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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 );
136 Read a file containing json and parse into a framework Jhash.
138 Using C i/o will speed this up, but I can't imagine that we need
139 speed reading the config file once in a while.
140 The file read comes from a stack overflow example:
141 stackoverflow.com/questions/2912520/read-file-contents-into-a-string-in-c
143 std::shared_ptr<xapp::Jhash> xapp::Config::jparse( std::string ufname ) {
146 std::ifstream ifs( fname );
147 std::string st( (std::istreambuf_iterator<char>( ifs ) ), (std::istreambuf_iterator<char>() ) );
149 auto new_jh = std::shared_ptr<xapp::Jhash>( new xapp::Jhash( st.c_str() ) );
150 return new_jh->Parse_errors() ? NULL : new_jh;
154 Read the configuration file from what we find as the filename in the environment (assumed
155 to be referenced by $XAPP_DESCRIPTOR_PATH/config-file.json. If the env var is not
156 defined we assume ./. The data is then parsed with the assumption that it's json.
158 The actual meaning of the environment variable is confusing. The name is "path" which
159 should mean that this is the directory in which the config file lives, but the examples
160 elsewhere suggest that this is a filename (either fully qualified or relative). For now
161 we will assume that it's a file name, though we could add some intelligence to determine
162 if it's a directory name or not if it comes to it.
164 std::shared_ptr<xapp::Jhash> xapp::Config::jparse( ) {
167 if( (data = getenv( (char *) "XAPP_DESCRIPTOR_PATH" )) == NULL ) {
168 data = (char *) "./config-file.json";
171 return jparse( std::string( data ) );
174 // --------------------- construction, destruction -------------------------------------------
177 By default expect to find XAPP_DESCRIPTOR_PATH in the environment and assume that it
178 is the directory name where we can find config-file.json. The build process will
179 read and parse the json allowing the user xAPP to invoke the supplied "obvious"
180 functions to retrieve data. If there is something in an xAPP's config that isn't
181 standard, it can get the raw Jhash object and go at it directly. The idea is that
182 the common things should be fairly painless to extract from the json goop.
184 xapp::Config::Config() :
190 Similar, except that it allows the xAPP to supply the filename (testing?)
192 xapp::Config::Config( std::string fname) :
193 jh( jparse( fname ) ),
199 Read and return the raw file blob as a single string. User can parse, or do
200 whatever they need (allows non-json things if necessary).
202 std::string xapp::Config::Get_contents( ) {
205 if( ! fname.empty() ) {
206 std::ifstream ifs( fname );
207 std::string st( (std::istreambuf_iterator<char>( ifs ) ), (std::istreambuf_iterator<char>() ) );
214 // ----- convience function for things we think an xAPP will likely need to pull from the config
218 Suss out the port for the named "interface". The interface is likely the application
221 std::string xapp::Config::Get_port( std::string name ) {
225 std::string rv = ""; // result value
226 std::string pname; // element port name in the json
233 if( jh->Set_blob( (char *) "messaging" ) ) {
234 nele = jh->Array_len( (char *) "ports" );
235 for( i = 0; i < nele; i++ ) {
236 if( jh->Set_blob_ele( (char *) "ports", i ) ) {
237 pname = jh->String( (char *) "name" );
238 if( pname.compare( name ) == 0 ) { // this element matches the name passed in
239 value = jh->Value( (char *) "port" );
240 rv = std::to_string( (int) value );
241 jh->Unset_blob( ); // leave hash in a known state
246 jh->Unset_blob( ); // Jhash requires bump to root, and array reselct to move to next ele
247 jh->Set_blob( (char *) "messaging" );
256 Suss out the named string from the controls object. If the resulting value is
257 missing or "", then the default is returned.
259 std::string xapp::Config::Get_control_str( std::string name, std::string defval ) {
261 std::string rv; // result value
269 if( jh->Set_blob( (char *) "controls" ) ) {
270 if( jh->Exists( name.c_str() ) ) {
271 value = jh->String( name.c_str() );
272 if( value.compare( "" ) != 0 ) {
283 Convenience funciton without default. "" returned if not found.
284 No default value; returns "" if not set.
286 std::string xapp::Config::Get_control_str( std::string name ) {
287 return Get_control_str( name, "" );
291 Suss out the named field from the controls object with the assumption that it is a boolean.
292 If the resulting value is missing then the defval is used.
294 bool xapp::Config::Get_control_bool( std::string name, bool defval ) {
296 bool rv; // result value
304 if( jh->Set_blob( (char *) "controls" ) ) {
305 if( jh->Exists( name.c_str() ) ) {
306 rv = jh->Bool( name.c_str() );
316 Convenience function without default.
318 bool xapp::Config::Get_control_bool( std::string name ) {
319 return Get_control_bool( name, false );
324 Suss out the named field from the controls object with the assumption that it is a value (float/int).
325 If the resulting value is missing then the defval is used.
327 double xapp::Config::Get_control_value( std::string name, double defval ) {
330 auto rv = defval; // return value; set to default
336 if( jh->Set_blob( (char *) "controls" ) ) {
337 if( jh->Exists( name.c_str() ) ) {
338 rv = jh->Value( name.c_str() );
348 Convenience function. If value is undefined, then 0 is returned.
350 double xapp::Config::Get_control_value( std::string name ) {
351 return Get_control_value( name, 0.0 );
355 // ---- notification support ---------------------------------------------------------------
359 Accept the user's notification function, and data that it needs (pointer to
360 something unknown), and stash that as a callback.
362 The fact that the user xAPP registers a callback also triggers the creation
363 of a thread to listen for changes on the config file.
365 void xapp::Config::Set_callback( notify_callback usr_func, void* usr_data ) {
366 cb = std::unique_ptr<Config_cb>( new Config_cb( usr_func, usr_data ) );
367 user_cb_data = usr_data;
369 if( listener == NULL ) { // start thread if needed
370 listener = new std::thread( &xapp::Config::Listener, this );