Add support for ICAP #128
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Add support for ICAP #128
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Description ----------- The ICAP protocol is defined in RFC 3507 [1]. Encoding of ICAP messages is very similar to that of HTTP. The generic structure of both ICAP and HTTP messages originates in RFC 822 (obsoleted by RFC 2822). Except for the generic structure, ICAP leans to the HTTP specification to encode the request/status lines, headers and chunked transfer-encoding for the message body. Hence, an HTTP parser can be used to parse an ICAP request/response headers, assuming the ICAP protocol version and URI scheme are properly handled. Moreover, as ICAP protocol deals with adaptation of HTTP messages, it makes a lot of sense to use the same crate to parse both ICAP messages and HTTP messages embedded in the body of ICAP messages. This commit adds a new crate feature `icap` which enables support for parsing ICAP messages. When enabled, `httparse` accepts the ICAP version `ICAP/1.0` where an HTTP version is expected. A parsed request/response of an ICAP message can be differentiated by the version number. For ICAP the minor protocol version is incremented by 100. In other words, the ICAP/1.0 protocol is denoted by version 100. While the HTTP/1.0 protocol is denoted by 0. Notes ----- The `expect2!` macro was added to support MSRV 1.39. It is not needed starting from `rustc 1.53.0`, which has added support for Or patterns [2]. Using Or patterns the existing `expect!` macro can be used as follows: ``` expect!(bytes.next() == (b'H'|b'I') => Err(Error::Version)); ``` [1] https://www.rfc-editor.org/rfc/rfc3507.html [2] https://blog.rust-lang.org/2021/06/17/Rust-1.53.0.html#or-patterns
Till now the `--all-features` flag was not required, because the only feature `std` was enabled by default. Now, with addition of the `icap` feature, we need to add the `--all-features` flag explicitly.
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This PR adds support for the ICAP protocol.
More elaborate explanation is in the commit messages.