feat: publish the Sandwich Hime source preview

Signed-off-by: Cole Speelman <gamertan@noreply.localhost>
2026-08-11 20:15:06 -04:00
commit 9b29b3d7f8
100 changed files with 10989 additions and 0 deletions
@@ -0,0 +1,11 @@
+SPDX-FileCopyrightText: 2025-2026 Cole Speelman
+SPDX-License-Identifier: Apache-2.0
+
+Original work in the Sandwich Hime sando runtime is Copyright (c) 2025-2026
+Cole Speelman except where a file or contribution identifies a different
+copyright holder. The project requires no copyright assignment; ownership of
+a contribution remains determined by applicable law and existing agreements.
+
+This file is an ownership record, not an Apache NOTICE file and not an
+additional license term. The runtime is licensed under the Apache License,
+Version 2.0, in LICENSE.
@@ -0,0 +1,201 @@
+                                 Apache License
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@@ -0,0 +1,19 @@
+<!-- SPDX-License-Identifier: Apache-2.0 -->
+
+# sando runtime
+
+`gamertan.com/sandwich-hime/sando` is the independent Apache-2.0 runtime ABI for Go generated by Sandwich Hime. It contains no compiler, router, HTTP server, middleware, reflection registry, project discovery, or development supervisor.
+
+The stable surface is:
+
+```go
+type Component interface {
+    Render(context.Context, io.Writer) error
+}
+
+type ComponentFunc func(context.Context, io.Writer) error
+```
+
+`Render` invokes components; generated code uses the context-specific writer helpers and checks `ABI`. Opaque `TrustedHTML`, `TrustedURL`, `TrustedJS`, and `TrustedCSS` values can be constructed only by conspicuous `Trust*` calls in trusted application code.
+
+The runtime has its own `go.mod`, Apache-2.0 license, `COPYRIGHT` record, semantic version, and `sando/vX.Y.Z` tags. It never imports the AGPL compiler. Importing the runtime does not make an application AGPL under the project's terms. Applications may license their own code and generated files under terms they choose to the extent they hold the necessary rights, while redistribution of the runtime remains subject to Apache-2.0.
@@ -0,0 +1,87 @@
+// SPDX-License-Identifier: Apache-2.0
+
+// Package sando is the small production runtime for code generated by Hime-san.
+// It contains rendering contracts and context-specific output helpers, but no
+// router, HTTP server, middleware, or development tooling.
+package sando
+
+import (
+	"context"
+	"errors"
+	"io"
+	"reflect"
+)
+
+// ABI identifies the generated-code contract implemented by this version of
+// the runtime. Generated files should reference this constant so that their
+// expected ABI is visible to readers and tooling.
+const ABI = "sando.v1"
+
+// RuntimeABI is a descriptive alias for ABI.
+const RuntimeABI = ABI
+
+var (
+	// ErrNilComponent is returned when Render is asked to render a nil
+	// component, including a typed nil held in a Component interface.
+	ErrNilComponent = errors.New("sando: nil component")
+	// ErrNilContext is returned when a component is rendered with a nil
+	// context.Context.
+	ErrNilContext = errors.New("sando: nil context")
+	// ErrNilWriter is returned when a component is rendered with a nil writer.
+	ErrNilWriter = errors.New("sando: nil writer")
+)
+
+// Component is the complete production rendering contract. Components are
+// values rather than HTTP handlers so applications retain ownership of
+// buffering, routing, headers, status codes, and error policy.
+type Component interface {
+	Render(context.Context, io.Writer) error
+}
+
+// ComponentFunc adapts a function to Component.
+type ComponentFunc func(context.Context, io.Writer) error
+
+// Render calls f with ctx and w.
+func (f ComponentFunc) Render(ctx context.Context, w io.Writer) error {
+	if f == nil {
+		return ErrNilComponent
+	}
+	if ctx == nil {
+		return ErrNilContext
+	}
+	if isNil(w) {
+		return ErrNilWriter
+	}
+	return f(ctx, w)
+}
+
+// Render renders component into w. It reports nil inputs as errors rather than
+// panicking, including typed nil component and writer values.
