charon: Redirect to the fully-resolved prefix more robustly

Compare (canonicalized) prefixes, not URLs, because that's more
precisely what we're concerned about here.

Construct the relative URL for redirection using proper URL handling.
The previous method for constructing the new URL was problematic for
several reasons, including that whether other query params were passed
along or not with the baseUrl depended on where they were relative to
the prefix param.  Also, while unlikely in this case, if a prefix value
appeared elsewhere in the URL earlier than the query param, it all broke
because of the split().

src/getDataset.js

@@ -144,15 +144,18 @@ const getDataset = async (req, res) => {
     return helpers.unauthorized(req, res);
   }
 
-  const baseUrl = req.url.split(query.prefix)[0];
-  let redirectUrl = baseUrl + '/' + resolvedPrefix;
-  if (query.type) {
-    redirectUrl += `&type=${query.type}`;
-  }
+  /* If we got a partial prefix and resolved it into a full one, redirect to
+   * that.  Auspice will notice and update its displayed URL appropriately.
+   */
+  if (resolvedPrefix !== helpers.canonicalizePrefix(query.prefix)) {
+    // A absolute base is required but we won't use it, so use something bogus.
+    const resolvedUrl = new URL(req.originalUrl, "http://x");
+    resolvedUrl.searchParams.set("prefix", resolvedPrefix);
+
+    const relativeResolvedUrl = resolvedUrl.pathname + resolvedUrl.search;
 
-  if (redirectUrl !== req.url) {
-    utils.log(`Redirecting client to: ${redirectUrl}`);
-    res.redirect(redirectUrl);
+    utils.log(`Redirecting client to resolved dataset URL: ${relativeResolvedUrl}`);
+    res.redirect(relativeResolvedUrl);
     return undefined;
   }
 

src/getDatasetHelpers.js

@@ -174,10 +174,17 @@ const parsePrefix = (prefix) => {
 };
 
 
+/* Round-trip prefix through split/join to canonicalize it for comparison.
+ */
+const canonicalizePrefix = (prefix) =>
+  joinPartsIntoPrefix(splitPrefixIntoParts(prefix));
+
+
 module.exports = {
   splitPrefixIntoParts,
   joinPartsIntoPrefix,
   handle500Error,
   unauthorized,
-  parsePrefix
+  parsePrefix,
+  canonicalizePrefix,
 };

test/smoke-test/auspice_client_requests.json

@@ -11,7 +11,7 @@
     "url": "/charon/getDataset?prefix=/flu",
     "expectStatusCode": 302,
     "responseIsJson": false,
-    "redirectsTo": "/charon/getDataset?prefix=/flu/seasonal/h3n2/ha/2y"
+    "redirectsTo": "/charon/getDataset?prefix=flu%2Fseasonal%2Fh3n2%2Fha%2F2y"
   },
   {
     "name": "Check that the main getAvailable API call returns a JSON",