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Adding New Startup Parameters in ntopng

doc/developers/README.Add_startup_param.md

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Adding New Startup Parameters in ntopng

This guide explains how to add a new command-line startup parameter to ntopng, using the --db-archive-dir parameter implementation as a reference example.

Overview

Adding a new startup parameter in ntopng requires modifications to three main files:

  • include/Prefs.h - Header file containing the Prefs class declaration
  • src/Prefs.cpp - Implementation of preferences handling and command-line parsing
  • src/LuaEngineNtop.cpp - Lua engine integration (if the parameter needs to be accessible from Lua scripts)

Step 1: Modify the Header File (include/Prefs.h)

1.1 Add the Member Variable

Add a new member variable to store the parameter value in the private section of the Prefs class:

cpp
char *data_dir, *install_dir, *docs_dir, *scripts_dir, *callbacks_dir,
    *pcap_dir, *clickhouse_archive_dir  // Add your new parameter here

1.2 Add the Getter Method

Add a public getter method to access the parameter value:

cpp
inline const char* get_clickhouse_archive_dir() { return (clickhouse_archive_dir); };

Note: Use inline const char* for string parameters that return directory paths or simple string values.

Step 2: Modify the Implementation File (src/Prefs.cpp)

2.1 Initialize the Member Variable

In the Prefs::Prefs(Ntop *_ntop) constructor, initialize your new member variable to NULL:

cpp
pcap_dir = NULL;
clickhouse_archive_dir = NULL;  // Add initialization here

2.2 Add Memory Cleanup

In the Prefs::~Prefs() destructor, add memory cleanup for your parameter:

cpp
if(pcap_dir) free(pcap_dir);
if(clickhouse_archive_dir) free(clickhouse_archive_dir);  // Add cleanup here

2.3 Update the Usage Function

Add your parameter's documentation to the usage() function:

cpp
"[--db-archive-dir|-6] <path>        | Directory used for archiving historical flows\n"
"                                    | recorded on ClickHouse when data retention is over.\n"
"                                    | Default: %s\n"

Make sure to add the corresponding format argument in the printf-style call:

cpp
CONST_DEFAULT_DOCS_DIR, CONST_DEFAULT_SCRIPTS_DIR,
CONST_DEFAULT_CALLBACKS_DIR, CONST_DEFAULT_DATA_DIR,
CONST_DEFAULT_DATA_DIR,  // Add default value here

2.4 Add Long Option Definition

Add your parameter to the long_options array:

cpp
{"pcap-dir",                required_argument, NULL, '5'},
{"db-archive-dir",          required_argument, NULL, '6'},  // Add your option here

Important:

  • Use a unique single character (like '6') for the option identifier
  • Set required_argument if the parameter requires a value
  • Set no_argument if it's a boolean flag

2.5 Update the Option String

Add your option character to the option string in loadFromCLI():

cpp
"k:eg:hi:w:r:sg:m:n:p:qd:t:x:y:1:2:3:4:5:6:l:L:uv:zA:B:c:CD:E:F:MN:G:I:O:Q:"
//                                        ^ Add your character here

Note: Add : after the character if the parameter requires an argument.

2.6 Implement Option Handling

Add a case in the setOption() function to handle your parameter:

cpp
case '6':
  if(clickhouse_archive_dir) free(clickhouse_archive_dir);
  clickhouse_archive_dir = strdup(optarg);
  break;

2.7 Add Default Value Assignment

In the checkOptions() function, set a default value if none was provided:

cpp
if(!pcap_dir) pcap_dir = strdup(ntop->get_working_dir());
if(!clickhouse_archive_dir) clickhouse_archive_dir = strdup(ntop->get_working_dir());

2.8 Add Path Validation

Add path validation for directory parameters:

cpp
docs_dir = ntop->getValidPath(docs_dir);
scripts_dir = ntop->getValidPath(scripts_dir);
callbacks_dir = ntop->getValidPath(callbacks_dir);
pcap_dir = ntop->getValidPath(pcap_dir);
clickhouse_archive_dir = ntop->getValidPath(clickhouse_archive_dir);

2.9 Add Directory Existence Check

Add validation to ensure the directory exists:

cpp
if(!pcap_dir[0]) {
  ntop->getTrace()->traceEvent(TRACE_ERROR, "Unable to locate pcap dir");
  return (-1);
}
if(!clickhouse_archive_dir[0]) {
  ntop->getTrace()->traceEvent(TRACE_ERROR, "Unable to locate ClickHouse archive dir");
  return (-1);
}

2.10 Add Trailing Slash Removal

Remove trailing slashes from directory paths:

cpp
ntop->removeTrailingSlash(docs_dir);
ntop->removeTrailingSlash(scripts_dir);
ntop->removeTrailingSlash(callbacks_dir);
ntop->removeTrailingSlash(pcap_dir);
ntop->removeTrailingSlash(clickhouse_archive_dir);

Step 3: Add Lua Integration (Optional)

If your parameter needs to be accessible from Lua scripts, modify src/LuaEngineNtop.cpp:

3.1 Update the ntop_get_dirs() Function

Add your parameter to the Lua table in the ntop_get_dirs() function:

cpp
lua_push_str_table_entry(vm, "callbacksdir",
                         ntop->getPrefs()->get_callbacks_dir());
lua_push_str_table_entry(vm, "pcapdir", ntop->getPrefs()->get_pcap_dir());
lua_push_str_table_entry(vm, "dbarchivedir", ntop->getPrefs()->get_clickhouse_archive_dir());

Note: Use a descriptive key name (like "dbarchivedir") that will be used in Lua scripts.

Best Practices

Parameter Naming

  • Use descriptive, kebab-case names for long options (e.g., --db-archive-dir)
  • Choose meaningful single characters for short options
  • Avoid conflicts with existing parameters

Memory Management

  • Always initialize pointers to NULL in the constructor
  • Always free allocated memory in the destructor
  • Use strdup() to copy string arguments
  • Check for existing values before reassigning (free first)

Validation

  • Validate directory paths using ntop->getValidPath()
  • Check directory existence and accessibility
  • Provide meaningful error messages
  • Set sensible default values

Documentation

  • Add comprehensive usage text explaining the parameter's purpose
  • Include default values in the usage text
  • Use consistent formatting with existing parameters

Testing

After implementing your new parameter:

  1. Compile ntopng to ensure no syntax errors
  2. Test the help output: ./ntopng --help should show your new parameter
  3. Test with the parameter: ./ntopng --db-archive-dir /path/to/archive
  4. Test without the parameter to ensure defaults work
  5. Test invalid paths to ensure error handling works
  6. Test Lua integration (if applicable) by accessing the parameter from Lua scripts

Example Usage

Once implemented, the parameter can be used as:

bash
# Long form
./ntopng --db-archive-dir /var/lib/ntopng/archive

# Short form  
./ntopng -6 /var/lib/ntopng/archive

And accessed from Lua scripts as:

lua
local dirs = ntop.getDirs()
local archive_dir = dirs["dbarchivedir"]