+func Render(ctx context.Context, w io.Writer, component Component) error {
+	if ctx == nil {
+		return ErrNilContext
+	}
+	if isNil(w) {
+		return ErrNilWriter
+	}
+	if isNil(component) {
+		return ErrNilComponent
+	}
+	return component.Render(ctx, w)
+}
+
+// isNil recognizes typed nil values stored in interfaces. It is intentionally
+// confined to API boundary validation and is not a component registry.
+func isNil(value any) bool {
+	if value == nil {
+		return true
+	}
+
+	rv := reflect.ValueOf(value)
+	switch rv.Kind() {
+	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Pointer, reflect.Slice:
+		return rv.IsNil()
+	default:
+		return false
+	}
+}
@@ -0,0 +1,98 @@
+// SPDX-License-Identifier: Apache-2.0
+
+package sando_test
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"io"
+	"testing"
+
+	"gamertan.com/sandwich-hime/sando"
+)
+
+func TestRender(t *testing.T) {
+	t.Parallel()
+
+	component := sando.ComponentFunc(func(ctx context.Context, w io.Writer) error {
+		_, err := io.WriteString(w, ctx.Value(contextKey{}).(string))
+		return err
+	})
+	ctx := context.WithValue(context.Background(), contextKey{}, "rendered")
+	var output bytes.Buffer
+
+	if err := sando.Render(ctx, &output, component); err != nil {
+		t.Fatalf("Render() error = %v", err)
+	}
+	if got, want := output.String(), "rendered"; got != want {
+		t.Fatalf("Render() output = %q, want %q", got, want)
+	}
+}
+
+func TestRenderPropagatesComponentError(t *testing.T) {
+	t.Parallel()
+
+	want := errors.New("render failed")
+	component := sando.ComponentFunc(func(context.Context, io.Writer) error { return want })
+	if got := sando.Render(context.Background(), io.Discard, component); !errors.Is(got, want) {
+		t.Fatalf("Render() error = %v, want %v", got, want)
+	}
+}
+
+func TestRenderRejectsNilInputs(t *testing.T) {
+	t.Parallel()
+
+	valid := sando.ComponentFunc(func(context.Context, io.Writer) error { return nil })
+	var nilFunc sando.ComponentFunc
+	var nilPointer *pointerComponent
+	var nilWriter *bytes.Buffer
+
+	tests := []struct {
+		name      string
+		ctx       context.Context
+		writer    io.Writer
+		component sando.Component
+		want      error
+	}{
+		{name: "nil context", writer: io.Discard, component: valid, want: sando.ErrNilContext},
+		{name: "nil writer", ctx: context.Background(), component: valid, want: sando.ErrNilWriter},
+		{name: "typed nil writer", ctx: context.Background(), writer: nilWriter, component: valid, want: sando.ErrNilWriter},
+		{name: "nil component", ctx: context.Background(), writer: io.Discard, want: sando.ErrNilComponent},
+		{name: "nil component func", ctx: context.Background(), writer: io.Discard, component: nilFunc, want: sando.ErrNilComponent},
+		{name: "typed nil component", ctx: context.Background(), writer: io.Discard, component: nilPointer, want: sando.ErrNilComponent},
+	}
+
+	for _, test := range tests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			if got := sando.Render(test.ctx, test.writer, test.component); !errors.Is(got, test.want) {
+				t.Fatalf("Render() error = %v, want %v", got, test.want)
+			}
+		})
+	}
+}
+
+func TestComponentFuncDirectValidation(t *testing.T) {
+	t.Parallel()
+
+	var nilFunc sando.ComponentFunc
+	if got := nilFunc.Render(context.Background(), io.Discard); !errors.Is(got, sando.ErrNilComponent) {
+		t.Fatalf("nil ComponentFunc.Render() error = %v", got)
+	}
+
+	valid := sando.ComponentFunc(func(context.Context, io.Writer) error { return nil })
+	if got := valid.Render(nil, io.Discard); !errors.Is(got, sando.ErrNilContext) {
+		t.Fatalf("ComponentFunc.Render(nil, writer) error = %v", got)
+	}
+	if got := valid.Render(context.Background(), nil); !errors.Is(got, sando.ErrNilWriter) {
+		t.Fatalf("ComponentFunc.Render(ctx, nil) error = %v", got)
+	}
+}
+
+type contextKey struct{}
+
+type pointerComponent struct{}
+
+func (*pointerComponent) Render(context.Context, io.Writer) error { return nil }
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0
+
+module gamertan.com/sandwich-hime/sando
+
+go 1.25
@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: Apache-2.0
+
+package sando
+
+// TrustedHTML is HTML whose author has deliberately accepted responsibility
+// for its safety. Its contents are opaque outside this package.
