README.md

@@ -96,11 +96,10 @@ expiration 1704067200:
 4. URL:
    `/v1/image/cdn.example.com/photos/cat.jpg/800x600.webp?sig=<base64url>&exp=1704067200`
 
-**Whitelist patterns:**
-
-- **Exact match**: `cdn.example.com` — matches only that host
-- **Suffix match**: `.example.com` — matches `cdn.example.com`,
-  `images.example.com`, and `example.com`
+**Whitelist entries** are exact host matches only (e.g.
+`cdn.example.com`). Suffix/wildcard matching is not supported —
+signatures are per-URL, so each allowed host must be listed
+explicitly.
 
 ### Configuration
 

config.example.yml

@@ -13,8 +13,7 @@ state_dir: ./data
 # Generate with: openssl rand -base64 32
 signing_key: "CHANGE_ME_generate_with_openssl_rand_base64_32"
 
-# Hosts that don't require signatures
-# Use "." prefix for wildcard subdomain matching (e.g., ".example.com" matches "cdn.example.com")
+# Hosts that don't require signatures (exact match only)
 whitelist_hosts:
   - s3.sneak.cloud
   - static.sneak.cloud

internal/imgcache/whitelist.go

@@ -5,23 +5,20 @@ import (
 	"strings"
 )
 
-// HostWhitelist implements the Whitelist interface for checking allowed source hosts.
+// HostWhitelist checks whether a source host is allowed without a signature.
+// Only exact host matches are supported. Signatures are per-URL, so
+// wildcard/suffix matching is intentionally not provided.
 type HostWhitelist struct {
 	// exactHosts contains hosts that must match exactly (e.g., "cdn.example.com")
 	exactHosts map[string]struct{}
-	// suffixHosts contains domain suffixes to match (e.g., ".example.com" matches "cdn.example.com")
-	suffixHosts []string
 }
 
-// NewHostWhitelist creates a whitelist from a list of host patterns.
-// Patterns starting with "." are treated as suffix matches.
-// Examples:
-//   - "cdn.example.com" - exact match only
-//   - ".example.com" - matches cdn.example.com, images.example.com, etc.
+// NewHostWhitelist creates a whitelist from a list of hostnames.
+// Each entry is treated as an exact host match. Leading dots are
+// stripped so that legacy ".example.com" entries become "example.com".
 func NewHostWhitelist(patterns []string) *HostWhitelist {
 	w := &HostWhitelist{
 		exactHosts: make(map[string]struct{}),
-		suffixHosts: make([]string, 0),
 	}
 
 	for _, pattern := range patterns {
@@ -30,9 +27,11 @@ func NewHostWhitelist(patterns []string) *HostWhitelist {
 			continue
 		}
 
-		if strings.HasPrefix(pattern, ".") {
-			w.suffixHosts = append(w.suffixHosts, pattern)
-		} else {
+		// Strip leading dot — suffix matching is no longer supported;
+		// ".example.com" is normalised to "example.com" as an exact entry.
+		pattern = strings.TrimPrefix(pattern, ".")
+
+		if pattern != "" {
 			w.exactHosts[pattern] = struct{}{}
 		}
 	}
@@ -40,7 +39,7 @@ func NewHostWhitelist(patterns []string) *HostWhitelist {
 	return w
 }
 
-// IsWhitelisted checks if a URL's host is in the whitelist.
+// IsWhitelisted checks if a URL's host is in the whitelist (exact match only).
 func (w *HostWhitelist) IsWhitelisted(u *url.URL) bool {
 	if u == nil {
 		return false
@@ -51,32 +50,17 @@ func (w *HostWhitelist) IsWhitelisted(u *url.URL) bool {
 		return false
 	}
 
-	// Check exact match
-	if _, ok := w.exactHosts[host]; ok {
-		return true
-	}
+	_, ok := w.exactHosts[host]
 
-	// Check suffix match
-	for _, suffix := range w.suffixHosts {
-		if strings.HasSuffix(host, suffix) {
-			return true
-		}
-		// Also match if host equals the suffix without the leading dot
-		// e.g., pattern ".example.com" should match "example.com"
-		if host == strings.TrimPrefix(suffix, ".") {
-			return true
-		}
-	}
-
-	return false
+	return ok
 }
 
