Check for agent version in client side stats (#3811)

Author: bwoebi

Cargo.lock

@@ -57,6 +57,8 @@ pub unsafe extern "C" fn ddog_apply_agent_info(
                 info.filter_tags_regex.as_ref().and_then(|f| f.require.as_deref()).unwrap_or(&[]).to_owned(),
                 info.filter_tags_regex.as_ref().and_then(|f| f.reject.as_deref()).unwrap_or(&[]).to_owned(),
                 info.ignore_resources.as_deref().unwrap_or(&[]).to_owned(),
+                info.client_drop_p0s.unwrap_or(false),
+                info.version.as_deref(),
             );
         }
     }
@@ -87,6 +89,8 @@ pub unsafe extern "C" fn ddog_apply_agent_info_concentrator_config(
             info.filter_tags_regex.as_ref().and_then(|f| f.require.as_deref()).unwrap_or(&[]).to_owned(),
             info.filter_tags_regex.as_ref().and_then(|f| f.reject.as_deref()).unwrap_or(&[]).to_owned(),
             info.ignore_resources.as_deref().unwrap_or(&[]).to_owned(),
+            info.client_drop_p0s.unwrap_or(false),
+            info.version.as_deref(),
         );
     }
 }

components-rs/agent_info.rs

@@ -181,6 +181,13 @@ bool ddog_exception_hash_limiter_inc(struct ddog_SidecarTransport *connection,
  */
 bool ddog_is_agent_info_ready(void);
 
+/**
+ * Returns true when the agent supports client-side stats computation:
+ * agent info has been received, `client_drop_p0s` is true, and the reported
+ * agent version is >= 7.65.0.
+ */
+bool ddog_agent_has_stats_computation(void);
+
 /**
  * Look up (or lazily create) the concentrator for `(env, version, service)` and invoke
  * `callback` with a shared reference to it while holding the global read lock.

components-rs/ddtrace.h

@@ -79,7 +79,7 @@ pub struct PhpSpanStats<'a> {
 }
 
 #[inline]
-fn char_slice_str(s: CharSlice) -> &str {
+fn char_slice_str(s: CharSlice<'_>) -> &str {
     s.try_to_utf8().unwrap_or("")
 }
 
@@ -232,6 +232,19 @@ static SPAN_CONCENTRATORS: LazyLock<RwLock<HashMap<String, SpanConcentrator>>> =
 /// i.e. the sidecar has received and applied the agent's /info response.
 static AGENT_INFO_RECEIVED: AtomicBool = AtomicBool::new(false);
 
+/// Set to true once agent info confirms `client_drop_p0s` is true and the
+/// reported agent version is >= 7.65.0.  Cached so the per-span hot-path is a
+/// single atomic load.
+static STATS_COMPUTATION_READY: AtomicBool = AtomicBool::new(false);
+
+fn agent_version_ge(version: Option<&str>, req_major: u32, req_minor: u32, req_patch: u32) -> bool {
+    let Some(v) = version else { return false; };
+    let v = v.split('-').next().unwrap_or(v); // strip agent version suffixes
+    let mut parts = v.split('.').filter_map(|p| p.parse::<u32>().ok());
+    let (Some(major), Some(minor), Some(patch)) = (parts.next(), parts.next(), parts.next()) else { return false; };
+    (major, minor, patch) >= (req_major, req_minor, req_patch)
+}
+
 /// Returns true once the agent /info has been received and applied.
 /// Used by the PHP extension to skip stats computation until the concentrator
 /// has been properly initialised with peer-tag keys and span kinds.
@@ -240,6 +253,14 @@ pub extern "C" fn ddog_is_agent_info_ready() -> bool {
     AGENT_INFO_RECEIVED.load(Ordering::Acquire)
 }
 
+/// Returns true when the agent supports client-side stats computation:
+/// agent info has been received, `client_drop_p0s` is true, and the reported
+/// agent version is >= 7.65.0.
+#[no_mangle]
+pub extern "C" fn ddog_agent_has_stats_computation() -> bool {
+    STATS_COMPUTATION_READY.load(Ordering::Acquire)
+}
+
 /// Desired concentrator configuration sourced from the agent's /info endpoint.
 /// Populated via `ddog_apply_agent_info`; applied to every concentrator
 /// at creation time and when the config changes.
@@ -253,6 +274,7 @@ static DESIRED_CONFIG: LazyLock<RwLock<DesiredConfig>> = LazyLock::new(|| RwLock
 
