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HTTP requests consist of two parts: the request proper, consisting of a request line and a set of headers, and (optionally) a body. The body might have a binary content-type, and even in the textual case its length is specified in bytes, not characters.

Therefore, HTTP is a fundamentally binary protocol. However the request line and headers are specified to be in a subset of ASCII, so they can be treated as text, provided that the port’s encoding is set to an ASCII-compatible one-byte-per-character encoding. ISO-8859-1 (latin-1) is just such an encoding, and happens to be very efficient for Guile.

So what Guile does when reading requests from the wire, or writing them out, is to set the port’s encoding to latin-1, and treating the request headers as text.

The request body is another issue. For binary data, the data is probably in a bytevector, so we use the R6RS binary output procedures to write out the binary payload. Textual data usually has to be written out to some character encoding, usually UTF-8, and then the resulting bytevector is written out to the port.

In summary, Guile reads and writes HTTP over latin-1 sockets, without any loss of generality.

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