these too

screenshot/src/validation.ts

@@ -0,0 +1,114 @@
+export class ValidationError extends Error {
+  status = 400;
+}
+
+export interface ValidatedScreenshotRequest {
+  pagePath: string;
+  qs: URLSearchParams;
+}
+
+const MAX_REPEATED_PARAMS = 40;
+const MAX_VALUE_LENGTH = 500;
+const NUMERIC_RE = /^-?(?:\d+|\d*\.\d+)$/;
+const PATH_RE = /^\/(?:invite\/[A-Za-z0-9]{1,20})?$/;
+const SAFE_VALUE_RE = /^[^\u0000-\u001f\u007f]+$/;
+const REPEATED_KEYS = ['filter', 'poi', 'tt'] as const;
+
+type Query = Record<string, unknown>;
+
+function validationError(message: string): never {
+  throw new ValidationError(message);
+}
+
+function firstString(query: Query, key: string): string | undefined {
+  const value = query[key];
+  if (value == null) return undefined;
+  if (Array.isArray(value)) {
+    validationError(`${key} must not be repeated`);
+  }
+  if (typeof value !== 'string') {
+    validationError(`${key} must be a string`);
+  }
+  return value || undefined;
+}
+
+function repeatedStrings(query: Query, key: string): string[] {
+  const value = query[key];
+  if (value == null) return [];
+  const values = Array.isArray(value) ? value : [value];
+  if (values.length > MAX_REPEATED_PARAMS) {
+    validationError(`${key} has too many values`);
+  }
+  return values.filter((item): item is string => {
+    if (typeof item !== 'string') {
+      validationError(`${key} values must be strings`);
+    }
+    return item.length > 0;
+  });
+}
+
+function assertSafeValue(key: string, value: string): void {
+  if (value.length > MAX_VALUE_LENGTH) {
+    validationError(`${key} is too long`);
+  }
+  if (!SAFE_VALUE_RE.test(value)) {
+    validationError(`${key} contains invalid characters`);
+  }
+}
+
+function appendBoundedNumber(
+  qs: URLSearchParams,
+  query: Query,
+  key: string,
+  min: number,
+  max: number,
+): void {
+  const value = firstString(query, key);
+  if (value == null) return;
+  if (value.length > 40 || !NUMERIC_RE.test(value)) {
+    validationError(`${key} must be a number`);
+  }
+  const numeric = Number(value);
+  if (!Number.isFinite(numeric) || numeric < min || numeric > max) {
+    validationError(`${key} is out of range`);
+  }
+  qs.set(key, value);
+}
+
+export function buildScreenshotRequest(query: Query): ValidatedScreenshotRequest {
+  const qs = new URLSearchParams();
+
+  appendBoundedNumber(qs, query, 'lat', -90, 90);
+  appendBoundedNumber(qs, query, 'lon', -180, 180);
+  appendBoundedNumber(qs, query, 'zoom', 0, 22);
+
+  const tab = firstString(query, 'tab');
+  if (tab != null) {
+    if (tab !== 'area' && tab !== 'properties') {
+      validationError('tab is invalid');
+    }
+    qs.set('tab', tab);
+  }
+
+  const og = firstString(query, 'og');
+  if (og != null) {
+    if (og !== '1') {
+      validationError('og is invalid');
+    }
+    qs.set('og', og);
+  }
+
+  for (const key of REPEATED_KEYS) {
+    for (const value of repeatedStrings(query, key)) {
+      assertSafeValue(key, value);
+      qs.append(key, value);
+    }
+  }
+
+  const pagePath = firstString(query, 'path') ?? '/';
+  if (!PATH_RE.test(pagePath)) {
+    validationError('path is invalid');
+  }
+
+  return { pagePath, qs };
+}