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3. Header Block Decoding

3.1. Header Block Processing​

A decoder processes a header block sequentially to reconstruct the original header list.

A header block is the concatenation of header field representations. The different possible header field representations are described in Section 6.

Once a header field is decoded and added to the reconstructed header list, the header field cannot be removed. A header field added to the header list can be safely passed to the application.

By passing the resulting header fields to the application, a decoder can be implemented with minimal transitory memory commitment in addition to the memory required for the dynamic table.

3.2. Header Field Representation Processing​

The processing of a header block to obtain a header list is defined in this section. To ensure that the decoding will successfully produce a header list, a decoder MUST obey the following rules.

All the header field representations contained in a header block are processed in the order in which they appear, as specified below. Details on the formatting of the various header field representations and some additional processing instructions are found in Section 6.

An indexed representation entails the following actions:

  • The header field corresponding to the referenced entry in either the static table or dynamic table is appended to the decoded header list.

A literal representation that is not added to the dynamic table entails the following action:

  • The header field is appended to the decoded header list.

A literal representation that is added to the dynamic table entails the following actions:

  • The header field is appended to the decoded header list.

  • The header field is inserted at the beginning of the dynamic table. This insertion could result in the eviction of previous entries in the dynamic table (see Section 4.4).

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