Add support for proxy_get_log_level (#43)

This lets the WASM code determine the log level set for the
"wasm" logger on the proxy host, which can be used to optimize
when log messages are generated.

Signed-off-by: Gregory Brail <gregbrail@google.com>

Author: gbrail

proxy_wasm_api.h

@@ -289,6 +289,9 @@ class ContextBase {
   // Called when a foreign function event arrives.
   virtual void onForeignFunction(uint32_t /* foreign_function_id */, uint32_t /* data_size */) {}
 
+  // Return the log level configured for the "wasm" logger in the host
+  WasmResult getLogLevel(LogLevel *level) { return proxy_get_log_level(level); }
+
   using HttpCallCallback =
       std::function<void(uint32_t, size_t, uint32_t)>; // headers, body_size, trailers
   using GrpcSimpleCallCallback = std::function<void(GrpcStatus status, size_t body_size)>;

proxy_wasm_externs.h

@@ -37,6 +37,7 @@ extern "C" WasmResult proxy_get_status(uint32_t *status_code_ptr, const char **m
 
 // Logging
 extern "C" WasmResult proxy_log(LogLevel level, const char *logMessage, size_t messageSize);
+extern "C" WasmResult proxy_get_log_level(LogLevel *level);
 
 // Timer (will be set for the root context, e.g. onStart, onTick).
 extern "C" WasmResult proxy_set_tick_period_milliseconds(uint32_t millisecond);

proxy_wasm_intrinsics.js

@@ -18,6 +18,7 @@
 mergeInto(LibraryManager.library, {
   proxy_get_configuration: function() {},
   proxy_log: function() {},
+  proxy_get_log_level: function() {},
   proxy_set_tick_period_milliseconds: function() {},
   proxy_get_current_time_nanoseconds: function() {},
   proxy_get_status: function() {},