HTTP Get

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4D v16.3

HTTP Get


HTTP Get ( url ; response {; headerNames ; headerValues}{; *} ) -> Function result

Parameter	Type	Description
url	Text	URL to which to send the request
response	Text, BLOB, Picture, Object	Result of request
headerNames	Text array	Header names of the request
		Returned header names
headerValues	Text array	Header values of the request
		Returned header values
*	Operator	If passed, connection is maintained (keep-alive) If omitted, connection is closed automatically
Function result	Longint	HTTP status code

Description

The HTTP Get command sends an HTTP GET request directly to a specific URL and processes the HTTP server response.

Pass the URL where you want the request sent in the url parameter. The syntax to use is:

http://[{user}:[{password}]@]host[:{port}][/{path}][?{queryString}]

For example, you can pass the following strings:

    http://www.myserver.com
    http://www.myserver.com/path
    http://www.myserver.com/path?name="jones"
    https://www.myserver.com/login (*)
    http://123.45.67.89:8083
    http://john:smith@123.45.67.89:8083

(*) During HTTPS requests, authority of the certificate is not checked.

After command execution, the response parameter receives the result of the request returned by the server. This result corresponds to the body of the response, with no headers.
You can pass different types of variables in response:

Text: When the result is expected to be text (see note below).
BLOB: When the result is expected to be in binary form.
Picture: When the result is expected to be a picture.
Object: When the result is expected to be a C_OBJECT object.

Note: When a text variable is passed in response, 4D will try to decode the data returned from the server. 4D first tries to retrieve the charset from the content-type header, then from the content using a BOM, and finally looks for any http-equiv charset (in html content) or encoding (for xml) attribute. If no charset can be detected, 4D will attempt to decode the response in ANSI. If the conversion fails, the resulting text will be empty. If you are unsure whether the server returns a charset information or a BOM, but you know the encoding, it is more accurate to pass response in BLOB and call Convert to text.

If you pass a BLOB, it contains the text, picture or any type of contents (.wav, .zip, etc.) returned by the server. You must then manage the recovery of these contents (headers are not included in the BLOB). When you pass a C_OBJECT type object, if the request returns a result with an "application/json" (or "something/json") content-type, 4D attempts to parse the JSON content in order to generate the object.

In headerNames and headerValues, you pass arrays containing the names and values of the request headers.
After this method is executed, these arrays contain the names and values of headers returned by the HTTP server. More specifically, this lets you manage cookies.

The * parameter enables the keep-alive mechanism for the server connection. By default, if this parameter is omitted, keep-alive is not enabled.

The command returns a standard HTTP status code (200=OK and so on) as returned by the server. The list of HTTP status codes is provided in RFC 2616.
If you are unable to connect to the server for a reason related to the network (DNS Failed, Server not reachable...), the command returns 0 and an error is generated. You can intercept errors using an error-handling method installed by the ON ERR CALL command.

Example 1

Retrieval of the 4D logo on the 4D Web site:

 C_TEXT(URLPic_t)

 URLPic_t:="http://www.4d.com/sites/all/themes/dimention/images/home/logo4D.jpg"

 ARRAY TEXT(HeaderNames_at;0)

 ARRAY TEXT(HeaderValues_at;0)

 C_PICTURE(Pic_i)

 $httpResponse:=HTTP Get(URLPic_t;Pic_i;HeaderNames_at;HeaderValues_at)

Example 2

Retrieval of an RFC:

 C_TEXT(URLText_t)

 C_TEXT(Text_t)

 URLText_t:="http://tools.ietf.org/rfc/rfc1.txt"

 ARRAY TEXT(HeaderNames_at;0)

 ARRAY TEXT(HeaderValues_at;0)

 $httpResponse:=HTTP Get(URLText_t;Text_t;HeaderNames_at;HeaderValues_at)

Example 3

Retrieval of a video:

 C_BLOB(vBlob)

 $httpResponse:=HTTP Get("http://www.example.com/video.flv";vBlob)

 BLOB TO DOCUMENT("video.flv";vBlob)