One document matched: draft-snell-httpbis-bohe-03.xml
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<rfc category="info" ipr="trust200811" docName="draft-snell-httpbis-bohe-03">
<front>
<title abbrev="application/merge-patch">
HTTP/2.0 Discussion: Binary Optimized Header Encoding
</title>
<author initials="J.M." surname="Snell" fullname="James M Snell">
<address>
<email>jasnell@gmail.com</email>
</address>
</author>
<date month="February" year="2013" />
<keyword>I-D</keyword>
<keyword>http</keyword>
<keyword>spdy</keyword>
<abstract>
<t>This memo describes a proposed alternative encoding for
headers within SPDY SYN_STREAM, SYN_REPLY and HEADERS
frames.</t>
</abstract>
</front>
<middle>
<section title="Binary Optimized Header Encoding">
<t>Binary Optimized Header Encoding is a proposed
alternative serialization for headers within SPDY SYN_STREAM,
SYN_REPLY and HEADERS frames that is designed to optimize
generation, consumption and processing of the most commonly
used HTTP headers.</t>
<figure><preamble>Alternate Header Block Serialization:</preamble><artwork>
+-------+---------+
| NUM | Headers |
+-------+---------+
</artwork></figure>
<t>'NUM' is a single unsigned 8-bit value indicating the total number
of distinct headers contained in the encoded block.</t>
<t>'Headers' consists of the complete set of encoded headers. The format
for each header is determined by whether the header name (the key) and
the header value are included in the static "default dictionary"
defined by this specification. The first two bits of each encoded
header record identify the specific header format used.</t>
<figure><preamble>Registered Key + Registered Value Pair</preamble><artwork>
+--+---+--+
|00|CNT|ID|
+--+---+--+
</artwork></figure>
<t>If the header name and value are both included in the default
dictionary, the associated index of the header as provided by the
dictionary is encoded as a variable-length, unsigned integer in
lists of no more than 63 items. For example, the headers ":path=/",
":method=GET" and ":scheme=https" would be compactly encoded as:
03 03 0F 06</t>
<figure><preamble>Registered Key + Unregistered Value</preamble><artwork>
+--+---+--+---+---+
|01|FLG|ID|LEN|VAL|
+--+---+--+---+---+
</artwork></figure>
<t>If the header name is included in the default dictionary, but the
value given is not, the header is encoded using five fields: the two-bit
opcode (01) followed by six flag bits as defined below, followed by the
numerically lowest index of the named header as provided by the default
dictionary encoded as a variable-length, unsigned integer, followed by
another variable-length, unsigned integer specifying the length of the
value, followed by the encoded value.</t>
<figure><preamble>Unregistered Key + Value Pair</preamble><artwork>
+--+---+------+---+------+---+
|10|FLG|LENkey|key|LENval|val|
+--+---+------+---+------+---+
</artwork></figure>
<t>If the header name and value are not included in the default dictionary,
the header is encoded using six distinct fields: the two-bit opcode (10)
followed by six flag bits as defined below, followed by a variable-length,
unsigned integer specifying the key length, followed by the ISO-8859-1
encoded key name, followed by a variable-length, unsigned integer specifying
the value length, followed by the encoded value.</t>
<figure><preamble>Flags:</preamble><artwork>
FLG = 000000
||||||
|||||Reserved
||||Date (Numeric val represents a date)
|||Numeric (val is one or more uvarints)
||Huffman-encoded
|UTF-8 or ISO8859-1 (1 or 0)
Binary | Text (1 or 0)
</artwork></figure>
<t>When the opcode is either 01 or 10, the six-bit FLG field is used to specify
additional properties about the header value. When the opcode is 00, the FLG
bits are unused and MUST NOT be set.</t>
<t>Moving from the most significant bit to the least, the flags are:
<list style="symbols">
<t>Binary or Text (0x32) - When set, the value is to be interpreted as
binary data. When unset, the value is to be interpreted as encoded-text.</t>
<t>UTF-8 or ISO-8859-1 (0x16) - When set, indicates that the text-encoded
value is UTF-8 encoded. Otherwise, ISO-8859-1 is assumed. Only used if the
Binary bit (0x32) is unset.</t>
<t>Huffman-encoded (0x08) - When set, indicates that the text-encoded
value has been static huffman encoded. The static dictionary used for the
encoding is dependent on whether the text is UTF-8 or ISO-8859-1 encoded.
