Make the JSON logger more robust

We now ignore connection / write errors.

src/libutil/logging.cc

@@ -196,6 +196,7 @@ struct JSONLogger : Logger {
 
     struct State
     {
+        bool enabled = true;
     };
 
     Sync<State> _state;
@@ -208,8 +209,18 @@ struct JSONLogger : Logger {
 
         /* Acquire a lock to prevent log messages from clobbering each
            other. */
+        try {
             auto state(_state.lock());
+            if (state->enabled)
                 writeLine(fd, line);
+        } catch (...) {
+            bool enabled = false;
+            std::swap(_state.lock()->enabled, enabled);
+            if (enabled) {
+                ignoreExceptionExceptInterrupt();
+                logger->warn("disabling JSON logger due to write errors");
+            }
+        }
     }
 
     void log(Verbosity lvl, std::string_view s) override

src/nix/main.cc

@@ -502,7 +502,11 @@ void mainWrapped(int argc, char * * argv)
     }
 
     if (!extLoggerSettings.jsonLogPath.get().empty()) {
+        try {
             logger = makeTeeLogger({logger, makeJSONLogger(std::filesystem::path(extLoggerSettings.jsonLogPath.get()), false)});
+        } catch (...) {
+            ignoreExceptionExceptInterrupt();
+        }
     }
 
     if (args.helpRequested) {