If the Conduit server asserts it has the "gzip" capability, compress requests

Summary:
Ref T13507. For various messy reasons we can't blindly assume the server supports "gzip" -- but if the server tells us it does, we're on firmer ground.

If the server returns an "X-Conduit-Capabilities: gzip" header and we have compression support locally, compress subsequent requests.

This restores D21073, which was reverted by D21076.

Test Plan: With a gzip-asserting server, added debugging code and ran various "arc" commands. Saw the 2nd..Nth calls hit compression code.

Maniphest Tasks: T13507

Differential Revision: https://secure.phabricator.com/D21119

src/conduit/ConduitClient.php

@@ -13,6 +13,7 @@ final class ConduitClient extends Phobject {
   private $privateKey;
   private $conduitToken;
   private $oauthToken;
+  private $capabilities = array();
 
   const AUTH_ASYMMETRIC = 'asymmetric';
 
@@ -86,6 +87,11 @@ final class ConduitClient extends Phobject {
     return $this;
   }
 
+  public function enableCapabilities(array $capabilities) {
+    $this->capabilities += array_fuse($capabilities);
+    return $this;
+  }
+
   public function callMethod($method, array $params) {
 
     $meta = array();
@@ -143,12 +149,28 @@ final class ConduitClient extends Phobject {
 
     // Always use the cURL-based HTTPSFuture, for proxy support and other
     // protocol edge cases that HTTPFuture does not support.
-    $core_future = new HTTPSFuture($uri, $data);
+    $core_future = new HTTPSFuture($uri);
     $core_future->addHeader('Host', $this->getHostStringForHeader());
 
     $core_future->setMethod('POST');
     $core_future->setTimeout($this->timeout);
 
+    // See T13507. If possible, try to compress requests. To compress requests,
+    // we must have "gzencode()" available and the server needs to have
+    // asserted it has the "gzip" capability.
+    $can_gzip =
+      (function_exists('gzencode')) &&
+      (isset($this->capabilities['gzip']));
+    if ($can_gzip) {
+      $gzip_data = phutil_build_http_querystring($data);
+      $gzip_data = gzencode($gzip_data);
+
+      $core_future->addHeader('Content-Encoding', 'gzip');
+      $core_future->setData($gzip_data);
+    } else {
+      $core_future->setData($data);
+    }
+
     if ($this->username !== null) {
       $core_future->setHTTPBasicAuthCredentials(
         $this->username,

src/conduit/ConduitFuture.php

@@ -3,6 +3,7 @@
 final class ConduitFuture extends FutureProxy {
 
   private $client;
+  private $engine;
   private $conduitMethod;
   private $profilerCallID;
 
@@ -40,6 +41,19 @@ final class ConduitFuture extends FutureProxy {
       throw $status;
     }
 
+    $capabilities = array();
+    foreach ($headers as $header) {
+      list($name, $value) = $header;
+      if (!strcasecmp($name, 'X-Conduit-Capabilities')) {
+        $capabilities = explode(' ', $value);
+        break;
+      }
+    }
+
+    if ($capabilities) {
+      $this->client->enableCapabilities($capabilities);
+    }
+
     $raw = $body;
 
     $shield = 'for(;;);';