diff --git a/src/future/http/HTTPSFuture.php b/src/future/http/HTTPSFuture.php
index ea3640f..ee96aed 100644
--- a/src/future/http/HTTPSFuture.php
+++ b/src/future/http/HTTPSFuture.php
@@ -1,694 +1,797 @@
 <?php
 
 /**
  * Very basic HTTPS future.
  */
 final class HTTPSFuture extends BaseHTTPFuture {
 
   private static $multi;
   private static $results = array();
   private static $pool = array();
   private static $globalCABundle;
 
   private $handle;
   private $profilerCallID;
   private $cabundle;
   private $followLocation = true;
   private $responseBuffer = '';
   private $responseBufferPos;
   private $files = array();
   private $temporaryFiles = array();
   private $rawBody;
   private $rawBodyPos = 0;
   private $fileHandle;
 
+  private $downloadPath;
+  private $downloadHandle;
+  private $parser;
+
   /**
    * Create a temp file containing an SSL cert, and use it for this session.
    *
    * This allows us to do host-specific SSL certificates in whatever client
    * is using libphutil. e.g. in Arcanist, you could add an "ssl_cert" key
    * to a specific host in ~/.arcrc and use that.
    *
    * cURL needs this to be a file, it doesn't seem to be able to handle a string
    * which contains the cert. So we make a temporary file and store it there.
    *
    * @param string The multi-line, possibly lengthy, SSL certificate to use.
    * @return this
    */
   public function setCABundleFromString($certificate) {
     $temp = new TempFile();
     Filesystem::writeFile($temp, $certificate);
     $this->cabundle = $temp;
     return $this;
   }
 
   /**
    * Set the SSL certificate to use for this session, given a path.
    *
    * @param string The path to a valid SSL certificate for this session
    * @return this
    */
   public function setCABundleFromPath($path) {
     $this->cabundle = $path;
     return $this;
   }
 
   /**
    * Get the path to the SSL certificate for this session.
    *
    * @return string|null
    */
   public function getCABundle() {
     return $this->cabundle;
   }
 
   /**
    * Set whether Location headers in the response will be respected.
    * The default is true.
    *
    * @param boolean true to follow any Location header present in the response,
    *                false to return the request directly
    * @return this
    */
   public function setFollowLocation($follow) {
     $this->followLocation = $follow;
     return $this;
   }
 
   /**
    * Get whether Location headers in the response will be respected.
    *
    * @return boolean
    */
   public function getFollowLocation() {
     return $this->followLocation;
   }
 
   /**
    * Set the fallback CA certificate if one is not specified
    * for the session, given a path.
    *
    * @param string The path to a valid SSL certificate
    * @return void
    */
   public static function setGlobalCABundleFromPath($path) {
     self::$globalCABundle = $path;
   }
   /**
    * Set the fallback CA certificate if one is not specified
    * for the session, given a string.
    *
    * @param string The certificate
    * @return void
    */
   public static function setGlobalCABundleFromString($certificate) {
     $temp = new TempFile();
     Filesystem::writeFile($temp, $certificate);
     self::$globalCABundle = $temp;
   }
 
   /**
    * Get the fallback global CA certificate
    *
    * @return string
    */
   public static function getGlobalCABundle() {
     return self::$globalCABundle;
   }
 
   /**
    * Load contents of remote URI. Behaves pretty much like
    * `@file_get_contents($uri)` but doesn't require `allow_url_fopen`.
    *
    * @param string
    * @param float
    * @return string|false
    */
   public static function loadContent($uri, $timeout = null) {
     $future = new HTTPSFuture($uri);
     if ($timeout !== null) {
       $future->setTimeout($timeout);
     }
     try {
       list($body) = $future->resolvex();
       return $body;
     } catch (HTTPFutureResponseStatus $ex) {
       return false;
     }
   }
 
