server : support preserving reasoning_content in assistant message (#18994)

* support reasoning_content input

* report template caps to webui

* add docs

* rm commented code

common/chat-parser.cpp

@@ -1630,7 +1630,7 @@ common_chat_msg common_chat_parse(const std::string & input, bool is_partial, co
     }
     auto msg = builder.result();
     if (!is_partial) {
-        LOG_DBG("Parsed message: %s\n", common_chat_msgs_to_json_oaicompat<json>({msg}).at(0).dump().c_str());
+        LOG_DBG("Parsed message: %s\n", common_chat_msgs_to_json_oaicompat({msg}).at(0).dump().c_str());
     }
     return msg;
 }
@@ -1663,7 +1663,7 @@ common_chat_msg common_chat_peg_parse(const common_peg_arena & parser, const std
         mapper.from_ast(ctx.ast, result);
     }
     if (!is_partial) {
-        LOG_DBG("Parsed message: %s\n", common_chat_msgs_to_json_oaicompat<json>({msg}).at(0).dump().c_str());
+        LOG_DBG("Parsed message: %s\n", common_chat_msgs_to_json_oaicompat({msg}).at(0).dump().c_str());
     }
     return msg;
 }

common/chat.cpp

@@ -7,9 +7,6 @@
 #include "log.h"
 #include "regex-partial.h"
 
-// #include <minja/chat-template.hpp>
-// #include <minja/minja.hpp>
-
 #include "jinja/parser.h"
 #include "jinja/value.h"
 #include "jinja/runtime.h"
@@ -56,39 +53,73 @@ static bool has_content_or_tool_calls(const common_chat_msg & msg) {
     return !msg.content.empty() || !msg.tool_calls.empty();
 }
 
-template <>
+json common_chat_msg::to_json_oaicompat(bool concat_typed_text) const {
-json common_chat_msg::to_json_oaicompat() const
+    if (!content.empty() && !content_parts.empty()) {
-{
+        throw std::runtime_error("Cannot specify both content and content_parts");
-    json message {
-        {"role", "assistant"},
-    };
-    if (!reasoning_content.empty()) {
-        message["reasoning_content"] = reasoning_content;
     }
-    if (content.empty() && !tool_calls.empty()) {
+    json jmsg {
-        message["content"] = json();
+        {"role", role},
+    };
+    if (!content.empty()) {
+        jmsg["content"] = content;
+    } else if (!content_parts.empty()) {
+        if (concat_typed_text) {
+            std::string text;
+            for (const auto & part : content_parts) {
+                if (part.type != "text") {
+                    LOG_WRN("Ignoring content part type: %s\n", part.type.c_str());
+                    continue;
+                }
+                if (!text.empty()) {
+                    text += '\n';
+                }
+                text += part.text;
+            }
+            jmsg["content"] = text;
+        } else {
+            auto & parts = jmsg["content"] = json::array();
+            for (const auto & part : content_parts) {
+                parts.push_back({
+                    {"type", part.type},
+                    {"text", part.text},
+                });
+            }
+        }
     } else {
-        message["content"] = content;
+        jmsg["content"] = "";
+    }
+    if (!reasoning_content.empty()) {
+        jmsg["reasoning_content"] = reasoning_content;
+    }
+    if (!tool_name.empty()) {
+        jmsg["name"] = tool_name;
+    }
+    if (!tool_call_id.empty()) {
+        jmsg["tool_call_id"] = tool_call_id;
     }
     if (!tool_calls.empty()) {
-        auto arr = json::array();
+        jmsg["tool_calls"] = json::array();
-        for (const auto & tc : tool_calls) {
+        auto & jtool_calls = jmsg["tool_calls"];
-            arr.push_back({
+        for (const auto & tool_call : tool_calls) {
+            json tc {
                 {"type", "function"},
                 {"function", {
-                    {"name", tc.name},
+                    {"name", tool_call.name},
-                    {"arguments", tc.arguments},
+                    {"arguments", tool_call.arguments},
                 }},
-                {"id", tc.id},
+            };
-                // // Some templates generate and require an id (sometimes in a very specific format, e.g. Mistral Nemo).
+            if (!tool_call.id.empty()) {
-                // // We only generate a random id for the ones that don't generate one by themselves
+                tc["id"] = tool_call.id;
-                // // (they also won't get to see it as their template likely doesn't use it, so it's all for the client)
+            }
-                // {"id", tc.id.empty() ? gen_tool_call_id() : tc.id},
+            // Some templates generate and require an id (sometimes in a very specific format, e.g. Mistral Nemo).
-            });
+            // We only generate a random id for the ones that don't generate one by themselves
+            // (they also won't get to see it as their template likely doesn't use it, so it's all for the client)
+            // {"id", tc.id.empty() ? gen_tool_call_id() : tc.id},
+            jtool_calls.push_back(tc);
         }
-        message["tool_calls"] = arr;
     }
-    return message;
+
+    return jmsg;
 }
 
