feat: localchat, a Go + Templ + HTMX chat app for local Gemma models

Streams replies over SSE from any OpenAI-compatible server (oMLX, llama.cpp, Ollama, ...). Single binary that can install itself as an OS service; docker compose bundles llama.cpp + Gemma 4 E2B.
2026-10-05 07:25:42 +02:00
commit bb71b49fde
@@ -0,0 +1,201 @@
+package web
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/http/cookiejar"
+	"net/http/httptest"
+	"net/url"
+	"regexp"
+	"strings"
+	"testing"
+	"time"
+
+	"git.b0b.be/bdeb/localchat/internal/config"
+)
+
+// fakeLLM streams back "echo: <last user message>" and records what it got.
+func fakeLLM(t *testing.T, seen *[][]map[string]string) *httptest.Server {
+	return httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path == "/v1/models" {
+			fmt.Fprint(w, `{"data":[{"id":"fake"}]}`)
+			return
+		}
+		var req struct {
+			Messages []map[string]string `json:"messages"`
+		}
+		json.NewDecoder(r.Body).Decode(&req)
+		*seen = append(*seen, req.Messages)
+		last := req.Messages[len(req.Messages)-1]["content"]
+		w.Header().Set("Content-Type", "text/event-stream")
+		for _, part := range []string{"echo: ", last, "\n\n**bold** <script>x</script>"} {
+			b, _ := json.Marshal(part)
+			fmt.Fprintf(w, "data: {\"choices\":[{\"delta\":{\"content\":%s}}]}\n\n", b)
+		}
+		fmt.Fprint(w, "data: [DONE]\n\n")
+	}))
+}
+
+func newTestApp(t *testing.T, llmURL string) (*httptest.Server, *http.Client) {
+	t.Helper()
+	cfg := config.Config{
+		BaseURL:      llmURL + "/v1",
+		SystemPrompt: "be nice",
+		Title:        "test",
+		MaxHistory:   20,
+		Timeout:      10 * time.Second,
+	}
+	app := httptest.NewServer(New(cfg, slog.New(slog.NewTextHandler(io.Discard, nil))).Handler())
+	t.Cleanup(app.Close)
+	jar, _ := cookiejar.New(nil)
+	return app, &http.Client{Jar: jar}
+}
+
+var streamURL = regexp.MustCompile(`sse-connect="(/chat/stream/[0-9a-f]+)"`)
+
+func get(t *testing.T, c *http.Client, u string) string {
+	t.Helper()
+	resp, err := c.Get(u)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	b, _ := io.ReadAll(resp.Body)
+	return string(b)
+}
+
+// ask posts a message, follows the SSE stream and returns the raw events.
+func ask(t *testing.T, app *httptest.Server, c *http.Client, msg string) string {
+	t.Helper()
+	resp, err := c.PostForm(app.URL+"/chat", url.Values{"message": {msg}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	body, _ := io.ReadAll(resp.Body)
+	resp.Body.Close()
+	m := streamURL.FindStringSubmatch(string(body))
+	if m == nil {
+		t.Fatalf("no stream url in %s", body)
+	}
+	return get(t, c, app.URL+m[1])
+}
+
+func TestChatFlow(t *testing.T) {
+	var seen [][]map[string]string
+	llm := fakeLLM(t, &seen)
+	defer llm.Close()
+	app, c := newTestApp(t, llm.URL)
+
+	if page := get(t, c, app.URL+"/"); !strings.Contains(page, `id="composer"`) {
+		t.Fatal("index page missing composer")
+	}
+	if h := get(t, c, app.URL+"/health"); !strings.Contains(h, "dot ok") || !strings.Contains(h, "fake") {
+		t.Fatalf("health: %s", h)
+	}
+
+	events := ask(t, app, c, "hi <b>there</b>")
+	for _, want := range []string{
+		"event: token\ndata: <span>echo: </span>",
+		"hi &lt;b&gt;there&lt;/b&gt;", // user text is escaped in tokens
