A function to get HTTP headers from the current client's HTTP request

[alexey-milovidov]

Use case

Obtain the relevant data when some application sends the data directly to ClickHouse without a separate backend.

CREATE TABLE test (something String DEFAULT getClientHTTPHeader('X-CloudFlare-WTF')) ...

Header names are case-insensitive. The function takes a constant String and returns a String.
Some headers such as X-ClickHouse-Password should be restricted.

Describe the solution you'd like

Save the header's map to ClientInfo, and then get it from the function.

[lingtaolf]

Could you let me try this ?

[alexey-milovidov]

@lingtaolf amazing, thank you!