server: add prompt processing progress streaming for /completion endpoint

- Add server_task_result_cmpl_progress struct for streaming progress updates
- Implement send_progress_response() function for real-time progress reporting
- Send progress info during prompt processing phase before token generation
- Support all compatibility modes (non-OAI, OAI completion, OAI chat)
- Include detailed progress data: n_past, n_prompt_tokens, n_prompt_tokens_processed, progress percentage
- Only send progress updates in streaming mode (stream: true)
- Maintains backward compatibility with existing clients

Closes #14685

Author: baonudesifeizhai

tools/server/server.cpp

@@ -1034,6 +1034,112 @@ struct server_task_result_cmpl_partial : server_task_result {
     }
 };
 
+struct server_task_result_cmpl_progress : server_task_result {
+    int index = 0;
+
+    int32_t n_past;
+    int32_t n_prompt_tokens;
+    int32_t n_prompt_tokens_processed;
+    float progress;
+
+    // OAI-compat fields
+    bool verbose = false;
+    oaicompat_type oaicompat = OAICOMPAT_TYPE_NONE;
+    std::string oaicompat_model;
+    std::string oaicompat_cmpl_id;
+
+    virtual int get_index() override {
+        return index;
+    }
+
+    virtual bool is_stop() override {
+        return false; // progress responses are not considered stop
+    }
+
+    virtual json to_json() override {
+        switch (oaicompat) {
+            case OAICOMPAT_TYPE_NONE:
+                return to_json_non_oaicompat();
+            case OAICOMPAT_TYPE_COMPLETION:
+                return to_json_oaicompat();
+            case OAICOMPAT_TYPE_CHAT:
+                return to_json_oaicompat_chat();
+            default:
+                GGML_ASSERT(false && "Invalid oaicompat_type");
+        }
+    }
+
+    json to_json_non_oaicompat() {
+        return json {
+            {"index", index},
+            {"stop", false},
+            {"id_slot", id_slot},
+            {"prompt_processing", json {
+                {"n_past", n_past},
+                {"n_prompt_tokens", n_prompt_tokens},
+                {"n_prompt_tokens_processed", n_prompt_tokens_processed},
+                {"progress", progress},
+            }},
+        };
+    }
+
+    json to_json_oaicompat() {
+        std::time_t t = std::time(0);
+        json res = json {
+            {"choices", json::array({
+                json{
+                    {"text", ""},
+                    {"index", index},
+                    {"logprobs", nullptr},
+                    {"finish_reason", nullptr},
+                }
+            })},
+            {"created", t},
+            {"model", oaicompat_model},
+            {"system_fingerprint", build_info},
+            {"object", "text_completion"},
+            {"id", oaicompat_cmpl_id},
+            {"prompt_processing", json {
+                {"n_past", n_past},
+                {"n_prompt_tokens", n_prompt_tokens},
+                {"n_prompt_tokens_processed", n_prompt_tokens_processed},
+                {"progress", progress},
+            }},
+        };
+
+        // extra fields for debugging purposes
+        if (verbose) {
+            res["__verbose"] = to_json_non_oaicompat();
+        }
+
+        return res;
+    }
+
+    json to_json_oaicompat_chat() {
+        std::time_t t = std::time(0);
+        return json {
+            {"choices", json::array({
+                json {
+                    {"finish_reason", nullptr},
+                    {"index", 0},
+                    {"delta", json::object()},
+                },
+            })},
+            {"created", t},
+            {"id", oaicompat_cmpl_id},
+            {"model", oaicompat_model},
+            {"system_fingerprint", build_info},
+            {"object", "chat.completion.chunk"},
+            {"prompt_processing", json {
+                {"n_past", n_past},
+                {"n_prompt_tokens", n_prompt_tokens},
+                {"n_prompt_tokens_processed", n_prompt_tokens_processed},
+                {"progress", progress},
+            }},
+        };
+    }
+};
+
 struct server_task_result_embd : server_task_result {
     int index = 0;
     std::vector<std::vector<float>> embedding;
@@ -2515,6 +2621,31 @@ struct server_context {
         queue_results.send(std::move(res));
     }
 
+    void send_progress_response(server_slot & slot) {
+        // Only send progress updates for streaming requests
+        if (!slot.params.stream) {
+            return;
+        }
+
+        auto res = std::make_unique<server_task_result_cmpl_progress>();
+
+        res->id      = slot.id_task;
+        res->id_slot = slot.id;
+        res->index   = slot.index;
+
+        res->n_past                     = slot.n_past;
+        res->n_prompt_tokens            = slot.n_prompt_tokens;
+        res->n_prompt_tokens_processed  = slot.n_prompt_tokens_processed;
+        res->progress                   = (float) slot.n_prompt_tokens_processed / slot.n_prompt_tokens;
+
+        res->verbose               = slot.params.verbose;
+        res->oaicompat             = slot.params.oaicompat;
+        res->oaicompat_model       = slot.params.oaicompat_model;
+        res->oaicompat_cmpl_id     = slot.params.oaicompat_cmpl_id;
+
+        queue_results.send(std::move(res));
+    }
+
     void send_final_response(server_slot & slot) {
         auto res = std::make_unique<server_task_result_cmpl_final>();
         res->id              = slot.id_task;
@@ -2725,6 +2856,7 @@ struct server_context {
             GGML_ASSERT(
                 dynamic_cast<server_task_result_cmpl_partial*>(result.get()) != nullptr
                 || dynamic_cast<server_task_result_cmpl_final*>(result.get()) != nullptr
+                || dynamic_cast<server_task_result_cmpl_progress*>(result.get()) != nullptr
             );
             if (!result_handler(result)) {
                 cancel_tasks(id_tasks);
@@ -3340,6 +3472,9 @@ struct server_context {
 
                     SLT_INF(slot, "prompt processing progress, n_past = %d, n_tokens = %d, progress = %f\n", slot.n_past, batch.n_tokens, (float) slot.n_prompt_tokens_processed / slot.n_prompt_tokens);
 
+                    // send progress update to client
+                    send_progress_response(slot);
+
                     // entire prompt has been processed
                     if (slot.n_past == slot.n_prompt_tokens) {
                         slot.state = SLOT_STATE_DONE_PROMPT;