+  public function setDownloadPath($download_path) {
+    $this->downloadPath = $download_path;
+
+    if (Filesystem::pathExists($download_path)) {
+      throw new Exception(
+        pht(
+          'Specified download path "%s" already exists, refusing to '.
+          'overwrite.'));
+    }
+
+    return $this;
+  }
+
   /**
    * Attach a file to the request.
    *
    * @param string  HTTP parameter name.
    * @param string  File content.
    * @param string  File name.
    * @param string  File mime type.
    * @return this
    */
   public function attachFileData($key, $data, $name, $mime_type) {
     if (isset($this->files[$key])) {
       throw new Exception(
         pht(
           '%s currently supports only one file attachment for each '.
           'parameter name. You are trying to attach two different files with '.
           'the same parameter, "%s".',
           __CLASS__,
           $key));
     }
 
     $this->files[$key] = array(
       'data' => $data,
       'name' => $name,
       'mime' => $mime_type,
     );
 
     return $this;
   }
 
   public function isReady() {
     if (isset($this->result)) {
       return true;
     }
 
     $uri = $this->getURI();
     $domain = id(new PhutilURI($uri))->getDomain();
 
+    $is_download = $this->isDownload();
+
+    // See T13396. For now, use the streaming response parser only if we're
+    // downloading the response to disk.
+    $use_streaming_parser = (bool)$is_download;
+
     if (!$this->handle) {
       $uri_object = new PhutilURI($uri);
       $proxy = PhutilHTTPEngineExtension::buildHTTPProxyURI($uri_object);
 
       $profiler = PhutilServiceProfiler::getInstance();
       $this->profilerCallID = $profiler->beginServiceCall(
         array(
           'type' => 'http',
           'uri' => $uri,
           'proxy' => (string)$proxy,
         ));
 
       if (!self::$multi) {
         self::$multi = curl_multi_init();
         if (!self::$multi) {
           throw new Exception(pht('%s failed!', 'curl_multi_init()'));
         }
       }
 
       if (!empty(self::$pool[$domain])) {
         $curl = array_pop(self::$pool[$domain]);
       } else {
         $curl = curl_init();
         if (!$curl) {
           throw new Exception(pht('%s failed!', 'curl_init()'));
         }
       }
 
       $this->handle = $curl;
       curl_multi_add_handle(self::$multi, $curl);
 
       curl_setopt($curl, CURLOPT_URL, $uri);
 
       if (defined('CURLOPT_PROTOCOLS')) {
         // cURL supports a lot of protocols, and by default it will honor
         // redirects across protocols (for instance, from HTTP to POP3). Beyond
         // being very silly, this also has security implications:
         //
         //   http://blog.volema.com/curl-rce.html
         //
         // Disable all protocols other than HTTP and HTTPS.
 
         $allowed_protocols = CURLPROTO_HTTPS | CURLPROTO_HTTP;
         curl_setopt($curl, CURLOPT_PROTOCOLS, $allowed_protocols);
         curl_setopt($curl, CURLOPT_REDIR_PROTOCOLS, $allowed_protocols);
       }
 
       if (strlen($this->rawBody)) {
         if ($this->getData()) {
           throw new Exception(
             pht(
               'You can not execute an HTTP future with both a raw request '.
               'body and structured request data.'));
         }
 
         // We aren't actually going to use this file handle, since we are
         // just pushing data through the callback, but cURL gets upset if
         // we don't hand it a real file handle.
         $tmp = new TempFile();
         $this->fileHandle = fopen($tmp, 'r');
 
         // NOTE: We must set CURLOPT_PUT here to make cURL use CURLOPT_INFILE.
         // We'll possibly overwrite the method later on, unless this is really
         // a PUT request.
         curl_setopt($curl, CURLOPT_PUT, true);
         curl_setopt($curl, CURLOPT_INFILE, $this->fileHandle);
         curl_setopt($curl, CURLOPT_INFILESIZE, strlen($this->rawBody));
         curl_setopt($curl, CURLOPT_READFUNCTION,
           array($this, 'willWriteBody'));
       } else {
         $data = $this->formatRequestDataForCURL();
         curl_setopt($curl, CURLOPT_POSTFIELDS, $data);
       }
 
       $headers = $this->getHeaders();
 
