Add fetch monkeypatches to subresource-loading spec WICG#708

This is a starting point of writing "fetch monkeypatches".

There are still many TODOs remaining, but we can refine iteratively.

subresource-loading.bs

@@ -8,18 +8,30 @@ Repository: WICG/webpackage
 URL: https://wicg.github.io/webpackage/subresource-loading.html
 Editor: Hayato Ito, Google Inc. https://google.com/, [email protected]
 Abstract: How UAs load subresources from Web Bundles.
-
 Complain About: accidental-2119 yes, missing-example-ids yes
 Markup Shorthands: markdown yes, css no
 Assume Explicit For: yes
 </pre>
+<pre class='biblio'>
+{
+  "draft-yasskin-wpack-bundled-exchanges": {
+    "href": "https://wicg.github.io/webpackage/draft-yasskin-wpack-bundled-exchanges.html",
+    "title": "Web Bundles"
+  }
+}
+</pre>
+<pre class='anchors'>
+spec: fetch; urlPrefix: https://fetch.spec.whatwg.org/#
+    type: dfn
+        text: fetch params; url: fetch-params
+</pre>
 <pre class="link-defaults">
+spec:fetch; type:dfn; for:/; text:request
 spec:fetch; type:dfn; for:/; text:response
 spec:html; type:element; text:link
+spec:url; type:dfn; for:/; text:url
 </pre>
 
-<section class="non-normative">
-
 # Introduction # {#intro}
 
 <em>This section is non-normative.</em>
@@ -31,7 +43,143 @@ specification describes how web browsers load those resources. It is expressed
 as several monkeypatches to the [[HTML]] and [[FETCH]] specification which call
 algorithms defined here.
 
