diff --git a/net/http/client.h b/net/http/client.h
index d2affab4..7a767786 100644
--- a/net/http/client.h
+++ b/net/http/client.h
@@ -48,9 +48,9 @@ class Client : public Object {
         Response resp;                            // response
         int status_code = -1;                     // status code in response
         bool enable_proxy;
-        IStream* body_stream = nullptr;           // use body_stream as body
-        using BodyWriter = Callback<Request*>;    // or call body_writer if body_stream
-        BodyWriter body_writer = {};              // is not set
+        IStream* body_stream = nullptr;                 // use body_stream as body
+        using BodyWriter = Delegate<ssize_t, Request*>; // or call body_writer if body_stream
+        BodyWriter body_writer = {};                    // is not set
 
         static Operation* create(Client* c, Verb v, std::string_view url,
                             uint16_t buf_size = 64 * 1024 - 1) {
diff --git a/net/http/test/client_function_test.cpp b/net/http/test/client_function_test.cpp
index 2604fb0e..29151c0d 100644
--- a/net/http/test/client_function_test.cpp
+++ b/net/http/test/client_function_test.cpp
@@ -186,7 +186,7 @@ TEST(http_client, post) {
     auto op2 = client->new_operation(Verb::POST, target);
     DEFER(delete op2);
     op2->req.headers.content_length(st.st_size);
-    auto writer = [&](Request *req)-> int {
+    auto writer = [&](Request *req)-> ssize_t {
         file->lseek(0, SEEK_SET);
         return req->write_stream(file, st.st_size);
     };
diff --git a/net/http/test/server_function_test.cpp b/net/http/test/server_function_test.cpp
index a42d5792..e50d547d 100644
--- a/net/http/test/server_function_test.cpp
+++ b/net/http/test/server_function_test.cpp
@@ -109,7 +109,7 @@ TEST(http_server, post) {
     DEFER(delete op);
     op->req.headers.content_length(10);
     std::string body = "1234567890";
-    auto writer = [&](Request *req)-> int {
+    auto writer = [&](Request *req)-> ssize_t {
         return req->write(body.data(), body.size());
     };
     op->body_writer = writer;
@@ -343,7 +343,7 @@ TEST(http_server, proxy_handler_post) {
     DEFER(delete op);
     std::string body = "1234567890";
     op->req.headers.content_length(10);
-    auto writer = [&](Request *req)-> int {
+    auto writer = [&](Request *req)-> ssize_t {
         return req->write(body.data(), body.size());
     };
     op->body_writer = writer;
@@ -405,7 +405,7 @@ TEST(http_server, proxy_handler_post_forward) {
     DEFER(delete op);
     std::string body = "1234567890";
     op->req.headers.content_length(10);
-    auto writer = [&](Request *req)-> int {
+    auto writer = [&](Request *req)-> ssize_t {
         return req->write(body.data(), body.size());
     };
     op->body_writer = writer;