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Include traceId as a response header #221

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Mar 9, 2023
Merged

Include traceId as a response header #221

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19 changes: 15 additions & 4 deletions barista/src/main/java/com/markelliot/barista/handlers/TracingHandler.java
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Original file line number Diff line number Diff line change
Expand Up @@ -22,10 +22,15 @@
import com.markelliot.barista.tracing.Traces;
import io.undertow.server.HttpHandler;
import io.undertow.server.HttpServerExchange;
import io.undertow.util.HttpString;
import java.util.concurrent.ThreadLocalRandom;
import java.util.function.Supplier;

public record TracingHandler(double rate, HttpHandler delegate) implements HttpHandler {
private static final HttpString TRACE_ID = HttpString.tryFromString("X-B3-TraceId");
private static final HttpString SAMPLED = HttpString.tryFromString("X-B3-Sampled");
private static final HttpString SPAN_ID = HttpString.tryFromString("X-B3-SpanId");

@Override
public void handleRequest(HttpServerExchange exchange) throws Exception {
Trace trace = getTraceForRequest(exchange);
Expand All @@ -35,25 +40,27 @@ public void handleRequest(HttpServerExchange exchange) throws Exception {
span.close();
next.proceed();
});
// Populate response before proceeding since later operations might commit the response.
setExchangeState(exchange, span);
delegate.handleRequest(exchange);
}

private Trace getTraceForRequest(HttpServerExchange exchange) {
String traceId = getId(exchange, "X-B3-TraceId");
String traceId = getId(exchange, TRACE_ID);
if (traceId != null) {
return Traces.create(traceId, isSampled(exchange));
}
return Traces.create(Ids.randomId(), ThreadLocalRandom.current().nextDouble() < rate);
}

private static boolean isSampled(HttpServerExchange exchange) {
String val = exchange.getRequestHeaders().getFirst("X-B3-Sampled");
String val = exchange.getRequestHeaders().getFirst(SAMPLED);
return val != null && (val.equals("1") || val.equalsIgnoreCase("true"));
}

private Span getSpanForRequest(HttpServerExchange exchange, Trace trace) {
Supplier<String> opName = opName(exchange);
String spanId = getId(exchange, "X-B3-SpanId");
String spanId = getId(exchange, SPAN_ID);
if (spanId != null) {
return trace.withParent(spanId, opName);
}
Expand All @@ -65,11 +72,15 @@ private static Supplier<String> opName(HttpServerExchange exchange) {
}

/** Gets the value of the named header the request and returns it if safe to handle. */
private static String getId(HttpServerExchange exchange, String header) {
private static String getId(HttpServerExchange exchange, HttpString header) {
String val = exchange.getRequestHeaders().getFirst(header);
if (val != null && val.length() <= 32) {
return val;
}
return null;
}

private static void setExchangeState(HttpServerExchange exchange, Span span) {
exchange.getResponseHeaders().put(TRACE_ID, span.traceId());
}
}