+type TrustedHTML struct{ value string }
+
+// TrustHTML marks value as deliberately trusted HTML. The caller is responsible
+// for supplying a balanced fragment that is valid at an HTML content boundary
+// and does not leave the parser in a different context. Prefer ordinary values
+// and WriteText whenever possible.
+func TrustHTML(value string) TrustedHTML { return TrustedHTML{value: value} }
+
+// TrustedURL is a URL whose author has deliberately accepted responsibility
+// for its scheme and navigation behavior. HTML attribute syntax is still
+// escaped when the value is written.
+type TrustedURL struct{ value string }
+
+// TrustURL marks value as a deliberately trusted URL, bypassing the ordinary
+// URL scheme allowlist. It does not bypass HTML attribute escaping.
+func TrustURL(value string) TrustedURL { return TrustedURL{value: value} }
+
+// TrustedJS is JavaScript whose author has deliberately accepted
+// responsibility for its safety. Its contents are opaque outside this package.
+type TrustedJS struct{ value string }
+
+// TrustJS marks value as deliberately trusted JavaScript. The caller is also
+// responsible for preventing an HTML </script sequence from terminating its
+// container. Plain strings cannot be passed to WriteJS.
+func TrustJS(value string) TrustedJS { return TrustedJS{value: value} }
+
+// TrustedCSS is CSS whose author has deliberately accepted responsibility for
+// its safety. Its contents are opaque outside this package.
+type TrustedCSS struct{ value string }
+
+// TrustCSS marks value as deliberately trusted CSS. The caller is also
+// responsible for preventing an HTML </style sequence from terminating its
+// container. Plain strings cannot be passed to WriteCSS.
+func TrustCSS(value string) TrustedCSS { return TrustedCSS{value: value} }
@@ -0,0 +1,184 @@
+// SPDX-License-Identifier: Apache-2.0
+
+package sando
+
+import (
+	"errors"
+	"fmt"
+	"html"
+	"io"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+// ErrUnsafeURL is the sentinel wrapped by URLSafetyError when an ordinary URL
+// value is ambiguous or uses a scheme outside the v1 allowlist.
+var ErrUnsafeURL = errors.New("sando: unsafe URL")
+
+// URLSafetyError reports why an ordinary URL was rejected. It intentionally
+// does not retain or print the complete value, which may contain sensitive
+// application data.
+type URLSafetyError struct {
+	Scheme string
+	Reason string
+}
+
+// Error implements error.
+func (e *URLSafetyError) Error() string {
+	if e.Scheme != "" {
+		return fmt.Sprintf("%v: scheme %q is not allowed", ErrUnsafeURL, e.Scheme)
+	}
+	if e.Reason != "" {
+		return fmt.Sprintf("%v: %s", ErrUnsafeURL, e.Reason)
+	}
+	return ErrUnsafeURL.Error()
+}
+
+// Unwrap permits errors.Is(err, ErrUnsafeURL).
+func (e *URLSafetyError) Unwrap() error { return ErrUnsafeURL }
+
+// WriteString writes a compiler-owned static literal and reports both writer
+// errors and contract-violating short writes. Application data must use the
+// context-specific helpers below instead.
+func WriteString(w io.Writer, value string) error {
+	return writeString(w, value)
+}
+
+// WriteText writes value escaped for an HTML text node.
