udpates after review:

* rename "--postFile" to just "--file"
* add unit tests for "--file"
* reword help description

client/go/internal/cli/cmd/query.go

@@ -56,7 +56,7 @@ can be set by the syntax [parameter-name]=[value].`,
 		},
 	}
 	cmd.Flags().BoolVarP(&printCurl, "verbose", "v", false, "Print the equivalent curl command for the query")
-	cmd.Flags().StringVarP(&postFile, "postFile", "", "", "Use the given JSON file, POST to the query API")
+	cmd.Flags().StringVarP(&postFile, "file", "", "", "Read query parameters from the given JSON file and send a POST request, with overrides from arguments")
 	cmd.Flags().StringVarP(&format, "format", "", "human", "Output format. Must be 'human' (human-readable) or 'plain' (no formatting)")
 	cmd.Flags().StringSliceVarP(&headers, "header", "", nil, "Add a header to the HTTP request, on the format 'Header: Value'. This can be specified multiple times")
 	cmd.Flags().IntVarP(&queryTimeoutSecs, "timeout", "T", 10, "Timeout for the query in seconds")
@@ -84,10 +84,6 @@ func printCurl(stderr io.Writer, req *http.Request, postFile string, service *ve
 	return err
 }
 
-type nopCloser struct{ io.Reader }
-
-func (nopCloser) Close() error { return nil }
-
 func query(cli *CLI, arguments []string, timeoutSecs int, curl bool, format string, postFile string, headers []string, waiter *Waiter) error {
 	target, err := cli.target(targetOptions{})
 	if err != nil {
@@ -102,10 +98,7 @@ func query(cli *CLI, arguments []string, timeoutSecs int, curl bool, format stri
 	default:
 		return fmt.Errorf("invalid format: %s", format)
 	}
-	url, _ := url.Parse(service.BaseURL + "/search/")
-	if strings.HasSuffix(service.BaseURL, "/") {
-		url, _ = url.Parse(service.BaseURL + "search/")
-	}
+	url, _ := url.Parse(strings.TrimSuffix(service.BaseURL, "/") + "/search/")
 	urlQuery := url.Query()
 	for i := range len(arguments) {
 		key, value := splitArg(arguments[i])
@@ -133,7 +126,7 @@ func query(cli *CLI, arguments []string, timeoutSecs int, curl bool, format stri
 		}
 		header.Set("Content-Type", "application/json")
 		hReq.Method = "POST"
-		hReq.Body = nopCloser{bytes.NewBuffer(bytes.Clone(json))}
+		hReq.Body = io.NopCloser(bytes.NewBuffer(bytes.Clone(json)))
 		if err != nil {
 			return fmt.Errorf("bad postFile '%s': %w", postFile, err)
 		}

client/go/internal/cli/cmd/query_test.go

@@ -6,10 +6,13 @@ package cmd
 
 import (
 	"net/http"
+	"os"
+	"path/filepath"
 	"strconv"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 	"github.com/vespa-engine/vespa/client/go/internal/mock"
 )
 
@@ -134,6 +137,51 @@ data: {
 	assertStreamingQuery(t, bodyWithError, bodyWithError, "--format=plain")
 }
 
+func TestQueryPostFile(t *testing.T) {
+	mockResponse := `{"query":"result"}"`
+	client := &mock.HTTPClient{ReadBody: true}
+	client.NextResponseString(200, mockResponse)
+	cli, stdout, _ := newTestCLI(t)
+	cli.httpClient = client
+
+	tmpFileName := filepath.Join(t.TempDir(), "tq1.json")
+	jsonQuery := []byte(`{"yql": "some yql here"}`)
+	require.Nil(t, os.WriteFile(tmpFileName, jsonQuery, 0644))
+
+	assert.Nil(t, cli.Run("-t", "http://127.0.0.1:8080", "query", "--file", tmpFileName))
+	assert.Equal(t, mockResponse+"\n", stdout.String())
+	assert.Equal(t, `{"timeout":"10s","yql":"some yql here"}`, string(client.LastBody))
+	assert.Equal(t, []string{"application/json"}, client.LastRequest.Header.Values("Content-Type"))
+	assert.Equal(t, "POST", client.LastRequest.Method)
+	assert.Equal(t, "http://127.0.0.1:8080/search/", client.LastRequest.URL.String())
+}
+
+func TestQueryPostFileWithArgs(t *testing.T) {
+	mockResponse := `{"query":"result"}"`
+	client := &mock.HTTPClient{ReadBody: true}
+	client.NextResponseString(200, mockResponse)
+	cli, _, _ := newTestCLI(t)
+	cli.httpClient = client
+
+	tmpFileName := filepath.Join(t.TempDir(), "tq2.json")
+	jsonQuery := []byte(`{"yql": "some yql here"}`)
+	require.Nil(t, os.WriteFile(tmpFileName, jsonQuery, 0644))
+
+	assert.Nil(t, cli.Run(
+		"-t", "http://foo.bar:1234/",
+		"query",
+		"--file", tmpFileName,
+		"yql=foo bar",
+		"tracelevel=3",
+		"dispatch.docsumRetryLimit=42"))
+	assert.Equal(t,
+		`{"dispatch.docsumRetryLimit":"42","timeout":"10s","tracelevel":"3","yql":"foo bar"}`,
+		string(client.LastBody))
+	assert.Equal(t, []string{"application/json"}, client.LastRequest.Header.Values("Content-Type"))
+	assert.Equal(t, "POST", client.LastRequest.Method)
+	assert.Equal(t, "http://foo.bar:1234/search/", client.LastRequest.URL.String())
+}
+
 func assertStreamingQuery(t *testing.T, expectedOutput, body string, args ...string) {
 	t.Helper()
 	client := &mock.HTTPClient{}