Add semantic attributes for HTTP content length. (#1376)

api/src/main/java/io/opentelemetry/trace/attributes/SemanticAttributes.java

@@ -98,6 +98,30 @@ public final class SemanticAttributes {
   /** The IP address of the original client behind all proxies, if known. */
   public static final StringAttributeSetter HTTP_CLIENT_IP =
       StringAttributeSetter.create("http.client_ip");
+  /**
+   * The size of the request payload body, in bytes. For payloads using transport encoding, this is
+   * the compressed size.
+   */
+  public static final StringAttributeSetter HTTP_REQUEST_CONTENT_LENGTH =
+      StringAttributeSetter.create("http.request_content_length");
+  /**
+   * The size of the uncompressed request payload body, in bytes. Only set for requests that use
+   * transport encoding.
+   */
+  public static final StringAttributeSetter HTTP_REQUEST_CONTENT_LENGTH_UNCOMPRESSED =
+      StringAttributeSetter.create("http.request_content_length_uncompressed");
+  /**
+   * The size of the response payload body, in bytes. For payloads using transport encoding, this is
+   * the compressed size.
+   */
+  public static final StringAttributeSetter HTTP_RESPONSE_CONTENT_LENGTH =
+      StringAttributeSetter.create("http.response_content_length");
+  /**
+   * The size of the uncompressed response payload body, in bytes. Only set for responses that use
+   * transport encoding.
+   */
+  public static final StringAttributeSetter HTTP_RESPONSE_CONTENT_LENGTH_UNCOMPRESSED =
+      StringAttributeSetter.create("http.response_content_length_uncompressed");
   /** The service name, must be equal to the $service part in the span name. */
   public static final StringAttributeSetter RPC_SERVICE =
       StringAttributeSetter.create("rpc.service");