Collapse very long lines in response viewers (#532)

apps/yaak-client/lib/docFingerprint.ts

@@ -0,0 +1,33 @@
+import { md5 } from "js-md5";
+
+/** How much of each end and the middle to hash */
+const SAMPLE_CHARS = 512;
+
+/**
+ * Identifies a document, so a cached editor state is never restored onto different content.
+ *
+ * Hashing the whole document costs about 4 ms per megabyte and is paid on every editor update
+ * as well as on restore, which is a lot of work for a document nobody can edit.
+ *
+ * `exact` decides how much certainty that buys. Editable documents get a full hash, because a
+ * collision there would restore undo history belonging to other content and let an undo write
+ * nonsense into the body. Read-only documents get a sampled one: they hold the megabyte-sized
+ * responses this exists for, their history can never be applied, and the worst a collision can
+ * do is put a fold or the cursor in the wrong place.
+ *
+ * Sampling still pins the exact length plus three windows, so a colliding pair has to agree on
+ * all four and differ only in between. Documents small enough to hash outright still are.
+ */
+export function docFingerprint(text: string, { exact }: { exact: boolean }): string {
+  if (exact || text.length <= SAMPLE_CHARS * 3) {
+    return `${text.length}:${md5(text)}`;
+  }
+
+  const middle = Math.floor((text.length - SAMPLE_CHARS) / 2);
+  return [
+    text.length,
+    md5(text.slice(0, SAMPLE_CHARS)),
+    md5(text.slice(middle, middle + SAMPLE_CHARS)),
+    md5(text.slice(-SAMPLE_CHARS)),
+  ].join(":");
+}