1 files changed, 109 insertions, 0 deletions
diff --git a/shared/apps-common/src/jet/prefetched-intents/server-data.ts b/shared/apps-common/src/jet/prefetched-intents/server-data.ts
new file mode 100644
index 0000000..fba215c
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+++ b/shared/apps-common/src/jet/prefetched-intents/server-data.ts
@@ -0,0 +1,109 @@
+import { isPOJO } from '@amp/web-apps-utils';
+
+// NOTE: be careful with imports here. This file is imported by browser code,
+// so we expect tree shaking to only keep these functions.
+
+const SERVER_DATA_ID = 'serialized-server-data';
+
+// Take care with < (which has special meaning inside script tags)
+// See: https://github.com/sveltejs/kit/blob/ff9a27b4/packages/kit/src/runtime/server/page/serialize_data.js#L4-L28
+const replacements = {
+    '<': '\\u003C',
+    '\u2028': '\\u2028',
+    '\u2029': '\\u2029',
+};
+
+const pattern = new RegExp(`[${Object.keys(replacements).join('')}]`, 'g');
+
+/**
+ * Serializes a POJO into a HTML <script> tag that can be read clientside by
+ * `deserializeServerData`.
+ *
+ * Use this to share data between serverside and clientside. Include the
+ * returned HTML in the response to a client to allow it to read this data.
+ *
+ * @param data data to serialize
+ * @returns serialized data (or empty string if serialization fails)
+ */
+export function serializeServerData(data: object): string {
+    try {
+        const sanitizedData = JSON.stringify(data).replace(
+            pattern,
+            (match) => replacements[match as keyof typeof replacements],
+        );
+        return `<script type="application/json" id="${SERVER_DATA_ID}">${sanitizedData}</script>`;
+    } catch (e) {
+        // Don't let recursive data (or other non-serializable things) throw.
+        // We'd rather just let the serialize no-op to avoid breaking consumers.
+        return '';
+    }
+}
+
+/**
+ * Deserializes data serialized on the server by `serializeServerData`.
+ *
+ * @returns deserialized data (or undefined if it doesn't exist/errors)
+ */
+export function deserializeServerData(): ReturnType<JSON['parse']> | undefined {
+    const script = document.getElementById(SERVER_DATA_ID);
+    if (!script) {
+        return;
+    }
+
+    script.parentNode?.removeChild(script);
+
+    try {
+        return JSON.parse(script.textContent || '');
+    } catch (e) {
+        // If the content is malformed, we want to avoid throwing. This
+        // situation should be impossible since we control the serialization
+        // above.
+        return;
+    }
+}
+
+/**
+ * JSON stringify a POJO value in a stable manner. Specifically, this means that
+ * objects which are structurally equal serialize to the same string.
+ *
+ * This is useful when comparing objects serialized by a server against objects
+ * build in browser. With plain JSON.stringify(), property order matters and is
+ * not guaranteed to be the same. In other words these two objects would
+ * JSON.stringify() differently:
+ *
+ *   { a: 1, b: 2 }
+ *   { b: 2, a: 1 }
+ *
+ * But these are structurally equal--they have the same keys and values.
+ *
+ * The expected use case for this function is generating keys for a Map for
+ * objects from a server that will be compared against objects from the browser.
+ * This function should be used on objects returned from `deserializeServerData`
+ * before they are used in such contexts.
+ *
+ * See: https://stackoverflow.com/a/43049877
+ */
+export function stableStringify(data: unknown): string {
+    if (Array.isArray(data)) {
+        const items = data.map(stableStringify).join(',');
+        return `[${items}]`;
+    }
+
+    // Sort object keys before serializing
+    if (isPOJO(data)) {
+        const keys = [...Object.keys(data)];
+        keys.sort();
+
+        const properties = keys
+            // undefined values should not get included in stringification
+            .filter((key) => typeof data[key] !== 'undefined')
+            .map(
+                (key) => `${JSON.stringify(key)}:${stableStringify(data[key])}`,
+            )
+            .join(',');
+
+        return `{${properties}}`;
+    }
+
+    return JSON.stringify(data);
+}