       $saw_expect = false;
       for ($ii = 0; $ii < count($headers); $ii++) {
         list($name, $value) = $headers[$ii];
         $headers[$ii] = $name.': '.$value;
         if (!strncasecmp($name, 'Expect', strlen('Expect'))) {
           $saw_expect = true;
         }
       }
       if (!$saw_expect) {
         // cURL sends an "Expect" header by default for certain requests. While
         // there is some reasoning behind this, it causes a practical problem
         // in that lighttpd servers reject these requests with a 417. Both sides
         // are locked in an eternal struggle (lighttpd has introduced a
         // 'server.reject-expect-100-with-417' option to deal with this case).
         //
         // The ostensibly correct way to suppress this behavior on the cURL side
         // is to add an empty "Expect:" header. If we haven't seen some other
         // explicit "Expect:" header, do so.
         //
         // See here, for example, although this issue is fairly widespread:
         //   http://curl.haxx.se/mail/archive-2009-07/0008.html
         $headers[] = 'Expect:';
       }
       curl_setopt($curl, CURLOPT_HTTPHEADER, $headers);
 
       // Set the requested HTTP method, e.g. GET / POST / PUT.
       curl_setopt($curl, CURLOPT_CUSTOMREQUEST, $this->getMethod());
 
       // Make sure we get the headers and data back.
       curl_setopt($curl, CURLOPT_HEADER, true);
       curl_setopt($curl, CURLOPT_WRITEFUNCTION,
         array($this, 'didReceiveDataCallback'));
 
       if ($this->followLocation) {
         curl_setopt($curl, CURLOPT_FOLLOWLOCATION, true);
         curl_setopt($curl, CURLOPT_MAXREDIRS, 20);
       }
 
       if (defined('CURLOPT_TIMEOUT_MS')) {
         // If CURLOPT_TIMEOUT_MS is available, use the higher-precision timeout.
         $timeout = max(1, ceil(1000 * $this->getTimeout()));
         curl_setopt($curl, CURLOPT_TIMEOUT_MS, $timeout);
       } else {
         // Otherwise, fall back to the lower-precision timeout.
         $timeout = max(1, ceil($this->getTimeout()));
         curl_setopt($curl, CURLOPT_TIMEOUT, $timeout);
       }
 
       // We're going to try to set CAINFO below. This doesn't work at all on
       // OSX around Yosemite (see T5913). On these systems, we'll use the
       // system CA and then try to tell the user that their settings were
       // ignored and how to fix things if we encounter a CA-related error.
       // Assume we have custom CA settings to start with; we'll clear this
       // flag if we read the default CA info below.
 
       // Try some decent fallbacks here:
       // - First, check if a bundle is set explicitly for this request, via
       //   `setCABundle()` or similar.
       // - Then, check if a global bundle is set explicitly for all requests,
       //   via `setGlobalCABundle()` or similar.
       // - Then, if a local custom.pem exists, use that, because it probably
       //   means that the user wants to override everything (also because the
       //   user might not have access to change the box's php.ini to add
       //   curl.cainfo).
       // - Otherwise, try using curl.cainfo. If it's set explicitly, it's
       //   probably reasonable to try using it before we fall back to what
       //   libphutil ships with.
       // - Lastly, try the default that libphutil ships with. If it doesn't
       //   work, give up and yell at the user.
 
       if (!$this->getCABundle()) {
         $caroot = dirname(phutil_get_library_root('phutil')).'/resources/ssl/';
         $ini_val = ini_get('curl.cainfo');
         if (self::getGlobalCABundle()) {
           $this->setCABundleFromPath(self::getGlobalCABundle());
         } else if (Filesystem::pathExists($caroot.'custom.pem')) {
           $this->setCABundleFromPath($caroot.'custom.pem');
         } else if ($ini_val) {
           // TODO: We can probably do a pathExists() here, even.
           $this->setCABundleFromPath($ini_val);
         } else {
           $this->setCABundleFromPath($caroot.'default.pem');
         }
       }
 
       if ($this->canSetCAInfo()) {
         curl_setopt($curl, CURLOPT_CAINFO, $this->getCABundle());
       }
 
       $verify_peer = 1;
       $verify_host = 2;
 
