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5 Copyright (c) 2020 Nokia
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23 Abstract: Support for reading config json.
25 The config structure allows simplified parsing of the json and
26 easy access to the things we belive all xAPPs will use (port
27 digging form the named "interface" and control settings). This
28 also supports the watching on the file and driving the user
29 callback when the config file appears to have changed (write
32 Accessing information from the json is serialised (mutex) as
33 with the random nature of file updates, we must ensure that
34 we don't change the json as we're trying to read from it. Locking
35 should be transparent to the user xAPP.
38 Author: E. Scott Daniels
44 #include <sys/inotify.h>
56 #include "config_cb.hpp"
61 // ----- private things --------
63 Notification listener. This function is started in a thread and listens for
64 changes to the config file. When it sees an interesting change (write close)
65 to the file, then it will read the new set of json, parse it, and drive the
68 We must watch the directory containing the file as if the file is edited and
69 replaced it's likely saved with a different referencing inode. We'd see the
70 first change, but not any subsequent changes as the inotify is based on inodes
71 and not directory entries.
73 void xapp::Config::Listener( ) {
74 struct inotify_event* ie; // event that popped
75 int ifd; // the inotify file des
76 int wfd; // the watched file des
78 char rbuf[4096]; // large read buffer as the event is var len
79 char* dname; // directory name
80 char* bname; // basename
83 ifd = inotify_init1( 0 ); // initialise watcher setting blocking read (no option)
85 fprintf( stderr, "<XFCPP> ### ERR ### unable to initialise file watch %s\n", strerror( errno ) );
89 dname = strdup( fname.c_str() ); // defrock the file name into dir and basename
90 if( (tok = strrchr( dname, '/' )) != NULL ) {
92 bname = strdup( tok+1 );
95 dname = strdup( "." );
96 bname = strdup( fname.c_str() );
99 wfd = inotify_add_watch( ifd, (char *) dname, IN_MOVED_TO | IN_CLOSE_WRITE ); // we only care about close write changes
102 fprintf( stderr, "<XFCPP> ### ERR ### unable to add watch on config file %s: %s\n", fname.c_str(), strerror( errno ) );
107 n = read( ifd, rbuf, sizeof( rbuf ) ); // read the event
109 if( errno == EAGAIN ) {
112 fprintf( stderr, "<XFCPP ### CRIT ### config listener read err: %s\n", strerror( errno ) );
117 ie = (inotify_event *) rbuf;
118 if( ie->len > 0 && strcmp( bname, ie->name ) == 0 ) {
120 auto njh = jparse( fname ); // reparse the file
123 if( njh != NULL && cb != NULL ) { // good parse, save and drive user callback
125 cb->Drive_cb( *this, user_cb_data );
133 Read a file containing json and parse into a framework Jhash.
135 Using C i/o will speed this up, but I can't imagine that we need
136 speed reading the config file once in a while.
137 The file read comes from a stack overflow example:
138 stackoverflow.com/questions/2912520/read-file-contents-into-a-string-in-c
140 std::shared_ptr<xapp::Jhash> xapp::Config::jparse( std::string ufname ) {
143 std::ifstream ifs( fname );
144 std::string st( (std::istreambuf_iterator<char>( ifs ) ), (std::istreambuf_iterator<char>() ) );
146 auto new_jh = std::shared_ptr<xapp::Jhash>( new xapp::Jhash( st.c_str() ) );
147 return new_jh->Parse_errors() ? NULL : new_jh;
151 Read the configuration file from what we find as the filename in the environment (assumed
152 to be referenced by $XAPP_DESCRIPTOR_PATH/config-file.json. If the env var is not
153 defined we assume ./. The data is then parsed with the assumption that it's json.
155 The actual meaning of the environment variable is confusing. The name is "path" which
156 should mean that this is the directory in which the config file lives, but the examples
157 elsewhere suggest that this is a filename (either fully qualified or relative). For now
158 we will assume that it's a file name, though we could add some intelligence to determine
159 if it's a directory name or not if it comes to it.
