Functions¶

Initialization¶

NF_STATUS nf_init(const char *driverName, NF_EventHandler *pHandler)¶

Parameters:

driverName – The bundle name of network extension.
pHandler – Pointer to NF_EventHandler object.

Returns:

NF_STATUS_SUCCESS on success, or other NF_STATUS error code on fail.

Description:

Call this function to initialize an attachment with the network extension and set the event handler object. The library calls NF_EventHandler methods from multiple threads.

By default the extension uses NF_ALLOW filtering flag and doesn’t filter the transmitted data. To filter the transmitted packets add the filtering rules with necessary flags using the function nf_addRule(Ex) or nf_setRules(Ex).

The function returns NF_STATUS_FAIL in case if some other process is already attached to network extension. The extension doesn’t allow multiple attachments. If additional process must filter the network data on the same system, it is possible to rename and register another copy of the extension, then use the new name in nf_init call from another process.

It is possible to call nf_setOptions before nf_init to specify additional parameters.

void nf_free()¶

Description:: Stops the filtering threads, aborts all filtered connections and detaches from the hooking extension.

This function aborts all filtered TCP connections, which means that all unsent buffered data will be lost. To avoid this it is possible to remove the filtering rules with a call nf_deleteRules, and wait until the filtered connections will close gracefully.

void nf_setOptions(DWORD nThreads, DWORD flags)¶

Parameters:

nThreads – Number of worker threads for NF_EventHandler events.
flags – Must be zero

Description:

Specifies the number of worker threads and initialization flags.

The function can be called before nf_init. If it is called after the initialization, the changes are not applied until the library is reinitialized. By default nThreads = 1 and flags = 0. It means that the events are indicated from a single thread and all flags are disabled. When nThreads=0 the code detects the number of logical processors and uses it as the number of worker threads.

Filtering rules¶

NF_STATUS nf_addRule(PNF_RULE pRule, int toHead)¶

Parameters:

pRule – A pointer to NF_RULE structure.
toHead – TRUE (1) - add rule to list head, FALSE (0) - add rule to list tail

Returns:

NF_STATUS_SUCCESS on success, or other NF_STATUS error code on fail.

Description:

Add the specified filtering rule to list.

NF_STATUS nf_addRuleEx(PNF_RULE_EX pRule, int toHead)¶

Parameters:

pRule – A pointer to NF_RULE_EX structure.
toHead – TRUE (1) - add rule to list head, FALSE (0) - add rule to list tail

Returns:

NF_STATUS_SUCCESS on success, or other NF_STATUS error code on fail.

Description:

Add the specified filtering rule to list.

The list of rules is scanned from the beginning and a first matching rule is applied. The new rules are added to the list head or tail, depending on toHead parameter. The extension doesn’t filter the network activity of the attached process. In effect the rules are not applied to the sockets created by a process that uses extension API. NF_RULE_EX rules are added to the same list with NF_RULE. NF_RULE is treated as NF_RULE_EX without additional condition. So it is possible to add both types of rules in any order.

NF_STATUS nf_setRules(PNF_RULE pRules, int count)¶

Parameters:

pRules – A pointer to array of NF_RULE structures.
count – Number of items in pRules array

Returns:

NF_STATUS_SUCCESS on success, or other NF_STATUS error code on fail.

Description:

Replace the rules in extension with the specified array.

It is an atomic operation, which means that the old rules are replaced with new list in a single synchronized call. If the rules list in extension is empty, the new list is assigned as current.

NF_STATUS nf_setRulesEx(PNF_RULE_EX pRules, int count)¶

Parameters:

pRules – A pointer to array of NF_RULE_EX structures.
count – Number of items in pRules array

Returns:

NF_STATUS_SUCCESS on success, or other NF_STATUS error code on fail.

Description:

Replace the rules in extension with the specified array.

It is an atomic operation, which means that the old rules are replaced with new list in a single synchronized call. If the rules list in extension is empty, the new list is assigned as current.

NF_STATUS nf_deleteRules()¶

Returns:: NF_STATUS_SUCCESS on success, or other NF_STATUS error code on fail.
Description:: Remove all added filtering rules.

The rules are removed automatically after closing the attached process. The filtering flags assigned to an active TCP connection persist even after removing the matching rules, until closing the connection or the process attached to extension.

TCP protocol¶

NF_STATUS nf_tcpClose(ENDPOINT_ID id)¶

Parameters:: id – Connection identifier
Returns:: NF_STATUS_SUCCESS on success, or other NF_STATUS error code on fail.
Description:: Closes the connection with given id.

