feat(docker): add /healthz endpoint and -healthcheck flag (#254)

Adds a Docker healthcheck and the small HTTP/CLI plumbing it needs.

- Expose `GET /healthz` on the HTTP-mode server.
- Add `-healthcheck` to dial `http://127.0.0.1:<port>/healthz` and exit with status.
- Add a Dockerfile `HEALTHCHECK` instruction using `-healthcheck`.
- Document HTTP-mode usage and stdio override guidance.

Closes https://gitea.com/gitea/gitea-mcp/issues/146

Assisted by Codet.

Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/254
Reviewed-by: silverwind <2021+silverwind@noreply.gitea.com>

cmd/cmd.go

@@ -5,6 +5,7 @@ import (
 	"flag"
 	"fmt"
 	"io"
+	"net/http"
 	"os"
 	"strconv"
 	"strings"
@@ -23,9 +24,11 @@ var (
 	tools                           string
 	scopes                          string
 	version                         bool
+	healthcheck                     bool
 	maxInlineAttachmentBytes        int
 	maxInlineAttachmentBytesFlagSet bool
 	osExit                          = os.Exit
+	healthcheckClient               = http.DefaultClient
 )
 
 func initFlagSet(fs *flag.FlagSet, args []string, getenv func(string) string, readFile func(string) ([]byte, error), stderr io.Writer) {
@@ -53,6 +56,7 @@ func initFlagSet(fs *flag.FlagSet, args []string, getenv func(string) string, re
 	fs.BoolVar(&flagPkg.Insecure, "insecure", false, "")
 	fs.BoolVar(&version, "v", false, "")
 	fs.BoolVar(&version, "version", false, "")
+	fs.BoolVar(&healthcheck, "healthcheck", false, "")
 	maxInlineAttachmentBytes = 5 * 1024 * 1024
 	fs.Func("max-inline-attachment-bytes", "", func(val string) error {
 		parsed, err := strconv.Atoi(val)
@@ -81,6 +85,7 @@ func initFlagSet(fs *flag.FlagSet, args []string, getenv func(string) string, re
 		fmt.Fprintf(w, "  -k, -insecure\tIgnore TLS certificate errors\n")
 		fmt.Fprintf(w, "  -max-inline-attachment-bytes <bytes>\tInline image attachments up to this size (default: 5242880)\n")
 		fmt.Fprintf(w, "  -v, -version\tPrint version and exit\n")
+		fmt.Fprintf(w, "  -healthcheck\tCheck a running HTTP server's /healthz endpoint and exit\n")
 		fmt.Fprintln(w)
 		fmt.Fprintln(w, "Environment variables:")
 		fmt.Fprintf(w, "  GITEA_ACCESS_TOKEN\tProvide access token\n")
@@ -183,6 +188,14 @@ func Execute() {
 		fmt.Fprintln(os.Stdout, flagPkg.Version)
 		return
 	}
+	if healthcheck {
+		if runHealthcheck(healthcheckClient, flagPkg.Port, os.Stdout, os.Stderr) {
+			osExit(0)
+		} else {
+			osExit(1)
+		}
+		return
+	}
 	if err := operation.Run(); err != nil {
 		if err == context.Canceled {
 			log.Info("Server shutdown due to context cancellation")

cmd/cmd_test.go

@@ -95,3 +95,12 @@ func TestInitFlagSetScopes(t *testing.T) {
 		})
 	}
 }
+
+func TestInitFlagSetHealthcheck(t *testing.T) {
+	t.Cleanup(func() { healthcheck = false })
+	fs := flag.NewFlagSet("test", flag.ContinueOnError)
+	initFlagSet(fs, []string{"-healthcheck"}, func(string) string { return "" }, func(string) ([]byte, error) { return nil, nil }, &bytes.Buffer{})
+	if !healthcheck {
+		t.Error("healthcheck = false, want true")
+	}
+}

cmd/healthcheck.go

@@ -0,0 +1,29 @@
+package cmd
+
+import (
+	"fmt"
+	"io"
+	"net/http"
+)
+
+// runHealthcheck dials the /healthz endpoint on 127.0.0.1:port and reports
+// success or failure. It returns true when the server responds with a 2xx
+// status.
+func runHealthcheck(client *http.Client, port int, stdout, stderr io.Writer) bool {
+	url := fmt.Sprintf("http://127.0.0.1:%d/healthz", port)
+
+	resp, err := client.Get(url)
+	if err != nil {
+		fmt.Fprintf(stderr, "healthcheck failed: %v\n", err)
+		return false
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode < http.StatusOK || resp.StatusCode >= http.StatusMultipleChoices {
+		fmt.Fprintf(stderr, "healthcheck failed: unexpected status %s\n", resp.Status)
+		return false
+	}
+
+	fmt.Fprintln(stdout, "healthy")
+	return true
+}

cmd/healthcheck_test.go

@@ -0,0 +1,81 @@
+package cmd
+
+import (
+	"bytes"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"strconv"
+	"strings"
+	"testing"
+)
+
+func TestRunHealthcheck(t *testing.T) {
+	tests := []struct {
+		name       string
+		handler    http.HandlerFunc
+		port       func(server *httptest.Server) int
+		wantOK     bool
+		wantStdout string
+	}{
+		{
+			name: "server responds 200 OK",
+			handler: func(w http.ResponseWriter, r *http.Request) {
+				w.WriteHeader(http.StatusOK)
+			},
+			port:       serverPort,
+			wantOK:     true,
+			wantStdout: "healthy",
+		},
+		{
+			name: "server responds with an error status",
+			handler: func(w http.ResponseWriter, r *http.Request) {
+				w.WriteHeader(http.StatusInternalServerError)
+			},
+			port:   serverPort,
+			wantOK: false,
+		},
+		{
+			name:   "nothing listening on the port",
+			port:   func(*httptest.Server) int { return 1 },
+			wantOK: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var server *httptest.Server
+			if tt.handler != nil {
+				server = httptest.NewServer(tt.handler)
+				defer server.Close()
+			}
+
+			var stdout, stderr bytes.Buffer
+			ok := runHealthcheck(http.DefaultClient, tt.port(server), &stdout, &stderr)
+
+			if ok != tt.wantOK {
+				t.Errorf("runHealthcheck() = %v, want %v", ok, tt.wantOK)
+			}
+			if tt.wantStdout != "" && !strings.Contains(stdout.String(), tt.wantStdout) {
+				t.Errorf("stdout = %q, want it to contain %q", stdout.String(), tt.wantStdout)
+			}
+			if tt.wantOK && stderr.Len() != 0 {
+				t.Errorf("stderr = %q, want empty on success", stderr.String())
+			}
+			if !tt.wantOK && stderr.Len() == 0 {
+				t.Error("stderr is empty, want a failure message")
+			}
+		})
+	}
+}
+
+func serverPort(server *httptest.Server) int {
+	_, portStr, err := net.SplitHostPort(server.Listener.Addr().String())
+	if err != nil {
+		panic(err)
+	}
+	port, err := strconv.Atoi(portStr)
+	if err != nil {
+		panic(err)
+	}
+	return port
+}