 // IsEmpty returns true if the whitelist has no entries.
 func (w *HostWhitelist) IsEmpty() bool {
-	return len(w.exactHosts) == 0 && len(w.suffixHosts) == 0
+	return len(w.exactHosts) == 0
 }
 
 // Count returns the total number of whitelist entries.
 func (w *HostWhitelist) Count() int {
-	return len(w.exactHosts) + len(w.suffixHosts)
+	return len(w.exactHosts)
 }

internal/imgcache/whitelist_test.go

@@ -31,41 +31,41 @@ func TestHostWhitelist_IsWhitelisted(t *testing.T) {
 			want:     false,
 		},
 		{
-			name:     "suffix match",
-			patterns: []string{".example.com"},
+			name:     "no suffix matching for subdomains",
+			patterns: []string{"example.com"},
 			testURL:  "https://cdn.example.com/image.jpg",
-			want:     true,
+			want:     false,
 		},
 		{
-			name:     "suffix match deep subdomain",
-			patterns: []string{".example.com"},
-			testURL:  "https://cdn.images.example.com/image.jpg",
-			want:     true,
-		},
-		{
-			name:     "suffix match apex domain",
+			name:     "leading dot stripped to exact match",
 			patterns: []string{".example.com"},
 			testURL:  "https://example.com/image.jpg",
 			want:     true,
 		},
 		{
-			name:     "suffix match not found",
+			name:     "leading dot does not enable suffix matching",
 			patterns: []string{".example.com"},
-			testURL:  "https://notexample.com/image.jpg",
+			testURL:  "https://cdn.example.com/image.jpg",
 			want:     false,
 		},
 		{
-			name:     "suffix match partial not allowed",
+			name:     "leading dot does not match deep subdomain",
 			patterns: []string{".example.com"},
-			testURL:  "https://fakeexample.com/image.jpg",
+			testURL:  "https://cdn.images.example.com/image.jpg",
 			want:     false,
 		},
 		{
-			name:     "multiple patterns",
-			patterns: []string{"cdn.example.com", ".images.org", "static.test.net"},
+			name:     "multiple patterns exact only",
+			patterns: []string{"cdn.example.com", "photos.images.org", "static.test.net"},
 			testURL:  "https://photos.images.org/image.jpg",
 			want:     true,
 		},
+		{
+			name:     "multiple patterns no suffix leak",
+			patterns: []string{"cdn.example.com", "images.org"},
+			testURL:  "https://photos.images.org/image.jpg",
+			want:     false,
+		},
 		{
 			name:     "empty whitelist",
 			patterns: []string{},
@@ -86,7 +86,7 @@ func TestHostWhitelist_IsWhitelisted(t *testing.T) {
 		},
 		{
 			name:     "whitespace in patterns",
-			patterns: []string{"  cdn.example.com  ", "  .other.com  "},
+			patterns: []string{"  cdn.example.com  ", "  other.com  "},
 			testURL:  "https://cdn.example.com/image.jpg",
 			want:     true,
 		},
@@ -139,6 +139,11 @@ func TestHostWhitelist_IsEmpty(t *testing.T) {
 			patterns: []string{"example.com"},
 			want:     false,
 		},
+		{
+			name:     "leading dot normalised to entry",
+			patterns: []string{".example.com"},
+			want:     false,
+		},
 	}
 
 	for _, tt := range tests {
@@ -168,14 +173,14 @@ func TestHostWhitelist_Count(t *testing.T) {
 			want:     3,
 		},
 		{
-			name:     "suffix hosts only",
+			name:     "leading dots normalised to exact",
 			patterns: []string{".a.com", ".b.com"},
 			want:     2,
 		},
 		{
-			name:     "mixed",
-			patterns: []string{"exact.com", ".suffix.com"},
-			want:     2,
+			name:     "mixed deduplication",
+			patterns: []string{"example.com", ".example.com"},
+			want:     1,
 		},
 	}