add "valid until" option to limit lifetime of signed requests

Closes #222

Co-authored-by: Will Norris <will@willnorris.com>

README.md

@@ -312,6 +312,14 @@ If both a whiltelist and signatureKey are specified, requests can match either.
 In other words, requests that match one of the allowed hosts don't necessarily
 need to be signed, though they can be.
 
+To limit how long a URL is valid (particularly useful for signed URLs),
+you can specify a "valid until" time using the `vu` option with a Unix timestamp.
+For example, the following signed URL would only be valid until 2020-01-01:
+
+```
+http://localhost:8080/vu1577836800,sjNcVf6LxzKEvR6Owgg3zhEMN7xbWxlpf-eyYbRfFK4A=/https://example.com/image
+```
+
 ### Default Base URL
 
 Typically, remote images to be proxied are specified as absolute URLs.

data.go

@@ -12,6 +12,7 @@ import (
 	"sort"
 	"strconv"
 	"strings"
+	"time"
 	"unicode"
 )
 
@@ -33,6 +34,7 @@ const (
 	optCropHeight      = "ch"
 	optSmartCrop       = "sc"
 	optTrim            = "trim"
+	optValidUntil      = "vu"
 )
 
 // URLError reports a malformed URL error.
@@ -86,6 +88,9 @@ type Options struct {
 
 	// If true, automatically trim pixels of the same color around the edges
 	Trim bool
+
+	// If non-zero, the URL is valid until this time.
+	ValidUntil time.Time
 }
 
 func (o Options) String() string {
@@ -132,7 +137,12 @@ func (o Options) String() string {
 	if o.Trim {
 		opts = append(opts, optTrim)
 	}
+	if !o.ValidUntil.IsZero() {
+		opts = append(opts, fmt.Sprintf("%s%d", optValidUntil, o.ValidUntil.Unix()))
+	}
+
 	sort.Strings(opts)
+
 	return strings.Join(opts, ",")
 }
 
@@ -235,6 +245,11 @@ func (o Options) transform() bool {
 // that have been resized or cropped.  The trim option is applied before other
 // options such as cropping or resizing.
 //
+// # Valid Until
+//
+// The "vu{unixtime}" option specifies a Unix timestamp at which the request URL is no longer valid.
+// For example, "vu1800000000" would mean the URL is valid until 2027-01-15T08:00:00Z.
+//
 // Examples
 //
 //	0x0         - no resizing
@@ -289,6 +304,11 @@ func ParseOptions(str string) Options {
 		case strings.HasPrefix(opt, optCropHeight):
 			value := strings.TrimPrefix(opt, optCropHeight)
 			options.CropHeight, _ = strconv.ParseFloat(value, 64)
+		case strings.HasPrefix(opt, optValidUntil):
+			value := strings.TrimPrefix(opt, optValidUntil)
+			if v, _ := strconv.ParseInt(value, 10, 64); v > 0 {
+				options.ValidUntil = time.Unix(v, 0)
+			}
 		case strings.Contains(opt, optSizeDelimiter):
 			size := strings.SplitN(opt, optSizeDelimiter, 2)
 			if w := size[0]; w != "" {

data_test.go

@@ -7,6 +7,7 @@ import (
 	"net/http"
 	"net/url"
 	"testing"
+	"time"
 )
 
 var emptyOptions = Options{}
@@ -25,8 +26,8 @@ func TestOptions_String(t *testing.T) {
 			"1x2,fh,fit,fv,q80,r90",
 		},
 		{
-			Options{Width: 0.15, Height: 1.3, Rotate: 45, Quality: 95, Signature: "c0ffee", Format: "png"},
-			"0.15x1.3,png,q95,r45,sc0ffee",
+			Options{Width: 0.15, Height: 1.3, Rotate: 45, Quality: 95, Signature: "c0ffee", Format: "png", ValidUntil: time.Unix(123, 0)},
+			"0.15x1.3,png,q95,r45,sc0ffee,vu123",
 		},
 		{
 			Options{Width: 0.15, Height: 1.3, CropX: 100, CropY: 200},
@@ -86,7 +87,7 @@ func TestParseOptions(t *testing.T) {
 		// flags, in different orders
 		{"q70,1x2,fit,r90,fv,fh,sc0ffee,png", Options{Width: 1, Height: 2, Fit: true, Rotate: 90, FlipVertical: true, FlipHorizontal: true, Quality: 70, Signature: "c0ffee", Format: "png"}},
 		{"r90,fh,sc0ffee,png,q90,1x2,fv,fit", Options{Width: 1, Height: 2, Fit: true, Rotate: 90, FlipVertical: true, FlipHorizontal: true, Quality: 90, Signature: "c0ffee", Format: "png"}},
-		{"cx100,cw300,1x2,cy200,ch400,sc,scaleUp", Options{Width: 1, Height: 2, ScaleUp: true, CropX: 100, CropY: 200, CropWidth: 300, CropHeight: 400, SmartCrop: true}},
+		{"cx100,cw300,1x2,cy200,ch400,sc,scaleUp,vu1234567890", Options{Width: 1, Height: 2, ScaleUp: true, CropX: 100, CropY: 200, CropWidth: 300, CropHeight: 400, SmartCrop: true, ValidUntil: time.Unix(1234567890, 0)}},
 	}
 
