chore(ci): fix trace exporter FFI examples (#1839)

# What does this PR do?

cleanup the FFI examples for the Trace Exporter and stop skipping them in the GH action that runs the examples.

# Motivation

Test coverage for FFI examples

# Additional Notes

Anything else we should know when reviewing?

# How to test the change?

Describe here in detail how the change can be validated.


Co-authored-by: edmund.kump <edmund.kump@datadoghq.com>

Author: ekump

examples/ffi/trace_exporter.c

@@ -1,14 +1,13 @@
 // Copyright 2021-Present Datadog, Inc. https://www.datadoghq.com/
 // SPDX-License-Identifier: Apache-2.0
 
-#include <assert.h>
+#include <stdint.h>
 #include <stdio.h>
 #include <string.h>
 #include <datadog/common.h>
 #include <datadog/data-pipeline.h>
 #include <datadog/log.h>
 
-#define UNUSED(x) (void)(x)
 #define SUCCESS 0
 
 void handle_error(ddog_TraceExporterError *err) {
@@ -81,20 +80,20 @@ int main(int argc, char** argv)
     ddog_CharSlice version = DDOG_CHARSLICE_C("1.0");
     ddog_CharSlice service = DDOG_CHARSLICE_C("test_app");
 
-    UNUSED(language_version);
-    UNUSED(language_interpreter);
-    UNUSED(hostname);
-    UNUSED(env);
-    UNUSED(version);
-    UNUSED(service);
-
     ddog_TraceExporterError *ret = NULL;
     ddog_TraceExporterConfig *config = NULL;
 
     ddog_trace_exporter_config_new(&config);
     ddog_trace_exporter_config_set_url(config, url);
     ddog_trace_exporter_config_set_tracer_version(config, tracer_version);
     ddog_trace_exporter_config_set_language(config, language);
+    ddog_trace_exporter_config_set_lang_version(config, language_version);
+    ddog_trace_exporter_config_set_lang_interpreter(config, language_interpreter);
+    ddog_trace_exporter_config_set_hostname(config, hostname);
+    ddog_trace_exporter_config_set_env(config, env);
+    ddog_trace_exporter_config_set_version(config, version);
+    ddog_trace_exporter_config_set_service(config, service);
+    ddog_trace_exporter_config_set_connection_timeout(config, 1000);
 
     ddog_TelemetryClientConfig telemetry_config = {
         .interval = 60000,
@@ -110,25 +109,59 @@ int main(int argc, char** argv)
     }
 
     ret = ddog_trace_exporter_new(&trace_exporter, config);
-
-    assert(ret == NULL);
-    assert(trace_exporter != NULL);
-
-    ddog_ByteSlice buffer = { .ptr = NULL, .len=0 };
-    ddog_TraceExporterResponse *response;
-
-    ret = ddog_trace_exporter_send(trace_exporter, buffer, &response);
-
-    assert(ret->code == DDOG_TRACE_EXPORTER_ERROR_CODE_SERDE);
     if (ret) {
         error = ret->code;
         handle_error(ret);
         goto error;
     }
 
-    ddog_trace_exporter_response_free(response);
+    printf("TraceExporter created successfully\n");
+
+    // Construct a minimal valid msgpack V04 trace payload: [[{span}]]
+    // One trace containing one span with the 7 required fields:
+    // service, name, resource, trace_id, span_id, start, duration
+    // Hand rolling a payload like this is not scalable. If we need to
+    // do this more than once, please write a helper function.
+    static const uint8_t trace_payload[] = {
+        0x91,                                                       // array(1): one trace
+        0x91,                                                       // array(1): one span
+        0x87,                                                       // map(7): span fields
+        0xa7, 's','e','r','v','i','c','e',                          // key: "service"
+        0xa8, 't','e','s','t','_','a','p','p',                      // val: "test_app"
+        0xa4, 'n','a','m','e',                                      // key: "name"
+        0xab, 'w','e','b','.','r','e','q','u','e','s','t',          // val: "web.request"
+        0xa8, 'r','e','s','o','u','r','c','e',                      // key: "resource"
+        0xaa, 'G','E','T',' ','/','h','e','l','l','o',              // val: "GET /hello"
+        0xa8, 't','r','a','c','e','_','i','d',                      // key: "trace_id"
+        0x01,                                                       // val: 1
+        0xa7, 's','p','a','n','_','i','d',                          // key: "span_id"
+        0x01,                                                       // val: 1
+        0xa5, 's','t','a','r','t',                                  // key: "start"
+        0xce, 0x3b, 0x9a, 0xca, 0x00,                              // val: 1000000000
+        0xa8, 'd','u','r','a','t','i','o','n',                      // key: "duration"
+        0xce, 0x1d, 0xcd, 0x65, 0x00,                              // val: 500000000
+    };
+    ddog_ByteSlice buffer = {
+        .ptr = trace_payload,
+        .len = sizeof(trace_payload)
+    };
+    ddog_TraceExporterResponse *response = NULL;
+
+    // Send will deserialize the payload and attempt to forward it to the agent.
+    // Without a running agent, this will fail with a network error.
+    ret = ddog_trace_exporter_send(trace_exporter, buffer, &response);
+    if (ret) {
+        printf("Send returned expected error (no agent running): %s\n", ret->msg);
+        ddog_trace_exporter_error_free(ret);
+    } else {
+        printf("Send succeeded\n");
+        ddog_trace_exporter_response_free(response);
+    }
+
     ddog_trace_exporter_free(trace_exporter);
+    trace_exporter = NULL;
     ddog_trace_exporter_config_free(config);
+    config = NULL;
 
     // Disable file logging if it was enabled
     if (log_path != NULL) {

tools/src/bin/ffi_test.rs

@@ -225,12 +225,7 @@ fn per_test_env(name: &str, project_root: &Path, work_dir: &Path) -> Vec<(String
 
 fn expected_failures() -> &'static HashMap<&'static str, &'static str> {
     static MAP: OnceLock<HashMap<&'static str, &'static str>> = OnceLock::new();
-    MAP.get_or_init(|| {
-        HashMap::from([(
-            "trace_exporter",
-            "expects trace data, fails on empty buffer",
-        )])
-    })
+    MAP.get_or_init(HashMap::new)
 }
 
 // Test data directories to symlink into work directory