fetch: make HTTP/2 multiplexing opt-in via http2_multiplex flag

HTTP/2 multiplexing (CURLPIPE_MULTIPLEX + HTTP_VERSION_2TLS +
PIPEWAIT) caused a 10-15% regression on LRCP files with CloudFerro.
Move it behind grk_stream_params::http2_multiplex (default false)
so callers can enable it when beneficial.

Author: Grok Compression

src/lib/core/grok.h

@@ -628,6 +628,9 @@ typedef struct _grk_stream_params
   /* 13 Fetch concurrency (0 = use default of 30) */
   uint32_t fetch_batch_size; /* max concurrent HTTP range requests */
 
+  /* 14 HTTP/2 multiplexing (0 = disabled, 1 = enabled) */
+  bool http2_multiplex;
+
 } grk_stream_params;
 
 /**

src/lib/core/stream/StreamGenerator.cpp

@@ -161,6 +161,7 @@ IStream* StreamGenerator::createCurlFetchStream(void)
   auth.max_retry_ = streamParams_.max_retry;
   auth.retry_delay_ = streamParams_.retry_delay;
   auth.fetch_batch_size_ = streamParams_.fetch_batch_size;
+  auth.http2_multiplex_ = streamParams_.http2_multiplex;
   grklog.debug("StreamGenerator: s3_allow_insecure: streamParams=%d, auth=%d",
                (int)streamParams_.s3_allow_insecure, (int)auth.s3_allow_insecure_);
   std::string_view file{streamParams_.file};

src/lib/core/stream/fetchers/CurlFetcher.cpp

@@ -76,7 +76,6 @@ CurlFetcher::CurlFetcher(void) : tileWriteCallback_(tileWriteCallback)
   if(!multi_handle_)
     throw std::runtime_error("Failed to initialize CURL multi handle");
   curl_multi_setopt(multi_handle_, CURLMOPT_MAX_TOTAL_CONNECTIONS, 100L);
-  curl_multi_setopt(multi_handle_, CURLMOPT_PIPELINING, CURLPIPE_MULTIPLEX);
   fetchThread_ = std::thread(&CurlFetcher::fetchWorker, this);
 }
 
@@ -120,6 +119,8 @@ void CurlFetcher::init(const std::string& path, const FetchAuth& auth)
     retryDelayMs_ = auth_.retry_delay_ * 1000;
   if(auth_.fetch_batch_size_ > 0)
     batchSize_ = auth_.fetch_batch_size_;
+  if(auth_.http2_multiplex_)
+    curl_multi_setopt(multi_handle_, CURLMOPT_PIPELINING, CURLPIPE_MULTIPLEX);
   parse(path);
   fetch_total_size();
 }
@@ -569,8 +570,11 @@ CURL* CurlFetcher::configureHandle(uint64_t offset, uint64_t end, FetchResult& r
   curl_easy_setopt(curl, CURLOPT_URL, url_.c_str());
   curl_initiate_retry(curl);
   curl_easy_setopt(curl, CURLOPT_VERBOSE, 0L);
-  curl_easy_setopt(curl, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2TLS);
-  curl_easy_setopt(curl, CURLOPT_PIPEWAIT, 1L);
+  if(auth_.http2_multiplex_)
+  {
+    curl_easy_setopt(curl, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_2TLS);
+    curl_easy_setopt(curl, CURLOPT_PIPEWAIT, 1L);
+  }
   curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, callback);
   curl_easy_setopt(curl, CURLOPT_WRITEDATA, &result);
   curl_easy_setopt(curl, CURLOPT_PRIVATE, &result);

src/lib/core/stream/fetchers/FetchCommon.h

@@ -82,6 +82,9 @@ struct FetchAuth
   // Fetch concurrency (0 = use default of 30)
   uint32_t fetch_batch_size_ = 0;
 
+  // HTTP/2 multiplexing (disabled by default)
+  bool http2_multiplex_ = false;
+
   FetchAuth() = default;
   FetchAuth(const std::string& u, const std::string& p, const std::string& t,
             const std::vector<std::string>& h = {}, const std::string& r = "",