 std::vector<common_chat_msg_diff> common_chat_msg_diff::compute_diffs(const common_chat_msg & msg_prv, const common_chat_msg & msg_new) {
@@ -256,7 +287,6 @@ bool common_chat_templates_support_enable_thinking(const common_chat_templates *
     return rendered_no_thinking.prompt != rendered_with_thinking.prompt;
 }
 
-template <>
 std::vector<common_chat_msg> common_chat_msgs_parse_oaicompat(const json & messages) {
     std::vector<common_chat_msg> msgs;
 
@@ -350,80 +380,15 @@ std::vector<common_chat_msg> common_chat_msgs_parse_oaicompat(const json & messa
     return msgs;
 }
 
-template <>
 json common_chat_msgs_to_json_oaicompat(const std::vector<common_chat_msg> & msgs, bool concat_typed_text) {
     json messages = json::array();
     for (const auto & msg : msgs) {
-        if (!msg.content.empty() && !msg.content_parts.empty()) {
+        json jmsg = msg.to_json_oaicompat(concat_typed_text);
-            throw std::runtime_error("Cannot specify both content and content_parts");
-        }
-        json jmsg {
-            {"role", msg.role},
-        };
-        if (!msg.content.empty()) {
-            jmsg["content"] = msg.content;
-        } else if (!msg.content_parts.empty()) {
-            if (concat_typed_text) {
-                std::string text;
-                for (const auto & part : msg.content_parts) {
-                    if (part.type != "text") {
-                        LOG_WRN("Ignoring content part type: %s\n", part.type.c_str());
-                        continue;
-                    }
-                    if (!text.empty()) {
-                        text += '\n';
-                    }
-                    text += part.text;
-                }
-                jmsg["content"] = text;
-            } else {
-                auto & parts = jmsg["content"] = json::array();
-                for (const auto & part : msg.content_parts) {
-                    parts.push_back({
-                        {"type", part.type},
-                        {"text", part.text},
-                    });
-                }
-            }
-        } else {
-            jmsg["content"] = "";
-        }
-        if (!msg.reasoning_content.empty()) {
-            jmsg["reasoning_content"] = msg.reasoning_content;
-        }
-        if (!msg.tool_name.empty()) {
-            jmsg["name"] = msg.tool_name;
-        }
-        if (!msg.tool_call_id.empty()) {
-            jmsg["tool_call_id"] = msg.tool_call_id;
-        }
-        if (!msg.tool_calls.empty()) {
-            auto & tool_calls = jmsg["tool_calls"] = json::array();
-            for (const auto & tool_call : msg.tool_calls) {
-                json tc {
-                    {"type", "function"},
-                    {"function", {
-                        {"name", tool_call.name},
-                        {"arguments", tool_call.arguments},
-                    }},
-                };
-                if (!tool_call.id.empty()) {
-                    tc["id"] = tool_call.id;
-                }
-                tool_calls.push_back(tc);
-            }
-        }
         messages.push_back(jmsg);
     }
     return messages;
 }
 
-template <>
-std::vector<common_chat_msg> common_chat_msgs_parse_oaicompat(const std::string & messages) {
-    return common_chat_msgs_parse_oaicompat(json::parse(messages));
-}
-
-template <>
 std::vector<common_chat_tool> common_chat_tools_parse_oaicompat(const json & tools) {
     std::vector<common_chat_tool> result;
 
@@ -459,12 +424,6 @@ std::vector<common_chat_tool> common_chat_tools_parse_oaicompat(const json & too
     return result;
 }
 
