cli: set content length on `operator api` requests (#14634)

http.NewRequestWithContext will only set the right value for
Content-Length if the input is *bytes.Buffer, *bytes.Reader, or
*strings.Reader [0].

Since os.Stdin is an os.File, POST requests made with the `nomad
operator api` command would always have Content-Length set to -1, which
is interpreted as an unknown length by web servers.

[0]: https://pkg.go.dev/net/http#NewRequestWithContext

.changelog/14634.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+cli: set content length on POST requests when using the `nomad operator api` command
+```

command/operator_api.go

@@ -1,9 +1,11 @@
 package command
 
 import (
+	"bytes"
 	"crypto/tls"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"net"
 	"net/http"
 	"net/url"
@@ -16,6 +18,10 @@ import (
 	"github.com/posener/complete"
 )
 
+// Stdin represents the system's standard input, but it's declared as a
+// variable here to allow tests to override it with a regular file.
+var Stdin = os.Stdin
+
 type OperatorAPICommand struct {
 	Meta
 
@@ -139,10 +145,18 @@ func (c *OperatorAPICommand) Run(args []string) int {
 
 	// Opportunistically read from stdin and POST unless method has been
 	// explicitly set.
-	stat, _ := os.Stdin.Stat()
+	stat, _ := Stdin.Stat()
 	if (stat.Mode() & os.ModeCharDevice) == 0 {
 		verbose("* Reading request body from stdin.")
-		c.body = os.Stdin
+
+		// Load stdin into a *bytes.Reader so that http.NewRequest can set the
+		// correct Content-Length value.
+		b, err := ioutil.ReadAll(Stdin)
+		if err != nil {
+			c.Ui.Error(fmt.Sprintf("Error reading stdin: %v", err))
+			return 1
+		}
+		c.body = bytes.NewReader(b)
 		if c.method == "" {
 			c.method = "POST"
 		}

command/operator_api_test.go

@@ -5,6 +5,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"net/url"
+	"os"
 	"testing"
 	"time"
 
@@ -170,3 +171,49 @@ func Test_pathToURL(t *testing.T) {
 		})
 	}
 }
+
+// TestOperatorAPICommand_ContentLength tests that requests have the proper
+// ContentLength set.
+//
+// Don't run it in parallel as it modifies the package's Stdin variable.
+func TestOperatorAPICommand_ContentLength(t *testing.T) {
+	contentLength := make(chan int, 1)
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		contentLength <- int(r.ContentLength)
+	}))
+	defer ts.Close()
+
+	// Setup a temp file to act as stdin.
+	input := []byte("test-input")
+	fakeStdin, err := os.CreateTemp("", "fake-stdin")
+	require.NoError(t, err)
+	defer os.Remove(fakeStdin.Name())
+
+	_, err = fakeStdin.Write(input)
+	require.NoError(t, err)
+	_, err = fakeStdin.Seek(0, 0)
+	require.NoError(t, err)
+
+	// Override the package's Stdin variable for testing.
+	Stdin = fakeStdin
+	defer func() { Stdin = os.Stdin }()
+
+	// Setup command.
+	buf := bytes.NewBuffer(nil)
+	ui := &cli.BasicUi{
+		ErrorWriter: buf,
+		Writer:      buf,
+	}
+	cmd := &OperatorAPICommand{Meta: Meta{Ui: ui}}
+
+	// Assert that a request has the expected content length.
+	exitCode := cmd.Run([]string{"-address=" + ts.URL, "/v1/jobs"})
+	require.Zero(t, exitCode, buf.String())
+
+	select {
+	case l := <-contentLength:
+		require.Equal(t, len(input), l)
+	case <-time.After(10 * time.Second):
+		t.Fatalf("timed out waiting for request")
+	}
+}