Permit '=' separator and '[ipv6]' in --add-host

Fixes docker/cli#4648

Make it easier to specify IPv6 addresses in the '--add-host' option by
permitting 'host=ip' in addition to 'host:ip', and allowing square
brackets around the address.

For example:

    --add-host=hostname:127.0.0.1
    --add-host=hostname:::1
    --add-host=hostname=::1
    --add-host=hostname=[::1]

Signed-off-by: Rob Murray <rob.murray@docker.com>

build/utils.go

@@ -65,7 +65,10 @@ func toBuildkitExtraHosts(ctx context.Context, inp []string, nodeDriver *driver.
 	}
 	hosts := make([]string, 0, len(inp))
 	for _, h := range inp {
-		host, ip, ok := strings.Cut(h, ":")
+		host, ip, ok := strings.Cut(h, "=")
+		if !ok {
+			host, ip, ok = strings.Cut(h, ":")
+		}
 		if !ok || host == "" || ip == "" {
 			return "", errors.Errorf("invalid host %s", h)
 		}
@@ -77,8 +80,16 @@ func toBuildkitExtraHosts(ctx context.Context, inp []string, nodeDriver *driver.
 				return "", errors.Wrap(err, "unable to derive the IP value for host-gateway")
 			}
 			ip = hgip.String()
-		} else if net.ParseIP(ip) == nil {
+		} else {
-			return "", errors.Errorf("invalid host %s", h)
+			// If the address is enclosed in square brackets, extract it (for IPv6, but
+			// permit it for IPv4 as well; we don't know the address family here, but it's
+			// unambiguous).
+			if len(ip) > 2 && ip[0] == '[' && ip[len(ip)-1] == ']' {
+				ip = ip[1 : len(ip)-1]
+			}
+			if net.ParseIP(ip) == nil {
+				return "", errors.Errorf("invalid host %s", h)
+			}
 		}
 		hosts = append(hosts, host+"="+ip)
 	}

build/utils_test.go

@@ -0,0 +1,148 @@
+package build
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestToBuildkitExtraHosts(t *testing.T) {
+	tests := []struct {
+		doc         string
+		input       []string
+		expectedOut string // Expect output==input if not set.
+		expectedErr string // Expect success if not set.
+	}{
+		{
+			doc:         "IPv4, colon sep",
+			input:       []string{`myhost:192.168.0.1`},
+			expectedOut: `myhost=192.168.0.1`,
+		},
+		{
+			doc:   "IPv4, eq sep",
+			input: []string{`myhost=192.168.0.1`},
+		},
+		{
+			doc:         "Weird but permitted, IPv4 with brackets",
+			input:       []string{`myhost=[192.168.0.1]`},
+			expectedOut: `myhost=192.168.0.1`,
+		},
+		{
+			doc:         "Host and domain",
+			input:       []string{`host.and.domain.invalid:10.0.2.1`},
+			expectedOut: `host.and.domain.invalid=10.0.2.1`,
+		},
+		{
+			doc:         "IPv6, colon sep",
+			input:       []string{`anipv6host:2003:ab34:e::1`},
+			expectedOut: `anipv6host=2003:ab34:e::1`,
+		},
+		{
+			doc:         "IPv6, colon sep, brackets",
+			input:       []string{`anipv6host:[2003:ab34:e::1]`},
+			expectedOut: `anipv6host=2003:ab34:e::1`,
+		},
+		{
+			doc:         "IPv6, eq sep, brackets",
+			input:       []string{`anipv6host=[2003:ab34:e::1]`},
+			expectedOut: `anipv6host=2003:ab34:e::1`,
+		},
+		{
+			doc:         "IPv6 localhost, colon sep",
+			input:       []string{`ipv6local:::1`},
+			expectedOut: `ipv6local=::1`,
+		},
+		{
+			doc:   "IPv6 localhost, eq sep",
+			input: []string{`ipv6local=::1`},
+		},
+		{
+			doc:         "IPv6 localhost, eq sep, brackets",
+			input:       []string{`ipv6local=[::1]`},
+			expectedOut: `ipv6local=::1`,
+		},
+		{
+			doc:         "IPv6 localhost, non-canonical, colon sep",
+			input:       []string{`ipv6local:0:0:0:0:0:0:0:1`},
+			expectedOut: `ipv6local=0:0:0:0:0:0:0:1`,
+		},
+		{
+			doc:   "IPv6 localhost, non-canonical, eq sep",
+			input: []string{`ipv6local=0:0:0:0:0:0:0:1`},
+		},
+		{
+			doc:         "IPv6 localhost, non-canonical, eq sep, brackets",
+			input:       []string{`ipv6local=[0:0:0:0:0:0:0:1]`},
+			expectedOut: `ipv6local=0:0:0:0:0:0:0:1`,
+		},
+		{
+			doc:         "Bad address, colon sep",
+			input:       []string{`myhost:192.notanipaddress.1`},
+			expectedErr: `invalid IP address in add-host: "192.notanipaddress.1"`,
+		},
+		{
+			doc:         "Bad address, eq sep",
+			input:       []string{`myhost=192.notanipaddress.1`},
+			expectedErr: `invalid IP address in add-host: "192.notanipaddress.1"`,
+		},
+		{
+			doc:         "No sep",
+			input:       []string{`thathost-nosemicolon10.0.0.1`},
+			expectedErr: `bad format for add-host: "thathost-nosemicolon10.0.0.1"`,
+		},
+		{
+			doc:         "Bad IPv6",
+			input:       []string{`anipv6host:::::1`},
+			expectedErr: `invalid IP address in add-host: "::::1"`,
+		},
+		{
+			doc:         "Bad IPv6, trailing colons",
+			input:       []string{`ipv6local:::0::`},
+			expectedErr: `invalid IP address in add-host: "::0::"`,
+		},
+		{
+			doc:         "Bad IPv6, missing close bracket",
+			input:       []string{`ipv6addr=[::1`},
+			expectedErr: `invalid IP address in add-host: "[::1"`,
+		},
+		{
+			doc:         "Bad IPv6, missing open bracket",
+			input:       []string{`ipv6addr=::1]`},
+			expectedErr: `invalid IP address in add-host: "::1]"`,
+		},
+		{
+			doc:         "Missing address, colon sep",
+			input:       []string{`myhost.invalid:`},
+			expectedErr: `invalid IP address in add-host: ""`,
+		},
+		{
+			doc:         "Missing address, eq sep",
+			input:       []string{`myhost.invalid=`},
+			expectedErr: `invalid IP address in add-host: ""`,
+		},
+		{
+			doc:         "No input",
+			input:       []string{``},
+			expectedErr: `bad format for add-host: ""`,
+		},
+	}
+
+	for _, tc := range tests {
+		tc := tc
+		if tc.expectedOut == "" {
+			tc.expectedOut = strings.Join(tc.input, ",")
+		}
+		t.Run(tc.doc, func(t *testing.T) {
+			actualOut, actualErr := toBuildkitExtraHosts(context.TODO(), tc.input, nil)
+			if tc.expectedErr == "" {
+				require.Equal(t, tc.expectedOut, actualOut)
+				require.Nil(t, actualErr)
+			} else {
+				require.Zero(t, actualOut)
+				require.Error(t, actualErr, tc.expectedErr)
+			}
+		})
+	}
+}