feat(cmd/server): support reading initial prompt from stdin (#139)

Supports passing initial prompt via stdin, e.g.

```
echo "a very long prompt" | agentapi server claude
```

Author: johnstcn

cmd/server/server.go

@@ -4,12 +4,14 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"io"
 	"log/slog"
 	"net/http"
 	"os"
 	"sort"
 	"strings"
 
+	"github.com/mattn/go-isatty"
 	"github.com/spf13/cobra"
 	"github.com/spf13/viper"
 	"golang.org/x/xerrors"
@@ -88,6 +90,19 @@ func runServer(ctx context.Context, logger *slog.Logger, argsToPass []string) er
 		return xerrors.Errorf("term height must be at least 10")
 	}
 
+	// Read stdin if it's piped, to be used as initial prompt
+	initialPrompt := viper.GetString(FlagInitialPrompt)
+	if initialPrompt == "" {
+		if !isatty.IsTerminal(os.Stdin.Fd()) {
+			if stdinData, err := io.ReadAll(os.Stdin); err != nil {
+				return xerrors.Errorf("failed to read stdin: %w", err)
+			} else if len(stdinData) > 0 {
+				initialPrompt = string(stdinData)
+				logger.Info("Read initial prompt from stdin", "bytes", len(stdinData))
+			}
+		}
+	}
+
 	printOpenAPI := viper.GetBool(FlagPrintOpenAPI)
 	var process *termexec.Process
 	if printOpenAPI {
@@ -112,7 +127,7 @@ func runServer(ctx context.Context, logger *slog.Logger, argsToPass []string) er
 		ChatBasePath:   viper.GetString(FlagChatBasePath),
 		AllowedHosts:   viper.GetStringSlice(FlagAllowedHosts),
 		AllowedOrigins: viper.GetStringSlice(FlagAllowedOrigins),
-		InitialPrompt:  viper.GetString(FlagInitialPrompt),
+		InitialPrompt:  initialPrompt,
 	})
 	if err != nil {
 		return xerrors.Errorf("failed to create server: %w", err)
@@ -213,7 +228,7 @@ func CreateServerCmd() *cobra.Command {
 		{FlagAllowedHosts, "a", []string{"localhost", "127.0.0.1", "[::1]"}, "HTTP allowed hosts (hostnames only, no ports). Use '*' for all, comma-separated list via flag, space-separated list via AGENTAPI_ALLOWED_HOSTS env var", "stringSlice"},
 		// localhost:3284 is the default origin when you open the chat interface in your browser. localhost:3000 and 3001 are used during development.
 		{FlagAllowedOrigins, "o", []string{"http://localhost:3284", "http://localhost:3000", "http://localhost:3001"}, "HTTP allowed origins. Use '*' for all, comma-separated list via flag, space-separated list via AGENTAPI_ALLOWED_ORIGINS env var", "stringSlice"},
-		{FlagInitialPrompt, "I", "", "Initial prompt for the agent (recommended only if the agent doesn't support initial prompt in interaction mode)", "string"},
+		{FlagInitialPrompt, "I", "", "Initial prompt for the agent. Recommended only if the agent doesn't support initial prompt in interaction mode. Will be read from stdin if piped (e.g., echo 'prompt' | agentapi server -- my-agent)", "string"},
 	}
 
 	for _, spec := range flagSpecs {

e2e/echo_test.go

@@ -22,7 +22,7 @@ import (
 
 const (
 	testTimeout        = 30 * time.Second
-	operationTimeout   = 5 * time.Second
+	operationTimeout   = 10 * time.Second
 	healthCheckTimeout = 10 * time.Second
 )
 
@@ -40,15 +40,14 @@ func TestE2E(t *testing.T) {
 	t.Run("basic", func(t *testing.T) {
 		ctx, cancel := context.WithTimeout(context.Background(), testTimeout)
 		defer cancel()
-		script, apiClient := setup(ctx, t)
-		require.NoError(t, waitAgentAPIStable(ctx, apiClient, operationTimeout))
+		script, apiClient := setup(ctx, t, nil)
 		messageReq := agentapisdk.PostMessageParams{
 			Content: "This is a test message.",
 			Type:    agentapisdk.MessageTypeUser,
 		}
 		_, err := apiClient.PostMessage(ctx, messageReq)
 		require.NoError(t, err, "Failed to send message via SDK")
-		require.NoError(t, waitAgentAPIStable(ctx, apiClient, operationTimeout))
+		require.NoError(t, waitAgentAPIStable(ctx, t, apiClient, operationTimeout, "post message"))
 		msgResp, err := apiClient.GetMessages(ctx)
 		require.NoError(t, err, "Failed to get messages via SDK")
 		require.Len(t, msgResp.Messages, 3)
@@ -61,7 +60,7 @@ func TestE2E(t *testing.T) {
 		ctx, cancel := context.WithTimeout(context.Background(), testTimeout)
 		defer cancel()
 
