diff --git a/Dockerfile b/Dockerfile
index efc11656f..f6a095230 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -9,7 +9,7 @@ RUN set -xe \
     && composer require guzzlehttp/guzzle
 
 
-FROM php:7.2
+FROM php:7.3
 
 RUN mkdir /guzzle
 
diff --git a/docs/request-options.rst b/docs/request-options.rst
index 7fbeeaa3e..47f5c66a7 100644
--- a/docs/request-options.rst
+++ b/docs/request-options.rst
@@ -737,7 +737,7 @@ progress
 
 The function accepts the following positional arguments:
 
-- the total number of bytes expected to be downloaded
+- the total number of bytes expected to be downloaded, zero if unknown
 - the number of bytes downloaded so far
 - the total number of bytes expected to be uploaded
 - the number of bytes uploaded so far
diff --git a/docs/testing.rst b/docs/testing.rst
index 5ac06691b..fd84d2cdb 100644
--- a/docs/testing.rst
+++ b/docs/testing.rst
@@ -32,7 +32,7 @@ a response or exception by shifting return values off of a queue.
 
     // Create a mock and queue two responses.
     $mock = new MockHandler([
-        new Response(200, ['X-Foo' => 'Bar']),
+        new Response(200, ['X-Foo' => 'Bar'], 'Hello, World'),
         new Response(202, ['Content-Length' => 0]),
         new RequestException('Error Communicating with Server', new Request('GET', 'test'))
     ]);
@@ -41,8 +41,11 @@ a response or exception by shifting return values off of a queue.
     $client = new Client(['handler' => $handlerStack]);
 
     // The first request is intercepted with the first response.
-    echo $client->request('GET', '/')->getStatusCode();
+    $response = $client->request('GET', '/');
+    echo $response->getStatusCode();
     //> 200
+    echo $response->getBody();
+    //> Hello, World
     // The second request is intercepted with the second response.
     echo $client->request('GET', '/')->getStatusCode();
     //> 202
diff --git a/src/Exception/GuzzleException.php b/src/Exception/GuzzleException.php
index 510778f6e..c232fa637 100644
--- a/src/Exception/GuzzleException.php
+++ b/src/Exception/GuzzleException.php
@@ -1,13 +1,20 @@
 <?php
 namespace GuzzleHttp\Exception;
 
-/**
- * @method string getMessage()
- * @method \Throwable|null getPrevious()
- * @method mixed getCode()
- * @method string getFile()
- * @method int getLine()
- * @method array getTrace()
- * @method string getTraceAsString()
- */
-interface GuzzleException {}
+use Throwable;
+
+if (interface_exists(Throwable::class)) {
+    interface GuzzleException extends Throwable {}
+} else {
+    /**
+     * @method string getMessage()
+     * @method \Throwable|null getPrevious()
+     * @method mixed getCode()
+     * @method string getFile()
+     * @method int getLine()
+     * @method array getTrace()
+     * @method string getTraceAsString()
+     */
+    interface GuzzleException {}
+}
+
diff --git a/src/Handler/CurlFactory.php b/src/Handler/CurlFactory.php
index ee4ec3539..e349bb4c4 100644
--- a/src/Handler/CurlFactory.php
+++ b/src/Handler/CurlFactory.php
@@ -14,6 +14,9 @@
  */
 class CurlFactory implements CurlFactoryInterface
 {
+    const CURL_VERSION_STR = 'curl_version';
+    const LOW_CURL_VERSION_NUMBER = '7.21.2';
+
     /** @var array */
     private $handles = [];
 
@@ -117,6 +120,7 @@ public static function finish(
     private static function invokeStats(EasyHandle $easy)
     {
         $curlStats = curl_getinfo($easy->handle);
+        $curlStats['appconnect_time'] = curl_getinfo($easy->handle, CURLINFO_APPCONNECT_TIME);
         $stats = new TransferStats(
             $easy->request,
             $easy->response,
@@ -136,7 +140,9 @@ private static function finishError(
         $ctx = [
             'errno' => $easy->errno,
             'error' => curl_error($easy->handle),
+            'appconnect_time' => curl_getinfo($easy->handle, CURLINFO_APPCONNECT_TIME),
         ] + curl_getinfo($easy->handle);
+        $ctx[self::CURL_VERSION_STR] = curl_version()['version'];
         $factory->release($easy);
 
         // Retry when nothing is present or when curl failed to rewind.
@@ -172,13 +178,22 @@ private static function createRejection(EasyHandle $easy, array $ctx)
                 )
             );
         }
-
-        $message = sprintf(
-            'cURL error %s: %s (%s)',
-            $ctx['errno'],
-            $ctx['error'],
-            'see https://curl.haxx.se/libcurl/c/libcurl-errors.html'
-        );
+        if (version_compare($ctx[self::CURL_VERSION_STR], self::LOW_CURL_VERSION_NUMBER)) {
+            $message = sprintf(
+                'cURL error %s: %s (%s)',
+                $ctx['errno'],
+                $ctx['error'],
+                'see https://curl.haxx.se/libcurl/c/libcurl-errors.html'
+            );
+        } else {
+            $message = sprintf(
+                'cURL error %s: %s (%s) for %s',
+                $ctx['errno'],
+                $ctx['error'],
+                'see https://curl.haxx.se/libcurl/c/libcurl-errors.html',
+                $easy->request->getUri()
+            );
+        }
 
