feat: build Go-based SearXNG-compatible search service

Implement an API-first Go rewrite with local engine adapters, upstream fallback, and Nix-based tooling so searches can run without matching the original UI while preserving response compatibility.

Made-with: Cursor

internal/upstream/client.go

@@ -0,0 +1,112 @@
+package upstream
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+
+	"github.com/ashie/gosearch/internal/contracts"
+)
+
+type Client struct {
+	baseURL string
+	http    *http.Client
+}
+
+func NewClient(baseURL string, timeout time.Duration) (*Client, error) {
+	if strings.TrimSpace(baseURL) == "" {
+		return nil, errors.New("upstream base URL is empty")
+	}
+
+	u, err := url.Parse(baseURL)
+	if err != nil {
+		return nil, fmt.Errorf("invalid upstream base URL: %w", err)
+	}
+	// Normalize: trim trailing slash to make URL concatenation predictable.
+	base := strings.TrimRight(u.String(), "/")
+
+	if timeout <= 0 {
+		timeout = 10 * time.Second
+	}
+
+	return &Client{
+		baseURL: base,
+		http: &http.Client{
+			Timeout: timeout,
+		},
+	}, nil
+}
+
+func (c *Client) SearchJSON(ctx context.Context, req contracts.SearchRequest, engines []string) (contracts.SearchResponse, error) {
+	// Always request upstream JSON; the Go service will handle csv/rss later.
+	form := url.Values{}
+	form.Set("q", req.Query)
+	form.Set("format", "json")
+	form.Set("pageno", fmt.Sprintf("%d", req.Pageno))
+	form.Set("safesearch", fmt.Sprintf("%d", req.Safesearch))
+	form.Set("language", req.Language)
+
+	if req.TimeRange != nil {
+		form.Set("time_range", *req.TimeRange)
+	}
+	if req.TimeoutLimit != nil {
+		form.Set("timeout_limit", formatFloat(*req.TimeoutLimit))
+	}
+	if len(req.Categories) > 0 {
+		form.Set("categories", strings.Join(req.Categories, ","))
+	}
+
+	if len(engines) > 0 {
+		form.Set("engines", strings.Join(engines, ","))
+	}
+
+	for engineName, kv := range req.EngineData {
+		for key, value := range kv {
+			// Mirror SearXNG's naming: `engine_data-<engine>-<key>=<value>`
+			form.Set(fmt.Sprintf("engine_data-%s-%s", engineName, key), value)
+		}
+	}
+
+	endpoint := c.baseURL + "/search"
+	httpReq, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, strings.NewReader(form.Encode()))
+	if err != nil {
+		return contracts.SearchResponse{}, err
+	}
+	httpReq.Header.Set("Content-Type", "application/x-www-form-urlencoded; charset=utf-8")
+
+	resp, err := c.http.Do(httpReq)
+	if err != nil {
+		return contracts.SearchResponse{}, err
+	}
+	defer resp.Body.Close()
+
+	body, err := io.ReadAll(io.LimitReader(resp.Body, 4*1024*1024))
+	if err != nil {
+		return contracts.SearchResponse{}, err
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		return contracts.SearchResponse{}, fmt.Errorf("upstream search failed: status=%d body=%q", resp.StatusCode, string(body))
+	}
+
+	// Decode upstream JSON into our contract types.
+	var out contracts.SearchResponse
+	dec := json.NewDecoder(strings.NewReader(string(body)))
+	if err := dec.Decode(&out); err != nil {
+		return contracts.SearchResponse{}, fmt.Errorf("decode upstream JSON: %w", err)
+	}
+
+	return out, nil
+}
+
+func formatFloat(f float64) string {
+	// Keep stable formatting for upstream parsing.
+	return strings.TrimRight(strings.TrimRight(fmt.Sprintf("%.6f", f), "0"), ".")
+}
+