-template <>
-std::vector<common_chat_tool> common_chat_tools_parse_oaicompat(const std::string & tools) {
-    return common_chat_tools_parse_oaicompat(json::parse(tools));
-}
-
-template <>
 json common_chat_tools_to_json_oaicompat(const std::vector<common_chat_tool> & tools) {
     if (tools.empty()) {
         return json();
@@ -484,7 +443,7 @@ json common_chat_tools_to_json_oaicompat(const std::vector<common_chat_tool> & t
     return result;
 }
 
-template <> json common_chat_msg_diff_to_json_oaicompat(const common_chat_msg_diff & diff) {
+json common_chat_msg_diff_to_json_oaicompat(const common_chat_msg_diff & diff) {
     json delta = json::object();
     if (!diff.reasoning_content_delta.empty()) {
         delta["reasoning_content"] = diff.reasoning_content_delta;
@@ -2867,13 +2826,13 @@ static common_chat_params common_chat_templates_apply_jinja(
     const struct common_chat_templates_inputs & inputs)
 {
     templates_params params;
-    params.tools = common_chat_tools_to_json_oaicompat<json>(inputs.tools);
+    params.tools = common_chat_tools_to_json_oaicompat(inputs.tools);
     const auto & tmpl = params.tools.is_array() && tmpls->template_tool_use
         ? *tmpls->template_tool_use
         : *tmpls->template_default;
     const auto & src = tmpl.source();
     const auto & caps = tmpl.original_caps();
-    params.messages = common_chat_msgs_to_json_oaicompat<json>(inputs.messages, /* concat_text= */ !tmpl.original_caps().requires_typed_content);
+    params.messages = common_chat_msgs_to_json_oaicompat(inputs.messages, /* concat_text= */ !tmpl.original_caps().requires_typed_content);
     params.add_generation_prompt = inputs.add_generation_prompt;
     params.tool_choice = inputs.tool_choice;
     params.reasoning_format = inputs.reasoning_format;
@@ -2943,6 +2902,10 @@ static common_chat_params common_chat_templates_apply_jinja(
         src.find("<arg_value>") != std::string::npos &&
         params.json_schema.is_null()) {
         workaround::func_args_not_string(params.messages);
+        if (!params.extra_context.contains("clear_thinking")) {
+            // by default, do not clear reasoning_content (added since GLM-4.7)
+            params.extra_context["clear_thinking"] = false;
+        }
         return common_chat_params_init_glm_4_5(tmpl, params);
     }
 
@@ -3174,3 +3137,9 @@ common_chat_params common_chat_templates_apply(
         ? common_chat_templates_apply_jinja(tmpls, inputs)
         : common_chat_templates_apply_legacy(tmpls, inputs);
 }
+
+std::map<std::string, bool> common_chat_templates_get_caps(const common_chat_templates * chat_templates) {
+    GGML_ASSERT(chat_templates != nullptr);
+    GGML_ASSERT(chat_templates->template_default != nullptr);
+    return chat_templates->template_default->caps.to_map();
+}

common/chat.h

@@ -10,6 +10,8 @@
 #include <vector>
 #include <map>
 
+#include <nlohmann/json_fwd.hpp>
+
 struct common_chat_templates;
 
 struct common_chat_tool_call {
@@ -26,6 +28,11 @@ struct common_chat_msg_content_part {
     std::string type;
     std::string text;
 
+    // TODO @ngxson : no known chat templates support reasoning_content in content parts yet
+    //                this can be useful for models with interleaved thinking (like Kimi-K2)
+    //                if you see any templates explicitly support this, please ping me
+    // std::string reasoning_content;
+
     bool operator==(const common_chat_msg_content_part & other) const {
         return type == other.type && text == other.text;
     }
@@ -40,7 +47,7 @@ struct common_chat_msg {
     std::string tool_name;
     std::string tool_call_id;
 
-    template <class T> T to_json_oaicompat() const;
+    nlohmann::ordered_json to_json_oaicompat(bool concat_typed_text = false) const;
 
     bool empty() const {
         return content.empty() && content_parts.empty() && tool_calls.empty() && reasoning_content.empty() && tool_name.empty() && tool_call_id.empty();
@@ -232,13 +239,13 @@ common_chat_tool_choice common_chat_tool_choice_parse_oaicompat(const std::strin
 bool common_chat_templates_support_enable_thinking(const common_chat_templates * chat_templates);
 