       $extensions = PhutilHTTPEngineExtension::getAllExtensions();
       foreach ($extensions as $extension) {
         if ($extension->shouldTrustAnySSLAuthorityForURI($uri_object)) {
           $verify_peer = 0;
         }
         if ($extension->shouldTrustAnySSLHostnameForURI($uri_object)) {
           $verify_host = 0;
         }
       }
 
       curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, $verify_peer);
       curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, $verify_host);
       curl_setopt($curl, CURLOPT_SSLVERSION, 0);
 
       // See T13391. Recent versions of cURL default to "HTTP/2" on some
       // connections, but do not support HTTP/2 proxies. Until HTTP/2
       // stabilizes, force HTTP/1.1 explicitly.
       curl_setopt($curl, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_1);
 
       if ($proxy) {
         curl_setopt($curl, CURLOPT_PROXY, (string)$proxy);
       }
+
+      if ($is_download) {
+        $this->downloadHandle = @fopen($this->downloadPath, 'wb+');
+        if (!$this->downloadHandle) {
+          throw new Exception(
+            pht(
+              'Failed to open filesystem path "%s" for writing.',
+              $this->downloadPath));
+        }
+      }
+
+      if ($use_streaming_parser) {
+        $streaming_parser = id(new PhutilHTTPResponseParser())
+          ->setFollowLocationHeaders($this->getFollowLocation());
+
+        if ($this->downloadHandle) {
+          $streaming_parser->setWriteHandle($this->downloadHandle);
+        }
+
+        $this->parser = $streaming_parser;
+      }
     } else {
       $curl = $this->handle;
 
       if (!self::$results) {
         // NOTE: In curl_multi_select(), PHP calls curl_multi_fdset() but does
         // not check the return value of &maxfd for -1 until recent versions
         // of PHP (5.4.8 and newer). cURL may return -1 as maxfd in some unusual
         // situations; if it does, PHP enters select() with nfds=0, which blocks
         // until the timeout is reached.
         //
         // We could try to guess whether this will happen or not by examining
         // the version identifier, but we can also just sleep for only a short
         // period of time.
         curl_multi_select(self::$multi, 0.01);
       }
     }
 
     do {
       $active = null;
       $result = curl_multi_exec(self::$multi, $active);
     } while ($result == CURLM_CALL_MULTI_PERFORM);
 
     while ($info = curl_multi_info_read(self::$multi)) {
       if ($info['msg'] == CURLMSG_DONE) {
         self::$results[(int)$info['handle']] = $info;
       }
     }
 
     if (!array_key_exists((int)$curl, self::$results)) {
       return false;
     }
 
     // The request is complete, so release any temporary files we wrote
     // earlier.
     $this->temporaryFiles = array();
 
     $info = self::$results[(int)$curl];
     $result = $this->responseBuffer;
     $err_code = $info['result'];
 
     if ($err_code) {
       if (($err_code == CURLE_SSL_CACERT) && !$this->canSetCAInfo()) {
         $status = new HTTPFutureCertificateResponseStatus(
           HTTPFutureCertificateResponseStatus::ERROR_IMMUTABLE_CERTIFICATES,
           $uri);
       } else {
         $status = new HTTPFutureCURLResponseStatus($err_code, $uri);
       }
 
       $body = null;
       $headers = array();
       $this->result = array($status, $body, $headers);
+    } else if ($this->parser) {
+      $streaming_parser = $this->parser;
+      try {
+        $responses = $streaming_parser->getResponses();
+        $final_response = last($responses);
+        $result = array(
+          $final_response->getStatus(),
+          $final_response->getBody(),
+          $final_response->getHeaders(),
+        );
+      } catch (HTTPFutureParseResponseStatus $ex) {
+        $result = array($ex, null, array());
+      }
+
+      $this->result = $result;
     } else {
       // cURL returns headers of all redirects, we strip all but the final one.
       $redirects = curl_getinfo($curl, CURLINFO_REDIRECT_COUNT);
       $result = preg_replace('/^(.*\r\n\r\n){'.$redirects.'}/sU', '', $result);
       $this->result = $this->parseRawHTTPResponse($result);
     }
 
     curl_multi_remove_handle(self::$multi, $curl);
     unset(self::$results[(int)$curl]);
 
