fix: Exports generate invalid internal links (#4639)

* refactoring

* Refactoring continues

* Refactor export, fix internal links in exported docs

* fix: Dupe document name detection

* sigh

server/utils/ZipHelper.ts

@@ -0,0 +1,115 @@
+import fs from "fs";
+import path from "path";
+import JSZip from "jszip";
+import { find } from "lodash";
+import tmp from "tmp";
+import { ValidationError } from "@server/errors";
+import { trace } from "@server/logging/tracing";
+import { deserializeFilename } from "./fs";
+
+export type FileTreeNode = {
+  /** The title, extracted from the file name */
+  title: string;
+  /** The file name including extension */
+  name: string;
+  /** Full path to the file within the zip file */
+  path: string;
+  /** Any nested children */
+  children: FileTreeNode[];
+};
+
+@trace()
+export default class ZipHelper {
+  /**
+   * Converts the flat structure returned by JSZIP into a nested file structure
+   * for easier processing.
+   *
+   * @param zip The JSZip instance
+   * @param maxFiles The maximum number of files to unzip (Prevent zip bombs)
+   */
+  public static toFileTree(
+    zip: JSZip,
+    /** The maximum number of files to unzip */
+    maxFiles = 10000
+  ) {
+    let fileCount = 0;
+    const paths = Object.keys(zip.files).map((filePath) => {
+      if (++fileCount > maxFiles) {
+        throw ValidationError("Too many files in zip");
+      }
+
+      return `/${filePath}`;
+    });
+    const tree: FileTreeNode[] = [];
+
+    paths.forEach(function (filePath) {
+      if (filePath.startsWith("/__MACOSX")) {
+        return;
+      }
+
+      const pathParts = filePath.split("/");
+
+      // Remove first blank element from the parts array.
+      pathParts.shift();
+
+      let currentLevel = tree; // initialize currentLevel to root
+
+      pathParts.forEach(function (name) {
+        // check to see if the path already exists.
+        const existingPath = find(currentLevel, {
+          name,
+        });
+
+        if (existingPath) {
+          // The path to this item was already in the tree, so don't add again.
+          // Set the current level to this path's children
+          currentLevel = existingPath.children;
+        } else if (name.endsWith(".DS_Store") || !name) {
+          return;
+        } else {
+          const newPart = {
+            name,
+            path: filePath.replace(/^\//, ""),
+            title: deserializeFilename(path.parse(path.basename(name)).name),
+            children: [],
+          };
+
+          currentLevel.push(newPart);
+          currentLevel = newPart.children;
+        }
+      });
+    });
+
+    return tree;
+  }
+
+  /**
+   * Write a zip file to a temporary disk location
+   *
+   * @param zip JSZip object
+   * @returns pathname of the temporary file where the zip was written to disk
+   */
+  public static async toTmpFile(zip: JSZip): Promise<string> {
+    return new Promise((resolve, reject) => {
+      tmp.file(
+        {
+          prefix: "export-",
+          postfix: ".zip",
+        },
+        (err, path) => {
+          if (err) {
+            return reject(err);
+          }
+          zip
+            .generateNodeStream({
+              type: "nodebuffer",
+              streamFiles: true,
+            })
+            .pipe(fs.createWriteStream(path))
+            .on("finish", () => resolve(path))
+            .on("error", reject);
+        }
+      );
+    });
+  }
+}