Plugin: Add hooks for log init and writing.

The two hooks being added are:

void HookLogInit(const std::string& writer, const std::string& instantiating_filter, bool local, bool remote, const logging::WriterBackend::WriterInfo& info, int num_fields, const threading::Field* const* fields);

which is called when a writer is being instantiated and contains
information about the fields being logged, as well as

bool HookLogWrite(const std::string& writer, const std::string& filter, const logging::WriterBackend::WriterInfo& info, int num_fields, const threading::Field* const* fields, threading::Value** vals);

which is called for each log line being written by each writer. It
contains all the data being written. The data can be changed in the
function call and lines can be prevented from being written.

This commit also fixes a few small problems with plugin hooks itself,
and extends the tests that were already there, besides introducing tests
for the added functionality.

testing/btest/plugins/logging-hooks-plugin/src/Plugin.cc

@@ -0,0 +1,60 @@
+
+#include "Plugin.h"
+
+#include <Func.h>
+#include <Event.h>
+#include <Conn.h>
+#include <threading/Formatter.h>
+
+namespace plugin { namespace Log_Hooks { Plugin plugin; } }
+
+using namespace plugin::Log_Hooks;
+
+plugin::Configuration Plugin::Configure()
+	{
+	round = 0;
+	EnableHook(HOOK_LOG_INIT);
+	EnableHook(HOOK_LOG_WRITE);
+
+	plugin::Configuration config;
+	config.name = "Log::Hooks";
+	config.description = "Exercises Log hooks";
+	config.version.major = 1;
+	config.version.minor = 0;
+	return config;
+	}
+
+void Plugin::HookLogInit(const std::string& writer, const std::string& instantiating_filter, bool local, bool remote, const logging::WriterBackend::WriterInfo& info, int num_fields, const threading::Field* const* fields)
+	{
+	ODesc d;
+
+	d.Add("{");
+	for ( int i=0; i < num_fields; i++ )
+		{
+		const threading::Field* f = fields[i];
+
+		if ( i > 0 )
+			d.Add(", ");
+
+		d.Add(f->name);
+		d.Add(" (");
+		d.Add(f->TypeName());
+		d.Add(")");
+		}
+	d.Add("}");
+
+	fprintf(stderr, "%.6f %-15s %s %d/%d %s\n", network_time, "| HookLogInit", info.path, local, remote, d.Description());
+	}
+
+bool Plugin::HookLogWrite(const std::string& writer, const std::string& filter, const logging::WriterBackend::WriterInfo& info, int num_fields, const threading::Field* const* fields, threading::Value** vals)
+	{
+	round++;
+	if ( round == 1 ) // do not output line
+		return false;
+	else if ( round == 2 )
+		vals[0]->val.int_val = 0;
+	else if ( round == 3 )
+		vals[1]->present = false;
+
+	return true;
+	}

testing/btest/plugins/logging-hooks-plugin/src/Plugin.h

@@ -0,0 +1,28 @@
+
+#ifndef BRO_PLUGIN_Log_Hooks
+#define BRO_PLUGIN_Log_Hooks
+
+#include <plugin/Plugin.h>
+
+namespace plugin {
+namespace Log_Hooks {
+
+class Plugin : public ::plugin::Plugin
+{
+protected:
+	void HookLogInit(const std::string& writer, const std::string& instantiating_filter, bool local, bool remote, const logging::WriterBackend::WriterInfo& info, int num_fields, const threading::Field* const* fields) override;
+	bool HookLogWrite(const std::string& writer, const std::string& filter, const logging::WriterBackend::WriterInfo& info, int num_fields, const threading::Field* const* fields, threading::Value** vals) override;
+
+	// Overridden from plugin::Plugin.
+	plugin::Configuration Configure() override;
+
+private:
+	int round;
+};
+
+extern Plugin plugin;
+
+}
+}
+
+#endif