BOOL WINAPI LlmSetRequestHeader(
	HCLIENT hClient,
	LPCTSTR lpszHeaderName,
	LPTSTR lpszHeaderValue
);

The LlmSetRequestHeader function sets the value of a custom HTTP header issued with subsequent requests.

Parameters

hClient

A handle to the client session.

lpszHeaderName

A pointer to a null-terminated string which specifies the name of the HTTP header field. Header names may only contain ASCII letters, numbers and a restricted subset of punctuation characters. Header names cannot contain Unicode or ANSI multi-byte character sequences.

lpszHeaderValue

A pointer to a null-terminated string which specifies the value of the HTTP header. Header values cannot contain carriage-return or linefeed characters. If the value contains Unicode characters, they will be UTF-8 encoded. If this parameter or NULL or a zero-length string, the header field is deleted from the request headers.

Return Value

If the function succeeds, the return value is non-zero. If the function fails, the return value is zero. To get extended error information, call LlmGetLastError. If the header name contains illegal characters or cannot be changed (e.g., attempting to change the Authorization header), the function will return zero and the last error code will be set to ST_ERROR_INVALID_HEADER_NAME. If the header value contains illegal characters, the last error code will be set to ST_ERROR_INVALID_HEADER_VALUE.

Remarks

The LlmSetRequestHeader function assigns a custom HTTP request header that will be included with subsequent requests made using the current client session. If the specified header already exists in the custom header list, its value will be replaced. If the header value is an empty string, the header will be removed.

This function is intended for advanced applications that require lower-level access to provider-specific functionality. Most applications should not need to use custom request headers. Some headers are managed internally by the library and cannot be overridden using this function. This includes headers required for authentication, content formatting, message length, host identification, and other protocol-specific functionality required by the current provider.

Examples of headers that are managed internally by the library include:

• Authorization
• Content-Length
• Content-Type
• Host
• User-Agent

Custom headers remain associated with the current client session until they are removed using the LlmClearHeaders function, the LlmResetSession function is called, or the connection is closed using the LlmDisconnect function.

Requirements

Minimum Desktop Platform: Windows 7 Service Pack 1
Minimum Server Platform: Windows Server 2008 R2 Service Pack 1
Header File: cstools12.h
Import Library: csllmv12.lib
Unicode: Implemented as Unicode and ANSI versions

See Also

LlmClearHeaders, LlmDisconnect, LlmGetResponseHeader, LlmResetSession, LlmSendMessage, LlmSetUserAgent

Copyright © 2026 Catalyst Development Corporation. All rights reserved.