+func WriteText(w io.Writer, value any) error {
+	if trusted, ok := value.(TrustedHTML); ok {
+		return writeString(w, trusted.value)
+	}
+	return writeString(w, html.EscapeString(normalizeText(stringValue(value))))
+}
+
+// WriteRCDATA writes value escaped for an HTML RCDATA element such as title
+// or textarea. Trusted wrappers are intentionally not honored in this context:
+// their contents are escaped like every other value so they cannot close the
+// containing element.
+func WriteRCDATA(w io.Writer, value any) error {
+	return writeString(w, html.EscapeString(normalizeText(stringValue(value))))
+}
+
+// WriteAttr writes value escaped for a quoted HTML attribute. Generated code
+// must always place this output inside a syntactically complete quoted value.
+func WriteAttr(w io.Writer, value any) error {
+	return writeString(w, html.EscapeString(normalizeText(stringValue(value))))
+}
+
+// WriteURL writes value escaped for a quoted URL-bearing HTML attribute.
+// Ordinary values are canonicalized and checked before any bytes are written.
+// TrustedURL bypasses the scheme check but never attribute escaping.
+func WriteURL(w io.Writer, value any) error {
+	if trusted, ok := value.(TrustedURL); ok {
+		return writeString(w, html.EscapeString(normalizeText(trusted.value)))
+	}
+
+	canonical, err := canonicalURL(stringValue(value))
+	if err != nil {
+		return err
+	}
+	return writeString(w, html.EscapeString(canonical))
+}
+
+// WriteHTML writes deliberately trusted HTML without escaping.
+func WriteHTML(w io.Writer, value TrustedHTML) error {
+	return writeString(w, value.value)
+}
+
+// WriteJS writes deliberately trusted JavaScript without escaping.
+func WriteJS(w io.Writer, value TrustedJS) error {
+	return writeString(w, value.value)
+}
+
+// WriteCSS writes deliberately trusted CSS without escaping.
+func WriteCSS(w io.Writer, value TrustedCSS) error {
+	return writeString(w, value.value)
+}
+
+func writeString(w io.Writer, value string) error {
+	if isNil(w) {
+		return ErrNilWriter
+	}
+
+	n, err := io.WriteString(w, value)
+	if err != nil {
+		return err
+	}
+	if n != len(value) {
+		return io.ErrShortWrite
+	}
+	return nil
+}
+
+func stringValue(value any) string {
+	switch value := value.(type) {
+	case TrustedHTML:
+		return value.value
+	case TrustedURL:
+		return value.value
+	case TrustedJS:
+		return value.value
+	case TrustedCSS:
+		return value.value
+	default:
+		return fmt.Sprint(value)
+	}
+}
+
+func normalizeText(value string) string {
+	if !utf8.ValidString(value) {
+		value = strings.ToValidUTF8(value, "\uFFFD")
+	}
+	return strings.ReplaceAll(value, "\x00", "\uFFFD")
+}
+
+func canonicalURL(value string) (string, error) {
+	value = normalizeText(value)
+	value = strings.TrimFunc(value, func(r rune) bool {
+		return unicode.IsSpace(r) || r == '\uFEFF'
+	})
+
+	for _, r := range value {
+		if r < 0x20 || r == 0x7f {
+			return "", &URLSafetyError{Reason: "control characters are not allowed"}
+		}
+	}
+
+	colon := strings.IndexByte(value, ':')
+	boundary := strings.IndexAny(value, "/?#")
+	if colon < 0 || boundary >= 0 && boundary < colon {
+		return value, nil
+	}
+
+	scheme := value[:colon]
+	if !validScheme(scheme) {
+		return "", &URLSafetyError{Reason: "ambiguous scheme syntax"}
+	}
+
+	scheme = strings.ToLower(scheme)
+	switch scheme {
+	case "http", "https", "mailto", "tel":
+		return value, nil
+	default:
