coder · ethanndickson · Aug 29, 2024 · Aug 28, 2024
diff --git a/cli/agent.go b/cli/agent.go
@@ -50,6 +50,8 @@ func (r *RootCmd) workspaceAgent() *serpent.Command {
 		slogJSONPath        string
 		slogStackdriverPath string
 		blockFileTransfer   bool
+		agentHeaderCommand  string
+		agentHeader         []string
 	)
 	cmd := &serpent.Command{
 		Use:   "agent",
@@ -176,6 +178,14 @@ func (r *RootCmd) workspaceAgent() *serpent.Command {
 			// with large payloads can take a bit. e.g. startup scripts
 			// may take a while to insert.
 			client.SDK.HTTPClient.Timeout = 30 * time.Second
+			// Attach header transport so we process --agent-header and
+			// --agent-header-command flags
+			headerTransport, err := headerTransport(ctx, r.agentURL, agentHeader, agentHeaderCommand)
+			if err != nil {
+				return xerrors.Errorf("configure header transport: %w", err)
+			}
+			headerTransport.Transport = client.SDK.HTTPClient.Transport
+			client.SDK.HTTPClient.Transport = headerTransport
 
 			// Enable pprof handler
 			// This prevents the pprof import from being accidentally deleted.
@@ -361,6 +371,18 @@ func (r *RootCmd) workspaceAgent() *serpent.Command {
 			Value:       serpent.StringOf(&pprofAddress),
 			Description: "The address to serve pprof.",
 		},
+		{
+			Flag:        "agent-header-command",
+			Env:         "CODER_AGENT_HEADER_COMMAND",
+			Value:       serpent.StringOf(&agentHeaderCommand),
+			Description: "An external command that outputs additional HTTP headers added to all requests. The command must output each header as `key=value` on its own line.",
+		},
+		{
+			Flag:        "agent-header",
+			Env:         "CODER_AGENT_HEADER",
+			Value:       serpent.StringArrayOf(&agentHeader),
+			Description: "Additional HTTP headers added to all requests. Provide as " + `key=value` + ". Can be specified multiple times.",
+		},
 		{
 			Flag: "no-reap",
 

diff --git a/cli/agent_test.go b/cli/agent_test.go
@@ -3,10 +3,13 @@ package cli_test
 import (
 	"context"
 	"fmt"
+	"net/http"
+	"net/http/httptest"
 	"os"
 	"path/filepath"
 	"runtime"
 	"strings"
+	"sync/atomic"
 	"testing"
 
 	"github.com/google/uuid"
@@ -229,6 +232,43 @@ func TestWorkspaceAgent(t *testing.T) {
 		require.Equal(t, codersdk.AgentSubsystemEnvbox, resources[0].Agents[0].Subsystems[0])
 		require.Equal(t, codersdk.AgentSubsystemExectrace, resources[0].Agents[0].Subsystems[1])
 	})
+	t.Run("Header", func(t *testing.T) {
+		t.Parallel()
+
+		var url string
+		var called int64
+		srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			assert.Equal(t, "wow", r.Header.Get("X-Testing"))
+			assert.Equal(t, "Ethan was Here!", r.Header.Get("Cool-Header"))
+			assert.Equal(t, "very-wow-"+url, r.Header.Get("X-Process-Testing"))
+			assert.Equal(t, "more-wow", r.Header.Get("X-Process-Testing2"))
+			atomic.AddInt64(&called, 1)
+			w.WriteHeader(http.StatusGone)
+		}))
+		defer srv.Close()
+		url = srv.URL
+		coderURLEnv := "$CODER_URL"
+		if runtime.GOOS == "windows" {
+			coderURLEnv = "%CODER_URL%"
+		}
+
+		logDir := t.TempDir()
+		inv, _ := clitest.New(t,
+			"agent",
+			"--auth", "token",
+			"--agent-token", "fake-token",
+			"--agent-url", srv.URL,
+			"--log-dir", logDir,
+			"--agent-header", "X-Testing=wow",
+			"--agent-header", "Cool-Header=Ethan was Here!",
+			"--agent-header-command", "printf X-Process-Testing=very-wow-"+coderURLEnv+"'\\r\\n'X-Process-Testing2=more-wow",
+		)
+
+		clitest.Start(t, inv)
+		require.Eventually(t, func() bool {
+			return atomic.LoadInt64(&called) > 0
+		}, testutil.WaitShort, testutil.IntervalFast)
+	})
 }
 
