Google App Engine

The fetch Function

The fetch() function makes a synchronous request to fetch a URL. This function is provided by the google.appengine.api.urlfetch package.

See also Asychronous Requests.

fetch(url, payload=None, method=GET, headers={}, allow_truncated=False, follow_redirects=True, deadline=5, validate_certificate=False)

Fetches a document at the URL given in url, and returns an object containing the details of the response. See Response Objects for details about the return value.

The fetch action is synchronous. fetch() will not return until the server responds. A slow remote server may cause your application's own request to time out.

Arguments

url
An http or https URL. If the URL is invalid, an InvalidURLError is raised. If you want to add query parameters in a GET request, append them to the URL, for example: https://www.example.com/?q=some+queryparam.
payload
Body content for a POST, PUT, or PATCH request.
method
The HTTP method to use for the request. Acceptable values include GET, POST, HEAD, PUT, DELETE, and PATCH. These values are constants provided by the package. The value can also be a string equivalent to the name of the method.
headers
The set of HTTP headers to include with the request, as a mapping of names and values. For security reasons, some HTTP headers cannot be modified by the application. See the URL Fetch Service overview.
allow_truncated
If False and the response data exceeds the maximum allowed response size, a ResponseTooLargeError exception is raised. If True, no exception is raised, and the response's content is truncated to the maximum size, and the response object's content_was_truncated attribute is set to True. For more information on limits, see the URL Fetch Service overview.
follow_redirects

If True, responses that are HTTP redirects are followed, up to 5 consecutive redirects. The response data is from the final location, as if the data were for the requested location. If False, redirects are not followed, and a redirect response is returned directly to the application, including the header information that describes the redirect.

Warning: Cookies are not handled upon redirection. If cookie handling is needed, set follow_redirects to False and handle both cookies and redirects manually.

deadline

The maximum amount of time to wait for a response from the remote host, as a number of seconds. If this parameter is not specified, the default value used will be a system-specific deadline, which is typically 5 seconds. If the remote host does not respond in this amount of time, a DownloadError is raised.

Time spent waiting for a request does not count toward the CPU quota for the request. It does count toward the request timer. If the app request timer expires before the URL Fetch call returns, the call is canceled.

The deadline can be up to a maximum of 60 seconds for request handlers and 10 minutes for tasks queue and cron job handlers.

validate_certificate

A value of True instructs the application to send a request to the server only if the certificate is valid and signed by a trusted certificate authority (CA), and also includes a hostname that matches the certificate. If the certificate validation fails, a SSLCertificateError exception is raised. A value of False instructs the application to perform no certificate validation. This parameter is ignored for non-HTTPS requests.

Note: This parameter currently defaults to False, but will default to True in the near future. If you rely upon making requests to a site with an invalid or untrusted certificate, you should explicitly pass validate_certificate=False to avoid errors in future versions.

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