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asl(3) BSD Library Functions Manual asl(3)

NAME

aassllooppeenn, aassllcclloossee, aassllnneeww, aassllffrreeee, aassllsseett, aassllsseettqquueerryy, aassllggeett, aasslluunnsseett, aasslllloogg, aassllvvlloogg, aassllsseenndd, aassllkkeeyy, aassllaaddddllooggffiillee, aassllrreemmoovveellooggffiillee, aassllsseettccuuttoofffflleevveell, aassllsseeaarrcchh, aassllrreessppoonnsseenneexxtt,

aassllrreessppoonnsseeffrreeee - system log message sending and searching functions

SYNOPSIS

##iinncclluuddee <>

aslclient aassllooppeenn(const char *ident, const char *facility, uint32t opts); void aassllcclloossee(aslclient asl); aslmsg aassllnneeww(uint32t type); void aassllffrreeee(aslmsg msg); int aassllsseett(aslmsg msg, const char *key, const char *value); int aassllsseettqquueerryy(aslmsg msg, const char *key, const char *value, uint32t op); const char * aassllkkeeyy(aslmsg msg, uint32t n); const char * aassllggeett(aslmsg msg, const char *key); int aasslluunnsseett(aslmsg msg, const char *key); int aasslllloogg(aslclient asl, aslmsg msg, int level, const char *format, ...); int aassllvvlloogg(aslclient asl, aslmsg msg, int level, const char *format, valist ap); int aassllsseenndd(aslclient asl, aslmsg msg); int aassllaaddddllooggffiillee(aslclient asl, int fd); int aassllrreemmoovveellooggffiillee(aslclient asl, int fd); int aassllsseettffiilltteerr(aslclient asl, int f); aslresponse aassllsseeaarrcchh(aslclient asl, aslmsg msg); aslmsg aassllrreessppoonnsseenneexxtt(aslresponse r); void aassllrreessppoonnsseeffrreeee(aslresponse a);

DESCRIPTION

These routines provide an interface to the Apple system log facility. They are intended to be a replacement for the syslog(3) API, which will continue to be supported for backwards compatibility. The new API allows client applications to create flexible, structured messages and send them to the ssyyssllooggdd server, where they may undergo additional processing. Messages received by the server are saved in a data store (subject to input filtering constraints). This API permits clients to create queries and search the message data store for matching messages. MMEESSSSAAGGEESS At the core of this API is the aslmsg structure. Although the structure is opaque and may not be directly manipulated, it contains a list of

key/value pairs. All keys and values are NULL-terminated C language

character strings. UTF-8 encoding may be used for non-ASCII characters.

Message structures are generally used to send log messages, and are cre-

ated thusly: aslmsg m = aslnew(ASLTYPEMSG); Another message type, ASLTYPEQUERY, is used to create queries when searching the data store. Query type messages and searching are described in detail in the SEARCHING section below. For the remainder of this section, the messages described will be of the ASLTYPEMSG variety. Each aslmsg contains a default set of keys and values associated with them. These keys are listed in the asl.h header file. They are:

#define ASLKEYTIME "Time"

#define ASLKEYHOST "Host"

#define ASLKEYSENDER "Sender"

#define ASLKEYPID "PID"

#define ASLKEYUID "UID"

#define ASLKEYGID "GID"

#define ASLKEYLEVEL "Level"

#define ASLKEYMSG "Message"

Many of these correspond to equivalent parts of messages described in the syslog(3) API. Values associated with these message keys are assigned appropriate defaults. The value for ASLKEYHOST is the local host name, the value associated with ASLKEYSENDER is the process name, the ASLKEYPID is the client's process ID number, and so on. Note the addition of the UID and GID keys. The values for UID and GID are set in library code by the message sender. The server will attempt to confirm the values, but no claim is made that these values cannot be maliciously overridden in an attempt to deceive a log message reader as to the identity of the sender of a message. The contents of log messages must be regarded as insecure. Also note the absence of a Facility key. The asl(3) API does not require a process to choose a facility name. The ssyyssllooggdd server will use a default value of ``user'' if a facility is not set. However, a client may set a facility name using: aslset(m, "Facility", "UsefulService"); An application may choose any facility name at will. Default values are set in the message for each of the keys listed above except for ASLKEYMSG, which may be explicitly set at any time using the aassllsseett routine, or implicitly set at the time the message is sent using

the aasslllloogg or aassllvvlloogg routines. These two routines also have an inte-

ger level parameter for specifying the log priority. The ASLKEYLEVEL value is set accordingly. Finally, the value associated with ASLKEYTIME is set in the sending routine. Although it may appear that there is significant overhead required to

send a log message using this API, the opposite is actually true. A sim-

ple ``Hello World'' program requires only:

#include

... asllog(NULL, NULL, ASLLEVELINFO, "Hello World!"); Both aasslllloogg and aassllvvlloogg will provide the appropriate default values when passed a NULL aslmsg argument. In this example, the aslclient argument is NULL. This is sufficient for

a single-threaded application, or for an application which only sends log

messages from a single thread. When logging from multiple threads, each thread must open a separate client handle using aassllooppeenn. The client handle may then be closed when it is no longer required using aassllcclloossee. When an application requires additional keys and values to be associated with each log message, a single message structure may be allocated and set up as ``template'' message of sorts: aslmsg m = aslnew(ASLTYPEMSG); aslset(m, "Facility", "Spy vs. Spy"); aslset(m, "Clearance", "Top Secret"); ... asllog(NULL, m, ASLLEVELNOTICE, "Message One"); ... asllog(NULL, m, ASLLEVELERR, "Message Two"); The message structure will carry the values set for the ``Facility'' and ``Clearance'' keys so that they are used in each call to aasslllloogg, while the log level and the message text are taken from the calling parameters. Key/value pairs may be removed from a message structure with aasslluunnsseett. A message may be freed using aassllffrreeee.

The aassllsseenndd routine is used by aasslllloogg and aassllvvlloogg to transmit a mes-

sage to the server. This routine sets the value associated with ASLKEYTIME and send the message. It may be called directly if all of a message's key/value pairs have been created using aassllsseett. CCLLIIEENNTT HHAANNDDLLEESS When logging is done from a single thread, a NULL value may be used in any of the routines that require an aslclient argument. In this case the library will open an internal client handle on behalf of the application. If multiple threads must do logging, or if client options are desired, then the application should call aassllooppeenn to create a client handle for each thread. As a convenience, the aassllooppeenn routine may be given an ident argument, which becomes the default value for the ASLKEYSENDER key, and a facility argument, which becomes the default facility name for the application. Several options are available when creating a client handle. They are: ASLOPTSTDERR adds stderr as an output file descriptor ASLOPTNODELAY connects to the server immediately

ASLOPTNOREMOTE disables remote-control filter adjustment

See the FILTERING section below, and the syslog(1) for additional details on filter controls. A client handle is closed and it's resources released using aassllcclloossee. Note that if additional file descriptors were added to the handle either using the ASLOPTSTDERR option or afterwards with the aassllaaddddllooggffiillee routine, those file descriptors are not closed by aassllcclloossee. LOGGING TO ADDITIONAL FILES If a client handle is opened with the ASLOPTSTDERR option to aassllooppeenn, a copy of each log message will be sent to stderr. Additional output streams may be include using aassllaaddddllooggffiillee. File descriptors may be removed from the list of outputs associated with a client handle with aassllrreemmoovveellooggffiillee. This routine simply removes the file descriptor from the output list. The file is not closed as a result. The ASLOPTSTDERR option may not be unset after a client handle has been opened. In the present release of Mac OS X, a ``raw'' format is used to format messages sent to file descriptors added to a client handle. Each message

is preceded by a 10-character field containing a message length. The

message length is padded with leading white space. The length gives the string length of the remainder of the output string. Following the length is a space character, and then the message. The message is encoded as a set of key/value pairs enclosed in square brackets, which are themselves separated by a space character. The key is separated from the value by space character. Embedded closing square brackets are escaped by a backslash. Embedded space characters in keys are escaped by a backslash; Embedded newlines are summarily turned into semicolons. The output is terminated by a trailing newline and a NUL character. SSEEAARRCCHHIINNGG The ssyyssllooggdd server archives received messages in a data store that may be searched using the aassllsseeaarrcchh, aassllrreessppoonnsseenneexxtt, and aassllrreessppoonnsseeffrreeee routines. A query message is created using: aslmsg q = aslnew(ASLTYPEQUERY); Search settings are made in the query using aassllsseettqquueerryy. A search is performed on the data store with aassllsseeaarrcchh. It returns an aslresponse structure. The caller may then call aassllrreessppoonnsseenneexxtt to iterate through matching messages. The aslresponse structure may be freed with aassllrreessppoonnsseeffrreeee. Like other messages, ASLTYPEQUERY messages contain keys and values. They also associate an operation with each key and value. The operation is used to decide if a message matches the query. The simplest operation

is ASLQUERYOPEQUAL, which tests for equality. For example, the fol-

lowing code snippet searches for messages with a Sender value equal to ``MyApp''. aslmsg m; aslresponse r; q = aslnew(ASLTYPEQUERY); aslsetquery(q, ASLKEYSENDER, "MyApp", ASLQUERYOPEQUAL); r = aslsearch(NULL, q); More complex searches may be performed using other query operations. ASLQUERYOPEQUAL value equality ASLQUERYOPGREATER value greater than ASLQUERYOPGREATEREQUAL value greater than or equal to ASLQUERYOPLESS value less than ASLQUERYOPLESSEQUAL value less than or equal to

ASLQUERYOPNOTEQUAL value not equal

ASLQUERYOPREGEX regular expression search

ASLQUERYOPTRUE always true - use to test for the existence

of a key Regular expression search uses regex(3) library. Patterns are compiled using the REGEXTENDED and REGNOSUB options.