+		return "", &URLSafetyError{Scheme: scheme}
+	}
+}
+
+func validScheme(value string) bool {
+	if value == "" || !isASCIIAlpha(value[0]) {
+		return false
+	}
+	for i := 1; i < len(value); i++ {
+		c := value[i]
+		if !isASCIIAlpha(c) && (c < '0' || c > '9') && c != '+' && c != '-' && c != '.' {
+			return false
+		}
+	}
+	return true
+}
+
+func isASCIIAlpha(c byte) bool {
+	return c >= 'A' && c <= 'Z' || c >= 'a' && c <= 'z'
+}
@@ -0,0 +1,288 @@
+// SPDX-License-Identifier: Apache-2.0
+
+package sando_test
+
+import (
+	"bytes"
+	"errors"
+	"io"
+	"strings"
+	"testing"
+	"unicode/utf8"
+
+	"gamertan.com/sandwich-hime/sando"
+)
+
+func TestWriteText(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name  string
+		value any
+		want  string
+	}{
+		{name: "quote and entity injection", value: `<script x="'&">alert(1)</script>`, want: `&lt;script x=&#34;&#39;&amp;&#34;&gt;alert(1)&lt;/script&gt;`},
+		{name: "unicode preserved", value: "姫 🍞 café", want: "姫 🍞 café"},
+		{name: "NUL replaced", value: "left\x00right", want: "left\uFFFDright"},
+		{name: "invalid UTF-8 replaced", value: string([]byte{'a', 0xff, 'b'}), want: "a\uFFFDb"},
+		{name: "non-string formatted", value: 42, want: "42"},
+		{name: "trusted HTML is deliberately raw in text context", value: sando.TrustHTML("<b>explicitly trusted</b>"), want: "<b>explicitly trusted</b>"},
+	}
+
+	for _, test := range tests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			var output bytes.Buffer
+			if err := sando.WriteText(&output, test.value); err != nil {
+				t.Fatalf("WriteText() error = %v", err)
+			}
+			if got := output.String(); got != test.want {
+				t.Fatalf("WriteText() = %q, want %q", got, test.want)
+			}
+			if !utf8.ValidString(output.String()) {
+				t.Fatal("WriteText() emitted invalid UTF-8")
+			}
+		})
+	}
+}
+
+func TestWriteAttr(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name  string
+		value any
+		want  string
+	}{
+		{name: "breakout characters", value: `x" autofocus onfocus="alert(1)&`, want: `x&#34; autofocus onfocus=&#34;alert(1)&amp;`},
+		{name: "angle and apostrophe", value: `<'value'>`, want: `&lt;&#39;value&#39;&gt;`},
+		{name: "unicode and NUL", value: "姫\x00さん", want: "姫\uFFFDさん"},
+	}
+
+	for _, test := range tests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			var output bytes.Buffer
+			if err := sando.WriteAttr(&output, test.value); err != nil {
+				t.Fatalf("WriteAttr() error = %v", err)
+			}
+			if got := output.String(); got != test.want {
+				t.Fatalf("WriteAttr() = %q, want %q", got, test.want)
+			}
+		})
+	}
+}
+
+func TestWriteRCDATAAlwaysEscapesTrustedValues(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name  string
+		value any
+		want  string
+	}{
+		{name: "plain", value: `</title><script>alert("x")</script>`, want: `&lt;/title&gt;&lt;script&gt;alert(&#34;x&#34;)&lt;/script&gt;`},
+		{name: "trusted HTML", value: sando.TrustHTML(`</textarea><script>alert(1)</script>`), want: `&lt;/textarea&gt;&lt;script&gt;alert(1)&lt;/script&gt;`},
+		{name: "trusted URL", value: sando.TrustURL(`javascript:</title>`), want: `javascript:&lt;/title&gt;`},
+		{name: "trusted JavaScript", value: sando.TrustJS(`</title><script>alert(1)</script>`), want: `&lt;/title&gt;&lt;script&gt;alert(1)&lt;/script&gt;`},
+		{name: "trusted CSS", value: sando.TrustCSS(`</textarea><style>*{display:none}</style>`), want: `&lt;/textarea&gt;&lt;style&gt;*{display:none}&lt;/style&gt;`},
