LibWeb: Implement integrity-metadata part of fetch algorithm

Specifically, this makes `<link>` elements with an `integrity` attribute
actually work. Previously, we would load their resource, and then drop
it on the floor without actually using it.

The Subresource Integrity code is in `LibWeb/SRI`, since SRI is the name
of the recommendation spec: https://www.w3.org/TR/SRI/

However, the Fetch spec links to the editor's draft, which varies
significantly from the recommendation, and so that is what the code is
based on and what the spec comments link to:
https://w3c.github.io/webappsec-subresource-integrity/

Fixes #18408

Userland/Libraries/LibWeb/CMakeLists.txt

@@ -470,6 +470,7 @@ set(SOURCES
     RequestIdleCallback/IdleDeadline.cpp
     ResizeObserver/ResizeObserver.cpp
     SecureContexts/AbstractOperations.cpp
+    SRI/SRI.cpp
     Streams/AbstractOperations.cpp
     Streams/ReadableByteStreamController.cpp
     Streams/ReadableStream.cpp

Userland/Libraries/LibWeb/Fetch/Fetching/Fetching.cpp

@@ -1,6 +1,7 @@
 /*
  * Copyright (c) 2022-2023, Linus Groh <linusg@serenityos.org>
  * Copyright (c) 2023, Luke Wilde <lukew@serenityos.org>
+ * Copyright (c) 2023, Sam Atkins <atkinssj@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -38,6 +39,7 @@
 #include <LibWeb/Loader/ResourceLoader.h>
 #include <LibWeb/Platform/EventLoopPlugin.h>
 #include <LibWeb/ReferrerPolicy/AbstractOperations.h>
+#include <LibWeb/SRI/SRI.h>
 #include <LibWeb/URL/URL.h>
 #include <LibWeb/WebIDL/DOMException.h>
 
@@ -479,22 +481,39 @@ WebIDL::ExceptionOr<Optional<JS::NonnullGCPtr<PendingResponse>>> main_fetch(JS::
             if (!request->integrity_metadata().is_empty()) {
                 // 1. Let processBodyError be this step: run fetch response handover given fetchParams and a network
                 //    error.
-                auto process_body_error = [&]() -> WebIDL::ExceptionOr<void> {
+                // FIXME: The spec disagrees on whether fully_read()'s process_body_error should take an argument or not.
-                    return fetch_response_handover(realm, fetch_params, Infrastructure::Response::network_error(vm, "Response body could not be processed"sv));
+                //        See https://github.com/whatwg/fetch/issues/1636
+                //        For now, define two versions of processBodyError
+                auto process_body_error_no_argument = [&realm, &vm, &fetch_params]() {
+                    TRY_OR_IGNORE(fetch_response_handover(realm, fetch_params, Infrastructure::Response::network_error(vm, "Response body could not be processed"sv)));
+                };
+                Infrastructure::Body::ProcessBodyErrorCallback process_body_error = [&realm, &vm, &fetch_params](auto&) {
+                    TRY_OR_IGNORE(fetch_response_handover(realm, fetch_params, Infrastructure::Response::network_error(vm, "Response body could not be processed"sv)));
                 };
 
                 // 2. If response’s body is null, then run processBodyError and abort these steps.
                 if (!response->body().has_value()) {
-                    TRY_OR_IGNORE(process_body_error());
+                    process_body_error_no_argument();
                     return;
                 }
 
-                // FIXME: 3. Let processBody given bytes be these steps:
+                // 3. Let processBody given bytes be these steps:
-                //     1. If bytes do not match request’s integrity metadata, then run processBodyError and abort these steps.
+                Infrastructure::Body::ProcessBodyCallback process_body = [&realm, &request, &response, &fetch_params, process_body_error = move(process_body_error_no_argument)](ByteBuffer bytes) {
-                //     2. Set response’s body to bytes as a body.
+                    // 1. If bytes do not match request’s integrity metadata, then run processBodyError and abort these steps.
-                //     3. Run fetch response handover given fetchParams and response.
+                    if (!TRY_OR_IGNORE(SRI::do_bytes_match_metadata_list(bytes, request->integrity_metadata()))) {
+                        process_body_error();
+                        return;
+                    }
 
