MXS-591 Add filter for injecting comments

Comments specified in the cnf file will be injected as a comment before
every sql statement.

Documentation/Filters/Comment.md

@@ -0,0 +1,70 @@
+
+# Comment Filter
+
+## Overview
+
+With the _comment_ filter it is possible to define comments that are
+injected before the actual statements. These comments appear as sql
+comments when they are received by the server.
+
+```
+[MyComment]
+type=filter
+module=comment
+inject=Comment to be injected
+
+[MyService]
+type=service
+router=readwritesplit
+servers=server1
+user=myuser
+passwd=mypasswd
+filters=MyComment
+```
+
+
+## Filter Parameters
+
+The Comment filter requires one mandatory parameter to be defined.
+
+### `inject`
+
+A parameter that contains the comment injected before the statements.
+There is also defined variable $IP that can be used to comment the
+IP address of the client in the injected comment.
+Variables must be written in all caps.
+
+
+## Examples
+
+### Example 1 - Inject IP address of the connected client into statements
+as comment.
+
+You want to see the IP addresses of the clients with the server so you
+define filter to comment the into the statements they send.
+
+
+```
+[IPComment]
+type=filter
+module=comment
+inject=IP=$IP
+
+[MyService]
+type=service
+router=readwritesplit
+servers=server1
+user=myuser
+passwd=mypasswd
+filters=IPComment
+```
+
+In this example when MaxScale receives statement like:
+```
+ SELECT user FROM people;
+```
+It would look like
+```
+/* IP=::ffff:127.0.0.1 */SELECT user FROM people;
+```
+when received by server.

server/modules/filter/CMakeLists.txt

@@ -16,3 +16,4 @@ add_subdirectory(tee)
 add_subdirectory(throttlefilter)
 add_subdirectory(topfilter)
 add_subdirectory(tpmfilter)
+add_subdirectory(comment)

server/modules/filter/comment/CMakeLists.txt

@@ -0,0 +1,4 @@
+add_library(comment SHARED commentfilter.cc commentfiltersession.cc)
+set_target_properties(comment PROPERTIES VERSION "1.0.0")
+install_module(comment core)
+

server/modules/filter/comment/commentfilter.cc

@@ -0,0 +1,91 @@
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2020-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+// All log messages from this module are prefixed with this
+#define MXS_MODULE_NAME "commentfilter"
+
+#include "commentfilter.hh"
+#include <string>
+#include <cstring>
+
+namespace
+{
+
+const char CN_INJECT[] = "inject";
+
+}
+
+// This declares a module in MaxScale
+extern "C" MXS_MODULE* MXS_CREATE_MODULE()
+{
+    static MXS_MODULE info =
+    {
+        MXS_MODULE_API_FILTER,
+        MXS_MODULE_IN_DEVELOPMENT,
+        MXS_FILTER_VERSION,
+        "A comment filter that can inject comments in sql queries",
+        "V1.0.0",
+        RCAP_TYPE_NONE,
+        &CommentFilter::s_object, // This is defined in the MaxScale filter template
+        NULL, /* Process init. */
+        NULL, /* Process finish. */
+        NULL, /* Thread init. */
+        NULL, /* Thread finish. */
+        {
+            { CN_INJECT, MXS_MODULE_PARAM_STRING, NULL, MXS_MODULE_OPT_REQUIRED },
+            { MXS_END_MODULE_PARAMS }
+        }
+    };
+
+    return &info;
+}
+
+CommentFilter::CommentFilter(std::string comment) : m_comment(comment)
+{
+    MXS_INFO("Comment filter with comment [%s] created.", m_comment.c_str());
+}
+
+CommentFilter::~CommentFilter()
+{
+}
+
+// static
+CommentFilter* CommentFilter::create(const char* zName, char** pzOptions, MXS_CONFIG_PARAMETER* pParams)
+{
+    return new CommentFilter(config_get_string(pParams, CN_INJECT));
+}
+
+CommentFilterSession* CommentFilter::newSession(MXS_SESSION* pSession)
+{
+    return CommentFilterSession::create(pSession, this);
+}
+
+// static
+void CommentFilter::diagnostics(DCB* pDcb) const
+{
+    dcb_printf(pDcb, "Comment filter with comment: %s", m_comment.c_str());
+}
+
+// static
+json_t* CommentFilter::diagnostics_json() const
+{
+    json_t* rval = json_object();
+    json_object_set_new(rval, "Comment", json_string(m_comment.c_str()));
+    return rval;
+}
+
+// static
+uint64_t CommentFilter::getCapabilities()
+{
+    return RCAP_TYPE_NONE;
+}

