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.

internal/config/config.go

@@ -0,0 +1,95 @@
+// Package config loads localchat settings from the environment and an
+// optional .env file.
+package config
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// DefaultSystemPrompt is used when SYSTEM_PROMPT is not set.
+const DefaultSystemPrompt = "You are a friendly, concise assistant running fully offline on the user's own machine. Answer clearly. Use Markdown when it helps."
+
+// Config holds all runtime settings.
+type Config struct {
+	Addr         string        // LOCALCHAT_ADDR: where the web UI listens
+	BaseURL      string        // LLM_BASE_URL: OpenAI-compatible API root, e.g. http://127.0.0.1:8000/v1
+	APIKey       string        // LLM_API_KEY: optional bearer token for the model server
+	Model        string        // LLM_MODEL: model id; empty means "first model the server lists"
+	SystemPrompt string        // SYSTEM_PROMPT
+	Title        string        // LOCALCHAT_TITLE: name shown in the UI
+	MaxHistory   int           // MAX_HISTORY: messages sent back to the model as context
+	Timeout      time.Duration // LLM_TIMEOUT: upper bound for a single reply
+}
+
+// Load reads the configuration from environment variables, applying defaults.
+func Load() (Config, error) {
+	c := Config{
+		Addr:         env("LOCALCHAT_ADDR", "127.0.0.1:3000"),
+		BaseURL:      strings.TrimRight(env("LLM_BASE_URL", "http://127.0.0.1:8000/v1"), "/"),
+		APIKey:       os.Getenv("LLM_API_KEY"),
+		Model:        os.Getenv("LLM_MODEL"),
+		SystemPrompt: env("SYSTEM_PROMPT", DefaultSystemPrompt),
+		Title:        env("LOCALCHAT_TITLE", "localchat"),
+		MaxHistory:   20,
+		Timeout:      5 * time.Minute,
+	}
+	if v := os.Getenv("MAX_HISTORY"); v != "" {
+		n, err := strconv.Atoi(v)
+		if err != nil || n < 1 {
+			return c, fmt.Errorf("MAX_HISTORY must be a positive integer, got %q", v)
+		}
+		c.MaxHistory = n
+	}
+	if v := os.Getenv("LLM_TIMEOUT"); v != "" {
+		d, err := time.ParseDuration(v)
+		if err != nil {
+			return c, fmt.Errorf("LLM_TIMEOUT: %w", err)
+		}
+		c.Timeout = d
+	}
+	return c, nil
+}
+
+func env(key, fallback string) string {
+	if v, ok := os.LookupEnv(key); ok && v != "" {
+		return v
+	}
+	return fallback
+}
+
+// LoadEnvFile sets variables from a KEY=VALUE file. Variables that are
+// already set in the environment win, so the real environment can override
+// the file. Blank lines and lines starting with # are ignored; values may be
+// wrapped in single or double quotes.
+func LoadEnvFile(path string) error {
+	f, err := os.Open(path)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	sc := bufio.NewScanner(f)
+	for n := 1; sc.Scan(); n++ {
+		line := strings.TrimSpace(sc.Text())
+		if line == "" || strings.HasPrefix(line, "#") {
+			continue
+		}
+		key, val, ok := strings.Cut(strings.TrimPrefix(line, "export "), "=")
+		if !ok {
+			return fmt.Errorf("%s:%d: expected KEY=VALUE", path, n)
+		}
+		key, val = strings.TrimSpace(key), strings.TrimSpace(val)
+		if len(val) >= 2 && (val[0] == '"' || val[0] == '\'') && val[len(val)-1] == val[0] {
+			val = val[1 : len(val)-1]
+		}
+		if _, set := os.LookupEnv(key); !set {
+			os.Setenv(key, val)
+		}
+	}
+	return sc.Err()
+}

internal/config/config_test.go

@@ -0,0 +1,45 @@
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestLoadEnvFile(t *testing.T) {
+	path := filepath.Join(t.TempDir(), ".env")
+	os.WriteFile(path, []byte(`
+# comment
+LLM_MODEL=from-file
+export LOCALCHAT_TITLE="My Chat"
+SYSTEM_PROMPT='Talk like a pirate = arr'
+LLM_BASE_URL=http://file/v1/
+`), 0o600)
+
+	t.Setenv("LLM_BASE_URL", "http://env/v1") // real env wins over the file
+	for _, k := range []string{"LLM_MODEL", "LOCALCHAT_TITLE", "SYSTEM_PROMPT"} {
+		t.Setenv(k, "")
+		os.Unsetenv(k)
+	}
+
+	if err := LoadEnvFile(path); err != nil {
+		t.Fatal(err)
+	}
+	c, err := Load()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if c.Model != "from-file" || c.Title != "My Chat" || c.SystemPrompt != "Talk like a pirate = arr" {
+		t.Fatalf("unexpected config: %+v", c)
+	}
+	if c.BaseURL != "http://env/v1" {
+		t.Fatalf("env should override file, got %q", c.BaseURL)
+	}
+}
+
+func TestLoadValidates(t *testing.T) {
+	t.Setenv("MAX_HISTORY", "zero")
+	if _, err := Load(); err == nil {
+		t.Fatal("want error for bad MAX_HISTORY")
+	}
+}