-                // FIXME: 4. Fully read response’s body given processBody and processBodyError.
+                    // 2. Set response’s body to bytes as a body.
+                    response->set_body(TRY_OR_IGNORE(Infrastructure::byte_sequence_as_body(realm, bytes)));
+
+                    // 3. Run fetch response handover given fetchParams and response.
+                    TRY_OR_IGNORE(fetch_response_handover(realm, fetch_params, *response));
+                };
+
+                // 4. Fully read response’s body given processBody and processBodyError.
+                TRY_OR_IGNORE(response->body()->fully_read(realm, move(process_body), move(process_body_error), fetch_params.task_destination()));
             }
             // 23. Otherwise, run fetch response handover given fetchParams and response.
             else {

Userland/Libraries/LibWeb/SRI/SRI.cpp

@@ -0,0 +1,191 @@
+/*
+ * Copyright (c) 2023, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Array.h>
+#include <AK/Base64.h>
+#include <AK/Vector.h>
+#include <LibCrypto/Hash/SHA2.h>
+#include <LibWeb/SRI/SRI.h>
+
+namespace Web::SRI {
+
+constexpr Array supported_hash_functions {
+    // These are sorted by strength, low to high.
+    // NOTE: We are specifically told to refuse MD5 and SHA1.
+    //       https://w3c.github.io/webappsec-subresource-integrity/#hash-functions
+    "sha256"sv,
+    "sha384"sv,
+    "sha512"sv,
+};
+
+// https://w3c.github.io/webappsec-subresource-integrity/#getprioritizedhashfunction
+static StringView get_prioritized_hash_function(StringView a, StringView b)
+{
+    if (a == b)
+        return ""sv;
+
+    auto a_priority = supported_hash_functions.first_index_of(a).value();
+    auto b_priority = supported_hash_functions.first_index_of(b).value();
+    if (a_priority > b_priority)
+        return a;
+    return b;
+}
+
+// https://w3c.github.io/webappsec-subresource-integrity/#apply-algorithm-to-response
+ErrorOr<String> apply_algorithm_to_bytes(StringView algorithm, ByteBuffer const& bytes)
+{
+    // NOTE: The steps are duplicated here because each hash algorithm returns a different result type.
+
+    if (algorithm == "sha256"sv) {
+        // 1. Let result be the result of applying algorithm to bytes.
+        auto result = Crypto::Hash::SHA256::hash(bytes);
+
+        // 2. Return the result of base64 encoding result.
+        return encode_base64(result.bytes());
+    }
+
+    if (algorithm == "sha384"sv) {
+        // 1. Let result be the result of applying algorithm to bytes.
+        auto result = Crypto::Hash::SHA384::hash(bytes);
+
+        // 2. Return the result of base64 encoding result.
+        return encode_base64(result.bytes());
+    }
+
+    if (algorithm == "sha512"sv) {
+        // 1. Let result be the result of applying algorithm to bytes.
+        auto result = Crypto::Hash::SHA512::hash(bytes);
+
+        // 2. Return the result of base64 encoding result.
+        return encode_base64(result.bytes());
+    }
+
+    VERIFY_NOT_REACHED();
+}
+
+// https://w3c.github.io/webappsec-subresource-integrity/#parse-metadata
+ErrorOr<Vector<Metadata>> parse_metadata(StringView metadata)
+{
+    // 1. Let result be the empty set.
+    Vector<Metadata> result;
+
+    // 2. For each item returned by splitting metadata on spaces:
+    TRY(metadata.for_each_split_view(' ', SplitBehavior::Nothing, [&](StringView item) -> ErrorOr<void> {
+        // 1. Let hash-with-opt-token-list be the result of splitting item on U+003F (?).
+        auto hash_with_opt_token_list = item.split_view('?');
+
+        // 2. Let hash-expression be hash-with-opt-token-list[0].
+        auto hash_expression = hash_with_opt_token_list[0];
+
+        // 3. Let base64-value be the empty string.
+        StringView base64_value;
+
+        // 4. Let hash-expr-token-list be the result of splitting hash-expression on U+002D (-).
+        auto hash_expr_token_list = hash_expression.split_view('-');
+
+        // 5. Let algorithm be hash-expr-token-list[0].
+        auto algorithm = hash_expr_token_list[0];
+
+        // 6. If hash-expr-token-list[1] exists, set base64-value to hash-expr-token-list[1].
+        if (hash_expr_token_list.size() >= 1)
+            base64_value = hash_expr_token_list[1];
+
+        // 7. If algorithm is not a hash function recognized by the user agent, continue.
