use client consts for environment variable names

It's slightly more verbose, but helps finding the purpose of each
of the environment variables. In tests, I kept the fixed strings.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/cli.go

@@ -411,7 +411,7 @@ func getServerHost(hosts []string, tlsOptions *tlsconfig.Options) (string, error
 	var host string
 	switch len(hosts) {
 	case 0:
-		host = os.Getenv("DOCKER_HOST")
+		host = os.Getenv(client.EnvOverrideHost)
 	case 1:
 		host = hosts[0]
 	default:
@@ -429,7 +429,7 @@ func UserAgent() string {
 // resolveContextName resolves the current context name with the following rules:
 // - setting both --context and --host flags is ambiguous
 // - if --context is set, use this value
-// - if --host flag or DOCKER_HOST is set, fallbacks to use the same logic as before context-store was added
+// - if --host flag or DOCKER_HOST (client.EnvOverrideHost) is set, fallbacks to use the same logic as before context-store was added
 // for backward compatibility with existing scripts
 // - if DOCKER_CONTEXT is set, use this value
 // - if Config file has a globally set "CurrentContext", use this value
@@ -444,7 +444,7 @@ func resolveContextName(opts *cliflags.CommonOptions, config *configfile.ConfigF
 	if len(opts.Hosts) > 0 {
 		return DefaultContextName, nil
 	}
-	if _, present := os.LookupEnv("DOCKER_HOST"); present {
+	if _, present := os.LookupEnv(client.EnvOverrideHost); present {
 		return DefaultContextName, nil
 	}
 	if ctxName, ok := os.LookupEnv("DOCKER_CONTEXT"); ok {

cli/command/context/list.go

@@ -10,6 +10,7 @@ import (
 	"github.com/docker/cli/cli/command/formatter"
 	"github.com/docker/cli/cli/context/docker"
 	flagsHelper "github.com/docker/cli/cli/flags"
+	"github.com/docker/docker/client"
 	"github.com/fvbommel/sortorder"
 	"github.com/spf13/cobra"
 )
@@ -73,9 +74,9 @@ func runList(dockerCli command.Cli, opts *listOptions) error {
 	if err := format(dockerCli, opts, contexts); err != nil {
 		return err
 	}
-	if os.Getenv("DOCKER_HOST") != "" {
-		fmt.Fprint(dockerCli.Err(), "Warning: DOCKER_HOST environment variable overrides the active context. "+
-			"To use a context, either set the global --context flag, or unset DOCKER_HOST environment variable.\n")
+	if os.Getenv(client.EnvOverrideHost) != "" {
+		fmt.Fprintf(dockerCli.Err(), "Warning: %[1]s environment variable overrides the active context. "+
+			"To use a context, either set the global --context flag, or unset %[1]s environment variable.\n", client.EnvOverrideHost)
 	}
 	return nil
 }

cli/command/context/use.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/docker/cli/cli/command"
 	"github.com/docker/cli/cli/context/store"
+	"github.com/docker/docker/client"
 	"github.com/spf13/cobra"
 )
 
@@ -41,9 +42,9 @@ func RunUse(dockerCli command.Cli, name string) error {
 	}
 	fmt.Fprintln(dockerCli.Out(), name)
 	fmt.Fprintf(dockerCli.Err(), "Current context is now %q\n", name)
-	if os.Getenv("DOCKER_HOST") != "" {
-		fmt.Fprintf(dockerCli.Err(), "Warning: DOCKER_HOST environment variable overrides the active context. "+
-			"To use %q, either set the global --context flag, or unset DOCKER_HOST environment variable.\n", name)
+	if os.Getenv(client.EnvOverrideHost) != "" {
+		fmt.Fprintf(dockerCli.Err(), "Warning: %[1]s environment variable overrides the active context. "+
+			"To use %[2]q, either set the global --context flag, or unset %[1]s environment variable.\n", client.EnvOverrideHost, name)
 	}
 	return nil
 }

cli/flags/common.go

@@ -7,6 +7,7 @@ import (
 
 	"github.com/docker/cli/cli/config"
 	"github.com/docker/cli/opts"
+	"github.com/docker/docker/client"
 	"github.com/docker/go-connections/tlsconfig"
 	"github.com/sirupsen/logrus"
 	"github.com/spf13/pflag"
@@ -36,9 +37,10 @@ Refer to https://docs.docker.com/go/formatting/ for more information about forma
 )
 
 var (
-	dockerCertPath  = os.Getenv("DOCKER_CERT_PATH")
-	dockerTLSVerify = os.Getenv("DOCKER_TLS_VERIFY") != ""
-	dockerTLS       = os.Getenv("DOCKER_TLS") != ""
+	dockerCertPath  = os.Getenv(client.EnvOverrideCertPath)
+	dockerTLSVerify = os.Getenv(client.EnvTLSVerify) != ""
+	// TODO(thaJeztah) the 'DOCKER_TLS' environment variable is not documented, and does not have a const.
+	dockerTLS = os.Getenv("DOCKER_TLS") != ""
 )
 
 // CommonOptions are options common to both the client and the daemon.
@@ -84,7 +86,7 @@ func (commonOpts *CommonOptions) InstallFlags(flags *pflag.FlagSet) {
 	hostOpt := opts.NewNamedListOptsRef("hosts", &commonOpts.Hosts, nil)
 	flags.VarP(hostOpt, "host", "H", "Daemon socket(s) to connect to")
 	flags.StringVarP(&commonOpts.Context, "context", "c", "",
-		`Name of the context to use to connect to the daemon (overrides DOCKER_HOST env var and default context set with "docker context use")`)
+		`Name of the context to use to connect to the daemon (overrides `+client.EnvOverrideHost+` env var and default context set with "docker context use")`)
 }
 
 // SetDefaultOptions sets default values for options after flag parsing is

internal/test/environment/testenv.go

@@ -7,6 +7,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/docker/docker/client"
 	"github.com/pkg/errors"
 	"gotest.tools/v3/icmd"
 	"gotest.tools/v3/poll"
@@ -19,15 +20,15 @@ func Setup() error {
 	if dockerHost == "" {
 		return errors.New("$TEST_DOCKER_HOST must be set")
 	}
-	if err := os.Setenv("DOCKER_HOST", dockerHost); err != nil {
+	if err := os.Setenv(client.EnvOverrideHost, dockerHost); err != nil {
 		return err
 	}
 
 	if dockerCertPath := os.Getenv("TEST_DOCKER_CERT_PATH"); dockerCertPath != "" {
-		if err := os.Setenv("DOCKER_CERT_PATH", dockerCertPath); err != nil {
+		if err := os.Setenv(client.EnvOverrideCertPath, dockerCertPath); err != nil {
 			return err
 		}
-		if err := os.Setenv("DOCKER_TLS_VERIFY", "1"); err != nil {
+		if err := os.Setenv(client.EnvTLSVerify, "1"); err != nil {
 			return err
 		}
 	}