 // Parses a JSON array of messages in OpenAI's chat completion API format.
-// T can be std::string containing JSON or nlohmann::ordered_json
+std::vector<common_chat_msg> common_chat_msgs_parse_oaicompat(const nlohmann::ordered_json & messages);
-template <class T> std::vector<common_chat_msg> common_chat_msgs_parse_oaicompat(const T & messages);
+nlohmann::ordered_json common_chat_msgs_to_json_oaicompat(const std::vector<common_chat_msg> & msgs, bool concat_typed_text = false);
-template <class T> T common_chat_msgs_to_json_oaicompat(const std::vector<common_chat_msg> & msgs, bool concat_typed_text = false);
 
-// Parses a JSON array of tools in OpenAI's chat completion tool call API format.
+std::vector<common_chat_tool> common_chat_tools_parse_oaicompat(const nlohmann::ordered_json & tools);
-// T can be std::string containing JSON or nlohmann::ordered_json
+nlohmann::ordered_json common_chat_tools_to_json_oaicompat(const std::vector<common_chat_tool> & tools);
-template <class T> std::vector<common_chat_tool> common_chat_tools_parse_oaicompat(const T & tools);
-template <class T> T common_chat_tools_to_json_oaicompat(const std::vector<common_chat_tool> & tools);
 
-template <class T> T common_chat_msg_diff_to_json_oaicompat(const common_chat_msg_diff & diff);
+nlohmann::ordered_json common_chat_msg_diff_to_json_oaicompat(const common_chat_msg_diff & diff);
+
+// get template caps, useful for reporting to server /props endpoint
+std::map<std::string, bool> common_chat_templates_get_caps(const common_chat_templates * chat_templates);

common/jinja/caps.cpp

@@ -61,14 +61,23 @@ static void caps_print_stats(value & v, const std::string & path) {
                 ops.c_str());
 }
 
+std::map<std::string, bool> caps::to_map() const {
+    return {
+        {"requires_typed_content", requires_typed_content},
+        {"supports_tools", supports_tools},
+        {"supports_tool_calls", supports_tool_calls},
+        {"supports_parallel_tool_calls", supports_parallel_tool_calls},
+        {"supports_system_role", supports_system_role},
+        {"supports_preserve_reasoning", supports_preserve_reasoning},
+    };
+}
+
 std::string caps::to_string() const {
     std::ostringstream ss;
     ss << "Caps(\n";
-    ss << "  requires_typed_content=" << requires_typed_content << "\n";
+    for (const auto & [key, value] : to_map()) {
-    ss << "  supports_tools=" << supports_tools << "\n";
+        ss << "  " << key << "=" << (value ? "true" : "false") << "\n";
-    ss << "  supports_tool_calls=" << supports_tool_calls << "\n";
+    }
-    ss << "  supports_parallel_tool_calls=" << supports_parallel_tool_calls << "\n";
-    ss << "  supports_system_role=" << supports_system_role << "\n";
     ss << ")";
     return ss.str();
 }
@@ -229,6 +238,40 @@ caps caps_get(jinja::program & prog) {
         }
     );
 
+    // case: preserve reasoning content in chat history
+    caps_try_execute(
+        prog,
+        [&]() {
+            // messages
+            return json::array({
+                {
+                    {"role", "user"},
+                    {"content", "User message"}
+                },
+                {
+                    {"role", "assistant"},
+                    {"content", "Assistant message"},
+                    {"reasoning_content", "Reasoning content"}
+                },
+                {
+                    {"role", "user"},
+                    {"content", "User message"}
+                },
+            });
+        },
+        [&]() {
+            // tools
+            return json::array();
+        },
+        [&](bool, value & messages, value &) {
+            auto & content = messages->at(1)->at("reasoning_content");
+            caps_print_stats(content, "messages[1].reasoning_content");
+            if (content->stats.used) {
+                result.supports_preserve_reasoning = true;
+            }
+        }
+    );
+
     JJ_DEBUG("%s\n", result.to_string().c_str());
 
     return result;

common/jinja/caps.h

@@ -3,6 +3,7 @@
 #include "runtime.h"
 
