Add an endpoint that lists all the saved prompt caches to server (#502)

Author: saood06

examples/server/server.cpp

@@ -3390,6 +3390,48 @@ int main(int argc, char ** argv) {
         res.status = 200; // HTTP OK
     };
 
+    const auto list_saved_prompts = [&ctx_server, &params](const httplib::Request& req, httplib::Response& res) {
+        res.set_header("Access-Control-Allow-Origin", req.get_header_value("Origin"));
+        json response = json::array();
+        namespace fs = std::filesystem;
+
+        try {
+            for (const auto& entry : fs::directory_iterator(params.slot_save_path)) {
+                if (!entry.is_regular_file() || entry.file_size() < 12) {
+                    continue;
+                }
+
+                std::ifstream file(entry.path(), std::ios::binary);
+                if (!file) continue;
+
+                uint32_t magic, version, n_token_count;
+                file.read(reinterpret_cast<char*>(&magic), sizeof(magic));
+                file.read(reinterpret_cast<char*>(&version), sizeof(version));
+                file.read(reinterpret_cast<char*>(&n_token_count), sizeof(n_token_count));
+
+                if (magic != LLAMA_STATE_SEQ_MAGIC ||
+                    version != LLAMA_STATE_SEQ_VERSION ||
+                    entry.file_size() < (12 + (n_token_count * sizeof(llama_token)))) {
+                    continue;
+                }
+
+                std::vector<llama_token> tokens(n_token_count);
+                file.read(reinterpret_cast<char*>(tokens.data()), tokens.size() * sizeof(llama_token));
+
+                response.push_back({
+                    {"filename", entry.path().filename().string()},
+                    {"filesize", entry.file_size()},
+                    {"token_count", n_token_count},
+                    {"prompt", tokens_to_str(ctx_server.ctx, tokens.cbegin(), tokens.cend())}
+                });
+            }
+        } catch (const std::exception& e) {
+            res.status = 500;
+            response = {{"error", e.what()}};
+        }
+        res.set_content(response.dump(), "application/json; charset=utf-8");
+    };
+
     auto handle_static_file = [](unsigned char * content, size_t len, const char * mime_type) {
         return [content, len, mime_type](const httplib::Request &, httplib::Response & res) {
             res.set_content(reinterpret_cast<const char*>(content), len, mime_type);
@@ -3448,8 +3490,9 @@ int main(int argc, char ** argv) {
     // Save & load slots
     svr->Get ("/slots",               handle_slots);
     if (!params.slot_save_path.empty()) {
-        // only enable slot endpoints if slot_save_path is set
+        // these endpoints rely on slot_save_path existing
         svr->Post("/slots/:id_slot",  handle_slots_action);
+        svr->Get ("/list",            list_saved_prompts);
     }
 
     //