Enhance existing http example to support w3c trace context propagation (#727)

Author: lalitb

examples/http/BUILD

@@ -2,7 +2,7 @@ cc_binary(
     name = "example_http_client",
     srcs = [
         "client.cc",
-        "tracer_common.hpp",
+        "tracer_common.h",
     ],
     # TODO: Move copts/linkopts for static CURL usage into shared bzl file.
     copts = [
@@ -30,8 +30,8 @@ cc_binary(
     name = "example_http_server",
     srcs = [
         "server.cc",
-        "server.hpp",
-        "tracer_common.hpp",
+        "server.h",
+        "tracer_common.h",
     ],
     deps = [
         "//api",

examples/http/README.md

@@ -5,11 +5,12 @@
 This is a simple example that demonstrates tracing an HTTP request from client to server. The example shows several aspects of tracing such as:
 
 * Using the `TracerProvider`
+* Using the `GlobalPropagator`
 * Span Attributes
 * Span Events
 * Using the ostream exporter
 * Nested spans (TBD)
-* W3c Trace Context Propagation (TBD)
+* W3C Trace Context Propagation
 
 ### Running the example
 
@@ -38,18 +39,20 @@ This is a simple example that demonstrates tracing an HTTP request from client t
    * Client console
 
    ```console
+
    {
      name          : /helloworld
-     trace_id      : 15c7ca1993b536085f4097f2818a7be4
-     span_id       : 7d9136e4eb4cb59d
+     trace_id      : baa922bc0da6f79d46373371f4416463
+     span_id       : 83bed4da7a01267d
+     tracestate    :
      parent_span_id: 0000000000000000
-     start         : 1617075613395810300
-     duration      : 1901100
+     start         : 1620287026111457000
+     duration      : 5164400
      description   :
      span kind     : Client
      status        : Unset
      attributes    :
-           http.header.Date: Tue, 30 Mar 2021 03:40:13 GMT
+           http.header.Date: Thu, 06 May 2021 07:43:46 GMT
            http.header.Content-Length: 0
            http.status_code: 200
            http.method: GET
@@ -58,30 +61,46 @@ This is a simple example that demonstrates tracing an HTTP request from client t
            http.header.Connection: keep-alive
            http.scheme: http
            http.url: h**p://localhost:8800/helloworld
+     events        :
+     links         :
+
    }
    ```
 
    * Server console
 
    ```console
+
    {
      name          : /helloworld
-     trace_id      : bfa611a4bbb8b1871ef6a222d6a0f4dd
-     span_id       : 19e3cda7df63c9b9
-     parent_span_id: 0000000000000000
-     start         : 1617075522491536300
+     trace_id      : baa922bc0da6f79d46373371f4416463
+     span_id       : c3e7e23042eb670e
+     tracestate    :
+     parent_span_id: 83bed4da7a01267d
+     start         : 1620287026115443300
      duration      : 50700
      description   :
      span kind     : Server
      status        : Unset
      attributes    :
+           http.header.Traceparent: 00-baa922bc0da6f79d46373371f4416463-83bed4da7a01267d-01
            http.header.Accept: */*
            http.request_content_length: 0
            http.header.Host: localhost:8800
            http.scheme: http
-           http.client_ip: 127.0.0.1:44616
+           http.client_ip: 127.0.0.1:50792
            http.method: GET
            net.host.port: 8800
            http.server_name: localhost
+     events        :
+           {
+             name          : Processing request
+             timestamp     : 1620287026115464000
+             attributes    :
+           }
+     links         :
+
    }
    ```
+
+   As seen from example above, `trace_id` and `parent_span_id` is propagated from client to server.

examples/http/client.cc

@@ -1,6 +1,6 @@
 #include "opentelemetry/ext/http/client/http_client_factory.h"
 #include "opentelemetry/ext/http/common/url_parser.h"
-#include "tracer_common.hpp"
+#include "tracer_common.h"
 
 namespace
 {
@@ -23,7 +23,14 @@ void sendRequest(const std::string &url)
                               options);
   auto scope = get_tracer("http-client")->WithActiveSpan(span);
 
-  opentelemetry::ext::http::client::Result result = http_client->Get(url);
+  // inject current context into http header
+  auto current_ctx = opentelemetry::context::RuntimeContext::GetCurrent();
+  HttpTextMapCarrier<opentelemetry::ext::http::client::Headers> carrier;
+  auto prop = opentelemetry::context::propagation::GlobalTextMapPropagator::GetGlobalPropagator();
+  prop->Inject(carrier, current_ctx);
+
+  // send http request
+  opentelemetry::ext::http::client::Result result = http_client->Get(url, carrier.headers_);
   if (result)
   {
     // set span attributes

examples/http/server.cc

@@ -1,5 +1,5 @@
-#include "server.hpp"
-#include "tracer_common.hpp"
+#include "server.h"
+#include "tracer_common.h"
 
 #include <iostream>
 #include <thread>
@@ -19,6 +19,15 @@ class RequestHandler : public HTTP_SERVER_NS::HttpRequestCallback
     options.kind          = opentelemetry::trace::SpanKind::kServer;  // server
     std::string span_name = request.uri;
 