The extension cancels all pending send and receive requests and aborts the connection. For graceful disconnect call nf_tcpPostSend and nf_tcpPostReceive with zero length buffer after receiving the calls NF_EventHandler::tcpSend and NF_EventHandler::tcpReceive with zero buffer.

NF_STATUS nf_tcpPostReceive(ENDPOINT_ID id, const char *buf, int len)¶

Parameters:

id – Connection identifier
buf – Pointer to data buffer
len – Buffer length

Returns:

NF_STATUS_SUCCESS on success, or other NF_STATUS error code on fail.

Description:

Pass the buffer to local process via TCP connection with specified id.

The method NF_EventHandler::tcpCanReceive is called when the internal packet buffer is empty. The function always returns NF_STATUS_SUCCESS after buffering the data. To optimize the usage of memory split large buffers to chunks and indicate each chunk after receiving tcpCanReceive. There is no need to wait for tcpCanReceive before indicating the first chunk. If len is zero, the extension sends a graceful disconnect request to local process for the specified TCP connection.

NF_STATUS nf_tcpPostSend(ENDPOINT_ID id, const char *buf, int len)¶

Parameters:

id – Connection identifier
buf – Pointer to data buffer
len – Buffer length

Returns:

NF_STATUS_SUCCESS on success, or other NF_STATUS error code on fail.

Description:

Pass the buffer to local process via TCP connection with specified id.

The method NF_EventHandler::tcpCanSend is called when the internal packet buffer is empty. The function always returns NF_STATUS_SUCCESS after buffering the data. To optimize the usage of memory split the large buffers to chunks and send each chunk after receiving tcpCanSend. There is no need to wait for tcpCanSend before sending the first chunk. If len is zero, the extension initiates a graceful disconnect for the specified TCP connection.

NF_STATUS nf_tcpSetConnectionState(ENDPOINT_ID id, int suspended)¶

Parameters:

id – Connection identifier
suspended – TRUE to suspend, FALSE to resume

Returns:

NF_STATUS_SUCCESS on success, or other NF_STATUS error code on fail.

Description:

Suspends or resumes indicating sends and receives for the specified TCP connection via NF_EventHandler methods.

The library automatically suspends the connections having large amount of data in send or receive buffers, to avoid wasting memory when the network application or remote server are too slow. The automatic suspending is temporary, and the library resumes indicating new packets after successful delivery of the buffered data.

NF_STATUS nf_tcpDisableFiltering(ENDPOINT_ID id)¶

Parameters:: id – Connection identifier
Returns:: NF_STATUS_SUCCESS on success, or other NF_STATUS error code on fail.
Description:: Disables calling TCP events for the specified endpoint.

This function allows to improve the performance, in case if the filtering application is not interested in packets transmitted via some filtered connection (with NF_FILTER flag assigned). It is possible to call this function in tcpConnected event to stop indicating new packets.

NF_STATUS nf_getTCPConnInfo(ENDPOINT_ID id, PNF_TCP_CONN_INFO pConnInfo)¶

Parameters:

id – Connection identifier
pConnInfo – Pointer to NF_TCP_CONN_INFO structure

Returns:

NF_STATUS_SUCCESS on success, or other NF_STATUS error code on fail.

Description:

Returns in pConnInfo the properties of TCP connection with specified id.

UDP protocol¶

The UDP filtering functions are currently disabled. Only access control is available for UDP using rules.

Common functions¶

NF_STATUS nf_getProcessName(unsigned int pid, char *buf, int len)¶

Parameters:

pid – Process identifier
buf – Memory buffer for process name
len – Size of buf, in characters.

Returns:

NF_STATUS_SUCCESS on success

Description:

Returns the process name for given process id.

nf_getProcessName returns the appropriate command line for the specified pid.

NF_STATUS nf_getUid(ENDPOINT_ID id, unsigned int *pUid)¶

Parameters:

id – Endpoint identifier
pUid – Pointer to user identifier

Returns:

NF_STATUS_SUCCESS on success

Description:

Returns the user identifier for given endpoint id.

NF_STATUS nf_getUserName(unsigned int uid, char *buf, int len)¶

Parameters:

uid – User identifier
buf – Memory buffer for user name
len – Size of buf, in characters.

Returns:

NF_STATUS_SUCCESS on success

Description:

Returns the process name for given user id.

NF_STATUS nf_requireFileLimit(int file_limit)¶

Parameters:: file_limit – New limit for the number of file handles
Returns:: NF_STATUS_SUCCESS on success
Description:: Sets a new process limit for the number of file handles

By default OS has a short limit on the number of file handles. It is possible to specify a larger limit in case if the filtering application uses own sockets.