+		{name: "unicode and NUL", value: "姫\x00さん", want: "姫\uFFFDさん"},
+	}
+
+	for _, test := range tests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			var output bytes.Buffer
+			if err := sando.WriteRCDATA(&output, test.value); err != nil {
+				t.Fatalf("WriteRCDATA() error = %v", err)
+			}
+			if got := output.String(); got != test.want {
+				t.Fatalf("WriteRCDATA() = %q, want %q", got, test.want)
+			}
+		})
+	}
+}
+
+func TestWriteRCDATAAlwaysEscapesTrustedHTML(t *testing.T) {
+	t.Parallel()
+
+	var output bytes.Buffer
+	value := sando.TrustHTML(`</textarea><script>alert(1)</script>`)
+	if err := sando.WriteRCDATA(&output, value); err != nil {
+		t.Fatal(err)
+	}
+	if got, want := output.String(), `&lt;/textarea&gt;&lt;script&gt;alert(1)&lt;/script&gt;`; got != want {
+		t.Fatalf("WriteRCDATA() = %q, want %q", got, want)
+	}
+}
+
+func TestWriteURLAllowsAndCanonicalizesOrdinaryValues(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name  string
+		value any
+		want  string
+	}{
+		{name: "root relative", value: "/items?q=tea&sort=name", want: "/items?q=tea&amp;sort=name"},
+		{name: "path relative", value: "../images/姫.png", want: "../images/姫.png"},
+		{name: "fragment", value: "#section", want: "#section"},
+		{name: "network path", value: "//static.example/assets", want: "//static.example/assets"},
+		{name: "HTTP scheme case insensitive", value: "HTTP://example.test/a", want: "HTTP://example.test/a"},
+		{name: "HTTPS", value: "https://example.test/", want: "https://example.test/"},
+		{name: "mail", value: "mailto:hime@example.test", want: "mailto:hime@example.test"},
+		{name: "telephone", value: "tel:+14165550123", want: "tel:+14165550123"},
+		{name: "surrounding whitespace trimmed", value: " \n\thttps://example.test/path\r ", want: "https://example.test/path"},
+		{name: "colon after query is relative", value: "/search?q=kind:value", want: "/search?q=kind:value"},
+		{name: "empty", value: "", want: ""},
+	}
+
+	for _, test := range tests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			var output bytes.Buffer
+			if err := sando.WriteURL(&output, test.value); err != nil {
+				t.Fatalf("WriteURL() error = %v", err)
+			}
+			if got := output.String(); got != test.want {
+				t.Fatalf("WriteURL() = %q, want %q", got, test.want)
+			}
+		})
+	}
+}
+
+func TestWriteURLRejectsDangerousAndAmbiguousValuesBeforeWriting(t *testing.T) {
+	t.Parallel()
+
+	values := []string{
+		"javascript:alert(1)",
+		"JaVaScRiPt:alert(1)",
+		"data:text/html,<script>alert(1)</script>",
+		"vbscript:msgbox(1)",
+		"file:///etc/passwd",
+		"ftp://example.test/file",
+		"java\nscript:alert(1)",
+		"java\tscript:alert(1)",
+		"java\x00script:alert(1)",
+		"javascript\x7f:alert(1)",
+		"java script:alert(1)",
+		"%6aavascript:alert(1)",
+		":ambiguous",
+	}
+
+	for _, value := range values {
+		value := value
+		t.Run(value, func(t *testing.T) {
+			t.Parallel()
+			var output bytes.Buffer
+			output.WriteString("last-good")
+			err := sando.WriteURL(&output, value)
+			if !errors.Is(err, sando.ErrUnsafeURL) {
+				t.Fatalf("WriteURL() error = %v, want ErrUnsafeURL", err)
+			}
+			if got := output.String(); got != "last-good" {
+				t.Fatalf("WriteURL() modified writer on validation failure: %q", got)
+			}
+		})
+	}
+}
+
+func TestTrustedWrites(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name  string
