diff options
Diffstat (limited to 'include/haproxy/hpack-tbl-t.h')
| -rw-r--r-- | include/haproxy/hpack-tbl-t.h | 143 |
1 files changed, 143 insertions, 0 deletions
diff --git a/include/haproxy/hpack-tbl-t.h b/include/haproxy/hpack-tbl-t.h new file mode 100644 index 0000000..4e5d536 --- /dev/null +++ b/include/haproxy/hpack-tbl-t.h @@ -0,0 +1,143 @@ +/* + * HPACK header table management (RFC7541) - type definitions + * + * Copyright (C) 2014-2020 Willy Tarreau <willy@haproxy.org> + * 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 <inttypes.h> + +/* 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 <used> == 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 */ |