+        if (!supported_hash_functions.contains_slow(algorithm))
+            return {};
+
+        // 8. Let metadata be the ordered map «["alg" → algorithm, "val" → base64-value]».
+        //    Note: Since no options are defined (see the §3.1 Integrity metadata), a corresponding entry is not set in metadata.
+        //    If options are defined in a future version, hash-with-opt-token-list[1] can be utilized as options.
+        auto metadata = Metadata {
+            .algorithm = TRY(String::from_utf8(algorithm)),
+            .base64_value = TRY(String::from_utf8(base64_value)),
+            .options = {},
+        };
+
+        // 9. Append metadata to result.
+        TRY(result.try_append(move(metadata)));
+
+        return {};
+    }));
+
+    // 3. Return result.
+    return result;
+}
+
+// https://w3c.github.io/webappsec-subresource-integrity/#get-the-strongest-metadata
+ErrorOr<Vector<Metadata>> get_strongest_metadata_from_set(Vector<Metadata> const& set)
+{
+    // 1. Let result be the empty set and strongest be the empty string.
+    Vector<Metadata> result;
+    Optional<Metadata> strongest;
+
+    // 2. For each item in set:
+    for (auto const& item : set) {
+        // 1. If result is the empty set, add item to result and set strongest to item, skip to the next item.
+        if (result.is_empty()) {
+            TRY(result.try_append(item));
+            strongest = item;
+            continue;
+        }
+
+        // 2. Let currentAlgorithm be the alg component of strongest.
+        auto& current_algorithm = strongest->algorithm;
+
+        // 3. Let newAlgorithm be the alg component of item.
+        auto& new_algorithm = item.algorithm;
+
+        // 4. If the result of getPrioritizedHashFunction(currentAlgorithm, newAlgorithm) is the empty string, add item to result.
+        auto prioritized_hash_function = get_prioritized_hash_function(current_algorithm, new_algorithm);
+        if (prioritized_hash_function.is_empty()) {
+            TRY(result.try_append(item));
+        }
+        //    If the result is newAlgorithm, set strongest to item, set result to the empty set, and add item to result.
+        else if (prioritized_hash_function == new_algorithm) {
+            strongest = item;
+            result.clear_with_capacity();
+            TRY(result.try_append(item));
+        }
+    }
+
+    // 3. Return result.
+    return result;
+}
+
+// https://w3c.github.io/webappsec-subresource-integrity/#does-response-match-metadatalist
+ErrorOr<bool> do_bytes_match_metadata_list(ByteBuffer const& bytes, StringView metadata_list)
+{
+    // 1. Let parsedMetadata be the result of parsing metadataList.
+    auto parsed_metadata = TRY(parse_metadata(metadata_list));
+
+    // 2. If parsedMetadata is empty set, return true.
+    if (parsed_metadata.is_empty())
+        return true;
+
+    // 3. Let metadata be the result of getting the strongest metadata from parsedMetadata.
+    auto metadata = TRY(get_strongest_metadata_from_set(parsed_metadata));
+
+    // 4. For each item in metadata:
+    for (auto const& item : metadata) {
+        // 1. Let algorithm be the item["alg"].
+        auto& algorithm = item.algorithm;
+
+        // 2. Let expectedValue be the item["val"].
+        auto& expected_value = item.base64_value;
+
+        // 3. Let actualValue be the result of applying algorithm to bytes.
+        auto actual_value = TRY(apply_algorithm_to_bytes(algorithm, bytes));
+
+        // 4. If actualValue is a case-sensitive match for expectedValue, return true.
+        if (actual_value == expected_value)
+            return true;
+    }
+
+    // 5. Return false.
+    return false;
+}
+
+}

Userland/Libraries/LibWeb/SRI/SRI.h

@@ -0,0 +1,25 @@
+/*
+ * Copyright (c) 2023, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/String.h>
+
+namespace Web::SRI {
+
+// https://w3c.github.io/webappsec-subresource-integrity/#integrity-metadata
+struct Metadata {
+    String algorithm;    // "alg"
+    String base64_value; // "val"
+    String options {};   // "opt"
+};
+
+ErrorOr<String> apply_algorithm_to_bytes(StringView algorithm, ByteBuffer const& bytes);
+ErrorOr<Vector<Metadata>> parse_metadata(StringView metadata);
+ErrorOr<Vector<Metadata>> get_strongest_metadata_from_set(Vector<Metadata> const& set);
+ErrorOr<bool> do_bytes_match_metadata_list(ByteBuffer const& bytes, StringView metadata_list);
+
+}