161 std::shared_ptr<xapp::Jhash> xapp::Config::jparse( ) {
164 if( (data = getenv( (char *) "XAPP_DESCRIPTOR_PATH" )) == NULL ) {
165 data = (char *) "./config-file.json";
168 return jparse( std::string( data ) );
171 // --------------------- construction, destruction -------------------------------------------
174 By default expect to find XAPP_DESCRIPTOR_PATH in the environment and assume that it
175 is the directory name where we can find config-file.json. The build process will
176 read and parse the json allowing the user xAPP to invoke the supplied "obvious"
177 functions to retrieve data. If there is something in an xAPP's config that isn't
178 standard, it can get the raw Jhash object and go at it directly. The idea is that
179 the common things should be fairly painless to extract from the json goop.
181 xapp::Config::Config() :
187 Similar, except that it allows the xAPP to supply the filename (testing?)
189 xapp::Config::Config( std::string fname) :
190 jh( jparse( fname ) ),
196 Read and return the raw file blob as a single string. User can parse, or do
197 whatever they need (allows non-json things if necessary).
199 std::string xapp::Config::Get_contents( ) {
202 if( ! fname.empty() ) {
203 std::ifstream ifs( fname );
204 std::string st( (std::istreambuf_iterator<char>( ifs ) ), (std::istreambuf_iterator<char>() ) );
211 // ----- convience function for things we think an xAPP will likely need to pull from the config
215 Suss out the port for the named "interface". The interface is likely the application
218 std::string xapp::Config::Get_port( std::string name ) {
222 std::string rv = ""; // result value
223 std::string pname; // element port name in the json
230 if( jh->Set_blob( (char *) "messaging" ) ) {
231 nele = jh->Array_len( (char *) "ports" );
232 for( i = 0; i < nele; i++ ) {
233 if( jh->Set_blob_ele( (char *) "ports", i ) ) {
234 pname = jh->String( (char *) "name" );
235 if( pname.compare( name ) == 0 ) { // this element matches the name passed in
236 value = jh->Value( (char *) "port" );
237 rv = std::to_string( (int) value );
238 jh->Unset_blob( ); // leave hash in a known state
243 jh->Unset_blob( ); // Jhash requires bump to root, and array reselct to move to next ele
244 jh->Set_blob( (char *) "messaging" );
253 Suss out the named string from the controls object. If the resulting value is
254 missing or "", then the default is returned.
256 std::string xapp::Config::Get_control_str( std::string name, std::string defval ) {
258 std::string rv; // result value
266 if( jh->Set_blob( (char *) "controls" ) ) {
267 if( jh->Exists( name.c_str() ) ) {
268 value = jh->String( name.c_str() );
269 if( value.compare( "" ) != 0 ) {
280 Convenience funciton without default. "" returned if not found.
281 No default value; returns "" if not set.
283 std::string xapp::Config::Get_control_str( std::string name ) {
284 return Get_control_str( name, "" );
288 Suss out the named field from the controls object with the assumption that it is a boolean.
289 If the resulting value is missing then the defval is used.
291 bool xapp::Config::Get_control_bool( std::string name, bool defval ) {
293 bool rv; // result value
301 if( jh->Set_blob( (char *) "controls" ) ) {
302 if( jh->Exists( name.c_str() ) ) {
303 rv = jh->Bool( name.c_str() );
313 Convenience function without default.
315 bool xapp::Config::Get_control_bool( std::string name ) {
316 return Get_control_bool( name, false );
321 Suss out the named field from the controls object with the assumption that it is a value (float/int).
322 If the resulting value is missing then the defval is used.
324 double xapp::Config::Get_control_value( std::string name, double defval ) {
327 auto rv = defval; // return value; set to default
333 if( jh->Set_blob( (char *) "controls" ) ) {
334 if( jh->Exists( name.c_str() ) ) {
335 rv = jh->Value( name.c_str() );
345 Convenience function. If value is undefined, then 0 is returned.
347 double xapp::Config::Get_control_value( std::string name ) {
348 return Get_control_value( name, 0.0 );
352 // ---- notification support ---------------------------------------------------------------
356 Accept the user's notification function, and data that it needs (pointer to
357 something unknown), and stash that as a callback.
359 The fact that the user xAPP registers a callback also triggers the creation
360 of a thread to listen for changes on the config file.
362 void xapp::Config::Set_callback( notify_callback usr_func, void* usr_data ) {
363 cb = std::unique_ptr<Config_cb>( new Config_cb( usr_func, usr_data ) );
364 user_cb_data = usr_data;
366 if( listener == NULL ) { // start thread if needed
367 listener = new std::thread( &xapp::Config::Listener, this );