public CompletableFuture<Result> feedSingle(String json) {
        if (closed) throw new IllegalStateException("Already closed");
        globalInflightOperations.incrementAndGet();
        CompletableFuture<Result> result = new CompletableFuture<>();
        try {
            SingleOperationParserAndExecutor parser = new SingleOperationParserAndExecutor(json.getBytes(UTF_8));
            parser.next().whenCompleteAsync((operationResult, error) -> {
                if (error != null) {
                    result.completeExceptionally(error);
                } else {
                    result.complete(operationResult);
                }
                globalInflightOperations.decrementAndGet();
            }, resultExecutor);
        } catch (Exception e) {
            resultExecutor.execute(() -> result.completeExceptionally(wrapException(e)));
            globalInflightOperations.decrementAndGet();
        }
        return result;
    }
Feeds single JSON feed operations on the form
 <pre>
   {
     "id": "id:ns:type::boo",
     "fields": { ... document fields ... }
   }
 </pre>
 Exceptional completion will use be an instance of {@link FeedException} or one of its sub-classes.
vespa-feed-client-api/src/main/java/ai/vespa/feed/client/JsonFeeder.java