Function encode_segment 

pub fn encode_segment(segment: &str) -> String

Percent-encodes a URI path segment.

Everything outside RFC 3986’s unreserved set is escaped. / is encoded, which is the whole point: an image ARN’s slashes would otherwise split into extra path segments and address something else. : is encoded too — legal unencoded in a path per the RFC, but AWS’s own SDKs encode it in labels and the signature must match whatever is sent.