feat(options): read sample rates from env vars (#1540)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: jpnurmi

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+**Features**:
+
+- Support `SENTRY_SAMPLE_RATE` and `SENTRY_TRACES_SAMPLE_RATE` environment variables. ([#1540](https://github.com/getsentry/sentry-native/pull/1540))
+
 **Fixes**:
 
 - Fix use-after-free on allocation failure when merging scope tags, extra, and contexts into a captured event. ([#1539](https://github.com/getsentry/sentry-native/pull/1539))

src/sentry_options.c

@@ -8,6 +8,7 @@
 #include "sentry_string.h"
 #include "sentry_sync.h"
 #include "sentry_transport.h"
+#include "sentry_utils.h"
 #include <stdlib.h>
 
 sentry_options_t *
@@ -69,10 +70,12 @@ sentry_options_new(void)
 #endif
     opts->backend = sentry__backend_new();
     opts->transport = sentry__transport_new_default();
-    opts->sample_rate = 1.0;
     opts->refcount = 1;
     opts->shutdown_timeout = SENTRY_DEFAULT_SHUTDOWN_TIMEOUT;
-    opts->traces_sample_rate = 0.0;
+    sentry_options_set_sample_rate(
+        opts, sentry__getenv_double("SENTRY_SAMPLE_RATE", 1.0));
+    sentry_options_set_traces_sample_rate(
+        opts, sentry__getenv_double("SENTRY_TRACES_SAMPLE_RATE", 0.0));
     opts->max_spans = SENTRY_SPANS_MAX;
     opts->handler_strategy = SENTRY_HANDLER_STRATEGY_DEFAULT;
 

src/sentry_utils.c

@@ -11,6 +11,7 @@
 #include "sentry_random.h"
 
 #include <locale.h>
+#include <math.h>
 #include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -563,6 +564,24 @@ sentry__strtod_c(const char *ptr, char **endptr)
 #endif
 }
 
+double
+sentry__getenv_double(const char *name, double fallback)
+{
+    const char *str = getenv(name);
+    if (!str) {
+        return fallback;
+    }
+    char *end = NULL;
+    double val = sentry__strtod_c(str, &end);
+    if (end == str || !isfinite(val)) {
+        return fallback;
+    }
+    if (end[strspn(end, " \t\r\n")] != '\0') {
+        return fallback;
+    }
+    return val;
+}
+
 int
 sentry__snprintf_c(char *buf, size_t buf_size, const char *fmt, ...)
 {

src/sentry_utils.h

@@ -215,6 +215,13 @@ uint64_t sentry__iso8601_to_usec(const char *iso);
  */
 double sentry__strtod_c(const char *ptr, char **endptr);
 
+/**
+ * Reads a double from the environment variable `name`.
+ * Returns `fallback` if the variable is unset, empty, or not a finite number.
+ * Leading and trailing whitespace is tolerated.
+ */
+double sentry__getenv_double(const char *name, double fallback);
+
 /**
  * Locale independent (or rather, using "C" locale) `snprintf`.
  */

tests/unit/test_utils.c

@@ -2,11 +2,17 @@
 #include "sentry_testsupport.h"
 #include "sentry_utils.h"
 #include "sentry_value.h"
+#include <stdlib.h>
 
 #ifdef SENTRY_PLATFORM_UNIX
 #    include "sentry_unix_pageallocator.h"
 #endif
 
+#ifdef SENTRY_PLATFORM_WINDOWS
+#    define setenv(k, v, o) _putenv_s(k, v)
+#    define unsetenv(k) _putenv_s(k, "")
+#endif
+
 SENTRY_TEST(iso_time)
 {
     uint64_t usec;
@@ -421,3 +427,36 @@ SENTRY_TEST(dsn_auth_header_invalid_dsn)
     sentry_free(auth_header);
     sentry__dsn_decref(dsn);
 }
+
+SENTRY_TEST(getenv_double)
+{
+    setenv("SENTRY_TEST_DOUBLE", "", 1);
+    TEST_CHECK(sentry__getenv_double("SENTRY_TEST_DOUBLE", 42.0) == 42.0);
+
+    setenv("SENTRY_TEST_DOUBLE", "0.5", 1);
+    TEST_CHECK(sentry__getenv_double("SENTRY_TEST_DOUBLE", 99.0) == 0.5);
+
+    setenv("SENTRY_TEST_DOUBLE", "-3.14", 1);
+    TEST_CHECK(sentry__getenv_double("SENTRY_TEST_DOUBLE", 99.0) == -3.14);
+
+    setenv("SENTRY_TEST_DOUBLE", "0", 1);
+    TEST_CHECK(sentry__getenv_double("SENTRY_TEST_DOUBLE", 99.0) == 0.0);
+
+    setenv("SENTRY_TEST_DOUBLE", " 1.0 \t", 1);
+    TEST_CHECK(sentry__getenv_double("SENTRY_TEST_DOUBLE", 99.0) == 1.0);
+
+    setenv("SENTRY_TEST_DOUBLE", "not_a_number", 1);
+    TEST_CHECK(sentry__getenv_double("SENTRY_TEST_DOUBLE", 42.0) == 42.0);
+
+    setenv("SENTRY_TEST_DOUBLE", "NaN", 1);
+    TEST_CHECK(sentry__getenv_double("SENTRY_TEST_DOUBLE", 42.0) == 42.0);
+
+    setenv("SENTRY_TEST_DOUBLE", "inf", 1);
+    TEST_CHECK(sentry__getenv_double("SENTRY_TEST_DOUBLE", 42.0) == 42.0);
+
+    setenv("SENTRY_TEST_DOUBLE", "-inf", 1);
+    TEST_CHECK(sentry__getenv_double("SENTRY_TEST_DOUBLE", 42.0) == 42.0);
+
+    unsetenv("SENTRY_TEST_DOUBLE");
+    TEST_CHECK(sentry__getenv_double("SENTRY_TEST_DOUBLE", 42.0) == 42.0);
+}

tests/unit/tests.inc

@@ -103,6 +103,7 @@ XX(feedback_with_null_hint)
 XX(feedback_without_hint)
 XX(formatted_log_messages)
 XX(fuzz_json)
+XX(getenv_double)
 XX(init_failure)
 XX(internal_uuid_api)
 XX(invalid_dsn)