Fix Guzzle SpanContext propagation (#170)

* Guzzle headers that are set should be dasherized versions

* Inject http headers with dasherized version

Author: chingor13

src/Trace/Propagator/HttpHeaderPropagator.php

@@ -75,7 +75,7 @@ public function extract($headers)
      */
     public function inject(SpanContext $context, $container)
     {
-        $header = str_replace('_', '-', preg_replace('/^HTTP_/', '', $this->header));
+        $header = $this->key();
         $value = $this->formatter->serialize($context);
         if (!headers_sent()) {
             header("$header: $value");
@@ -102,6 +102,6 @@ public function formatter()
      */
     public function key()
     {
-        return $this->header;
+        return str_replace('_', '-', preg_replace('/^HTTP_/', '', $this->header));
     }
 }

tests/unit/Trace/Integrations/Guzzle/EventSubscriberTest.php

@@ -72,8 +72,8 @@ public function testAddsSpanContextHeader()
 
         $request = $history->getLastRequest();
         $headers = $request->getHeaders();
-        $this->assertArrayHasKey('HTTP_X_CLOUD_TRACE_CONTEXT', $headers);
-        $this->assertRegExp('/[0-9a-f]+\/4660;o=1/', $headers['HTTP_X_CLOUD_TRACE_CONTEXT'][0]);
+        $this->assertArrayHasKey('X-CLOUD-TRACE-CONTEXT', $headers);
+        $this->assertRegExp('/[0-9a-f]+\/4660;o=1/', $headers['X-CLOUD-TRACE-CONTEXT'][0]);
 
         $rt->onExit();
     }

tests/unit/Trace/Integrations/Guzzle/MiddlewareTest.php

@@ -63,7 +63,7 @@ public function testAddsSpanContextHeader()
         $req = $this->prophesize(RequestInterface::class);
         $req->getMethod()->willReturn('GET')->shouldBeCalled();
         $req->getUri()->willReturn('/')->shouldBeCalled();
-        $req->withHeader('HTTP_X_CLOUD_TRACE_CONTEXT', Argument::that(function ($val) {
+        $req->withHeader('X-CLOUD-TRACE-CONTEXT', Argument::that(function ($val) {
             return preg_match('/[0-9a-f]+\/4660;o=1/', $val);
         }))->willReturn($req->reveal())->shouldBeCalled();
         $request = $req->reveal();