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8. Content Parameters

8.5 Transfer Encodings

Transfer encoding values are used to indicate an encoding transformation that has been, can be, or may need to be applied to an Entity-Body in order to ensure safe transport through the network. Transfer encodings are only used with entities destined for or retrieved from MIME-conformant systems, and thus will rarely occur in an HTTP/1.0 message. This differs from an encoding-mechanism in that the transfer encoding is a property of the message, not of the original resource.

transfer-encoding	=	"binary" | "8bit" | "7bit"
	|	"quoted-printable" | "base64"
	|	token
All transfer-encoding values are case-insensitive. HTTP/1.0 uses transfer-encoding values in the Accept-Encoding (Section 5.4.3) and Content-Transfer-Encoding (Section 7.1.5) header fields.

The values "7bit", "8bit", and "binary" are used to indicate that no transfer encoding has been performed. Instead, they describe the sort of encoding that might be needed for transmission through an unsafe transport system. Binary indicates that the body may contain any set of octets. 8bit adds the restrictions that CR and LF characters only occur as part of CRLF line separators, all lines are short (less than 1000 octets), and no NULs (octet 0) are present. 7bit adds a further restriction that all octets are 7-bit US-ASCII characters.

The "quoted-printable" and "base64" values indicate that the associated encoding (as defined in MIME [6]) has been applied to the body. These encodings consist entirely of 7-bit US-ASCII characters.

T. Berners-Lee, R. T. Fielding, H. Frystyk Nielsen - 12 MAR 95

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