 #include <string>
+#include <map>
 
 namespace jinja {
 
@@ -11,14 +12,17 @@ struct caps {
     bool supports_tool_calls = true;
     bool supports_system_role = true;
     bool supports_parallel_tool_calls = true;
+    bool supports_preserve_reasoning = false; // support assistant message with reasoning_content
 
     bool requires_typed_content = false; // default: use string content
 
+    // for reporting on server
+    std::map<std::string, bool> to_map() const;
+
     // for debugging
     std::string to_string() const;
 };
 
 caps caps_get(jinja::program & prog);
-void debug_print_caps(const caps & c);
 
 } // namespace jinja

tests/test-chat.cpp

@@ -462,9 +462,9 @@ static void test_parser_with_streaming(const common_chat_msg & expected, const s
     for (size_t i = 1; i <= raw_message.size(); ++i) {
         auto curr_msg = parse_msg(std::string(utf8_truncate_safe_view(std::string_view(raw_message).substr(0, i))));
         if (curr_msg == simple_assist_msg("")) continue;
-        LOG_INF("Streaming msg: %s\n", common_chat_msgs_to_json_oaicompat<json>({curr_msg}).dump().c_str());
+        LOG_INF("Streaming msg: %s\n", common_chat_msgs_to_json_oaicompat({curr_msg}).dump().c_str());
         for (auto diff: common_chat_msg_diff::compute_diffs(last_msg, curr_msg)) {
-            LOG_INF("Streaming diff: %s\n", common_chat_msg_diff_to_json_oaicompat<json>(diff).dump().c_str());
+            LOG_INF("Streaming diff: %s\n", common_chat_msg_diff_to_json_oaicompat(diff).dump().c_str());
             if (!diff.reasoning_content_delta.empty()) {
                 merged.reasoning_content += diff.reasoning_content_delta;
             }
@@ -480,7 +480,7 @@ static void test_parser_with_streaming(const common_chat_msg & expected, const s
                     merged.tool_calls.back().arguments += diff.tool_call_delta.arguments;
                 }
             }
-            LOG_INF("Streaming merged: %s\n", common_chat_msgs_to_json_oaicompat<json>({merged}).dump().c_str());
+            LOG_INF("Streaming merged: %s\n", common_chat_msgs_to_json_oaicompat({merged}).dump().c_str());
         }
         assert_msg_equals(curr_msg, merged, true);
         last_msg = curr_msg;
@@ -622,7 +622,7 @@ static void test_msgs_oaicompat_json_conversion() {
         message_assist_call_code_interpreter,
     };
     for (const auto & msg : msgs) {
-        auto oai_json = common_chat_msgs_to_json_oaicompat<json>({msg});
+        auto oai_json = common_chat_msgs_to_json_oaicompat({msg});
         auto msgs2 = common_chat_msgs_parse_oaicompat(oai_json);
         assert_equals((size_t) 1, msgs2.size());
         auto msg2 = msgs2[0];
@@ -646,7 +646,7 @@ static void test_msgs_oaicompat_json_conversion() {
             "  }\n"
             "]"
         ),
-        common_chat_msgs_to_json_oaicompat<json>({message_user_parts}).dump(2));
+        common_chat_msgs_to_json_oaicompat({message_user_parts}).dump(2));
 
     assert_equals(
         std::string(
@@ -666,7 +666,7 @@ static void test_msgs_oaicompat_json_conversion() {
             "  }\n"
             "]"
         ),
-        common_chat_msgs_to_json_oaicompat<json>({message_assist_call_python}).dump(2));
+        common_chat_msgs_to_json_oaicompat({message_assist_call_python}).dump(2));
 
     auto res = common_chat_msgs_parse_oaicompat(json::parse("[{\"role\": \"assistant\", \"tool_calls\": []}]"));
     assert_equals<size_t>(1, res.size());
@@ -693,7 +693,7 @@ static void test_tools_oaicompat_json_conversion() {
     };
 
     for (const auto & tool : tools) {
-        auto oai_json = common_chat_tools_to_json_oaicompat<json>({tool});
+        auto oai_json = common_chat_tools_to_json_oaicompat({tool});
         auto tools2 = common_chat_tools_parse_oaicompat(oai_json);
         assert_equals((size_t) 1, tools2.size());
         auto tool2 = tools2[0];
@@ -726,7 +726,7 @@ static void test_tools_oaicompat_json_conversion() {
             "  }\n"
             "]"
         ),
-        common_chat_tools_to_json_oaicompat<json>({special_function_tool}).dump(2));
+        common_chat_tools_to_json_oaicompat({special_function_tool}).dump(2));
 
