Revert propagation header partial changes

Author: chingor13

src/Trace/RequestTracer.php

@@ -128,11 +128,7 @@ public static function start(ReporterInterface $reporter, array $options = [])
             ? $samplerOptions
             : SamplerFactory::build($samplerOptions);
 
-        $propagationFormatter = new HttpHeaderFormater();
-
-        self::$instance = new RequestHandler($reporter, $sampler, $propagationFormatter, $options);
-        self::$instance->start($options);
-        return self::$instance;
+        return self::$instance = new RequestHandler($reporter, $sampler, $options);
     }
 
     /**

src/Trace/TraceContext.php

@@ -52,6 +52,26 @@ class TraceContext
      */
     private $enabled;
 
+    /**
+     * Parses a headers array (normally the $_SERVER variable) and builds a TraceContext objects
+     *
+     * @param  array $headers The headers array (normally the $_SERVER variable)
+     * @return TraceContext
+     */
+    public static function fromHeaders($headers)
+    {
+        if (array_key_exists(self::HTTP_HEADER, $headers) &&
+            preg_match(self::CONTEXT_HEADER_FORMAT, $headers[self::HTTP_HEADER], $matches)) {
+            return new static(
+                $matches[1],
+                array_key_exists(2, $matches) ? $matches[2] : null,
+                array_key_exists(3, $matches) ? $matches[3] == '1' : null,
+                true
+            );
+        }
+        return new static();
+    }
+
     /**
      * Creates a new TraceContext instance
      *