server: allow stream for exec_shell_command (#25526)

* init stream

* add stream for shell tool

* add test

* nits

* update docs

tools/server/server-tools.h

@@ -2,15 +2,27 @@
 
 #include "server-common.h"
 #include "server-http.h"
+#include "server-queue.h"
+
+#include <atomic>
+#include <functional>
 
 struct server_tool {
     std::string name;
     std::string display_name;
     bool permission_write = false;
+    bool support_stream = false; // if true, output can be streamed
 
     virtual ~server_tool() = default;
     virtual json get_definition() const = 0;
-    virtual json invoke(json params) const = 0;
+
+    struct stream {
+        server_response & qr;
+        int id;
+        std::function<bool()> alive;
+        void push(const std::string & chunk);
+    };
+    virtual json invoke(json params, stream * st = nullptr) const = 0;
 
     json to_json() const;
 };
@@ -18,8 +30,11 @@ struct server_tool {
 struct server_tools {
     std::vector<std::unique_ptr<server_tool>> tools;
 
+    // for streaming
+    server_response queue_res;
+    std::atomic<int> res_id{0};
+
     void setup(const std::vector<std::string> & enabled_tools);
-    json invoke(const std::string & name, const json & params);
 
     server_http_context::handler_t handle_get;
     server_http_context::handler_t handle_post;