
+  }
+
   @Override public final void connect() throws IOException {
     initHttpEngine();
     boolean success;
@@ -547,7 +552,11 @@ public class HttpURLConnectionImpl extends HttpURLConnection {
     if (field == null) {
       throw new NullPointerException("field == null");
     }
-    rawRequestHeaders.set(field, newValue);
+    if ("X-Android-Transports".equals(field)) {
+      setTransports(newValue, false /* append */);
+    } else {
+      rawRequestHeaders.set(field, newValue);
+    }
   }
 
   @Override public final void addRequestProperty(String field, String value) {
@@ -557,6 +566,54 @@ public class HttpURLConnectionImpl extends HttpURLConnection {
     if (field == null) {
       throw new NullPointerException("field == null");
     }
-    rawRequestHeaders.add(field, value);
+
+    if ("X-Android-Transports".equals(field)) {
+      setTransports(value, true /* append */);
+    } else {
+      rawRequestHeaders.add(field, value);
+    }
+  }
+
+  /*
+   * Splits and validates a comma-separated string of transports.
+   * When append == false, we require that the transport list contains "http/1.1".
+   */
+  private void setTransports(String transportsString, boolean append) {
+    if (transportsString == null) {
+      throw new NullPointerException("transportsString == null");
+    }
+
+    String[] transports = transportsString.split(",", -1);
+    ArrayList<String> transportsList = new ArrayList<String>();
+    if (!append) {
+      // If we're not appending to the list, we need to make sure
+      // the list contains "http/1.1". We do this in a separate loop
+      // to avoid modifying any state before we validate the input.
+      boolean containsHttp = false;
+      for (int i = 0; i < transports.length; ++i) {
+        if ("http/1.1".equals(transports[i])) {
+          containsHttp = true;
+          break;
+        }
+      }
+
+      if (!containsHttp) {
+        throw new IllegalArgumentException("Transport list doesn't contain http/1.1");
+      }
+    } else {
+      transportsList.addAll(this.transports);
+    }
+
+    for (int i = 0; i < transports.length; ++i) {
+      if (transports[i].length() == 0) {
+        throw new IllegalArgumentException("Transport list contains an empty transport");
+      }
+
+      if (!transportsList.contains(transports[i])) {
+        transportsList.add(transports[i]);
+      }
+    }
+
+    this.transports = Util.immutableList(transportsList);
   }
 }

okhttp/src/main/java/com/squareup/okhttp/internal/http/ResponseHeaders.java

@@ -42,6 +42,9 @@ public final class ResponseHeaders {
   /** HTTP synthetic header with the response source. */
   static final String RESPONSE_SOURCE = "X-Android-Response-Source";
 
+  /** HTTP synthetic header with the selected transport (spdy/3, http/1.1, etc.) */
+  static final String SELECTED_TRANSPORT = "X-Android-Selected-Transport";
+
   private final URI uri;
   private final RawHeaders headers;
 
@@ -278,6 +281,10 @@ public final class ResponseHeaders {
     headers.set(RESPONSE_SOURCE, responseSource.toString() + " " + headers.getResponseCode());
   }
 
+  public void setTransport(String transport) {
+    headers.set(SELECTED_TRANSPORT, transport);
+  }
+
   /**
    * Returns the current age of the response, in milliseconds. The calculation
    * is specified by RFC 2616, 13.2.3 Age Calculations.

okhttp/src/main/java/com/squareup/okhttp/internal/http/SpdyTransport.java

@@ -71,7 +71,10 @@ public final class SpdyTransport implements Transport {
     RawHeaders rawHeaders = RawHeaders.fromNameValueBlock(nameValueBlock);
     rawHeaders.computeResponseStatusLineFromSpdyHeaders();
     httpEngine.receiveHeaders(rawHeaders);
-    return new ResponseHeaders(httpEngine.uri, rawHeaders);
+
+    ResponseHeaders headers = new ResponseHeaders(httpEngine.uri, rawHeaders);
+    headers.setTransport("spdy/3");
+    return headers;
   }
 
   @Override public InputStream getTransferStream(CacheRequest cacheRequest) throws IOException {