config values: added relative symlink

Author: sy-c

doc/README.md

@@ -143,8 +143,13 @@ General settings are defined in section `[readout]`.
 Section names ending with `-*` can be used to define default parameters. They are applied to all section with similar names. Existing key-value pairs are not overwritten, but are defined according to defaults if they don't exist. For example, it is possible to define the TFperiod for all equipments by adding a section named `[equipment-*]` with `TFperiod=32`.
 
 Values can be symbolic links to a value stored in another configuration file. The syntax is: @LINK,URI,entryPoint,path
-For example: @LINK,file:/local/readout-test-config-link1.cfg,,bank.size
-Parameters are similar to the command-line arguments of o2-readout-exe, see ```Usage``` below.
+The URI can be absolute (file:, consul-ini://) or relative (./, ../) to the current configuration URI used by o2-readout-exe (whatever the backend).
+For example:
+  - @LINK,file:/local/readout-test-config-link1.cfg,,bank.size
+  - @LINK,consul-ini://alio2-cr1-hv-mvs00.cern.ch:8500/o2/components/readout/ANY/any/readout-global-params,,bank.size
+  - @LINK,./readout-test-config-link1.cfg,,bank.size
+  - @LINK,../readout-test-config-link1.cfg,,bank.size
+Parameters URI and entryPoint are similar to the command-line arguments of o2-readout-exe, see ```Usage``` below.
 Files are cached, i.e. the corresponding configuration tree is loaded only once if several values use a link to the same URI/entryPoint.
 Links substitutions are done at the end of the configuration tree aggregation (sections merging, etc).
 It is done recursively (up to 5 iterations, after which it fails to avoid circular dependencies).

doc/releaseNotes.md

@@ -648,3 +648,6 @@ This file describes the main feature changes for each readout.exe released versi
 
 ## v2.26.3 - 22/10/2024
 - Minor release for osx compatibility.
+
+## next version
+- Added symbolic links with relative path in configuration. See @LINK syntax.

src/mainReadout.cxx

@@ -934,7 +934,7 @@ int Readout::_configure(const boost::property_tree::ptree& properties)
   std::vector<ConfigCache> cfgCache;
   int nSubstitutions = 0;
   std::function<void(boost::property_tree::ptree &, const std::string &)> resolveLinks;
-  resolveLinks = [&resolveLinks, &cfgLinksErrors, &cfgCache, &loadConfig, &nSubstitutions](boost::property_tree::ptree &pt, const std::string &key) -> void {
+  resolveLinks = [&resolveLinks, &cfgLinksErrors, &cfgCache, &loadConfig, &nSubstitutions, this](boost::property_tree::ptree &pt, const std::string &key) -> void {
     if (pt.empty()) {
       std::string value = pt.data();
       const std::string keywordLink = "@LINK";
@@ -952,6 +952,18 @@ int Readout::_configure(const boost::property_tree::ptree& properties)
 	const char* cfgLinkUri = linkArgs[1].c_str();
 	const char* cfgLinkEntryPoint = linkArgs[2].c_str();
 	const char* cfgLinkPath = linkArgs[3].c_str();
+
+        // check if link URI starts with a relative path - and if so, compute address from current URI
+        // https://en.wikipedia.org/wiki/Uniform_Resource_Identifier
+        // theLog.log(LogInfoSupport, "Resolving %s / %s", cfgFileURI, cfgLinkUri);
+        std::string resolvedUri;
+        if (!strncmp(cfgLinkUri, "../", 3) || !strncmp(cfgLinkUri, "./", 2)) {
+	  std::pair<std::string, std::string> splitPath = splitURI(cfgFileURI);
+          resolvedUri = splitPath.first + std::filesystem::path((std::filesystem::path(splitPath.second).parent_path().string() + "/" + cfgLinkUri)).lexically_normal().string();
+          theLog.log(LogInfoSupport, "Using relative path: %s -> %s", cfgLinkUri, resolvedUri.c_str());
+          cfgLinkUri = resolvedUri.c_str();
+	}
+
 	// search for file in cache
 	unsigned int ix = 0;
 	for(;ix < cfgCache.size(); ix++) {