Willy Tarreau | b7eba10 | 2006-12-04 02:20:02 +0100 | [diff] [blame] | 1 | /* |
| 2 | include/types/hdr_idx.h |
| 3 | This file defines everything related to fast header indexation. |
| 4 | |
| 5 | Copyright (C) 2000-2006 Willy Tarreau - w@1wt.eu |
| 6 | |
| 7 | This library is free software; you can redistribute it and/or |
| 8 | modify it under the terms of the GNU Lesser General Public |
| 9 | License as published by the Free Software Foundation, version 2.1 |
| 10 | exclusively. |
| 11 | |
| 12 | This library is distributed in the hope that it will be useful, |
| 13 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 14 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 15 | Lesser General Public License for more details. |
| 16 | |
| 17 | You should have received a copy of the GNU Lesser General Public |
| 18 | License along with this library; if not, write to the Free Software |
| 19 | Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
| 20 | */ |
| 21 | |
| 22 | |
| 23 | /* |
| 24 | * The type of structure described here is a finite linked list used to |
| 25 | * reference small number of objects of small size. This is typically used |
| 26 | * to index HTTP headers within one request or response, in order to be able |
| 27 | * to add, remove, modify and check them in an efficient way. The overhead is |
| 28 | * very low : 32 bits are used per list element. This is enough to reference |
| 29 | * 32k headers of at most 64kB each, with one bit to indicate if the header |
| 30 | * is terminated by 1 or 2 chars. It may also evolve towards something like |
| 31 | * 1k headers of at most 64B for the name and 32kB of data + CR/CRLF. |
| 32 | * |
| 33 | * A future evolution of this concept may allow for fast header manipulation |
| 34 | * without data movement through the use of vectors. This is not yet possible |
| 35 | * in this version, whose goal is only to avoid parsing whole lines for each |
| 36 | * consultation. |
| 37 | * |
| 38 | */ |
| 39 | |
| 40 | |
| 41 | #ifndef _TYPES_HDR_IDX_H |
| 42 | #define _TYPES_HDR_IDX_H |
| 43 | |
| 44 | /* |
| 45 | * This describes one element of the hdr_idx array. |
| 46 | * It's a tiny linked list of at most 32k 32bit elements. The first one has a |
| 47 | * special meaning, it's used as the head of the list and cannod be removed. |
| 48 | * That way, we know that 'next==0' is not possible so we use it to indicate |
| 49 | * an end of list. Also, [0]->next always designates the head of the list. The |
| 50 | * first allocatable element is at 1. By convention, [0]->len indicates how |
| 51 | * many chars should be skipped in the original buffer before finding the first |
| 52 | * header. |
| 53 | * |
| 54 | */ |
| 55 | |
| 56 | struct hdr_idx_elem { |
| 57 | unsigned len :16; /* length of this header not counting CRLF. 0=unused entry. */ |
| 58 | unsigned cr : 1; /* CR present (1=CRLF, 0=LF). Total line size=len+cr+1. */ |
| 59 | unsigned next :15; /* offset of next header if len>0. 0=end of list. */ |
| 60 | }; |
| 61 | |
| 62 | /* |
| 63 | * This structure provides necessary information to store, find, remove |
| 64 | * index entries from a list. This list cannot reference more than 32k |
| 65 | * elements of 64k each. |
| 66 | */ |
| 67 | struct hdr_idx { |
| 68 | struct hdr_idx_elem *v; /* the array itself */ |
| 69 | short size; /* size of the array including the head */ |
| 70 | short used; /* # of elements really used (1..size) */ |
| 71 | short last; /* length of the allocated area (1..size) */ |
| 72 | signed short tail; /* last used element, 0..size-1 */ |
| 73 | }; |
| 74 | |
| 75 | |
| 76 | |
| 77 | #endif /* _TYPES_HDR_IDX_H */ |
| 78 | |
| 79 | /* |
| 80 | * Local variables: |
| 81 | * c-indent-level: 8 |
| 82 | * c-basic-offset: 8 |
| 83 | * End: |
| 84 | */ |