fix: Store fixed-size strings inline in dd_core_config_t

include-c/datadog/core.h

@@ -16,7 +16,15 @@
 
 // These values establish the size of string buffers in the C API; they do not imply
 // that the Datadog platform imposes any such limits
-#define DATADOG_MAX_SERVICE_NAME_LEN 127
+#define DATADOG_MAX_APPLICATION_STORAGE_PATH_LEN 511
+#define DATADOG_MAX_CLIENT_TOKEN_LEN 63
+#define DATADOG_MAX_SERVICE_LEN 127
+#define DATADOG_MAX_ENV_LEN 127
+#define DATADOG_MAX_VERSION_LEN 127
+#define DATADOG_MAX_VARIANT_LEN 127
+#define DATADOG_INTERNAL_MAX_CUSTOM_ENDPOINT_URL_LEN 255
+#define DATADOG_INTERNAL_MAX_SOURCE_LEN 15
+#define DATADOG_INTERNAL_MAX_SDK_VERSION_LEN 31
 
 #ifdef __cplusplus
 extern "C" {
@@ -130,9 +138,9 @@ typedef enum {
  */
 typedef struct dd_internal_options {
   bool flush_http_requests_on_stop;
-  const char* custom_endpoint_url;
-  const char* source;
-  const char* sdk_version;
+  char custom_endpoint_url[DATADOG_INTERNAL_MAX_CUSTOM_ENDPOINT_URL_LEN + 1];
+  char source[DATADOG_INTERNAL_MAX_SOURCE_LEN + 1];
+  char sdk_version[DATADOG_INTERNAL_MAX_SDK_VERSION_LEN + 1];
 } dd_internal_options_t;
 
 /**
@@ -145,13 +153,13 @@ typedef struct dd_core_config {
   void* diagnostic_handler_userdata;
   dd_diagnostic_level_t diagnostic_threshold;
   dd_tracking_consent_t tracking_consent;
-  char application_storage_path[512];
+  char application_storage_path[DATADOG_MAX_APPLICATION_STORAGE_PATH_LEN + 1];
   dd_site_t site;
-  const char* client_token;
-  const char* service;
-  const char* env;
-  const char* application_version;
-  const char* variant;
+  char client_token[DATADOG_MAX_CLIENT_TOKEN_LEN + 1];
+  char service[DATADOG_MAX_SERVICE_LEN + 1];
+  char env[DATADOG_MAX_ENV_LEN + 1];
+  char application_version[DATADOG_MAX_VERSION_LEN + 1];
+  char variant[DATADOG_MAX_VARIANT_LEN + 1];
   dd_batch_size_t batch_size;
   dd_upload_frequency_t upload_frequency;
   dd_batch_processing_level_t batch_processing_level;

include-c/datadog/logging.h

@@ -43,7 +43,7 @@ typedef enum {
 typedef struct dd_logger_config {
   uint32_t version;
   float remote_sample_rate;
-  char service[DATADOG_MAX_SERVICE_NAME_LEN + 1];
+  char service[DATADOG_MAX_SERVICE_LEN + 1];
   char name[DATADOG_MAX_LOGGER_NAME_LEN + 1];
   dd_log_level_t remote_log_threshold;
   size_t initial_attribute_capacity;
@@ -69,8 +69,8 @@ DATADOG_API void dd_logger_config_set_remote_sample_rate(
  * logger will use the service name configured globally via dd_core_config_t.
  *
  * Config stores a copy of provided string value. If the given string value exceeds
- * DATADOG_MAX_SERVICE_NAME_LEN, it will be truncated to that length. Both NULL and ""
- * will be interepreted as no value, causing the logger to use the default service name.
+ * DATADOG_MAX_SERVICE_LEN, it will be truncated to that length. Both NULL and "" will
+ * be interepreted as no value, causing the logger to use the default service name.
  */
 DATADOG_API void dd_logger_config_set_service(
     dd_logger_config_t* config, const char* value

src/datadog/c/config_string.hpp

@@ -0,0 +1,72 @@
+// Unless explicitly stated otherwise all files in this repository are licensed
+// under the Apache License Version 2.0.
+//
+// This product includes software developed at Datadog (https://www.datadoghq.com/).
+// Copyright 2025-Present Datadog, Inc.
+
+#pragma once
+
+#include <cstddef>
+#include <cstdio>
+#include <cstring>
+
+#include "datadog/impl/core/util/diagnostics.hpp"
+
+// Expands a macro constant to a string literal, e.g. DATADOG_CSTR(63) -> "63".
+// Used to embed DATADOG_MAX_* limit values in static diagnostic message strings
+// without any runtime formatting.
+#define DATADOG_CSTR_(x) #x
+#define DATADOG_CSTR(x) DATADOG_CSTR_(x)
+
+/**
+ * Copies `src` into the fixed-size buffer `dest[0..dest_size)`, truncating if
+ * the source string is too long. If truncation occurs, emits `truncation_msg`
+ * at warning level via `logger`. Both `src` and `truncation_msg` may be null:
+ * a null or empty `src` writes an empty string; a null `truncation_msg` skips
+ * the diagnostic (intended for callers with no diagnostic handler available).
+ */
+static inline void assign_string_truncate(
+    char* dest,
+    size_t dest_size,
+    const char* src,
+    const datadog::impl::DiagnosticLogger& logger,
+    const char* truncation_msg
+) {
+  if (!src || src[0] == '\0') {
+    dest[0] = '\0';
+    return;
+  }
+  // NOLINTNEXTLINE(cppcoreguidelines-pro-type-vararg)
+  int written = std::snprintf(dest, dest_size, "%s", src);
+  if (truncation_msg && written >= 0 && static_cast<size_t>(written) >= dest_size) {
+    logger.Warning(truncation_msg);
+  }
+}
+
+/**
+ * Copies `src` into the fixed-size buffer `dest[0..dest_size)`, refusing if
+ * the source string would overflow the buffer. A null or empty `src` writes an
+ * empty string. If the string is too long, emits `overflow_msg` at error level
+ * via `logger` and leaves `dest` unchanged; pass a null `overflow_msg` to
+ * suppress the diagnostic.
+ */
+static inline void assign_string_strict(
+    char* dest,
+    size_t dest_size,
+    const char* src,
+    const datadog::impl::DiagnosticLogger& logger,
+    const char* overflow_msg
+) {
+  if (!src || src[0] == '\0') {
+    dest[0] = '\0';
+    return;
+  }
+  if (!std::memchr(src, '\0', dest_size)) {
+    if (overflow_msg) {
+      logger.Error(overflow_msg);
+    }
+    return;
+  }
+  // NOLINTNEXTLINE(cppcoreguidelines-pro-type-vararg)
+  std::snprintf(dest, dest_size, "%s", src);
+}