Table Of Contents

HEAD (G Dataflow)

Version:
    Last Modified: January 12, 2018

    Sends a web request that returns headers from a server, web page, or web service. This node uses the HEAD HTTP method. This node does not submit any data to the server or receive body data. The minimal data exchange makes the HEAD node useful for testing the validity of a URL.

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    client handle

    Unique value that identifies the web request. You can use the same client handle to wire together multiple HTTP nodes to preserve authentication credentials, HTTP headers, and cookies. Client handles are not required when making independent web requests without persistent data such as headers or credentials.

    Default: 0

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    url

    URL of the server, web page, or web service where this node will send the web request.

    Relative URL behavior

    If you do not specify a URL scheme on a Web Server target, each URL you enter is relative to the location the WebVI is hosted. The WebVI sends HTTP requests to the server at the relative URL. For example, if you host the WebVI on http://website.com/MyApp/, specifying the relative URL subdirectory/myfile.txt sends an HTTP request to http://website.com/MyApp/subdirectory/myfile.txt.

    If you do not specify a URL scheme on a non-Web Server target, the node prefixes http:// to the URL and treats it as an absolute URL.

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    error in

    Error conditions that occur before this node runs.

    The node responds to this input according to standard error behavior.

    Standard Error Behavior

    Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

    error in does not contain an error error in contains an error
    If no error occurred before the node runs, the node begins execution normally.

    If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

    If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

    Default: No error

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    timeout

    Amount of time in milliseconds the node has to wait for a response from the server before the web request times out. A value of -1 defers timeout monitoring to the operating system.

    Default: 10000 ms

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    status code

    Status code information returned by the server.

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    client handle out

    Unique value that identifies the web request. Use this value to refer to this web request in subsequent node calls.

    You can use the same client handle to wire together multiple HTTP nodes to preserve authentication credentials, HTTP headers, and cookies.

    Client handles are not required when making independent web requests without persistent data such as headers or credentials.

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    headers

    Header fields returned by the server. Refer to the World Wide Web Consortium website at www.w3.org for more information about header field definitions including available headers, descriptions, and syntax.

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    error out

    Error information.

    The node produces this output according to standard error behavior.

    Standard Error Behavior

    Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

    error in does not contain an error error in contains an error
    If no error occurred before the node runs, the node begins execution normally.

    If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.

    If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

    Web Server Details

    CORS Restrictions on HTTP Requests

    Requests from HTTP clients are subject to CORS restrictions when the WebVI communicates with a web service on a different origin. The web service responding to the HTTP request must return a valid CORS configuration for the HTTP request to complete successfully.

    On non-Web Server targets, HTTP requests are not subject to CORS restrictions. The VI can make HTTP requests regardless of the CORS configuration of the server.

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    Note  

    If an HTTP request fails on the Web Server target, the HTTP node returns the generic network error code 363650 because it cannot track the exact cause of the failure. You must use the output tab or developer tools specific to the browser to gather additional information about the cause of the failure.

    Cached Response Behavior for Repeat Requests

    HTTP nodes on a Web Server target may create caches of responses to HTTP requests. If a duplicate request occurs, the HTTP nodes can avoid querying the network by returning a previous response from the cache. The specific browser environment and server configuration determine the behavior of the cache.

    On non-Web Server targets, every HTTP request creates a unique network request.

    Forbidden Headers on a Web Server

    A WebVI cannot transmit or receive specific forbidden headers in HTTP requests. For header transmissions, the request to the server does not include forbidden headers. When the HTTP nodes receive a forbidden header from a server, they exclude the header from the headers output. Additionally, the CORS configuration of a server may exclude some headers in server requests or from server responses.

    On non-Web Server targets, you do not need to account for forbidden headers in HTTP requests.

    Where This Node Can Run:

    Desktop OS: Windows

    FPGA: Not supported

    Web Server: Supported in VIs that run in a web application


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