         // Create a connection exception if it was a specific error code.
         $error = isset($connectionErrors[$easy->errno])
diff --git a/src/Handler/CurlMultiHandler.php b/src/Handler/CurlMultiHandler.php
index 7097835d1..d8297623c 100644
--- a/src/Handler/CurlMultiHandler.php
+++ b/src/Handler/CurlMultiHandler.php
@@ -88,7 +88,7 @@ public function tick()
     {
         // Add any delayed handles if needed.
         if ($this->delays) {
-            $currentTime = microtime(true);
+            $currentTime = \GuzzleHttp\_current_time();
             foreach ($this->delays as $id => $delay) {
                 if ($currentTime >= $delay) {
                     unset($this->delays[$id]);
@@ -140,7 +140,7 @@ private function addRequest(array $entry)
         if (empty($easy->options['delay'])) {
             curl_multi_add_handle($this->_mh, $easy->handle);
         } else {
-            $this->delays[$id] = microtime(true) + ($easy->options['delay'] / 1000);
+            $this->delays[$id] = \GuzzleHttp\_current_time() + ($easy->options['delay'] / 1000);
         }
     }
 
@@ -192,7 +192,7 @@ private function processMessages()
 
     private function timeToNext()
     {
-        $currentTime = microtime(true);
+        $currentTime = \GuzzleHttp\_current_time();
         $nextTime = PHP_INT_MAX;
         foreach ($this->delays as $time) {
             if ($time < $nextTime) {
diff --git a/src/Handler/StreamHandler.php b/src/Handler/StreamHandler.php
index 741e02d2a..0dedd7da4 100644
--- a/src/Handler/StreamHandler.php
+++ b/src/Handler/StreamHandler.php
@@ -33,7 +33,7 @@ public function __invoke(RequestInterface $request, array $options)
             usleep($options['delay'] * 1000);
         }
 
-        $startTime = isset($options['on_stats']) ? microtime(true) : null;
+        $startTime = isset($options['on_stats']) ? \GuzzleHttp\_current_time() : null;
 
         try {
             // Does not support the expect header.
@@ -82,7 +82,7 @@ private function invokeStats(
             $stats = new TransferStats(
                 $request,
                 $response,
-                microtime(true) - $startTime,
+                \GuzzleHttp\_current_time() - $startTime,
                 $error,
                 []
             );
diff --git a/src/functions.php b/src/functions.php
index 5081bb5fa..3c472bc6a 100644
--- a/src/functions.php
+++ b/src/functions.php
@@ -331,3 +331,15 @@ function json_encode($value, $options = 0, $depth = 512)
 
     return $json;
 }
+
+/**
+ * Wrapper for the hrtime() or microtime() functions
+ * (depending on the PHP version, one of the two is used)
+ *
+ * @return float|mixed UNIX timestamp
+ * @internal
+ */
+function _current_time()
+{
+    return function_exists('hrtime') ? hrtime(true) / 1e9 : microtime(true);
+}
diff --git a/tests/Cookie/CookieJarTest.php b/tests/Cookie/CookieJarTest.php
index 8416c9a24..f0fad497d 100644
--- a/tests/Cookie/CookieJarTest.php
+++ b/tests/Cookie/CookieJarTest.php
@@ -1,6 +1,9 @@
 <?php
 namespace GuzzleHttp\Tests\CookieJar;
 