     // NOTE: We want to use keepalive if possible. Return the handle to a
     // pool for the domain; don't close it.
     if ($this->shouldReuseHandles()) {
       self::$pool[$domain][] = $curl;
     }
 
+    if ($is_download) {
+      if ($this->downloadHandle) {
+        fflush($this->downloadHandle);
+        fclose($this->downloadHandle);
+        $this->downloadHandle = null;
+      }
+    }
+
     $profiler = PhutilServiceProfiler::getInstance();
     $profiler->endServiceCall($this->profilerCallID, array());
 
     return true;
   }
 
 
   /**
    * Callback invoked by cURL as it reads HTTP data from the response. We save
    * the data to a buffer.
    */
   public function didReceiveDataCallback($handle, $data) {
-    $this->responseBuffer .= $data;
+    if ($this->parser) {
+      $this->parser->readBytes($data);
+    } else {
+      $this->responseBuffer .= $data;
+    }
+
     return strlen($data);
   }
 
 
   /**
    * Read data from the response buffer.
    *
    * NOTE: Like @{class:ExecFuture}, this method advances a read cursor but
    * does not discard the data. The data will still be buffered, and it will
    * all be returned when the future resolves. To discard the data after
    * reading it, call @{method:discardBuffers}.
    *
    * @return string Response data, if available.
    */
   public function read() {
+    if ($this->isDownload()) {
+      throw new Exception(
+        pht(
+          'You can not read the result buffer while streaming results '.
+          'to disk: there is no in-memory buffer to read.'));
+    }
+
+    if ($this->parser) {
+      throw new Exception(
+        pht(
+          'Streaming reads are not currently supported by the streaming '.
+          'parser.'));
+    }
+
     $result = substr($this->responseBuffer, $this->responseBufferPos);
     $this->responseBufferPos = strlen($this->responseBuffer);
     return $result;
   }
 
 
   /**
    * Discard any buffered data. Normally, you call this after reading the
    * data with @{method:read}.
    *
    * @return this
    */
   public function discardBuffers() {
+    if ($this->isDownload()) {
+      throw new Exception(
+        pht(
+          'You can not discard the result buffer while streaming results '.
+          'to disk: there is no in-memory buffer to discard.'));
+    }
+
+    if ($this->parser) {
+      throw new Exception(
+        pht(
+          'Buffer discards are not currently supported by the streaming '.
+          'parser.'));
+    }
+
     $this->responseBuffer = '';
     $this->responseBufferPos = 0;
     return $this;
   }
 
 
   /**
    * Produces a value safe to pass to `CURLOPT_POSTFIELDS`.
    *
    * @return wild   Some value, suitable for use in `CURLOPT_POSTFIELDS`.
    */
   private function formatRequestDataForCURL() {
     // We're generating a value to hand to cURL as CURLOPT_POSTFIELDS. The way
     // cURL handles this value has some tricky caveats.
 
     // First, we can return either an array or a query string. If we return
     // an array, we get a "multipart/form-data" request. If we return a
     // query string, we get an "application/x-www-form-urlencoded" request.
 
     // Second, if we return an array we can't duplicate keys. The user might
     // want to send the same parameter multiple times.
 
     // Third, if we return an array and any of the values start with "@",
     // cURL includes arbitrary files off disk and sends them to an untrusted
     // remote server. For example, an array like:
     //
     //   array('name' => '@/usr/local/secret')
     //
     // ...will attempt to read that file off disk and transmit its contents with
     // the request. This behavior is pretty surprising, and it can easily
     // become a relatively severe security vulnerability which allows an
     // attacker to read any file the HTTP process has access to. Since this
     // feature is very dangerous and not particularly useful, we prevent its
     // use. Broadly, this means we must reject some requests because they
     // contain an "@" in an inconvenient place.
 
     // Generally, to avoid the "@" case and because most servers usually
     // expect "application/x-www-form-urlencoded" data, we try to return a
     // string unless there are files attached to this request.
 