-<p class="note">
-  This specification is under construct. See
-  <a href="https://github.com/WICG/webpackage/issues/708">#708</a>.
-</p>
+Note: This specification is under construct. See <a href="https://github.com/WICG/webpackage/issues/708">#708</a>.
+
+# Structures # {#structures}
+
+A <dfn>fetched web bundle</dfn> is a representation of a web bundle format
+defined in [[draft-yasskin-wpack-bundled-exchanges]].
+
+A <dfn>bundle rule</dfn> is a [=struct=] with the following
+[=struct/items=]:
+
+- <dfn for="bundle rule">source</dfn>, a [=URL=].
+- <dfn for="bundle rule">credentials</dfn>, a [=request/mode=].
+- <dfn for="bundle rule">resources</dfn>, a list of [=URLs=].
+- <dfn for="bundle rule">scopes</dfn>, a list of [=URLs=].
+
+A <dfn>web bundle</dfn> is a [=struct=] with the following [=struct/items=]:
+
+- <dfn for="web bundle">fetched bundle</dfn>, a [=fetched web bundle=] or null.
+- <dfn for="web bundle">rule</dfn>, a [=bundle rule=].
+- <dfn for="web bundle">state</dfn>, an internal state which is "fetching", "fetched", or "failed". Initially "fetching".
+
+# New Document fields # {#new-document-fields}
+
+A {{Document}} has a <dfn for=document>web bundle list</dfn>, which is a list of [=web bundles=].
+
+# Fetch web bundle # {#fetch-web-bundle-section}
+
+<div algorithm>
+To <dfn>fetch web bundle</dfn> given [=web bundle=] |web bundle| and [=fetch params=] |fetch params|:
+
+1. Assert:  |webbundle|'s [=web bundle/state=] is "fetching".
+
+1. Let |request| be |fetch params|'s [=request=].
+
+1. Let |request|'s [=request/url=] is |webbundle|'s [=web bundle/rule=]'s [=bundle rule/source=].
+
+     Note: Source URL is resolved on document's base URL.
+
+1. Let |request|'s [=request/destination=] is "webbundle",
+
+1. Let |request|'s [=request/mode=] is "cors",
+
+1. Let |request|'s [=request/credentials mode=] be |web bundle|'s [=web bundle/rule=]'s [=bundle rule/credentials=] if [=bundle rule/credentials=] is non-null. Otherwise "same-origin"
+
+1. Append a [=header=], a tuple of ("Accept", "application/webbundle;v=1"), to |request|'s [=request/header list=].
+
+    Note: Chromium's experimental implementation uses "application/webbundle;v=b2" as a header value.
+    Once the web bundle format ([[draft-yasskin-wpack-bundled-exchanges]]) goes RFC, Chromium would use "1" as a version number.
+
+1. Let |response| be the result of running <a spec="fetch">HTTP-network-or-cache fetch</a> given |fetch params|.
+
+    Note: Chromium's current implementation doesn't allow a *nested bundle*.
+    A Web bundle is never fetched from other web bundles.
+
+1. If |response|'s [=response/status=] is 200,
+
+    1. Let |webbundle|'s [=web bundle/fetched bundle=] be the result of parsing |response|'s body ([[draft-yasskin-wpack-bundled-exchanges]]) and |webbundle|' [=web bundle/state=] be "fetched". If parsing fails, or any other conformance is violated, let [=web bundle/fetched bundle=] be null and [=web bundle/state=] be "failed".
+
+        Note: In parsing, Chromium's experimental implementation only accepts "b2" as a web bundle format version number ([[draft-yasskin-wpack-bundled-exchanges]]).
+        Once the web bundle format goes RFC, Chromium would accept "1" as a web bundle format version number.
+
+1. Otherwise, let |webbundle|' [=web bundle/state=] be "failed".
+
+</div>
+
+# HTML monkeypatches  # {#html-monkeypatches}
+
+## Script ## {#script}
+
+Note: TODO. This section uses [=fetch web bundle=].
+
+# Fetch monkeypatches # {#fetch-monkeypatches}
+
+## Fetch subresource from web bundle  ## {#fetch-subresource-from-web-bundle}
+
+In <a spec="fetch">HTTP-network-or-cache fetch</a>, before
+
+> 8.22. Set httpCache to the result of determining the HTTP cache partition, given|httpRequest|.
+
+add the following steps:
+
+22.  Set the |response| to the result of [=fetch from web bundle=], given |httpRequest|.
+
+    1. If |response| is [=network error=], return [=network error=].
+
+    2. If |response| is non-null, skip the steps 8.22-8.24 and goto the step 9.
+
+        Note: That means a subresource from a webbundle never interacts with HttpCache.
+        We plan to support HttpCache as a feature enhancement in the future.
+
+<div algorithm>
+To <dfn>fetch from web bundle</dfn> given [=request=] |httpRequest|:
+
+    1. For each |web bundle| of [=document=]'s [=document/web bundle list=]:
+
+        1. If the result of running [=match url with web bundle=] given |httpRequest|'s [=request/url=] and |web bundle| is true:
+
+            1. Let |response| be the result of [=get response from web bundle=] given |httpRequest|'s [=request/url=] and |web bundle|.
+
+            2. If |response| is null, return a [=network error=].
+
+                Note: This means a browser does not fallback to fetch a subresource from network.
+
+            3. Otherwise, return |response|.
+
+    2. Return null.
+
+</div>
+
+<div algorithm>
+  To <dfn>match url with web bundle</dfn> given [=url=] |url| and [=web bundle=] |web bundle|:
+
+    1. If |url| doesn't meet a path restriction rule, given |web bundle|'s [=web bundle/rule=]'s [=bundle rule/source=], then return false.
+
+        Issue: Clarify path restriction rule in algorithm.
+
+
+    2. If |url| matches any of |web bundle|'s [=web bundle/rule=]'s [=bundle rule/resources=], then return true.
+
+    2. If |url|'s prefix matches any of |web bundle|'s [=web bundle/rule=]'s [=bundle rule/scopes=], then return true.
+
+    3. Otherwise, return false.
+
+</div>
+
+<div algorithm>
+  To <dfn>get response from web bundle</dfn> given [=url=] |url| and [=web bundle=] |web bundle|:
+
+    1. If |web bundle|'s [=web bundle/state=] is "fetching", await until [=web bundle/state=] becomes "fetched" or "failed" asynchronously.
+
+    1. If |web bundle|'s [=web bundle/state=] is "failed", return null.
+
+    2. Assert: |web bundle|'s [=web bundle/fetched bundle=] is non-null.
+
+    3. Returns [=response=] from |web bundle|'s [=web bundle/fetched bundle=] given |url| ([[draft-yasskin-wpack-bundled-exchanges]]).  If a representation of |url| is not found in [=web bundle/fetched bundle=], return null.
+</div>
+
+## Navigation ## {#navigation}
+
+Note: TODO