Learning HTTP/2

Appendix A. HTTP/2 Frames

This appendix is a quick reference for the HTTP/2 framing layer. Each section includes the frame type number, the binary layout for the frame, a description of the frame, and a list of flags specific to that frame.

The Frame Header

As described in Chapter 5, each frame starts with the same nine bytes:

See Table 5-1 for a description of each field.

DATA

DATA frames contain arbitrary sequences of octets. This is a fancy way of saying these frames contain the requested/sent objects. Object data is split up across one or more frames depending on the maximum frame length. The padding length field and the padding itself are conditionally included to hide the size of the message for security purposes:

DATA Frame Fields

Name	Length	Description
Pad Length	1 byte	Indicates the length of the padding field. Will only be present if the PADDED flag is set in the frame header.
Data	Variable	The content of the frame.
Padding	Variable	Length set by the Pad Length field. All bytes are set to zero.

DATA Frame Flags

Name	Bit	Description
END_STREAM	0x1	Indicates this is the frame in the stream
PADDED	0x8	Indicates that the Pad Length and Padding fields are used

HEADERS

HEADERS frames are used to start streams and send message headers ...