-		script, apiClient := setup(ctx, t)
+		script, apiClient := setup(ctx, t, nil)
 		messageReq := agentapisdk.PostMessageParams{
 			Content: "What is the answer to life, the universe, and everything?",
 			Type:    agentapisdk.MessageTypeUser,
@@ -71,7 +70,7 @@ func TestE2E(t *testing.T) {
 		statusResp, err := apiClient.GetStatus(ctx)
 		require.NoError(t, err)
 		require.Equal(t, agentapisdk.StatusRunning, statusResp.Status)
-		require.NoError(t, waitAgentAPIStable(ctx, apiClient, 5*time.Second))
+		require.NoError(t, waitAgentAPIStable(ctx, t, apiClient, 5*time.Second, "post message"))
 		msgResp, err := apiClient.GetMessages(ctx)
 		require.NoError(t, err, "Failed to get messages via SDK")
 		require.Len(t, msgResp.Messages, 3)
@@ -82,11 +81,45 @@ func TestE2E(t *testing.T) {
 		require.Equal(t, script[1].ResponseMessage, strings.TrimSpace(parts[0]))
 		require.Equal(t, script[2].ResponseMessage, strings.TrimSpace(parts[1]))
 	})
+
+	t.Run("stdin", func(t *testing.T) {
+		ctx, cancel := context.WithTimeout(context.Background(), testTimeout)
+		defer cancel()
+
+		script, apiClient := setup(ctx, t, &params{
+			cmdFn: func(ctx context.Context, t testing.TB, serverPort int, binaryPath, cwd, scriptFilePath string) (string, []string) {
+				defCmd, defArgs := defaultCmdFn(ctx, t, serverPort, binaryPath, cwd, scriptFilePath)
+				script := fmt.Sprintf(`echo "hello agent" | %s %s`, defCmd, strings.Join(defArgs, " "))
+				return "/bin/sh", []string{"-c", script}
+			},
+		})
+		require.NoError(t, waitAgentAPIStable(ctx, t, apiClient, 5*time.Second, "stdin"))
+		msgResp, err := apiClient.GetMessages(ctx)
+		require.NoError(t, err, "Failed to get messages via SDK")
+		require.Len(t, msgResp.Messages, 3)
+		require.Equal(t, script[0].ExpectMessage, strings.TrimSpace(msgResp.Messages[1].Content))
+		require.Equal(t, script[0].ResponseMessage, strings.TrimSpace(msgResp.Messages[2].Content))
+	})
 }
 
-func setup(ctx context.Context, t testing.TB) ([]ScriptEntry, *agentapisdk.Client) {
+type params struct {
+	cmdFn func(ctx context.Context, t testing.TB, serverPort int, binaryPath, cwd, scriptFilePath string) (string, []string)
+}
+
+func defaultCmdFn(ctx context.Context, t testing.TB, serverPort int, binaryPath, cwd, scriptFilePath string) (string, []string) {
+	return binaryPath, []string{"server", fmt.Sprintf("--port=%d", serverPort), "--", "go", "run", filepath.Join(cwd, "echo.go"), scriptFilePath}
+}
+
+func setup(ctx context.Context, t testing.TB, p *params) ([]ScriptEntry, *agentapisdk.Client) {
 	t.Helper()
 
+	if p == nil {
+		p = &params{}
+	}
+	if p.cmdFn == nil {
+		p.cmdFn = defaultCmdFn
+	}
+
 	scriptFilePath := filepath.Join("testdata", filepath.Base(t.Name())+".json")
 	data, err := os.ReadFile(scriptFilePath)
 	require.NoError(t, err, "Failed to read test script file: %s", scriptFilePath)
@@ -116,10 +149,9 @@ func setup(ctx context.Context, t testing.TB) ([]ScriptEntry, *agentapisdk.Clien
 	cwd, err := os.Getwd()
 	require.NoError(t, err, "Failed to get current working directory")
 
-	cmd := exec.CommandContext(ctx, binaryPath, "server",
-		fmt.Sprintf("--port=%d", serverPort),
-		"--",
-		"go", "run", filepath.Join(cwd, "echo.go"), scriptFilePath)
+	bin, args := p.cmdFn(ctx, t, serverPort, binaryPath, cwd, scriptFilePath)
+	t.Logf("Running command: %s %s", bin, strings.Join(args, " "))
+	cmd := exec.CommandContext(ctx, bin, args...)
 
 	// Capture output for debugging
 	stdout, err := cmd.StdoutPipe()
@@ -160,7 +192,7 @@ func setup(ctx context.Context, t testing.TB) ([]ScriptEntry, *agentapisdk.Clien
 	apiClient, err := agentapisdk.NewClient(serverURL)
 	require.NoError(t, err, "Failed to create agentapi SDK client")
 
-	require.NoError(t, waitAgentAPIStable(ctx, apiClient, operationTimeout))
+	require.NoError(t, waitAgentAPIStable(ctx, t, apiClient, operationTimeout, "setup"))
 	return script, apiClient
 }
 
@@ -198,21 +230,30 @@ func waitForServer(ctx context.Context, t testing.TB, url string, timeout time.D
 	}
 }
 
-func waitAgentAPIStable(ctx context.Context, apiClient *agentapisdk.Client, waitFor time.Duration) error {
+func waitAgentAPIStable(ctx context.Context, t testing.TB, apiClient *agentapisdk.Client, waitFor time.Duration, msg string) error {
+	t.Helper()
 	waitCtx, waitCancel := context.WithTimeout(ctx, waitFor)
 	defer waitCancel()
 
-	tick := time.NewTicker(100 * time.Millisecond)
+	start := time.Now()
+	tick := time.NewTicker(time.Millisecond)
 	defer tick.Stop()
+	var prevStatus agentapisdk.AgentStatus
+	defer func() {
+		elapsed := time.Since(start)
+		t.Logf("%s: agent API status: %s (elapsed: %s)", msg, prevStatus, elapsed.Round(100*time.Millisecond))
+	}()
 	for {
 		select {
 		case <-waitCtx.Done():
 			return waitCtx.Err()
 		case <-tick.C:
+			tick.Reset(100 * time.Millisecond)
 			sr, err := apiClient.GetStatus(ctx)
 			if err != nil {
 				continue
 			}
+			prevStatus = sr.Status
 			if sr.Status == agentapisdk.StatusStable {
 				return nil
 			}

e2e/testdata/stdin.json

@@ -0,0 +1,6 @@
+[
+  {
+    "expectMessage": "hello agent",
+    "responseMessage": "Hello! I'm ready to help you. Please send me a message to echo back."
+  }
+]