Function process_header_substitution 

pub fn process_header_substitution<B>(
    value: &str,
    req: &Request<B>,
) -> Result<String>

Process header value substitutions

Replaces placeholders in the header value with actual values:

• {header.Name} - value of request header with that name
• {uuid} - generates a random UUID
• {env.VAR} - value of environment variable VAR

Arguments

• value - The header value template with placeholders
• req - The HTTP request to extract headers from

Returns

The processed header value with all placeholders replaced

Example

let result = process_header_substitution("X-Request-ID: {uuid}", &req)?;
assert!(result.contains("X-Request-ID:"));