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/search/response.go

@@ -0,0 +1,223 @@
+package search
+
+import (
+	"bytes"
+	"encoding/csv"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/url"
+	"encoding/xml"
+	"strconv"
+	"strings"
+)
+
+func WriteSearchResponse(w http.ResponseWriter, format OutputFormat, resp SearchResponse) error {
+	switch format {
+	case FormatJSON:
+		w.Header().Set("Content-Type", "application/json; charset=utf-8")
+		return json.NewEncoder(w).Encode(resp)
+	case FormatCSV:
+		w.Header().Set("Content-Type", "text/csv; charset=utf-8")
+		if err := writeCSV(w, resp); err != nil {
+			return err
+		}
+		return nil
+	case FormatRSS:
+		w.Header().Set("Content-Type", "text/xml; charset=utf-8")
+		if err := writeRSS(w, resp); err != nil {
+			return err
+		}
+		return nil
+	case FormatHTML:
+		w.WriteHeader(http.StatusNotImplemented)
+		_, _ = w.Write([]byte("format=html not implemented yet"))
+		return nil
+	default:
+		return fmt.Errorf("unsupported format: %s", format)
+	}
+}
+
+// csvRowHeader matches the SearXNG CSV writer key order.
+var csvRowHeader = []string{"title", "url", "content", "host", "engine", "score", "type"}
+
+func writeCSV(w http.ResponseWriter, resp SearchResponse) error {
+	cw := csv.NewWriter(w)
+	defer cw.Flush()
+
+	if err := cw.Write(csvRowHeader); err != nil {
+		return err
+	}
+
+	for _, r := range resp.Results {
+		urlStr := ""
+		if r.URL != nil {
+			urlStr = *r.URL
+		}
+		host := hostFromURL(urlStr)
+		scoreStr := strconv.FormatFloat(r.Score, 'f', -1, 64)
+		row := []string{
+			r.Title,
+			urlStr,
+			r.Content,
+			host,
+			r.Engine,
+			scoreStr,
+			"result",
+		}
+		if err := cw.Write(row); err != nil {
+			return err
+		}
+	}
+
+	for _, ans := range resp.Answers {
+		title := asString(ans["title"])
+		urlStr := asString(ans["url"])
+		content := asString(ans["content"])
+		engine := asString(ans["engine"])
+		scoreStr := scoreString(ans["score"])
+		host := hostFromURL(urlStr)
+
+		row := []string{
+			title,
+			urlStr,
+			content,
+			host,
+			engine,
+			scoreStr,
+			"answer",
+		}
+		if err := cw.Write(row); err != nil {
+			return err
+		}
+	}
+
+	for _, s := range resp.Suggestions {
+		row := []string{s, "", "", "", "", "", "suggestion"}
+		if err := cw.Write(row); err != nil {
+			return err
+		}
+	}
+
+	for _, c := range resp.Corrections {
+		row := []string{c, "", "", "", "", "", "correction"}
+		if err := cw.Write(row); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func writeRSS(w http.ResponseWriter, resp SearchResponse) error {
+	q := resp.Query
+	escapedTitle := xmlEscape("SearXNG search: " + q)
+	escapedDesc := xmlEscape("Search results for \"" + q + "\" - SearXNG")
+	escapedQueryTerms := xmlEscape(q)
+
+	link := "/search?q=" + url.QueryEscape(q)
+	opensearchQuery := fmt.Sprintf(`<opensearch:Query role="request" searchTerms="%s" startPage="1" />`, escapedQueryTerms)
+
+	// SearXNG template uses the number of results for both totalResults and itemsPerPage.
+	nr := resp.NumberOfResults
+
+	var items bytes.Buffer
+	for _, r := range resp.Results {
+		title := xmlEscape(r.Title)
+		urlStr := ""
+		if r.URL != nil {
+			urlStr = *r.URL
+		}
+		linkEsc := xmlEscape(urlStr)
+		desc := xmlEscape(r.Content)
+
+		pub := ""
+		if r.Pubdate != nil && strings.TrimSpace(*r.Pubdate) != "" {
+			pub = "<pubDate>" + xmlEscape(*r.Pubdate) + "</pubDate>"
+		}
+
+		items.WriteString(
+			fmt.Sprintf(
+				`<item><title>%s</title><type>result</type><link>%s</link><description>%s</description>%s</item>`,
+				title,
+				linkEsc,
+				desc,
+				pub,
+			),
+		)
+	}
+
+	xml := fmt.Sprintf(
+		`<?xml version="1.0" encoding="UTF-8"?>
+<?xml-stylesheet href="/rss.xsl" type="text/xsl"?>
+<rss version="2.0"
+     xmlns:opensearch="http://a9.com/-/spec/opensearch/1.1/"
+     xmlns:atom="http://www.w3.org/2005/Atom">
+  <channel>
+    <title>%s</title>
+    <link>%s</link>
+    <description>%s</description>
+    <opensearch:totalResults>%d</opensearch:totalResults>
+    <opensearch:startIndex>1</opensearch:startIndex>
+    <opensearch:itemsPerPage>%d</opensearch:itemsPerPage>
+    <atom:link rel="search" type="application/opensearchdescription+xml" href="/opensearch.xml"/>
+    %s
+    %s
+  </channel>
+</rss>
+`,
+		escapedTitle,
+		xmlEscape(link),
+		escapedDesc,
+		nr,
+		nr,
+		opensearchQuery,
+		items.String(),
+	)
+
+	_, err := w.Write([]byte(xml))
+	return err
+}
+
+func xmlEscape(s string) string {
+	var b bytes.Buffer
+	_ = xml.EscapeText(&b, []byte(s))
+	return b.String()
+}
+
+func hostFromURL(urlStr string) string {
+	if strings.TrimSpace(urlStr) == "" {
+		return ""
+	}
+	u, err := url.Parse(urlStr)
+	if err != nil {
+		return ""
+	}
+	return u.Host
+}
+
+func asString(v any) string {
+	s, _ := v.(string)
+	return s
+}
+
+func scoreString(v any) string {
+	switch t := v.(type) {
+	case float64:
+		return strconv.FormatFloat(t, 'f', -1, 64)
+	case float32:
+		return strconv.FormatFloat(float64(t), 'f', -1, 64)
+	case int:
+		return strconv.Itoa(t)
+	case int64:
+		return strconv.FormatInt(t, 10)
+	case json.Number:
+		if f, err := t.Float64(); err == nil {
+			return strconv.FormatFloat(f, 'f', -1, 64)
+		}
+		return ""
+	default:
+		return ""
+	}
+}
+