Only used if the Binary bit (0x32) is unset.</t>
<t>Numeric (0x04) - When set, indicates that the value is encoded as a
variable-length unsigned integer. Only used if the Binary bit (0x32) is
set (indicating a binary value).</t>
<t>Date (0x02) - When set, indicates that the value is a date and time
encoded as a variable-length unsigned integer representing the total
number of seconds that have ellapsed since midnight on January 1st, 1990,
GMT. Only used if the Binary (0x32) and Numeric (0x04) bits are both set.</t>
<t>The final bit (0x01) is reserved.</t>
</list>
</t>
</section>
<section title="Value Encoding">
<t>Header values can be encoded as one of four distinct types: Binary, Text, Numeric
or Date. Each is indicated by the FLG field.</t>
<t><list style="symbols">
<t>Binary Header values are encoded as a raw, uninterpreted sequence of binary
octets.</t>
<t>Numeric values are encoded as variable-length, unsigned integers.</t>
<t>Date values are encoded as variable-length, unsigned integers representing
the total number of seconds that have ellapsed since midnight on January
1st, 1990.</t>
<t>Text values are encoded as a sequence one or more length-prefixed octet
sequences representing ISO-8859-1 or UTF-8 encoded characters, conforming to
the following structure:</t>
</list></t>
<figure><artwork>
string_val = COUNT 1*(LENGTH VAL)
</artwork></figure>
<t>Where COUNT is an unsigned 8-bit value specifying the number of octet sequences,
LENGTH is an unsigned variable-length integer specifying the length of each
sequence, and VAL is the specific sequence of encoded octets.</t>
</section>
<section title="Example Headers">
<t>Assuming the following (incomplete) default dictionary:</t>
<texttable>
<ttcol>ID</ttcol>
<ttcol>Key</ttcol>
<ttcol>Value</ttcol>
<c>0</c><c>date</c><c></c>
<c>1</c><c>:scheme</c><c></c>
<c>2</c><c>:scheme</c><c>http</c>
<c>3</c><c>:scheme</c><c>https</c>
<c>4</c><c>:scheme</c><c>ftp</c>
<c>5</c><c>:method</c><c></c>
<c>6</c><c>:method</c><c>get</c>
<c>7</c><c>:method</c><c>post</c>
<c>8</c><c>:method</c><c>put</c>
<c>9</c><c>:method</c><c>delete</c>
<c>10</c><c>:method</c><c>options</c>
<c>11</c><c>:method</c><c>connect</c>
<c>12</c><c>:method</c><c>patch</c>
<c>13</c><c>:method</c><c>link</c>
<c>14</c><c>:path</c><c></c>
<c>15</c><c>:path</c><c>/</c>
<c>16</c><c>:host</c><c></c>
<c>17</c><c>cookie</c><c></c>
<c>18</c><c>:status</c><c></c>
<c>19</c><c>:status</c><c>200</c>
<c>20</c><c>:status</c><c>201</c>
<c>21</c><c>:status</c><c>202</c>
<c>22</c><c>:status</c><c>204</c>
<c>23</c><c>:status</c><c>205</c>
<c>24</c><c>:status-text</c><c></c>
<c>25</c><c>:status-text</c><c>OK</c>
<c>26</c><c>:version</c><c></c>
<c>27</c><c>:version</c><c>1.0</c>
<c>28</c><c>:version</c><c>1.1</c>
<c>29</c><c>:version</c><c>2.0</c>
<c>30</c><c>accept</c><c></c>
<c>31</c><c>accept-charset</c><c></c>
