Add static registration configuration to access logs (#166)

To enable access logs to be statically registered in Envoy, a name and custom configuration struct will have to be provided.

api/BUILD

@@ -2,12 +2,6 @@ load("//bazel:api_build_system.bzl", "api_proto_library")
 
 licenses(["notice"])  # Apache 2
 
-api_proto_library(
-    name = "accesslog",
-    srcs = ["accesslog.proto"],
-    deps = [":base"],
-)
-
 api_proto_library(
     name = "address",
     srcs = ["address.proto"],

api/filter/http_connection_manager.proto

@@ -91,45 +91,12 @@ message AccessLogFilter {
   }
 }
 
-// Extra headers to include when doing AccessLogs via proto format.
+// Custom configuration for an AccessLog that writes log entries directly to a file.
-message HeaderSelection {
+// Configures the built-in "envoy.file_access_log" AccessLog.
-  // Request headers to include in the AccessLog.
+message FileAccessLog {
-  repeated string request_headers = 1;
+  // A path to a local file to which to write the access log entries.
-  // Response headers to include in the AccessLog.
-  repeated string response_headers = 2;
-}
-
-message AccessLog {
-  // Destination location the access log is written to.
-  //
-  // Envoy supports logging to both RPC endpoints and local disk files.
-  // Behavior is set by choosing which of these is used:
-  oneof destination {
-    // A path to a local file
   string path = 1;
-    // The name of an upstream cluster that hosts RPC endpoints for the
-    // AccessLog sink. The cluster must provide an endpoint capable of
-    // receiving the AccessLog API. The exact flavor of API spoken will
-    // depend on the statically registered log interface module specified
-    // in Envoy's startup configuration.
-    string cluster = 5;
-  }
 
-  // Content included in log entries.
-  //
-  // When logging to a file this is a format string which specifies what is
-  // included.
-  //
-  // When logging to an RPC endpoint all of the named fields in accesslog.proto
-  // are populated by default if the relevant data is available for the logged
-  // request. Additional headers desired for logging can be specified in the
-  // HeaderSelection.
-  oneof content {
-    // Access log format for file logging.
-    //
-    // Envoy supports custom access log formats as well as a
-    // default format.
-    //
   // [V2-API-DIFF] In addition to the existing format specifiers, the following
   // additional specifiers will be available:
   // %TLS_SNI_HOSTNAME%: SNI from handshake.
@@ -141,13 +108,19 @@ message AccessLog {
   // TODO(htuch): Document how envoy.http_connection_manager.access_log values
   // can be accessed in the format specifier.
   string format = 2;
+}
 
-    // Extra headers to include when RPC logging.
+message AccessLog {
-    HeaderSelection headers = 4;
+  // The name of the access log implementation to instantiate. The name must
-  }
+  // match a statically registered access log.
+  string name = 1;
 
   // Filter which is used to determine if the access log needs to be written.
-  AccessLogFilter filter = 3;
+  AccessLogFilter filter = 2;
+
+  // Custom configuration that depends on the access log being instantiated.
+  // See the supported AccessLogs for further documentation.
+  google.protobuf.Struct config = 3;
 }
 
 message HttpFilter {