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e16a7d8f3b
`et` means `expandtab`. ```sh rg 'vi: .* :vi' -l -0 | \ xargs -0 sed -i '' 's/vi: \(.*\) et\(.*\) :vi/vi: \1 xoet\2:vi/' rg 'vi: .* :vi' -l -0 | \ xargs -0 sed -i '' 's/vi: \(.*\)noet\(.*\):vi/vi: \1et\2 :vi/' rg 'vi: .* :vi' -l -0 | \ xargs -0 sed -i '' 's/vi: \(.*\)xoet\(.*\):vi/vi: \1noet\2:vi/' ```
92 lines
4.5 KiB
C
92 lines
4.5 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi │
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2022 Justine Alexandra Roberts Tunney │
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│ │
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "net/http/tokenbucket.h"
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#include "libc/intrin/atomic.h"
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/**
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* Atomically increments all signed bytes in array, without overflowing.
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*
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* Under the token bucket model, operations are denied by default unless
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* tokens exist to allow them. This function must be called periodically
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* from a single background thread to replenish the buckets with tokens.
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* For example, this function may be called once per second which allows
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* one operation per second on average with bursts up to 127 per second.
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* This policy needn't be applied uniformly. For example, you might find
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* out that a large corporation funnels all their traffic through one ip
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* address, so you could replenish their tokens multiple times a second.
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*
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* @param w is word array that aliases byte token array
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* @param n is number of 64-bit words in `w` array
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*/
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void ReplenishTokens(atomic_uint_fast64_t *w, size_t n) {
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for (size_t i = 0; i < n; ++i) {
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uint64_t a = atomic_load_explicit(w + i, memory_order_relaxed);
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if (a == 0x7f7f7f7f7f7f7f7f) continue;
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uint64_t b = 0x8080808080808080;
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uint64_t c = 0x7f7f7f7f7f7f7f7f ^ a;
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uint64_t d = ((((c >> 1 | b) - c) & b) ^ b) >> 7;
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atomic_fetch_add_explicit(w + i, d, memory_order_relaxed);
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}
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}
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/**
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* Atomically decrements signed byte index if it's positive.
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*
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* Multiple threads are able to call this method, to determine if enough
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* tokens exist to perform an operation. Return values greater than zero
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* mean a token was atomically acquired. Values less than, or equal zero
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* means the bucket is empty. There must exist `1 << c` signed bytes (or
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* buckets) in the `b` array.
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*
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* Since this design uses signed bytes, your returned number may be used
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* to control how much burstiness is allowed. For example:
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*
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* int t = AcquireToken(tok.b, ip, 22);
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* if (t < 64) {
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* if (t > 8) write(client, "HTTP/1.1 429 \r\n\r\n", 17);
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* close(client);
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* return;
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* }
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*
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* Could be used to send rejections to clients that exceed their tokens,
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* whereas clients who've grossly exceeded their tokens, could simply be
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* dropped.
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*
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* @param b is array of token buckets
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* @param x is ipv4 address
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* @param c is cidr
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*/
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int AcquireToken(atomic_schar *b, uint32_t x, int c) {
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uint32_t i = x >> (32 - c);
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int t = atomic_load_explicit(b + i, memory_order_relaxed);
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if (t <= 0) return t;
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return atomic_fetch_add_explicit(b + i, -1, memory_order_relaxed);
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}
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/**
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* Returns current number of tokens in bucket.
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*
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* @param b is array of token buckets
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* @param x is ipv4 address
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* @param c is cidr
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*/
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int CountTokens(atomic_schar *b, uint32_t x, int c) {
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uint32_t i = x >> (32 - c);
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return atomic_load_explicit(b + i, memory_order_relaxed);
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}
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