+    // extract context from http header
+    const HttpTextMapCarrier<std::map<std::string, std::string>> carrier(
+        (std::map<std::string, std::string> &)request.headers);
+    auto prop = opentelemetry::context::propagation::GlobalTextMapPropagator::GetGlobalPropagator();
+    auto current_ctx = opentelemetry::context::RuntimeContext::GetCurrent();
+    auto new_context = prop->Extract(carrier, current_ctx);
+    options.parent   = GetSpanFromContext(new_context)->GetContext();
+
+    // start span with parent context extracted from http header
     auto span = get_tracer("http-server")
                     ->StartSpan(span_name,
                                 {{"http.server_name", server_name},
@@ -30,6 +39,7 @@ class RequestHandler : public HTTP_SERVER_NS::HttpRequestCallback
                                 options);
 
     auto scope = get_tracer("http_server")->WithActiveSpan(span);
+
     for (auto &kv : request.headers)
     {
       span->SetAttribute("http.header." + std::string(kv.first.data()), kv.second);

examples/http/server.h

@@ -0,0 +1,50 @@
+#pragma once
+#include <atomic>
+#include <string>
+#include "opentelemetry/ext/http/server/http_server.h"
+
+namespace
+{
+
+class HttpServer : public HTTP_SERVER_NS::HttpRequestCallback
+{
+
+protected:
+  HTTP_SERVER_NS::HttpServer server_;
+  std::string server_url_;
+  uint16_t port_;
+  std::atomic<bool> is_running_{false};
+
+public:
+  HttpServer(std::string server_name = "test_server", uint16_t port = 8800) : port_(port)
+  {
+    server_.setServerName(server_name);
+    server_.setKeepalive(false);
+  }
+
+  void AddHandler(std::string path, HTTP_SERVER_NS::HttpRequestCallback *request_handler)
+  {
+    server_.addHandler(path, *request_handler);
+  }
+
+  void Start()
+  {
+    if (!is_running_.exchange(true))
+    {
+      server_.addListeningPort(port_);
+      server_.start();
+    }
+  }
+
+  void Stop()
+  {
+    if (is_running_.exchange(false))
+    {
+      server_.stop();
+    }
+  }
+
+  ~HttpServer() { Stop(); }
+};
+
+}  // namespace

examples/http/server.hpp

@@ -0,0 +1,95 @@
+#pragma once
+#include "opentelemetry/exporters/ostream/span_exporter.h"
+#include "opentelemetry/sdk/trace/simple_processor.h"
+#include "opentelemetry/sdk/trace/tracer_provider.h"
+#include "opentelemetry/trace/provider.h"
+
+#include "opentelemetry/context/propagation/global_propagator.h"
+#include "opentelemetry/context/propagation/text_map_propagator.h"
+#include "opentelemetry/trace/propagation/http_trace_context.h"
+
+#include <cstring>
+#include <iostream>
+#include <vector>
+#include "opentelemetry/ext/http/client/http_client.h"
+#include "opentelemetry/nostd/shared_ptr.h"
+
+namespace
+{
+// TBD - This function be removed once #723 is merged
+inline nostd::shared_ptr<opentelemetry::trace::Span> GetSpanFromContext(
+    const opentelemetry::context::Context &context)
+{
+  opentelemetry::context::ContextValue span = context.GetValue(opentelemetry::trace::kSpanKey);
+  if (nostd::holds_alternative<nostd::shared_ptr<opentelemetry::trace::Span>>(span))
+  {
+    return nostd::get<nostd::shared_ptr<opentelemetry::trace::Span>>(span);
+  }
+  static nostd::shared_ptr<opentelemetry::trace::Span> invalid_span{
+      new opentelemetry::trace::DefaultSpan(opentelemetry::trace::SpanContext::GetInvalid())};
+  return invalid_span;
+}
+
+template <typename T>
+class HttpTextMapCarrier : public opentelemetry::context::propagation::TextMapCarrier
+{
+public:
+  HttpTextMapCarrier<T>(T &headers) : headers_(headers) {}
+  HttpTextMapCarrier() = default;
+  virtual nostd::string_view Get(nostd::string_view key) const noexcept override
+  {
+    std::string key_to_compare = key.data();
+    // Header's first letter seems to be  automatically capitaliazed by our test http-server, so
+    // compare accordingly.
+    if (key == opentelemetry::trace::propagation::kTraceParent)
+    {
+      key_to_compare = "Traceparent";
+    }
+    else if (key == opentelemetry::trace::propagation::kTraceState)
+    {
+      key_to_compare == "Tracestate";
+    }
+    auto it = headers_.find(key_to_compare);
+    if (it != headers_.end())
+    {
+      return it->second;
+    }
+    return "";
+  }
+
+  virtual void Set(nostd::string_view key, nostd::string_view value) noexcept override
+  {
+    headers_.insert(std::pair<std::string, std::string>(std::string(key), std::string(value)));
+  }
+
+  T headers_;
+};
+
+void initTracer()
+{
+  auto exporter = std::unique_ptr<sdktrace::SpanExporter>(
+      new opentelemetry::exporter::trace::OStreamSpanExporter);
+  auto processor = std::unique_ptr<sdktrace::SpanProcessor>(
+      new sdktrace::SimpleSpanProcessor(std::move(exporter)));
+  std::vector<std::unique_ptr<sdktrace::SpanProcessor>> processors;
+  processors.push_back(std::move(processor));
+  // Default is an always-on sampler.
+  auto context  = std::make_shared<sdktrace::TracerContext>(std::move(processors));
+  auto provider = nostd::shared_ptr<opentelemetry::trace::TracerProvider>(
+      new sdktrace::TracerProvider(context));
+  // Set the global trace provider
+  opentelemetry::trace::Provider::SetTracerProvider(provider);
+
+  // set global propagator
+  opentelemetry::context::propagation::GlobalTextMapPropagator::SetGlobalPropagator(
+      nostd::shared_ptr<opentelemetry::context::propagation::TextMapPropagator>(
+          new opentelemetry::trace::propagation::HttpTraceContext()));
+}
+
+nostd::shared_ptr<opentelemetry::trace::Tracer> get_tracer(std::string tracer_name)
+{
+  auto provider = opentelemetry::trace::Provider::GetTracerProvider();
+  return provider->GetTracer(tracer_name);
+}
+
+}  // namespace