[core] more robust max-age parsing

src/mbgl/storage/http_request_base.cpp

@@ -1,18 +1,18 @@
 #include <mbgl/storage/http_request_base.hpp>
 
+#include <mbgl/util/http_header.hpp>
 #include <mbgl/util/chrono.hpp>
 
 namespace mbgl {
 
 int64_t HTTPRequestBase::parseCacheControl(const char *value) {
     if (value) {
-        unsigned long long seconds = 0;
-        // TODO: cache-control may contain other information as well:
-        // http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9
-        if (std::sscanf(value, "max-age=%llu", &seconds) == 1) {
+        const auto cacheControl = http::CacheControl::parse(value);
+
+        if (cacheControl.maxAge) {
             return std::chrono::duration_cast<std::chrono::seconds>(
                        std::chrono::system_clock::now().time_since_epoch()).count() +
-                   seconds;
+                   *cacheControl.maxAge;
         }
     }