     $data = $this->getData();
     $files = $this->files;
 
     $any_data = ($data || (is_string($data) && strlen($data)));
     $any_files = (bool)$this->files;
 
     if (!$any_data && !$any_files) {
       // No files or data, so just bail.
       return null;
     }
 
     if (!$any_files) {
       // If we don't have any files, just encode the data as a query string,
       // make sure it's not including any files, and we're good to go.
       if (is_array($data)) {
         $data = phutil_build_http_querystring($data);
       }
 
       $this->checkForDangerousCURLMagic($data, $is_query_string = true);
 
       return $data;
     }
 
     // If we've made it this far, we have some files, so we need to return
     // an array. First, convert the other data into an array if it isn't one
     // already.
 
     if (is_string($data)) {
       // NOTE: We explicitly don't want fancy array parsing here, so just
       // do a basic parse and then convert it into a dictionary ourselves.
       $parser = new PhutilQueryStringParser();
       $pairs = $parser->parseQueryStringToPairList($data);
 
       $map = array();
       foreach ($pairs as $pair) {
         list($key, $value) = $pair;
         if (array_key_exists($key, $map)) {
           throw new Exception(
             pht(
               'Request specifies two values for key "%s", but parameter '.
               'names must be unique if you are posting file data due to '.
               'limitations with cURL.',
               $key));
         }
         $map[$key] = $value;
       }
 
       $data = $map;
     }
 
     foreach ($data as $key => $value) {
       $this->checkForDangerousCURLMagic($value, $is_query_string = false);
     }
 
     foreach ($this->files as $name => $info) {
       if (array_key_exists($name, $data)) {
         throw new Exception(
           pht(
             'Request specifies a file with key "%s", but that key is also '.
             'defined by normal request data. Due to limitations with cURL, '.
             'requests that post file data must use unique keys.',
             $name));
       }
 
       $tmp = new TempFile($info['name']);
       Filesystem::writeFile($tmp, $info['data']);
       $this->temporaryFiles[] = $tmp;
 
       // In 5.5.0 and later, we can use CURLFile. Prior to that, we have to
       // use this "@" stuff.
 
       if (class_exists('CURLFile', false)) {
         $file_value = new CURLFile((string)$tmp, $info['mime'], $info['name']);
       } else {
         $file_value = '@'.(string)$tmp;
       }
 
       $data[$name] = $file_value;
     }
 
     return $data;
   }
 
 
   /**
    * Detect strings which will cause cURL to do horrible, insecure things.
    *
    * @param string  Possibly dangerous string.
    * @param bool    True if this string is being used as part of a query string.
    * @return void
    */
   private function checkForDangerousCURLMagic($string, $is_query_string) {
     if (empty($string[0]) || ($string[0] != '@')) {
       // This isn't an "@..." string, so it's fine.
       return;
     }
 
     if ($is_query_string) {
       if (version_compare(phpversion(), '5.2.0', '<')) {
         throw new Exception(
           pht(
             'Attempting to make an HTTP request, but query string data begins '.
             'with "%s". Prior to PHP 5.2.0 this reads files off disk, which '.
             'creates a wide attack window for security vulnerabilities. '.
             'Upgrade PHP or avoid making cURL requests which begin with "%s".',
             '@',
             '@'));
       }
 
       // This is safe if we're on PHP 5.2.0 or newer.
       return;
     }
 
     throw new Exception(
       pht(
         'Attempting to make an HTTP request which includes file data, but the '.
         'value of a query parameter begins with "%s". PHP interprets these '.
         'values to mean that it should read arbitrary files off disk and '.
         'transmit them to remote servers. Declining to make this request.',
         '@'));
   }
 
 
   /**
    * Determine whether CURLOPT_CAINFO is usable on this system.
    */
   private function canSetCAInfo() {
     // We cannot set CAInfo on OSX after Yosemite.
 
