server : enable gzip compression (zlib)

CMakeLists.txt

@@ -142,6 +142,7 @@ option(LLAMA_TESTS_INSTALL "llama: install tests" ON)
 
 # 3rd party libs
 option(LLAMA_OPENSSL    "llama: use openssl to support HTTPS" ON)
+option(LLAMA_ZLIB       "llama: use zlib to support HTTP gzip compression" ON)
 option(LLAMA_SUBPROCESS "llama-common: use subprocess, required by server tools and server router mode" ${LLAMA_SUBPROCESS_DEFAULT})
 option(LLAMA_LLGUIDANCE "llama-common: include LLGuidance library for structured output in common utils" OFF)
 

tools/server/server-http.cpp

@@ -143,6 +143,11 @@ bool server_http_context::init(const common_params & params) {
     });
 
     srv->set_error_handler([](const httplib::Request &, httplib::Response & res) {
+        // a provider-backed response (e.g. proxied from a child server) already
+        // carries its error body; set_content() on top would conflict with it
+        if (res.content_provider_) {
+            return;
+        }
         if (res.status == 404) {
             res.set_content(
                 safe_json_to_str(json {

tools/server/server-models.cpp

@@ -2483,6 +2483,17 @@ server_http_proxy::server_http_proxy(
                 msg.content_type = value;
                 continue;
             }
+            if (lowered == "content-encoding") {
+                // strip codings the httplib client already decoded; unknown
+                // codings pass through undecoded and keep the header
+                bool decoded = false;
+#ifdef CPPHTTPLIB_ZLIB_SUPPORT
+                decoded |= to_lower_copy(string_strip(value)) == "gzip";
+#endif
+                if (decoded) {
+                    continue;
+                }
+            }
             msg.headers[key] = value;
         }
         return msg;
@@ -2525,12 +2536,25 @@ server_http_proxy::server_http_proxy(
     {
         req.method = method;
         req.path = path;
+        // explicit identity: with the header absent, the httplib client injects
+        // its own default and transparently decompresses the response
+        req.set_header("Accept-Encoding", "identity");
         for (const auto & [key, value] : headers) {
             const auto lowered = to_lower_copy(key);
             if (lowered == "accept-encoding") {
-                // disable Accept-Encoding to avoid compressed responses
                 continue;
             }
+            if (lowered == "content-encoding") {
+                // the httplib server already decoded the incoming body; forwarding
+                // the header with the plain body would make the child decode it again
+                bool decoded = false;
+#ifdef CPPHTTPLIB_ZLIB_SUPPORT
+                decoded |= to_lower_copy(string_strip(value)) == "gzip";
+#endif
+                if (decoded) {
+                    continue;
+                }
+            }
             if (lowered == "transfer-encoding") {
                 // the body is already decoded
                 continue;

vendor/cpp-httplib/CMakeLists.txt

@@ -37,6 +37,18 @@ target_compile_definitions(${TARGET} PRIVATE
     CPPHTTPLIB_TCP_NODELAY=1
 )
 
+if (LLAMA_ZLIB)
+    find_package(ZLIB)
+    if (ZLIB_FOUND)
+        message(STATUS "ZLIB found: ${ZLIB_VERSION_STRING}")
+        # PUBLIC: the define changes httplib.h declarations, so all consumers must agree
+        target_compile_definitions(${TARGET} PUBLIC CPPHTTPLIB_ZLIB_SUPPORT)
+        target_link_libraries(${TARGET} PUBLIC ZLIB::ZLIB)
+    else()
+        message(WARNING "ZLIB not found, HTTP gzip compression disabled")
+    endif()
+endif()
+
 set(OPENSSL_NO_ASM ON CACHE BOOL "Disable OpenSSL ASM code when building BoringSSL or LibreSSL")
 
 if (LLAMA_BUILD_BORINGSSL)