     {
         auto tools_no_params = common_chat_tools_parse_oaicompat(json::parse(

tools/server/README.md

@@ -781,6 +781,7 @@ By default, it is read-only. To make POST request to change global properties, y
   "total_slots": 1,
   "model_path": "../models/Meta-Llama-3.1-8B-Instruct-Q4_K_M.gguf",
   "chat_template": "...",
+  "chat_template_caps": {},
   "modalities": {
     "vision": false
   },
@@ -793,6 +794,7 @@ By default, it is read-only. To make POST request to change global properties, y
 - `total_slots` - the total number of slots for process requests (defined by `--parallel` option)
 - `model_path` - the path to model file (same with `-m` argument)
 - `chat_template` - the model's original Jinja2 prompt template
+- `chat_template_caps` - capabilities of the chat template (see `common/jinja/caps.h` for more info)
 - `modalities` - the list of supported modalities
 - `is_sleeping` - sleeping status, see [Sleeping on idle](#sleeping-on-idle)
 
@@ -1267,6 +1269,12 @@ This provides information on the performance of the server. It also allows calcu
 
 The total number of tokens in context is equal to `prompt_n + cache_n + predicted_n`
 
+*Reasoning support*
+
+The server supports parsing and returning reasoning via the `reasoning_content` field, similar to Deepseek API.
+
+Reasoning input (preserve reasoning in history) is also supported by some specific templates. For more details, please refer to [PR#18994](https://github.com/ggml-org/llama.cpp/pull/18994).
+
 ### POST `/v1/responses`: OpenAI-compatible Responses API
 
 *Options:*

tools/server/server-context.cpp

@@ -2903,6 +2903,7 @@ server_context_meta server_context::get_meta() const {
         /* pooling_type           */ llama_pooling_type(impl->ctx),
 
         /* chat_params            */ impl->chat_params,
+        /* chat_template_caps     */ common_chat_templates_get_caps(impl->chat_params.tmpls.get()),
 
         /* bos_token_str          */ bos_token_str,
         /* eos_token_str          */ eos_token_str,
@@ -3410,6 +3411,7 @@ void server_routes::init_routes() {
             { "webui",                       params.webui },
             { "webui_settings",              meta->json_webui_settings },
             { "chat_template",               tmpl_default },
+            { "chat_template_caps",          meta->chat_template_caps },
             { "bos_token",                   meta->bos_token_str },
             { "eos_token",                   meta->eos_token_str },
             { "build_info",                  meta->build_info },

tools/server/server-context.h

@@ -22,6 +22,7 @@ struct server_context_meta {
 
     // chat params
     server_chat_params & chat_params;
+    std::map<std::string, bool> chat_template_caps;
 
     // tokens
     std::string bos_token_str;

tools/server/server-task.cpp

@@ -700,7 +700,7 @@ json server_task_result_cmpl_final::to_json_oaicompat_chat() {
     json choice {
         {"finish_reason", finish_reason},
         {"index", index},
-        {"message", msg.to_json_oaicompat<json>()},
+        {"message", msg.to_json_oaicompat()},
     };
 
     if (!stream && probs_output.size() > 0) {
@@ -750,7 +750,7 @@ json server_task_result_cmpl_final::to_json_oaicompat_chat_stream() {
                 json {
                     {"finish_reason", nullptr},
                     {"index", 0},
-                    {"delta", common_chat_msg_diff_to_json_oaicompat<json>(diff)},
+                    {"delta", common_chat_msg_diff_to_json_oaicompat(diff)},
                 },
             })},
             {"created", t},
@@ -1383,7 +1383,7 @@ json server_task_result_cmpl_partial::to_json_oaicompat_chat() {
     }
 
     for (const auto & diff : oaicompat_msg_diffs) {
-        add_delta(common_chat_msg_diff_to_json_oaicompat<json>(diff));
+        add_delta(common_chat_msg_diff_to_json_oaicompat(diff));
     }
 
     if (!deltas.empty()) {