+		write func(io.Writer) error
+		want  string
+	}{
+		{name: "HTML", write: func(w io.Writer) error {
+			return sando.WriteHTML(w, sando.TrustHTML(`<strong data-x="1">Hime</strong>`))
+		}, want: `<strong data-x="1">Hime</strong>`},
+		{name: "URL bypasses scheme but not attribute escaping", write: func(w io.Writer) error { return sando.WriteURL(w, sando.TrustURL(`custom:"<&`)) }, want: `custom:&#34;&lt;&amp;`},
+		{name: "JavaScript", write: func(w io.Writer) error { return sando.WriteJS(w, sando.TrustJS(`window.hime = "<3";`)) }, want: `window.hime = "<3";`},
+		{name: "CSS", write: func(w io.Writer) error { return sando.WriteCSS(w, sando.TrustCSS(`.hime::after { content: "<3"; }`)) }, want: `.hime::after { content: "<3"; }`},
+	}
+
+	for _, test := range tests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			var output bytes.Buffer
+			if err := test.write(&output); err != nil {
+				t.Fatalf("trusted write error = %v", err)
+			}
+			if got := output.String(); got != test.want {
+				t.Fatalf("trusted write = %q, want %q", got, test.want)
+			}
+		})
+	}
+}
+
+func TestWriteHelpersPropagateWriterFailures(t *testing.T) {
+	t.Parallel()
+
+	want := errors.New("disk full")
+	tests := []struct {
+		name  string
+		write func(io.Writer) error
+	}{
+		{name: "static literal", write: func(w io.Writer) error { return sando.WriteString(w, "hello") }},
+		{name: "text", write: func(w io.Writer) error { return sando.WriteText(w, "hello") }},
+		{name: "RCDATA", write: func(w io.Writer) error { return sando.WriteRCDATA(w, "hello") }},
+		{name: "attribute", write: func(w io.Writer) error { return sando.WriteAttr(w, "hello") }},
+		{name: "URL", write: func(w io.Writer) error { return sando.WriteURL(w, "/hello") }},
+		{name: "HTML", write: func(w io.Writer) error { return sando.WriteHTML(w, sando.TrustHTML("hello")) }},
+		{name: "JavaScript", write: func(w io.Writer) error { return sando.WriteJS(w, sando.TrustJS("hello")) }},
+		{name: "CSS", write: func(w io.Writer) error { return sando.WriteCSS(w, sando.TrustCSS("hello")) }},
+	}
+
+	for _, test := range tests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			if got := test.write(errorWriter{err: want}); !errors.Is(got, want) {
+				t.Fatalf("write error = %v, want %v", got, want)
+			}
+			if got := test.write(shortWriter{}); !errors.Is(got, io.ErrShortWrite) {
+				t.Fatalf("short write error = %v, want io.ErrShortWrite", got)
+			}
+			if got := test.write(nil); !errors.Is(got, sando.ErrNilWriter) {
+				t.Fatalf("nil writer error = %v, want ErrNilWriter", got)
+			}
+		})
+	}
+}
+
+func TestURLSafetyErrorDoesNotEchoSensitiveValue(t *testing.T) {
+	t.Parallel()
+
+	const secret = "user:password@example.test"
+	err := sando.WriteURL(io.Discard, "custom:"+secret)
+	if err == nil {
+		t.Fatal("WriteURL() unexpectedly accepted custom scheme")
+	}
+	if strings.Contains(err.Error(), secret) {
+		t.Fatalf("error leaks URL contents: %q", err)
+	}
+	var safetyError *sando.URLSafetyError
+	if !errors.As(err, &safetyError) {
+		t.Fatalf("error type = %T, want *sando.URLSafetyError", err)
+	}
+}
+
+type errorWriter struct{ err error }
+
+func (w errorWriter) Write([]byte) (int, error) { return 0, w.err }
+
+type shortWriter struct{}
+
+func (shortWriter) Write(value []byte) (int, error) {
+	if len(value) == 0 {
+		return 0, nil
+	}
+	return len(value) - 1, nil
+}