/* * HPACK header table management (RFC7541) - type definitions * * Copyright (C) 2014-2020 Willy Tarreau * Copyright (C) 2017 HAProxy Technologies * * Permission is hereby granted, free of charge, to any person obtaining * a copy of this software and associated documentation files (the * "Software"), to deal in the Software without restriction, including * without limitation the rights to use, copy, modify, merge, publish, * distribute, sublicense, and/or sell copies of the Software, and to * permit persons to whom the Software is furnished to do so, subject to * the following conditions: * * The above copyright notice and this permission notice shall be * included in all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR * OTHER DEALINGS IN THE SOFTWARE. */ #ifndef _HAPROXY_HPACK_TBL_T_H #define _HAPROXY_HPACK_TBL_T_H #include /* Dynamic Headers Table, usable for tables up to 4GB long and values of 64kB-1. * The model can be improved by using offsets relative to the table entry's end * or to the end of the area, or by moving the descriptors at the end of the * table and the data at the beginning. This entry is 8 bytes long, which is 1/4 * of the bookkeeping planned by the HPACK spec. Thus it saves 24 bytes per * header field, meaning that even with a single header, 24 extra bytes can be * stored (ie one such descriptor). At 29.2 average bytes per header field as * found in the hpack test case, that's slightly more than 1.5kB of space saved * from a 4kB block, resulting in contiguous space almost always being * available. * * Principle: the table is stored in a contiguous array containing both the * descriptors and the contents. Descriptors are stored at the beginning of the * array while contents are stored starting from the end. Most of the time there * is enough room left in the table to insert a new header field, thanks to the * savings on the descriptor size. Thus by inserting headers from the end it's * possible to maximize the delay before a collision of DTEs and data. In order * to always insert from the right, we need to keep a reference to the latest * inserted element and look before it. The last inserted cell's address defines * the lowest known address still in use, unless the area wraps in which case * the available space lies between the end of the tail and the beginning of the * head. * * In order to detect collisions between data blocks and DTEs, we also maintain * an index to the lowest element facing the DTE table, called "front". This one * is updated each time an element is inserted before it. Once the buffer wraps, * this element doesn't have to be updated anymore until it is released, in * which case the buffer doesn't wrap anymore and the front element becomes the * head again. * * Various heuristics are possible concerning the opportunity to wrap the * entries to limit the risk of collisions with the DTE, but experimentation * shows that thanks to the important savings made on the descriptors, the * likeliness of finding a large amount of free space at the end of the area is * much higher than the risk of colliding, so in the end the most naive * algorithms work pretty fine. Typical ratios of 1 collision per 2000 requests * have been observed. * * The defragmentation should be rare ; a study on live data shows on average * 29.2 bytes used per header field. This plus the 32 bytes overhead fix an * average of 66.9 header fields per 4kB table. This brings a 1606 bytes saving * using the current storage description, ensuring that oldest headers are * linearly removed by the sender before fragmentation occurs. This means that * for all smaller header fields there will not be any requirement to defragment * the area and most of the time it will even be possible to copy the old values * directly within the buffer after creating a new entry. On average within the * available space there will be enough room to store 1606/(29.2+8)=43 extra * header fields without switching to another place. * * The table header fits in the table itself, it only takes 16 bytes, so in the * worst case (1 single header) it's possible to store 4096 - 16 - 8 = 4072 * data bytes, which is larger than the 4064 the protocol requires (4096 - 32). */ /* * Gcc before 3.0 needs [0] to declare a variable-size array */ #ifndef VAR_ARRAY #if defined(__GNUC__) && (__GNUC__ < 3) #define VAR_ARRAY 0 #else #define VAR_ARRAY #endif #endif /* One dynamic table entry descriptor */ struct hpack_dte { uint32_t addr; /* storage address, relative to the dte address */ uint16_t nlen; /* header name length */ uint16_t vlen; /* header value length */ }; /* Note: the table's head plus a struct hpack_dte must be smaller than or equal to 32 * bytes so that a single large header can always fit. Here that's 16 bytes for * the header, plus 8 bytes per slot. * Note that when == 0, front, head, and wrap are undefined. */ struct hpack_dht { uint32_t size; /* allocated table size in bytes */ uint32_t total; /* sum of nlen + vlen in bytes */ uint16_t front; /* slot number of the first node after the idx table */ uint16_t wrap; /* number of allocated slots, wraps here */ uint16_t head; /* last inserted slot number */ uint16_t used; /* number of slots in use */ struct hpack_dte dte[VAR_ARRAY]; /* dynamic table entries */ }; /* supported hpack encoding/decoding errors */ enum { HPACK_ERR_NONE = 0, /* no error */ HPACK_ERR_ALLOC_FAIL, /* memory allocation error */ HPACK_ERR_UNKNOWN_OPCODE, /* invalid first byte */ HPACK_ERR_TRUNCATED, /* truncated stream */ HPACK_ERR_HUFFMAN, /* huffman decoding error */ HPACK_ERR_INVALID_PHDR, /* invalid pseudo header field name */ HPACK_ERR_MISPLACED_PHDR, /* pseudo header field after a regular header field */ HPACK_ERR_DUPLICATE_PHDR, /* duplicate pseudo header field */ HPACK_ERR_DHT_INSERT_FAIL, /* failed to insert into DHT */ HPACK_ERR_TOO_LARGE, /* decoded request/response is too large */ HPACK_ERR_MISSING_METHOD, /* :method is missing */ HPACK_ERR_MISSING_SCHEME, /* :scheme is missing */ HPACK_ERR_MISSING_PATH, /* :path is missing */ HPACK_ERR_MISSING_AUTHORITY, /* :authority is missing with CONNECT */ HPACK_ERR_SCHEME_NOT_ALLOWED, /* :scheme not allowed with CONNECT */ HPACK_ERR_PATH_NOT_ALLOWED, /* :path not allowed with CONNECT */ HPACK_ERR_INVALID_ARGUMENT, /* an invalid argument was passed */ }; /* static header table as in RFC7541 Appendix A. [0] unused. */ #define HPACK_SHT_SIZE 62 #endif /* _HAPROXY_HPACK_TBL_T_H */