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HPACK: Header Compression for HTTP/2


The raw-data directory has original stories of header data in json.

Other than raw-data directory, the HPACK implementations have their own directories to store the result of its encoder.

You can perform interoperability testing for your implementation with them.

File Name

Each json in story-#{n}.json is story case and shares compression context. Each story is either series of requests or responses.

JSON Format

Each json has:

  • description: general description of encoding strategy or implementation.
  • cases: array of test cases.
    • seqno: a sequence number. 0 origin.
    • header_table_size: the header table size sent in SETTINGS_HEADER_TABLE_SIZE and ACKed just before this case. The first case should contain this field. If omitted, the default value, 4,096, is used.
    • wire: encoded wire data in hex string.
    • headers: decoded http header in hash.

To test the decoder implementation, for each story file, for each case in cases in the order they appear, decode compressed header block in wire and verify the result against the header set in headers. Please note that elements in cases share the same compression context.

To test the encoder implementation, generate json story files by encoding header sets in headers. Using json files in raw-data is handy. Then use your decoder to verify that it can successfully decode the compressed header block. If you can play with other HPACK decoder implementations, try decoding your encoded data with them. If there is any mismatch, then there must be a bug in somewhere either encoder or decoder, or both.

  "description": "Encoded request headers with Literal without index only.",
  "cases": [
      "seqno": 0,
      "header_table_size": 4096,
      "wire": "1234567890abcdef",
      "headers": [
        { ":method": "GET" },
        { ":scheme": "http" },
        { ":authority": "" },
        { ":path": "/" },
        { "x-my-header": "value1,value2" }

Original Data

These Header Data are converted from

Compression Ratio


  • jxck
  • summerwind
  • kazu-yamamoto
  • tatsuhiro-t


The MIT License (MIT)

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