Modifiers that change the behavior of these operations may also be speci-

fied by ORing the modifier value with the operation. The modifiers are:

ASLQUERYOPCASEFOLD string comparisons are case-folded

ASLQUERYOPPREFIX match a leading substring ASLQUERYOPSUFFIX match a trailing substring ASLQUERYOPSUBSTRING match any substring ASLQUERYOPNUMERIC values are converted to integer using aattooii The only modifier that is checked for ASLQUERYOPREGEX search is ASLQUERYOPCASEFOLD. This causes the regular expression to be compiled with the REGICASE option. If a query message contains more than one set of key/value/operation triples, the result will be a logical AND. For example, to find messages from ``MyApp'' with a priority level less than or equal to ``3'': aslmsg q; aslresponse r; q = aslnew(ASLTYPEQUERY); aslsetquery(q, ASLKEYSENDER, "MyApp", ASLQUERYOPEQUAL); aslsetquery(q, ASLKEYLEVEL, "3", ASLQUERYOPLESSEQUAL | ASLQUERYOPNUMERIC); r = aslsearch(NULL, q); After calling aassllsseeaarrcchh to get an aslresponse structure, use aassllrreessppoonnsseenneexxtt to iterate through all matching messages. To iterate through the keys and values in a message, use aassllkkeeyy to iterate through the keys, then call aassllggeett to get the value associated with each key. aslmsg q, m; int i; const char *key, *val; ... r = aslsearch(NULL, q); while (NULL != (m = aslresponsenext(r))) { for (i = 0; (NULL != (key = aslkey(m, i))); i++) { val = aslget(m, key); ... } } aslresponsefree(r); FFIILLTTEERRIINNGG AANNDD RREEMMOOTTEE CCOONNTTRROOLL

Clients may set a filter mask value with aassllsseettffiilltteerr. The mask speci-

fies which messages should be sent to the ssyyssllooggdd daemon by specifying a yes/no setting for each priority level. Clients typically set a filter mask to avoid sending relatively unimportant messages. For example, Debug or Info priority level messages are generally only useful for debugging operations. By setting a filter mask, a process can improve

performance by avoiding sending messages that are in most cases unneces-

sary.

As a convenience, the macros ASLFILTERMASK(level) and ASLFIL-

TERMASKUPTO(level) may be used to construct a bit mask corresponding to a given priority level, or corresponding to a bit mask for all priority levels from ASLLEVELEMERG to a given input level. The default filter mask is ASLFILTERMASKUPTO(ASLLEVELNOTICE). This

means that by default, and in the absence of remote-control changes

(described below), ASLLEVELDEBUG and ASLLEVELINFO priority level mes-

sages are not sent to the server. Three different filters exist for each application. The first is the

filter mask set using aassllsseettffiilltteerr as described above. The Apple Sys-

tem Log facility also manages a ``master'' filter mask. The master fil-

ter mask usually has a value that indicates to the library that it is ``off'', and thus it has no effect. However, the mask filter mask may be

enabled by giving it a value using the ssyysslloogg command, using the -cc 0

option. When the master filter mask has been set, it takes precedence over the client's filter mask. The client's mask is unmodified, and will

become active again if remote-control filtering is disabled.

In addition to the master filter mask, The Apple System Log facility also

manages a per-client remote-control filter mask. Like the master filter

mask, the per-client mask is usually ``off'', having no effect on a

client. If a per-client filter mask is set using the ssyysslloogg command,

using the -cc process option, then it takes precedence over both the

client's filter mask and the master filter mask. As is the case with the

master filter mask, a per-client mask ceases having any effect when if is

disabled.

The ASLOPTNOREMOTE option to aassllooppeenn causes both the master and per-

client remote-control masks to be ignored in the library. In that case,

only the client's own filter mask is used to determine which messages are sent to the server. This may be useful for Applications that produce log messages that should never be filtered due to security considerations. Note that root (administrator) access is required to set or change the

master filter mask, and that only root may change a per-client remote-

control filter mask for a root (UID 0) process. HISTORY These functions first appeared in Mac OS X 10.4.