refactor: separate transit sources and request service

src/data/transitProxy.js

@@ -1,3 +1,9 @@
+import { validTransitIdentifier } from '../sources/transitHistory.js';
+export {
+  validTransitIdentifier,
+  fetchTransitHistory,
+} from '../sources/transitHistory.js';
+
 /**
  * @module transitProxy
  * @description Pure server-side mechanics for the `/api/transit` proxy.
@@ -67,18 +73,6 @@ export const TRANSIT_BACKOFF_LADDER_MS = Object.freeze([
  * @param {string} url Request URL relative to the mount point.
  * @returns {{ route: 'feeds' } | { route: 'vehicles', feed: object } | null}
  */
-/** Validate the entire decoded identifier, including UTF-8 length. */
-export function validTransitIdentifier(value) {
-  return (
-    typeof value === 'string' &&
-    value.length > 0 &&
-    !/[\u0000-\u001f\u007f/\\]/u.test(value) &&
-    value !== '.' &&
-    value !== '..' &&
-    new TextEncoder().encode(value).length <= 256 &&
-    !/[\uD800-\uDFFF]/u.test(value)
-  );
-}
 export function resolveTransitRoute(url) {
   const pathname = String(url || '').split('?')[0];
   if (pathname === '/feeds' || pathname === '/feeds/')
@@ -101,91 +95,6 @@ export function resolveTransitRoute(url) {
     : null;
 }
 
-/** Selection reads are bounded and cancellable through body parsing. */
-export async function fetchTransitHistory(
-  feedId,
-  vehicleId,
-  signal,
-  fetchImpl = fetch,
-) {
-  if (!validTransitIdentifier(vehicleId))
-    throw new TypeError('Invalid transit vehicle identifier');
-  const response = await fetchImpl(
-    `/api/transit/trail/${encodeURIComponent(feedId)}/${encodeURIComponent(vehicleId)}`,
-    { signal, headers: { Accept: 'application/json' } },
-  );
-  if (!response.ok) throw new Error(`Transit history HTTP ${response.status}`);
-  const reader = response.body?.getReader?.();
-  let text = '';
-  if (reader) {
-    const decoder = new TextDecoder();
-    let bytes = 0;
-    try {
-      while (true) {
-        signal?.throwIfAborted();
-        const chunk = await reader.read();
-        if (chunk.done) break;
-        bytes += chunk.value.byteLength;
-        if (bytes > 32768)
-          throw new RangeError('Transit history exceeds response limit');
-        text += decoder.decode(chunk.value, { stream: true });
-      }
-      text += decoder.decode();
-    } finally {
-      await reader.cancel().catch(() => {});
-    }
-  } else {
-    text = await response.text();
-    if (new TextEncoder().encode(text).length > 32768)
-      throw new RangeError('Transit history exceeds response limit');
-  }
-  signal?.throwIfAborted();
-  const payload = JSON.parse(text);
-  if (
-    payload.version !== 1 ||
-    payload.feedId !== feedId ||
-    payload.vehicleId !== vehicleId ||
-    !Array.isArray(payload.fixes) ||
-    payload.fixes.length > 128 ||
-    !Array.isArray(payload.epochs) ||
-    payload.epochs.length > 8
-  )
-    throw new TypeError('Invalid transit history response');
-  let previous = -Infinity;
-  const epochs = new Set();
-  for (const epoch of payload.epochs) {
-    if (
-      !Number.isInteger(epoch.id) ||
-      epoch.id < 1 ||
-      epoch.id > 0xffffffff ||
-      epochs.has(epoch.id) ||
-      !['trip', 'route', 'mode'].every(
-        (key) =>
-          typeof epoch[key] === 'string' &&
-          new TextEncoder().encode(epoch[key]).length <= 256,
-      )
-    )
-      throw new TypeError('Invalid transit history epoch');
-    epochs.add(epoch.id);
-  }
-  for (const fix of payload.fixes) {
-    if (
-      !Array.isArray(fix) ||
-      fix.length !== 5 ||
-      !fix.every(Number.isFinite) ||
-      fix[0] < 0 ||
-      fix[0] <= previous ||
-      Math.abs(fix[1]) > 90 ||
-      Math.abs(fix[2]) > 180 ||
-      !Number.isInteger(fix[3]) ||
-      !epochs.has(fix[4])
-    )
-      throw new TypeError('Invalid transit history fix');
-    previous = fix[0];
-  }
-  return payload;
-}
-
 /**
  * Request headers for one upstream fetch.
  *