+		"event: done",
+		"<strong>bold</strong>",     // final reply is rendered Markdown
+		"<!-- raw HTML omitted -->", // ... with raw HTML from the model dropped
+	} {
+		if !strings.Contains(events, want) {
+			t.Errorf("stream missing %q:\n%s", want, events)
+		}
+	}
+	if strings.Contains(events, "<script>") {
+		t.Error("raw <script> leaked into the page")
+	}
+
+	// second turn sends system prompt + full history
+	ask(t, app, c, "again")
+	last := seen[len(seen)-1]
+	roles := []string{}
+	for _, m := range last {
+		roles = append(roles, m["role"])
+	}
+	if got := strings.Join(roles, ","); got != "system,user,assistant,user" {
+		t.Fatalf("history roles = %s", got)
+	}
+
+	// page reload shows the history, reset clears it
+	if page := get(t, c, app.URL+"/"); strings.Count(page, `class="msg `) != 4 {
+		t.Fatal("expected 4 messages after reload")
+	}
+	resp, _ := c.Post(app.URL+"/chat/reset", "", nil)
+	resp.Body.Close()
+	if page := get(t, c, app.URL+"/"); strings.Contains(page, `class="msg `) {
+		t.Fatal("reset did not clear history")
+	}
+}
+
+func TestStreamReconnectDoesNotRegenerate(t *testing.T) {
+	var seen [][]map[string]string
+	llm := fakeLLM(t, &seen)
+	defer llm.Close()
+	app, c := newTestApp(t, llm.URL)
+
+	resp, _ := c.PostForm(app.URL+"/chat", url.Values{"message": {"once"}})
+	body, _ := io.ReadAll(resp.Body)
+	resp.Body.Close()
+	path := streamURL.FindStringSubmatch(string(body))[1]
+
+	get(t, c, app.URL+path)
+	again := get(t, c, app.URL+path)
+	if len(seen) != 1 {
+		t.Fatalf("model called %d times, want 1", len(seen))
+	}
+	if strings.Contains(again, "event: token") || !strings.Contains(again, "echo: once") {
+		t.Fatalf("reconnect should replay the final message only:\n%s", again)
+	}
+}
+
+func TestSessionsAreIsolated(t *testing.T) {
+	var seen [][]map[string]string
+	llm := fakeLLM(t, &seen)
+	defer llm.Close()
+	app, alice := newTestApp(t, llm.URL)
+	jar, _ := cookiejar.New(nil)
+	bob := &http.Client{Jar: jar}
+
+	ask(t, app, alice, "alice secret")
+	if strings.Contains(get(t, bob, app.URL+"/"), "alice secret") {
+		t.Fatal("bob can see alice's chat")
+	}
+	resp, _ := bob.PostForm(app.URL+"/chat", url.Values{"message": {"x"}})
+	body, _ := io.ReadAll(resp.Body)
+	resp.Body.Close()
+	path := streamURL.FindStringSubmatch(string(body))[1]
+	if out := get(t, alice, app.URL+path); !strings.Contains(out, "lost") {
+		t.Fatalf("alice should not be able to stream bob's reply:\n%s", out)
+	}
+}
+
+func TestEmptyMessageRejected(t *testing.T) {
+	var seen [][]map[string]string
+	llm := fakeLLM(t, &seen)
+	defer llm.Close()
+	app, c := newTestApp(t, llm.URL)
+
+	resp, _ := c.PostForm(app.URL+"/chat", url.Values{"message": {"   "}})
+	resp.Body.Close()
+	if resp.StatusCode != http.StatusBadRequest {
+		t.Fatalf("status %d", resp.StatusCode)
+	}
+}
+
+func TestModelOffline(t *testing.T) {
+	app, c := newTestApp(t, "http://127.0.0.1:1") // nothing listens here
+	if h := get(t, c, app.URL+"/health"); !strings.Contains(h, "model offline") {
+		t.Fatalf("health: %s", h)
+	}
+	events := ask(t, app, c, "hello?")
+	if !strings.Contains(events, "event: done") || !strings.Contains(events, `class="error"`) {
+		t.Fatalf("want an error bubble:\n%s", events)
+	}
+}