fix(http): check curl_slist_append (silent header loss + leak on OOM)

README.md

@@ -121,7 +121,7 @@ make coverage     # Code coverage report (requires lcov)
 include(FetchContent)
 FetchContent_Declare(ncei-cpp
     GIT_REPOSITORY https://github.com/Reddimus/ncei-cpp.git
-    GIT_TAG v0.3.0
+    GIT_TAG v0.3.1
 )
 FetchContent_MakeAvailable(ncei-cpp)
 target_link_libraries(myapp PRIVATE ncei)

src/core/rate_limit.cpp

@@ -1,5 +1,7 @@
 #include "ncei/rate_limit.hpp"
 
+#include <limits>
+
 namespace ncei {
 
 RateLimiter::RateLimiter(Config config)
@@ -81,7 +83,11 @@ std::uint16_t RateLimiter::available_tokens() const noexcept {
 std::int32_t RateLimiter::daily_requests_remaining() const noexcept {
 	std::lock_guard<std::mutex> lock(mutex_);
 	if (config_.daily_limit <= 0) {
-		return 0;
+		// daily_limit <= 0 means "no daily cap" (see rate_limit.hpp). Signal
+		// unlimited headroom — NOT 0, which callers (CDOClient::do_get) treat
+		// as quota-exhausted and would reject every request when the cap is
+		// intentionally disabled.
+		return std::numeric_limits<std::int32_t>::max();
 	}
 	return config_.daily_limit - daily_requests_used_;
 }

src/http/client.cpp

@@ -89,13 +89,27 @@ Result<HttpResponse> HttpClient::get(std::string_view path) const {
 	}
 
 	// Set Accept header and extra headers
+	// curl_slist_append returns nullptr on allocation failure WITHOUT freeing
+	// the existing list — assigning its result straight back to `headers` would
+	// then leak the prior nodes and silently drop headers. Capture, check, free
+	// + error on failure.
 	struct curl_slist* headers = nullptr;
 	std::string accept_header = "Accept: " + impl_->config.accept;
-	headers = curl_slist_append(headers, accept_header.c_str());
+	struct curl_slist* appended = curl_slist_append(headers, accept_header.c_str());
+	if (appended == nullptr) {
+		curl_slist_free_all(headers);
+		return std::unexpected(Error::network("failed to build request headers"));
+	}
+	headers = appended;
 
 	for (const std::pair<std::string, std::string>& hdr : impl_->config.extra_headers) {
 		std::string header_line = hdr.first + ": " + hdr.second;
-		headers = curl_slist_append(headers, header_line.c_str());
+		appended = curl_slist_append(headers, header_line.c_str());
+		if (appended == nullptr) {
+			curl_slist_free_all(headers);
+			return std::unexpected(Error::network("failed to build request headers"));
+		}
+		headers = appended;
 	}
 
 	curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);

tests/test_rate_limit.cpp

@@ -1,6 +1,8 @@
 #include "ncei/rate_limit.hpp"
 
+#include <cstdint>
 #include <gtest/gtest.h>
+#include <limits>
 
 namespace ncei {
 namespace {
@@ -127,6 +129,12 @@ TEST(RateLimiterTest, NoDailyLimitWhenZero) {
 	EXPECT_TRUE(limiter.try_acquire());
 	EXPECT_TRUE(limiter.try_acquire());
 	EXPECT_TRUE(limiter.try_acquire());
+
+	// Regression: a disabled daily limit must report "unlimited" headroom, NOT
+	// 0. CDOClient::do_get() rejects with quota_exceeded when remaining <= 0, so
+	// returning 0 here would block every request whenever the cap is disabled.
+	EXPECT_GT(limiter.daily_requests_remaining(), 0);
+	EXPECT_EQ(limiter.daily_requests_remaining(), std::numeric_limits<std::int32_t>::max());
 }
 
 TEST(RateLimiterTest, DailyCounterResetsOnReset) {