<c>32</c><c>accept-encoding</c><c></c>
<c>33</c><c>accept-language</c><c></c>
<c>34</c><c>accept-ranges</c><c></c>
<c>35</c><c>allow</c><c></c>
<c>36</c><c>authorizations</c><c></c>
<c>37</c><c>cache-control</c><c></c>
<c>38</c><c>content-base</c><c></c>
<c>39</c><c>content-encoding</c><c></c>
<c>40</c><c>content-length</c><c></c>
<c>41</c><c>content-location</c><c></c>
<c>42</c><c>content-md5</c><c></c>
<c>43</c><c>content-range</c><c></c>
<c>44</c><c>content-type</c><c></c>
<c>45</c><c>etag</c><c></c>
<c>46</c><c>expect</c><c></c>
<c>47</c><c>expires</c><c></c>
<c>48</c><c>from</c><c></c>
<c>49</c><c>if-match</c><c></c>
<c>50</c><c>if-modified-since</c><c></c>
<c>51</c><c>if-none-match</c><c></c>
<c>52</c><c>if-range</c><c></c>
<c>53</c><c>if-unmodified-since</c><c></c>
<c>54</c><c>last-modified</c><c></c>
<c>55</c><c>location</c><c></c>
<c>56</c><c>max-forwards</c><c></c>
<c>57</c><c>origin</c><c></c>
<c>58</c><c>pragma</c><c></c>
<c>59</c><c>proxy-authenticate</c><c></c>
<c>60</c><c>proxy-authorization</c><c></c>
<c>61</c><c>range</c><c></c>
<c>62</c><c>referer</c><c></c>
<c>63</c><c>retry-after</c><c></c>
<c>64</c><c>server</c><c></c>
<c>65</c><c>set-cookie</c><c></c>
<c>66</c><c>status</c><c></c>
<c>67</c><c>te</c><c></c>
<c>68</c><c>trailer</c><c></c>
<c>69</c><c>transfer-encoding</c><c></c>
<c>70</c><c>transfer-encoding</c><c>gzip</c>
<c>71</c><c>upgrade</c><c></c>
<c>72</c><c>user-agent</c><c></c>
<c>73</c><c>vary</c><c></c>
<c>74</c><c>via</c><c></c>
<c>75</c><c>warning</c><c></c>
<c>76</c><c>www-authenticate</c><c></c>
<c>77</c><c>access-control-allow-origin</c><c></c>
<c>78</c><c>content-disposition</c><c></c>
<c>79</c><c>get-dictionary</c><c></c>
<c>80</c><c>p3p</c><c></c>
<c>81</c><c>x-content-type-options</c><c></c>
<c>82</c><c>x-frame-options</c><c></c>
<c>83</c><c>x-powered-by</c><c></c>
<c>84</c><c>x-xss-protection</c><c></c>
<c>85</c><c>connection</c><c></c>
<c>86</c><c>connection</c><c>keep-alive</c>
</texttable>
<figure><preamble>The header :version=2.0 would be encoded as:</preamble><artwork>
01 1D |..|
</artwork></figure>
<figure><preamble>The header :method=GET would be encoded as:</preamble><artwork>
01 06 |..|
</artwork></figure>
<figure><preamble>The headers :version=2.0 and :method=GET would be encoded as:</preamble><artwork>
02 06 1D |..|
</artwork></figure>
<figure><preamble>The header :method=foo would be encoded as:</preamble><artwork>
56 05 05 01 03 66 6F 6F |.....foo|
</artwork></figure>
<figure><preamble>The header foo=bar would be encoded as:</preamble><artwork>
b6 03 66 6f 6f 05 01 |..foo...|
03 62 61 72 |.bar|
</artwork></figure>
</section>
<section title="Security Considerations">
<t>TBD</t>
</section>
</middle>
<back>
<references title="Normative References">
&rfc2119;
</references>
</back>
</rfc>
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