feat(api): fw-7456 add CORS support for JSON API endpoints

Add Access-Control-Allow-Origin and Access-Control-Allow-Credentials
headers to all JSON API responses, and handle OPTIONS preflight
requests with 204 No Content. This ensures cross-origin requests from
browsers work consistently regardless of CDN cache state.

Author: swkatmask

src/jsons/health.nim

@@ -11,5 +11,11 @@ proc createJsonApiHealthRouter*(cfg: Config) =
   router jsonapi_health:
     get "/api/health":
       cond cfg.enableJsonApi
-      let headers = {"Content-Type": "application/json; charset=utf-8"}
+      let origin = corsOrigin()
+      let headers = {
+        "Content-Type": "application/json; charset=utf-8",
+        "Vary": "Origin",
+        "Access-Control-Allow-Origin": origin,
+        "Access-Control-Allow-Credentials": "true"
+      }
       resp Http200, headers, """{"message": "OK"}"""

src/nitter.nim

@@ -1,5 +1,5 @@
 # SPDX-License-Identifier: AGPL-3.0-only
-import asyncdispatch, strformat, logging
+import asyncdispatch, strformat, logging, re
 from net import Port
 from htmlgen import a
 from os import getEnv
@@ -71,6 +71,18 @@ settings:
   reusePort = true
 
 routes:
+  # CORS preflight handler for API routes
+  options re"/api/.*":
+    let origin = if request.headers.hasKey("Origin"): request.headers["Origin"] else: "*"
+    resp Http204, {
+      "Vary": "Origin",
+      "Access-Control-Allow-Origin": origin,
+      "Access-Control-Allow-Methods": "GET, POST, OPTIONS",
+      "Access-Control-Allow-Headers": "Content-Type, Authorization, DNT",
+      "Access-Control-Allow-Credentials": "true",
+      "Access-Control-Max-Age": "300"
+    }, ""
+
   get "/":
     resp renderMain(renderSearch(), request, cfg, themePrefs())
 

src/routes/router_utils.nim

@@ -43,25 +43,51 @@ template getCursor*(req: Request): string =
 proc getNames*(name: string): seq[string] =
   name.strip(chars={'/'}).split(",").filterIt(it.len > 0)
 
+template corsOrigin*(): string {.dirty.} =
+  if request.headers.hasKey("Origin"): request.headers["Origin"] else: "*"
+
 template respJson*(node: JsonNode) =
-  resp $node, "application/json"
+  let origin = corsOrigin()
+  resp Http200, {
+    "Content-Type": "application/json",
+    "Vary": "Origin",
+    "Access-Control-Allow-Origin": origin,
+    "Access-Control-Allow-Credentials": "true"
+  }, $node
 
 template respJsonSuccess*(data: JsonNode) =
+  let origin = corsOrigin()
   let successResponse = %*{
     "code": 0,
     "data": data
   }
-  resp $successResponse, "application/json"
+  resp Http200, {
+    "Content-Type": "application/json",
+    "Vary": "Origin",
+    "Access-Control-Allow-Origin": origin,
+    "Access-Control-Allow-Credentials": "true"
+  }, $successResponse
 
 template respJsonError*(message: string, errorType: string = "", httpCode: HttpCode = Http200) =
+  let origin = corsOrigin()
   var errorResponse = %*{
     "code": -1,
     "error": message
   }
   if errorType.len > 0:
     errorResponse["error_type"] = %errorType
-  resp httpCode, $errorResponse, "application/json"
+  resp httpCode, {
+    "Content-Type": "application/json",
+    "Vary": "Origin",
+    "Access-Control-Allow-Origin": origin,
+    "Access-Control-Allow-Credentials": "true"
+  }, $errorResponse
 
 template respJsonNull*() =
-  let nullResponse = newJNull()
-  resp $nullResponse, "application/json"
+  let origin = corsOrigin()
+  resp Http200, {
+    "Content-Type": "application/json",
+    "Vary": "Origin",
+    "Access-Control-Allow-Origin": origin,
+    "Access-Control-Allow-Credentials": "true"
+  }, $newJNull()