 /// Apply updated concentrator config (peer-tag keys, span kinds, trace filters) to
 /// `DESIRED_CONFIG` and propagate peer-tag / span-kind changes to all open concentrators.
+/// Also updates the `STATS_COMPUTATION_READY` flag based on `client_drop_p0s` and `version`.
 pub(crate) fn apply_concentrator_config(
     peer_tag_keys: Vec<String>,
     span_kinds: Vec<String>,
@@ -261,12 +283,16 @@ pub(crate) fn apply_concentrator_config(
     regex_require: Vec<String>,
     regex_reject: Vec<String>,
     ignore_resources: Vec<String>,
+    client_drop_p0s: bool,
+    version: Option<&str>,
 ) {
     let compiled = trace_filter::compile_trace_filter(
         &tags_require, &tags_reject, &regex_require, &regex_reject, &ignore_resources,
     );
     trace_filter::set_trace_filter(compiled);
     AGENT_INFO_RECEIVED.store(true, Ordering::Release);
+    let ready = client_drop_p0s && agent_version_ge(version, 7, 65, 0);
+    STATS_COMPUTATION_READY.store(ready, Ordering::Release);
     {
         let mut dc = DESIRED_CONFIG.write().unwrap();
         dc.peer_tag_keys = peer_tag_keys.clone();

components-rs/stats.rs

@@ -1534,7 +1534,7 @@ ddog_SpanBytes *ddtrace_serialize_span_to_rust_span(ddtrace_span_data *span, ddo
         ZEND_HASH_FOREACH_END();
 
 
-        if (!span_sampling_applied && DDTRACE_G(sidecar) && get_DD_TRACE_STATS_COMPUTATION_ENABLED() && ddog_is_agent_info_ready()) {
+        if (!span_sampling_applied && DDTRACE_G(sidecar) && get_DD_TRACE_STATS_COMPUTATION_ENABLED() && ddog_agent_has_stats_computation()) {
             if (inferred_span) {
                 // Inferred span won't be serialized, so feed it to the concentrator here.
                 ddtrace_span_precomputed inferred_pre;
@@ -1779,7 +1779,7 @@ ddog_SpanBytes *ddtrace_serialize_span_to_rust_span(ddtrace_span_data *span, ddo
     zend_string_release(Z_STR(prop_root_service_as_string));
     zend_string_release(Z_STR(prop_service_as_string));
 
-    if (DDTRACE_G(sidecar) && get_DD_TRACE_STATS_COMPUTATION_ENABLED() && ddog_is_agent_info_ready()) {
+    if (DDTRACE_G(sidecar) && get_DD_TRACE_STATS_COMPUTATION_ENABLED() && ddog_agent_has_stats_computation()) {
         ddtrace_feed_span_to_concentrator(span, &pre);
     }
 

ext/serializer.c

@@ -2,6 +2,23 @@
 Client-side SHM span stats are computed and flushed to the agent on trace flush
 --SKIPIF--
 <?php include __DIR__ . '/../includes/skipif_no_dev_env.inc'; ?>
+<?php
+if (PHP_VERSION_ID < 70400) die("skip: Before PHP 7.4, the skip-task would cause the sidecar to fetch the info already.");
+if (PHP_VERSION_ID >= 80100) {
+    echo "nocache\n";
+}
+$ctx = stream_context_create([
+    'http' => [
+        'method' => 'PUT',
+        'header' => [
+            'Content-Type: application/json',
+            'X-Datadog-Test-Session-Token: client_side_stats',
+        ],
+        'content' => json_encode(['version' => '7.65.0', 'client_drop_p0s' => true]),
+    ]
+]);
+file_get_contents('http://request-replayer/set-agent-info', false, $ctx);
+?>
 --ENV--
 DD_AGENT_HOST=request-replayer
 DD_TRACE_AGENT_PORT=80
@@ -21,8 +38,7 @@ include __DIR__ . '/../includes/request_replayer.inc';
 
 $rr = new RequestReplayer();
 
-// Block until the sidecar has received the agent's /info response so that
-// ddog_is_agent_info_ready() returns true before stats are computed.
+// Block until the sidecar has received the agent's /info response before stats are computed
 dd_trace_internal_fn('await_agent_info');
 
 $root = \DDTrace\start_trace_span();

tests/ext/request-replayer/client_side_stats.phpt

@@ -14,7 +14,7 @@ $ctx = stream_context_create([
             'Content-Type: application/json',
             'X-Datadog-Test-Session-Token: client_side_stats_peer_tags',
         ],
-        'content' => '{"peer_tags":["db.hostname"]}',
+        'content' => json_encode(['version' => '7.65.0', 'client_drop_p0s' => true, 'peer_tags' => ['db.hostname']]),
     ]
 ]);
 file_get_contents('http://request-replayer/set-agent-info', false, $ctx);

tests/ext/request-replayer/client_side_stats_peer_tags.phpt

@@ -24,6 +24,8 @@ $ctx = stream_context_create([
             'X-Datadog-Test-Session-Token: client_side_stats_trace_filters',
         ],
         'content' => json_encode([
+            'version' => '7.65.0',
+            'client_drop_p0s' => true,
             'filter_tags' => [
                 'require' => ['filter_required:yes'],
                 'reject'  => ['filter_reject:yes'],