     $osx_version = PhutilExecutionEnvironment::getOSXVersion();
     if ($osx_version) {
       if (version_compare($osx_version, 14, '>=')) {
         return false;
       }
     }
 
     return true;
   }
 
 
   /**
    * Write a raw HTTP body into the request.
    *
    * You must write the entire body before starting the request.
    *
    * @param string Raw body.
    * @return this
    */
   public function write($raw_body) {
     $this->rawBody = $raw_body;
     return $this;
   }
 
 
   /**
    * Callback to pass data to cURL.
    */
   public function willWriteBody($handle, $infile, $len) {
     $bytes = substr($this->rawBody, $this->rawBodyPos, $len);
     $this->rawBodyPos += $len;
     return $bytes;
   }
 
   private function shouldReuseHandles() {
     $curl_version = curl_version();
     $version = idx($curl_version, 'version');
 
     // NOTE: cURL 7.43.0 has a bug where the POST body length is not recomputed
     // properly when a handle is reused. For this version of cURL, disable
     // handle reuse and accept a small performance penalty. See T8654.
     if ($version == '7.43.0') {
       return false;
     }
 
     return true;
   }
 
+  private function isDownload() {
+   return ($this->downloadPath !== null);
+  }
 
 }
diff --git a/src/parser/http/PhutilHTTPResponse.php b/src/parser/http/PhutilHTTPResponse.php
index 60d33b6..756847a 100644
--- a/src/parser/http/PhutilHTTPResponse.php
+++ b/src/parser/http/PhutilHTTPResponse.php
@@ -1,40 +1,62 @@
 <?php
 
 final class PhutilHTTPResponse
   extends Phobject {
 
   private $headers = array();
   private $body;
   private $status;
+  private $writeHandle;
 
   public function __construct() {
     $this->body = new PhutilRope();
   }
 
   public function setHeaders(array $headers) {
     $this->headers = $headers;
     return $this;
   }
 
   public function getHeaders() {
     return $this->headers;
   }
 
   public function setStatus(HTTPFutureResponseStatus $status) {
     $this->status = $status;
     return $this;
   }
 
   public function getStatus() {
     return $this->status;
   }
 
   public function appendBody($bytes) {
-    $this->body->append($bytes);
+    if ($this->writeHandle !== null) {
+      $result = @fwrite($this->writeHandle, $bytes);
+      if ($result !== strlen($bytes)) {
+        throw new Exception(
+          pht('Failed to write response to disk. (Maybe the disk is full?)'));
+      }
+    } else {
+      $this->body->append($bytes);
+    }
   }
 
   public function getBody() {
+    if ($this->writeHandle !== null) {
+      return null;
+    }
+
     return $this->body->getAsString();
   }
 
+  public function setWriteHandle($write_handle) {
+    $this->writeHandle = $write_handle;
+    return $this;
+  }
+
+  public function getWriteHandle() {
+    return $this->writeHandle;
+  }
+
 }
diff --git a/src/parser/http/PhutilHTTPResponseParser.php b/src/parser/http/PhutilHTTPResponseParser.php
index cfec39d..9689605 100644
--- a/src/parser/http/PhutilHTTPResponseParser.php
+++ b/src/parser/http/PhutilHTTPResponseParser.php
@@ -1,174 +1,190 @@
 <?php
 
 final class PhutilHTTPResponseParser extends Phobject {
 
   private $followLocationHeaders;
   private $responses = array();
   private $response;
   private $buffer;
   private $state = 'headers';
+  private $writeHandle;
 
   public function setFollowLocationHeaders($follow_location_headers) {
     $this->followLocationHeaders = $follow_location_headers;
     return $this;
   }
 
   public function getFollowLocationHeaders() {
     return $this->followLocationHeaders;
   }
 
+  public function setWriteHandle($write_handle) {
+    $this->writeHandle = $write_handle;
+    return $this;
+  }
+
+  public function getWriteHandle() {
+    return $this->writeHandle;
+  }
+
   public function readBytes($bytes) {
     if ($this->state == 'discard') {
       return $this;
     }
 
     $this->buffer .= $bytes;
 
     while (true) {
       if ($this->state == 'headers') {
         $matches = null;
 
         $ok = preg_match(
           "/(\r?\n\r?\n)/",
           $this->buffer,
           $matches,
           PREG_OFFSET_CAPTURE);
         if (!$ok) {
           break;
         }
 
