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CORS in Nexios ​

Got it! I'll go through each CORS configuration setting in Nexios, explaining what it does and how it impacts requests.

Basic CORS Configuration in Nexios ​

Before diving into individual settings, here's a simple CORS setup using CorsConfig:

python
from nexios import NexiosApp
from nexios.middleware.cors import CorsConfig
from nexios.middleware.cors import CORSMiddleware

cors_config = CorsConfig(
    allow_origins=["https://example.com"],
    allow_methods=["GET", "POST"],
    allow_headers=["Authorization", "X-Requested-With"],
    allow_credentials=True,
    max_age=600,
    debug=True
)
app = NexiosApp()
app.add_middleware(CORSMiddleware(config=cors_config))
py
from nexios import NexiosApp, MakeConfig
from nexios.middleware.cors import CorsConfig
from nexios.middleware.cors import CORSMiddleware

config = MakeConfig(
    cors = CorsConfig(
    allow_origins=["https://example.com"],
    allow_methods=["GET", "POST"],
    allow_headers=["Authorization", "X-Requested-With"],
    allow_credentials=True,
    max_age=600,
    debug=True
)
)
app = NexiosApp(config = config)
app.add_middleware(CORSMiddleware())

we can break it down further:

allow_origins ​

  • Purpose: Specifies which domains can access the API.
  • Example:
python
# Using CorsConfig with recommended approach
cors_config = CorsConfig(
    allow_origins=["https://example.com", "https://another-site.com"]
)
app.add_middleware(CORSMiddleware(config=cors_config))
  • Special cases:
    • Use ["*"] to allow requests from any origin (not safe if credentials are enabled).
    • If an origin is not listed here, the request will be blocked.

blacklist_origins ​

  • Purpose: Specifies which origins should beblocked, even if they match allow_origins.
  • Example:
python
cors_config = CorsConfig(
        blacklist_origins=["https://bad-actor.com"]
    )
app.add_middleware(CORSMiddleware(config=cors_config))
  • Use case: If you allow all origins (["*"]), but want to exclude specific ones.

allow_methods ​

  • Purpose: Defines which HTTP methods (GET, POST, etc.) are allowed in cross-origin requests.
  • Example:
python
cors_config = CorsConfig(
    allow_methods=["GET", "POST", "PUT"]
)
app.add_middleware(CORSMiddleware(config=cors_config))
  • Default: All methods (["DELETE", "GET", "HEAD", "OPTIONS", "PATCH", "POST", "PUT"]) are allowed.

allow_headers ​

  • Purpose: Specifies which request headers are permitted in cross-origin requests.
  • Example:
python
cors_config = CorsConfig(
        allow_headers=["Authorization", "X-Custom-Header"]
    )
app.add_middleware(CORSMiddleware(config=cors_config))
  • Default: Basic headers like Accept, Content-Type, etc., are always allowed.

blacklist_headers ​

  • Purpose: Defines headers that shouldnot be allowed in requests.
  • Example:
python
cors_config = CorsConfig(
    blacklist_headers=["X-Disallowed-Header"]
)
app.add_middleware(CORSMiddleware(config=cors_config))
  • Use case: If you allow most headers but want to restrict specific ones.

allow_credentials ​

  • Purpose: Determines whether credentials (cookies, authorization headers) are allowed in requests.
  • Example:
python
cors_config = CorsConfig(
        allow_credentials=True
    )
app.add_middleware(CORSMiddleware(config=cors_config))
  • Important:
    • If True, the browser allows requests with credentials (e.g., session cookies).
    • If True, allow_origins cannot be "*" (security restriction).
    • If False, credentials are blocked.

allow_origin_regex ​

  • Purpose: Uses a regex pattern to match allowed origins dynamically.
  • Example:
python
cors_config = CorsConfig(
        allow_origin_regex=r"https://.*\.trusted-site\.com"
    )
app.add_middleware(CORSMiddleware(config=cors_config))
  • Use case: When you want to allow multiple subdomains without listing them individually.

👁️ expose_headers ​

  • Purpose: Specifies which response headers the client is allowed to access.
  • Example:
python
cors_config = CorsConfig(
        expose_headers=["X-Response-Time"]
    )
app.add_middleware(CORSMiddleware(config=cors_config))
  • Default: Only basic headers are exposed unless configured.

⏱️ max_age ​

  • Purpose: Defines how long the preflight (OPTIONS) response can be cached.
  • Example:
python
cors_config = CorsConfig(
        max_age=600  # Cache for 10 minutes
    )
app.add_middleware(CORSMiddleware(config=cors_config))
  • Impact: Reduces unnecessary preflight requests for frequent API calls.

strict_origin_checking ​

  • Purpose: If enabled, requestsmust include an Origin header.
  • Example:
python
cors_config = CorsConfig(
        strict_origin_checking=True
    )
app.add_middleware(CORSMiddleware(config=cors_config))
  • Use case: When you want to strictly enforce CORS checks, especially for security.

debug ​

  • Purpose: Enables logging to troubleshoot CORS issues.
  • Example:
python
cors_config = CorsConfig(
        debug=True
    )
app.add_middleware(CORSMiddleware(config=cors_config))
  • Impact:
    • Prints logs when a request is blocked due to CORS.
    • Useful for debugging in development.

custom_error_status & custom_error_messages ​

  • Purpose: Allows custom error handling for CORS failures.
  • Example:
python
cors_config = CorsConfig(
        custom_error_status=403,
        custom_error_messages={
            "disallowed_origin": "This origin is not allowed.",
            "missing_origin": "The request is missing an origin."
        }
    )
app.add_middleware(CORSMiddleware(config=cors_config))
  • Use case: When you want meaningful error messages instead of generic CORS errors.