From 830939c15c1837c656193008b0e3d6f2f795e822 Mon Sep 17 00:00:00 2001
From: Bill Wallace <wayfarer3130@gmail.com>
Date: Mon, 6 May 2024 16:33:11 -0400
Subject: [PATCH] fix: Race condition on downloading the same file twice

---
 test/data-options.test.js |  2 +-
 test/testUtils.js         | 23 ++++++++++++++++-------
 2 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/test/data-options.test.js b/test/data-options.test.js
index 6b22eec8..c475d7d4 100644
--- a/test/data-options.test.js
+++ b/test/data-options.test.js
@@ -169,7 +169,7 @@ it("noCopy test_fragment_multiframe", async () => {
         "https://github.com/dcmjs-org/data/releases/download/encapsulation/encapsulation-fragment-multiframe.dcm";
     const dcmPath = await getTestDataset(
         url,
-        "encapsulation-fragment-multiframe-b.dcm"
+        "encapsulation-fragment-multiframe.dcm"
     );
     const file = fs.readFileSync(dcmPath);
 
diff --git a/test/testUtils.js b/test/testUtils.js
index 2a92bbb3..7353077d 100644
--- a/test/testUtils.js
+++ b/test/testUtils.js
@@ -55,9 +55,9 @@ function ensureTestDataDir() {
 }
 
 async function getZippedTestDataset(url, filename, unpackDirectory) {
-    var dir = ensureTestDataDir();
-    var targetPath = path.join(dir, filename);
-    var unpackPath = path.join(dir, unpackDirectory);
+    const dir = ensureTestDataDir();
+    const targetPath = path.join(dir, filename);
+    const unpackPath = path.join(dir, unpackDirectory);
     if (!fs.existsSync(unpackPath)) {
         await downloadToFile(url, targetPath);
         await unzip(targetPath, unpackPath);
@@ -65,12 +65,21 @@ async function getZippedTestDataset(url, filename, unpackDirectory) {
     return unpackPath;
 }
 
+/**
+ * Stores the required downloads to prevent async reading before download completed.
+ */
+const asyncDownloadMap = new Map();
+
 async function getTestDataset(url, filename) {
-    var dir = ensureTestDataDir();
-    var targetPath = path.join(dir, filename);
-    if (!fs.existsSync(targetPath)) {
-        await downloadToFile(url, targetPath);
+    const dir = ensureTestDataDir();
+    const targetPath = path.join(dir, filename);
+    let filePromise = asyncDownloadMap.get(targetPath);
+    if (!filePromise && !fs.existsSync(targetPath)) {
+        filePromise = downloadToFile(url, targetPath);
+        asyncDownloadMap.set(targetPath,filePromise);
     }
+    // This returns immediately if filePromise is undefined - eg if the file already downloaded.
+    await filePromise;
     return targetPath;
 }