 	for _, tt := range tests {

imageproxy.go

@@ -101,6 +101,8 @@ type Proxy struct {
 	// remote server specifies 'private' or 'no-store' in the cache-control
 	// header.
 	ForceCache bool
+
+	timeNow time.Time // current time, used for testing
 }
 
 // NewProxy constructs a new proxy.  The provided http RoundTripper will be
@@ -278,7 +280,6 @@ func (p *Proxy) serveImage(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 	resp, err := p.Client.Do(actualReq)
-
 	if err != nil {
 		msg := fmt.Sprintf("error fetching remote image: %v", err)
 		p.log(msg)
@@ -371,15 +372,29 @@ var (
 	errDeniedHost       = errors.New("request contains a denied host")
 	errNotAllowed       = errors.New("request does not contain an allowed host or valid signature")
 	errTooManyRedirects = errors.New("too many redirects")
+	errNotValid         = errors.New("request is no longer valid")
 
 	msgNotAllowed           = "requested URL is not allowed"
 	msgNotAllowedInRedirect = "requested URL in redirect is not allowed"
 )
 
+func (p *Proxy) now() time.Time {
+	if !p.timeNow.IsZero() {
+		return p.timeNow
+	}
+	return time.Now()
+}
+
 // allowed determines whether the specified request contains an allowed
 // referrer, host, and signature.  It returns an error if the request is not
-// allowed.
+// allowed or not valid any longer.
 func (p *Proxy) allowed(r *Request) error {
+	if !r.Options.ValidUntil.IsZero() {
+		if !p.now().Before(r.Options.ValidUntil) {
+			return errNotValid
+		}
+	}
+
 	if len(p.Referrers) > 0 && !referrerMatches(p.Referrers, r.Original) {
 		return errReferrer
 	}

imageproxy_test.go

@@ -110,8 +110,11 @@ func TestAllowed(t *testing.T) {
 		return req
 	}
 
+	now := time.Date(2020, 1, 1, 0, 0, 0, 0, time.UTC)
+
 	tests := []struct {
 		url        string
+		now        time.Time
 		options    Options
 		allowHosts []string
 		denyHosts  []string
@@ -153,6 +156,11 @@ func TestAllowed(t *testing.T) {
 		{url: "http://test/image", options: Options{Signature: "NDx5zZHx7QfE8E-ijowRreq6CJJBZjwiRfOVk_mkfQQ="}, denyHosts: []string{"test"}, keys: key, allowed: false},
 		{url: "http://127.0.0.1/image", denyHosts: []string{"127.0.0.0/8"}, allowed: false},
 		{url: "http://127.0.0.1:3000/image", denyHosts: []string{"127.0.0.0/8"}, allowed: false},
+
+		// valid until options
+		{url: "http://test/image", now: now, options: Options{ValidUntil: now.Add(time.Second)}, allowed: true},
+		{url: "http://test/image", now: now, options: Options{ValidUntil: now.Add(-time.Second)}, allowed: false},
+		{url: "http://test/image", now: now, options: Options{ValidUntil: now}, allowed: false},
 	}
 
 	for _, tt := range tests {
@@ -161,6 +169,7 @@ func TestAllowed(t *testing.T) {
 		p.DenyHosts = tt.denyHosts
 		p.SignatureKeys = tt.keys
 		p.Referrers = tt.referrers
+		p.timeNow = tt.now
 
 		u, err := url.Parse(tt.url)
 		if err != nil {