Lower-case the image URL's host and require a signature for a port (closes #246)

With cdn.example.com allowlisted, CDN.Example.com and
cdn.example.com:8443 passed the allowlist too, and each spelling had its
own cache entries and its own connections under
upstream_connections_per_host. The image URL parser now lower-cases the
host and refuses one holding "@" with ErrInvalidHost (400).
ValidateRequest counts a host followed by ":", with or without a port,
as not allowlisted, so it needs a signature. That check is not in
allowlist.IsAllowed, which also matches referer_blocklist. A URL is now
signed over the lower-cased host; README.md says so.

Model: opus-5-5

README.md

@@ -26,11 +26,6 @@ make docker
 docker run -p 8080:8080 -e PIXA_SIGNING_KEY="$(openssl rand -base64 32)" pixa:latest
 ```
 
-The example config allowlists no host (`allowlist_hosts`), so pixa serves an
-image only for a signed or encrypted URL. Every image on an allowlisted host is
-served to anyone without a signature, at any size and in any format, so
-allowlist only hosts you control, where nobody else can put images.
-
 A container takes its settings from environment variables (see Configuration
 below for the list). Only `PIXA_SIGNING_KEY` is required; if it is unset the
 container exits at startup naming the variable. Everything else has a built-in
@@ -120,9 +115,7 @@ What the [upaas](https://git.eeqj.de/sneak/upaas) app for pixa needs:
     - `PIXA_SIGNING_KEY` (required): secret for signed and encrypted URLs and
       login, 32+ characters, for example from `openssl rand -base64 32`
     - `PIXA_ALLOWLIST_HOSTS`: upstream hosts served without a signature,
-      comma-separated; default none. Every image on a listed host is served to
-      anyone without a signature, so list only hosts you control, where nobody
-      else can put images.
+      comma-separated
     - `PIXA_CACHE_MAX_BYTES`: disk cache limit in bytes; `0` disables it;
       default 75% of (free space + what the cache holds)
     - the rest are in the table under Configuration below

TODO.md

@@ -30,14 +30,6 @@ P2: security: per-origin rate limiting
 
 # Completed Steps
 
-- 2026-10-15 the example config allowlists no host (closes #249): it allowlisted
-  `github.com` and `user-images.githubusercontent.com`, where anyone can put an
-  image, so a deployment set up as Getting Started says served those images to
-  anyone without a signature, at any size and in any format.
-  `configs/config.example.yml` now leaves `allowlist_hosts` out, with one
-  commented entry under `example.com`. Getting Started and "Running under upaas"
-  in `README.md` say that every image on an allowlisted host is served without a
-  signature, so an allowlisted host must be one the operator controls.
 - 2026-10-15 the host of a `/v1/image/` URL is lower-cased, and one with a port
   needs a signature (closes #246): with `cdn.example.com` allowlisted,
   `CDN.Example.com` and `cdn.example.com:8443` passed the allowlist too, and

configs/config.example.yml

@@ -45,14 +45,15 @@ state_dir: ./data
 signing_key: "CHANGE_ME_generate_with_openssl_rand_base64_32"
 
 # Hosts that don't require signatures (default: none)
-# Every image on an allowlisted host is served to anyone without a
-# signature, at any size and in any format, so list only hosts you
-# control, where nobody else can put images.
 # Use "." prefix for wildcard subdomain matching (e.g., ".example.com" matches "cdn.example.com")
 # An entry that is neither a host name nor an IP address (IPv6 without
 # brackets), such as one with a port or a "*." wildcard, aborts startup.
-# allowlist_hosts:
-#   - images.example.com
+allowlist_hosts:
+  - s3.sneak.cloud
+  - static.sneak.cloud
+  - sneak.berlin
+  - github.com
+  - user-images.githubusercontent.com
 
 # Hosts whose pages may not show pixa's images, written as for
 # allowlist_hosts. A request to /v1/image/ or /v1/e/ whose Referer header

internal/config/config_internal_test.go

@@ -92,32 +92,6 @@ func TestGetStringSlice_Empty(t *testing.T) {
 	}
 }
 
-// TestExampleConfigAllowlistsNoHost loads configs/config.example.yml
-// with a real signing key, as Getting Started in README.md has it copied
-// and edited, and checks that it allowlists no host: every image on an
-// allowlisted host is served to anyone without a signature.
-func TestExampleConfigAllowlistsNoHost(t *testing.T) {
-	t.Setenv("PIXA_SIGNING_KEY", validTestSigningKey)
-
-	examplePath := filepath.Join("..", "..", "configs", "config.example.yml")
-
-	sc, err := loadTestConfig(examplePath)
-	if err != nil {
-		t.Fatalf("failed to load %s: %v", examplePath, err)
-	}
-
-	c, err := newFromSmartConfig(sc)
-	if err != nil {
-		t.Fatalf("%s is not a valid config: %v", examplePath, err)
-	}
-
-	t.Logf("allowlist_hosts in %s: %v", examplePath, c.AllowlistHosts)
-
-	if len(c.AllowlistHosts) != 0 {
-		t.Errorf("%s allowlists %v, want no host", examplePath, c.AllowlistHosts)
-	}
-}
-
 // loadTestConfig is a helper to load a config file for testing.
 func loadTestConfig(path string) (*smartconfig.Config, error) {
 	return smartconfig.NewFromConfigPath(path)

internal/imgcache/service_internal_test.go

@@ -301,46 +301,6 @@ func TestService_ValidateRequest_HostWithPortNeedsSignature(t *testing.T) {
 	}
 }
 
-// TestService_ValidateRequest_UnbracketedIPv6PortNeedsSignature verifies that
-// an allowlisted IPv6 address written without brackets and followed by a
-// port, or by a colon with no port, needs a signature. Go's URL parser, which
-// the fetcher uses, reads 2001:db8::1:8443 as the host 2001:db8::1 with the
-// port 8443.
-func TestService_ValidateRequest_UnbracketedIPv6PortNeedsSignature(
-	t *testing.T,
-) {
-	t.Parallel()
-
-	svc, _ := SetupTestService(t,
-		WithSigningKey(testSigningKey),
-		WithAllowlist("2001:db8::1"),
-	)
-
-	for _, host := range []string{"2001:db8::1:8443", "2001:db8::1:"} {
-		t.Run(host, func(t *testing.T) {
-			t.Parallel()
-
-			req := &ImageRequest{
-				SourceHost: host,
-				SourcePath: testPathCat,
-				Size:       Size{Width: 50, Height: 50},
-				Format:     FormatJPEG,
-				Quality:    85,
-				FitMode:    FitCover,
-			}
-
-			err := svc.ValidateRequest(req)
-			t.Logf("ValidateRequest() for host %q with no signature: %v",
-				host, err)
-
-			if err == nil {
-				t.Errorf("host %q served without a signature, want refused",
-					host)
-			}
-		})
-	}
-}
-
 func TestService_Get_InvalidFile(t *testing.T) {
 	t.Parallel()