+use DateInterval;
+use DateTime;
+use DateTimeImmutable;
 use GuzzleHttp\Cookie\CookieJar;
 use GuzzleHttp\Cookie\SetCookie;
 use GuzzleHttp\Psr7\Request;
@@ -366,7 +369,7 @@ public function testCanConvertToAndLoadFromArray()
     public function testAddsCookiesWithEmptyPathFromResponse()
     {
         $response = new Response(200, array(
-            'Set-Cookie' => "fpc=foobar; expires=Fri, 02-Mar-2019 02:17:40 GMT; path=;"
+            'Set-Cookie' => "fpc=foobar; expires={$this->futureExpirationDate()}; path=;"
         ));
         $request = new Request('GET', 'http://www.example.com');
         $this->jar->extractCookies($request, $response);
@@ -396,11 +399,11 @@ public function testCookiePathWithEmptySetCookiePath($uriPath, $cookiePath)
         $response = (new Response(200))
             ->withAddedHeader(
                 'Set-Cookie',
-                "foo=bar; expires=Fri, 02-Mar-2019 02:17:40 GMT; domain=www.example.com; path=;"
+                "foo=bar; expires={$this->futureExpirationDate()}; domain=www.example.com; path=;"
             )
             ->withAddedHeader(
                 'Set-Cookie',
-                "bar=foo; expires=Fri, 02-Mar-2019 02:17:40 GMT; domain=www.example.com; path=foobar;"
+                "bar=foo; expires={$this->futureExpirationDate()}; domain=www.example.com; path=foobar;"
             )
         ;
         $request = (new Request('GET', $uriPath))->withHeader('Host', 'www.example.com');
@@ -409,4 +412,9 @@ public function testCookiePathWithEmptySetCookiePath($uriPath, $cookiePath)
         $this->assertSame($cookiePath, $this->jar->toArray()[0]['Path']);
         $this->assertSame($cookiePath, $this->jar->toArray()[1]['Path']);
     }
+
+    private function futureExpirationDate()
+    {
+        return (new DateTimeImmutable)->add(new DateInterval('P1D'))->format(DateTime::COOKIE);
+    }
 }
diff --git a/tests/Handler/CurlFactoryTest.php b/tests/Handler/CurlFactoryTest.php
index af52c58d2..d1e4e9980 100644
--- a/tests/Handler/CurlFactoryTest.php
+++ b/tests/Handler/CurlFactoryTest.php
@@ -685,6 +685,7 @@ public function testInvokesOnStatsOnSuccess()
             (string) $gotStats->getRequest()->getUri()
         );
         $this->assertGreaterThan(0, $gotStats->getTransferTime());
+        $this->assertArrayHasKey('appconnect_time', $gotStats->getHandlerStats());
     }
 
     public function testInvokesOnStatsOnError()
@@ -711,6 +712,7 @@ public function testInvokesOnStatsOnError()
         );
         $this->assertInternalType('float', $gotStats->getTransferTime());
         $this->assertInternalType('int', $gotStats->getHandlerErrorData());
+        $this->assertArrayHasKey('appconnect_time', $gotStats->getHandlerStats());
     }
 
     public function testRewindsBodyIfPossible()
diff --git a/tests/Handler/CurlHandlerTest.php b/tests/Handler/CurlHandlerTest.php
index 25c499020..6a4d233a0 100644
--- a/tests/Handler/CurlHandlerTest.php
+++ b/tests/Handler/CurlHandlerTest.php
@@ -47,9 +47,9 @@ public function testDoesSleep()
         Server::enqueue([$response]);
         $a = new CurlHandler();
         $request = new Request('GET', Server::$url);
-        $s = microtime(true);
+        $s = \GuzzleHttp\_current_time();
         $a($request, ['delay' => 0.1])->wait();
-        $this->assertGreaterThan(0.0001, microtime(true) - $s);
+        $this->assertGreaterThan(0.0001, \GuzzleHttp\_current_time() - $s);
     }
 
     public function testCreatesCurlErrorsWithContext()
diff --git a/tests/Handler/CurlMultiHandlerTest.php b/tests/Handler/CurlMultiHandlerTest.php
index 6c987afb8..03043f5ff 100644
--- a/tests/Handler/CurlMultiHandlerTest.php
+++ b/tests/Handler/CurlMultiHandlerTest.php
@@ -68,10 +68,10 @@ public function testDelaysConcurrently()
         Server::flush();
         Server::enqueue([new Response()]);
         $a = new CurlMultiHandler();
-        $expected = microtime(true) + (100 / 1000);
+        $expected = \GuzzleHttp\_current_time() + (100 / 1000);
         $response = $a(new Request('GET', Server::$url), ['delay' => 100]);
         $response->wait();
-        $this->assertGreaterThanOrEqual($expected, microtime(true));
+        $this->assertGreaterThanOrEqual($expected, \GuzzleHttp\_current_time());
     }
 
     public function testUsesTimeoutEnvironmentVariables()
diff --git a/tests/Handler/StreamHandlerTest.php b/tests/Handler/StreamHandlerTest.php
index 6c10ec3f0..f62994896 100644
--- a/tests/Handler/StreamHandlerTest.php
+++ b/tests/Handler/StreamHandlerTest.php
@@ -506,9 +506,9 @@ public function testDoesSleep()
         Server::enqueue([$response]);
         $a = new StreamHandler();
         $request = new Request('GET', Server::$url);
-        $s = microtime(true);
+        $s = \GuzzleHttp\_current_time();
         $a($request, ['delay' => 0.1])->wait();
-        $this->assertGreaterThan(0.0001, microtime(true) - $s);
+        $this->assertGreaterThan(0.0001, \GuzzleHttp\_current_time() - $s);
     }
 
     /**
diff --git a/tests/functionsTest.php b/tests/functionsTest.php
index fd65d41b6..bf5c8d8b8 100644
--- a/tests/functionsTest.php
+++ b/tests/functionsTest.php
@@ -128,6 +128,11 @@ public function testDecodesJsonAndThrowsOnError()
     {
         \GuzzleHttp\json_decode('{{]]');
     }
+
+    public function testCurrentTime()
+    {
+        $this->assertGreaterThan(0, GuzzleHttp\_current_time());
+    }
 }
 
 final class StrClass