server/modules/filter/comment/commentfilter.hh

@@ -0,0 +1,53 @@
+#pragma once
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2020-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+#include <maxscale/cppdefs.hh>
+#include <maxscale/filter.hh>
+#include "commentfiltersession.hh"
+#include <string>
+
+class CommentFilter : public maxscale::Filter<CommentFilter, CommentFilterSession>
+{
+public:
+    // Prevent copy-constructor and assignment operator usage
+    CommentFilter(const CommentFilter&) = delete;
+    CommentFilter& operator = (const CommentFilter&) = delete;
+
+    ~CommentFilter();
+
+    // Creates a new filter instance
+    static CommentFilter* create(const char* zName, char** pzOptions, MXS_CONFIG_PARAMETER* ppParams);
+
+    // Creates a new session for this filter
+    CommentFilterSession* newSession(MXS_SESSION* pSession);
+
+    // Print diagnostics to a DCB
+    void diagnostics(DCB* pDcb) const;
+
+
+    // Returns JSON form diagnostic data
+    json_t* diagnostics_json() const;
+
+    // Get filter capabilities
+    uint64_t getCapabilities();
+    std::string comment() const
+    {
+        return m_comment;
+    }
+
+private:
+    std::string m_comment;
+    // Used in the create function
+    CommentFilter(std::string comment);
+};

server/modules/filter/comment/commentfiltersession.cc

@@ -0,0 +1,80 @@
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2020-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+// All log messages from this module are prefixed with this
+#define MXS_MODULE_NAME "commentfilter"
+
+#include "commentfiltersession.hh"
+#include "commentfilter.hh"
+#include <maxscale/modutil.hh>
+#include <string>
+#include <regex>
+
+using namespace std;
+
+CommentFilterSession::CommentFilterSession(MXS_SESSION* pSession, const CommentFilter* pFilter)
+    : maxscale::FilterSession(pSession),
+      m_filter(*pFilter)
+{
+}
+
+CommentFilterSession::~CommentFilterSession()
+{
+}
+
+//static
+CommentFilterSession* CommentFilterSession::create(MXS_SESSION* pSession, const CommentFilter* pFilter)
+{
+    return new CommentFilterSession(pSession, pFilter);
+}
+
+void CommentFilterSession::close()
+{
+}
+
+int CommentFilterSession::routeQuery(GWBUF* pPacket)
+{
+    if (modutil_is_SQL(pPacket))
+    {
+        string sql = mxs::extract_sql(pPacket);
+        string comment = parseComment(m_filter.comment());
+        string newsql = string("/* ").append(comment).append(" */").append(sql);
+        pPacket = modutil_replace_SQL(pPacket, (char*)newsql.c_str());
+        //maxscale expects contiguous memory to arrive from client so we must make the buffer contiguous
+        //after using modutil_replace_SQL.
+        GWBUF* pModified_packet = gwbuf_make_contiguous(pPacket);
+        if (pModified_packet)
+        {
+            pPacket = pModified_packet;
+        }
+        else
+        {
+            gwbuf_free(pPacket);
+            pPacket = NULL;
+        }
+    }
+
+    return pPacket ? mxs::FilterSession::routeQuery(pPacket) : 1;
+}
+
+int CommentFilterSession::clientReply(GWBUF* pPacket)
+{
+    return mxs::FilterSession::clientReply(pPacket);
+}
+//TODO this probably should be refactored in some way in case we add more variables
+string CommentFilterSession::parseComment(string comment)
+{
+    string ip = m_pSession->client_dcb->remote;
+    string parsedComment = std::regex_replace(comment, std::regex("\\$IP"), ip);
+    return parsedComment;
+}

server/modules/filter/comment/commentfiltersession.hh

@@ -0,0 +1,48 @@
+#pragma once
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2020-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+#include <maxscale/cppdefs.hh>
+#include <maxscale/filter.hh>
+#include <string>
+
+class CommentFilter;
+
+class CommentFilterSession : public maxscale::FilterSession
+{
+    // Prevent copy-constructor and assignment operator usage
+    CommentFilterSession(const CommentFilterSession&);
+    CommentFilterSession& operator = (const CommentFilterSession&);
+
+public:
+    ~CommentFilterSession();
+
+    // Called when a client session has been closed
+    void close();
+
+    // Create a new filter session
+    static CommentFilterSession* create(MXS_SESSION* pSession, const CommentFilter* pFilter);
+
+    // Handle a query from the client
+    int routeQuery(GWBUF* pPacket);
+
+    // Handle a reply from server
+    int clientReply(GWBUF* pPacket);
+
+private:
+
+    // Used in the create function
+    CommentFilterSession(MXS_SESSION* pSession, const CommentFilter* pFilter);
+    const CommentFilter& m_filter;
+    std::string parseComment(std::string comment);
+};