%HTTP_HEAD

Request document headers from a server

WTSupported in traditional Synergy on Windows

WNSupported in Synergy .NET on Windows

USupported on UNIX

VSupported on OpenVMS

status = %HTTP_HEAD(uri, [timeout], receive_document, error, in_headers, out_headers,
&        [log_file], [protocols], [ciphers], [cert_file], [CA_file], [HTTP_RELURI][, version])

Return value

status

Returns 0 if successful or an error number if unsuccessful.

Arguments

uri

The absolute URI (Uniform Resource Indicator) of the document to get headers for. (a)

timeout

(optional) The number of seconds to wait from the time a request is sent (after the connection to the server) until a response is received from the server. The default is 0, which specifies wait forever. (n)

receive_document

The document received in response to the get request. (System.String)

error

Returned with an error message if status is nonzero. Otherwise, it is ^NULL. (System.String)

in_headers

A dynamic array of one or more HTTP header strings. Each string has the form header_name[:value]. If not needed, pass ^NULL. ([*]System.String)

out_headers

A dynamic array System.String to receive one or more returne4d HTTP header strings. If no headers are returned, this is ^NULL. ([*]System.String)

log_file

(optional) The name and location of a log file to log HTTP packet contents. (a)

protocols

(optional) One or more SSL protocol versions in effect, separated by a plus sign (for example, SSLVER_TLS1_1+SSLVER_TLS1_2): (n)

SSLVER_ALL = All protocols are available.

SSLVER_TLS1_2 = TLS version 1.2 (default)

SSLVER_SSL2 = SSL version 2 (deprecated)

SSLVER_SSL3 = SSL version 3 (deprecated)

SSLVER_TLS1 = TLS version 1.0 (deprecated)

SSLVER_TLS1_1 = TLS version 1.1 (deprecated)

ciphers

(optional) A cipher list that specifies the encryption methods in effect. (a)

cert_file

(optional) The name of the client certificate file. (a)

CA_file

(optional) The name of a file containing certificate authorities that the client trusts. (a)

HTTP_RELURI

(optional) If passed, the absolute URI is translated and sent as a relative path in the HTTP request. If not passed, the absolute URI is sent with the path exactly as specified. (n)

version

(optional) A string that contains the HTTP version number to be placed in the document header. The default version number is 1.0. (a)

Discussion

%HTTP_HEAD sends a header request to an HTTP or HTTPS server to retrieve the headers for a document. %HTTP_HEAD is similar to %HTTP_GET, except it only returns headers, allowing you to find out what %HTTP_GET would return if you were to call it.

%HTTP_HEAD is functionally equivalent to %HTTP_CLIENT_HEAD, except it uses objects for certain parameters and its maximum HTTP header size is larger. Although it must be present, the receive_document parameter is not used, as %HTTP_HEAD does not return a document

The value of uri determines what type of connection will be made to the server. If you pass an HTTP URI, the client establishes an HTTP connection. If you pass an HTTPS URI, the client establishes an SSL connection.

For most applications, the standard default HTTP headers will work as provided. However, some HTTP servers require extra header values to process the HTTP message properly. The in_headers argument therefore enables you to add or modify headers for client requests. If you pass in a header name that was previously set, the last header value passed for that name will be the one sent in the HTTP message. The maximum HTTP header size for %HTTP_HEAD is 2048. An HTTP header array is limited to a maximum of 100 elements, and each element can have up to 2048 bytes with %HTTP_HEAD.

Passing a log_file causes both the HTTP request packet and the HTTP response packet to be logged to the specified file. This logging feature is available primarily for debugging purposes and should not normally be turned on in a secure production environment. Logs of a request packet include the HTTP method (in this case, HEAD), the URI, the HTTP version, all HTTP headers, and the body of the HTTP packet. Logs of a response packet include the HTTP version, status, reason, all HTTP headers, and the body of the HTTP packet. Log entries are always appended to an existing log file. If the log file does not exist, it is created. A log file can only be created on a local drive; remote drives are not supported.

If ciphers is not specified, the ciphers designated by the cipher list format value DEFAULT are in effect. See Ciphers for more information and a list of supported ciphers.

If specified, cert_file and CA_file must be the names of existing files in PEM or DER format. A PEM certificate file may contain both the certificate and private key. If it doesn’t contain the private key, the Synergy HTTP document transport API will load a PEM-based key file whose name is derived by appending “key.pem” to the end of the certificate filename. For example, if a certificate file is named test.der or test.pem, the API will load a key file named testkey.pem. If an authentication error occurs, the error is returned and the connection is terminated.

Chunked encoding is supported with HTTP versions of 1.1 and higher.