feat: add traces_sampler

CHANGELOG.md

@@ -5,7 +5,7 @@
 **Features**:
 
 - Add option to set debug log level. ([#1107](https://github.com/getsentry/sentry-native/pull/1107))
-
+- Add `traces_sampler` ([#1108](https://github.com/getsentry/sentry-native/pull/1108))
 ## 0.7.17
 
 **Features**:

include/sentry.h

@@ -1533,6 +1533,18 @@ SENTRY_EXPERIMENTAL_API void sentry_options_set_traces_sample_rate(
 SENTRY_EXPERIMENTAL_API double sentry_options_get_traces_sample_rate(
     sentry_options_t *opts);
 
+struct sentry_sampling_context_s;
+typedef struct sentry_sampling_context_s sentry_sampling_context_t;
+typedef double (*sentry_traces_sampler_function)(
+    sentry_sampling_context_t *sampling_ctx);
+
+/**
+ * Sets the traces sampler callback. Should be a function that returns a double
+ * and (TODO takes in a samplingContext object)
+ */
+SENTRY_EXPERIMENTAL_API void sentry_options_set_traces_sampler(
+    sentry_options_t *opts, sentry_traces_sampler_function callback);
+
 #ifdef SENTRY_PLATFORM_LINUX
 
 /**

src/CMakeLists.txt

@@ -24,6 +24,8 @@ sentry_target_sources_cwd(sentry
 	sentry_random.h
 	sentry_ratelimiter.c
 	sentry_ratelimiter.h
+	sentry_sampling_context.c
+	sentry_sampling_context.h
 	sentry_scope.c
 	sentry_scope.h
 	sentry_session.c

src/sentry_core.c

@@ -457,9 +457,15 @@ sentry__should_send_transaction(sentry_value_t tx_cxt)
 
     bool send = false;
     SENTRY_WITH_OPTIONS (options) {
-        send = sentry__roll_dice(options->traces_sample_rate);
-        // TODO(tracing): Run through traces sampler function if rate is
-        // unavailable.
+        if (options->traces_sampler) {
+            // TODO use samplingContext instead of only tx_cxt
+            double result
+                = ((double (*)(void *))options->traces_sampler)(&tx_cxt);
+            send = sentry__roll_dice(result);
+        } else {
+            // TODO if there is a parent sampling decision, use it
+            send = sentry__roll_dice(options->traces_sample_rate);
+        }
     }
     return send;
 }
@@ -875,6 +881,8 @@ sentry_transaction_start_ts(sentry_transaction_context_t *opaque_tx_cxt,
     sentry_value_remove_by_key(tx, "timestamp");
 
     sentry__value_merge_objects(tx, tx_cxt);
+    // TODO construct a sampling context based on tx_cxt and
+    //  sampling_ctx, pass it into should_send_transaction
 
     bool should_sample = sentry__should_send_transaction(tx_cxt);
     sentry_value_set_by_key(

src/sentry_options.c

@@ -615,6 +615,13 @@ sentry_options_get_traces_sample_rate(sentry_options_t *opts)
     return opts->traces_sample_rate;
 }
 
+void
+sentry_options_set_traces_sampler(
+    sentry_options_t *opts, sentry_traces_sampler_function callback)
+{
+    opts->traces_sampler = callback;
+}
+
 void
 sentry_options_set_backend(sentry_options_t *opts, sentry_backend_t *backend)
 {

src/sentry_options.h

@@ -61,6 +61,7 @@ typedef struct sentry_options_s {
 
     /* Experimentally exposed */
     double traces_sample_rate;
+    sentry_traces_sampler_function traces_sampler;
     size_t max_spans;
 
     /* everything from here on down are options which are stored here but

src/sentry_sampling_context.c

@@ -0,0 +1,28 @@
+// sentry_sampling_context.c
+#include "sentry_sampling_context.h"
+#include <sentry_alloc.h>
+#include <stdlib.h>
+
+sentry_sampling_context_t *
+sentry_sampling_context_new(sentry_transaction_context_t *transaction_context)
+{
+    sentry_sampling_context_t *context = SENTRY_MAKE(sentry_sampling_context_t);
+    if (context) {
+        context->transaction_context = transaction_context; // todo incref?
+        context->custom_sampling_context = NULL;
+    }
+    return context;
+}
+
+sentry_sampling_context_t *
+sentry_sampling_context_new_with_custom(
+    sentry_transaction_context_t *transaction_context,
+    void *custom_sampling_context)
+{
+    sentry_sampling_context_t *context
+        = sentry_sampling_context_new(transaction_context);
+    if (context) {
+        context->custom_sampling_context = custom_sampling_context;
+    }
+    return context;
+}

src/sentry_sampling_context.h

@@ -0,0 +1,19 @@
+// sentry_sampling_context.h
+#ifndef SENTRY_SAMPLING_CONTEXT_H_INCLUDED
+#define SENTRY_SAMPLING_CONTEXT_H_INCLUDED
+
+#include "sentry_tracing.h"
+
+typedef struct sentry_sampling_context_s {
+    sentry_transaction_context_t *transaction_context;
+    void *custom_sampling_context; // TODO what type should this be?
+} sentry_sampling_context_t;
+
+// TODO add refcounting for this; users might want to reuse this
+sentry_sampling_context_t *sentry_sampling_context_new(
+    sentry_transaction_context_t *transaction_context);
+sentry_sampling_context_t *sentry_sampling_context_new_with_custom(
+    sentry_transaction_context_t *transaction_context,
+    void *custom_sampling_context);
+
+#endif // SENTRY_SAMPLING_CONTEXT_H_INCLUDED