         $headers_len = $matches[1][1];
         $boundary_len = strlen($matches[1][0]);
         $raw_headers = substr($this->buffer, 0, $headers_len);
         $this->buffer = substr($this->buffer, $headers_len + $boundary_len);
 
         $header_lines = phutil_split_lines($raw_headers);
         $first_line = array_shift($header_lines);
         $response_valid = true;
 
         $matches = null;
         $ok = preg_match(
           '(^HTTP/\S+\s+(\d+)(?:\s+(.*))?$)i',
           $first_line,
           $matches);
 
         if ($ok) {
           $http_code = (int)$matches[1];
           $http_status = phutil_utf8_strtolower($matches[2]);
         } else {
           $response_valid = false;
         }
 
         $header_list = array();
         $saw_location = false;
         foreach ($header_lines as $header_line) {
           $pos = strpos($header_line, ':');
           if ($pos === false) {
             $response_valid = false;
             break;
           }
 
           $name = substr($header_line, 0, $pos);
           $value = ltrim(substr($header_line, $pos + 1), ' ');
 
           if (phutil_utf8_strtolower($name) == 'location') {
             $saw_location = true;
           }
 
           $header_list[] = array(
             $name,
             $value,
           );
         }
 
         // If the response didn't start with a properly formatted "HTTP/..."
         // line, or any of the header lines were not formatted correctly, add
         // a malformed response to the response list and discard anything else
         // we're given.
         if (!$response_valid) {
           $malformed = new HTTPFutureParseResponseStatus(
             HTTPFutureParseResponseStatus::ERROR_MALFORMED_RESPONSE,
             $raw_headers);
 
-          $this->newHTTPRepsonse()
+          $this->newHTTPResponse()
             ->setStatus($malformed);
 
           $this->buffer = '';
           $this->state = 'discard';
           break;
         }
 
         // Otherwise, we have a valid set of response headers.
         $response_status = new HTTPFutureHTTPResponseStatus(
           $http_code,
           null,
           $header_list);
 
         $this->newHTTPResponse()
           ->setStatus($response_status)
           ->setHeaders($header_list);
 
         $is_https_proxy =
           ($http_code === 200) &&
           ($http_status === 'connection established');
 
         if ($http_code === 100) {
           // If this is "HTTP/1.1 100 Continue", this is just the server
           // telling us that everything is okay. This response won't have
           // a body associated with it.
           $more_headers = true;
         } else if ($is_https_proxy) {
           // If this is "HTTP/1.1 200 Connection Established", this is a
           // response to a CONNECT request made automatically by cURL to
           // an HTTPS proxy. This response won't have a body associated
           // with it, and the real body will follow later.
           $more_headers = true;
         } else if ($saw_location && $this->followLocationHeaders) {
           // If we're following location headers and this response had
           // a location header, cURL will automatically follow it. This
           // response shouldn't have a body.
           $more_headers = true;
         } else {
           $more_headers = false;
         }
 
         // If we're expecting more headers, we're going to stay in the
         // "headers" state and parse another set of headers. Otherwise,
         // we transition to the "body" state and look for a body.
         if (!$more_headers) {
           $this->state = 'body';
         }
 
         continue;
       }
 
       if ($this->state == 'body') {
         if (strlen($this->buffer)) {
           $this->response->appendBody($this->buffer);
           $this->buffer = '';
         }
         break;
       }
     }
 
     return $this;
   }
 
   public function getResponses() {
     if ($this->state !== 'body') {
       throw new HTTPFutureParseResponseStatus(
         HTTPFutureParseResponseStatus::ERROR_MALFORMED_RESPONSE,
         $this->buffer);
     }
 
     return $this->responses;
   }
 
   private function newHTTPResponse() {
     $response = new PhutilHTTPResponse();
+
+    $write_handle = $this->getWriteHandle();
+    if ($write_handle) {
+      $response->setWriteHandle($write_handle);
+    }
+
     $this->responses[] = $response;
     $this->response = $response;
     return $response;
   }
 
 }