 func matchAgentWithVersion(rs []codersdk.WorkspaceResource) bool {

diff --git a/cli/root.go b/cli/root.go
@@ -550,44 +550,7 @@ func (r *RootCmd) InitClient(client *codersdk.Client) serpent.MiddlewareFunc {
 // HeaderTransport creates a new transport that executes `--header-command`
 // if it is set to add headers for all outbound requests.
 func (r *RootCmd) HeaderTransport(ctx context.Context, serverURL *url.URL) (*codersdk.HeaderTransport, error) {
-	transport := &codersdk.HeaderTransport{
-		Transport: http.DefaultTransport,
-		Header:    http.Header{},
-	}
-	headers := r.header
-	if r.headerCommand != "" {
-		shell := "sh"
-		caller := "-c"
-		if runtime.GOOS == "windows" {
-			shell = "cmd.exe"
-			caller = "/c"
-		}
-		var outBuf bytes.Buffer
-		// #nosec
-		cmd := exec.CommandContext(ctx, shell, caller, r.headerCommand)
-		cmd.Env = append(os.Environ(), "CODER_URL="+serverURL.String())
-		cmd.Stdout = &outBuf
-		cmd.Stderr = io.Discard
-		err := cmd.Run()
-		if err != nil {
-			return nil, xerrors.Errorf("failed to run %v: %w", cmd.Args, err)
-		}
-		scanner := bufio.NewScanner(&outBuf)
-		for scanner.Scan() {
-			headers = append(headers, scanner.Text())
-		}
-		if err := scanner.Err(); err != nil {
-			return nil, xerrors.Errorf("scan %v: %w", cmd.Args, err)
-		}
-	}
-	for _, header := range headers {
-		parts := strings.SplitN(header, "=", 2)
-		if len(parts) < 2 {
-			return nil, xerrors.Errorf("split header %q had less than two parts", header)
-		}
-		transport.Header.Add(parts[0], parts[1])
-	}
-	return transport, nil
+	return headerTransport(ctx, serverURL, r.header, r.headerCommand)
 }
 
 func (r *RootCmd) configureClient(ctx context.Context, client *codersdk.Client, serverURL *url.URL, inv *serpent.Invocation) error {
@@ -1273,3 +1236,46 @@ type roundTripper func(req *http.Request) (*http.Response, error)
 func (r roundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
 	return r(req)
 }
+
+// HeaderTransport creates a new transport that executes `--header-command`
+// if it is set to add headers for all outbound requests.
+func headerTransport(ctx context.Context, serverURL *url.URL, header []string, headerCommand string) (*codersdk.HeaderTransport, error) {
+	transport := &codersdk.HeaderTransport{
+		Transport: http.DefaultTransport,
+		Header:    http.Header{},
+	}
+	headers := header
+	if headerCommand != "" {
+		shell := "sh"
+		caller := "-c"
+		if runtime.GOOS == "windows" {
+			shell = "cmd.exe"
+			caller = "/c"
+		}
+		var outBuf bytes.Buffer
+		// #nosec
+		cmd := exec.CommandContext(ctx, shell, caller, headerCommand)
+		cmd.Env = append(os.Environ(), "CODER_URL="+serverURL.String())
+		cmd.Stdout = &outBuf
+		cmd.Stderr = io.Discard
+		err := cmd.Run()
+		if err != nil {
+			return nil, xerrors.Errorf("failed to run %v: %w", cmd.Args, err)
+		}
+		scanner := bufio.NewScanner(&outBuf)
+		for scanner.Scan() {
+			headers = append(headers, scanner.Text())
+		}
+		if err := scanner.Err(); err != nil {
+			return nil, xerrors.Errorf("scan %v: %w", cmd.Args, err)
+		}
+	}
+	for _, header := range headers {
+		parts := strings.SplitN(header, "=", 2)
+		if len(parts) < 2 {
+			return nil, xerrors.Errorf("split header %q had less than two parts", header)
+		}
+		transport.Header.Add(parts[0], parts[1])
+	}
+	return transport, nil
+}
diff --git a/cli/testdata/coder_agent_--help.golden b/cli/testdata/coder_agent_--help.golden
@@ -15,6 +15,15 @@ OPTIONS:
       --log-stackdriver string, $CODER_AGENT_LOGGING_STACKDRIVER
           Output Stackdriver compatible logs to a given file.
 
+      --agent-header string-array, $CODER_AGENT_HEADER
+          Additional HTTP headers added to all requests. Provide as key=value.
+          Can be specified multiple times.
+
+      --agent-header-command string, $CODER_AGENT_HEADER_COMMAND
+          An external command that outputs additional HTTP headers added to all
+          requests. The command must output each header as `key=value` on its
+          own line.
+
       --auth string, $CODER_AGENT_AUTH (default: token)
           Specify the authentication type to use for the agent.