File

util-src/ringbuffer.c @ 12631:9524bb7f3944

mod_storage_sql: Drop archive timestamp precision pending schema update The "when" column is an INTEGER which will probably be unhappy about storing higher precision timestamps, so we keep the older behavior for now.
author Kim Alvefur <zash@zash.se>
date Sun, 14 Aug 2022 17:29:39 +0200
parent 12575:1f6f05a98fcd
child 12976:a187600ec7d6
line wrap: on
line source


#include <stdlib.h>
#include <unistd.h>
#include <string.h>

#include <lua.h>
#include <lauxlib.h>

#if (LUA_VERSION_NUM < 504)
#define luaL_pushfail lua_pushnil
#endif

typedef struct {
	size_t rpos; /* read position */
	size_t wpos; /* write position */
	size_t alen; /* allocated size */
	size_t blen; /* current content size */
	char buffer[];
} ringbuffer;

/* Translate absolute idx to a wrapped index within the buffer,
   based on current read position */
static int wrap_pos(const ringbuffer *b, const long idx, long *pos) {
	if(idx > (long)b->blen) {
		return 0;
	}
	if(idx + (long)b->rpos > (long)b->alen) {
		*pos = idx - (b->alen - b->rpos);
	} else {
		*pos = b->rpos + idx;
	}
	return 1;
}

static int calc_splice_positions(const ringbuffer *b, long start, long end, long *out_start, long *out_end) {
	if(start < 0) {
		start = 1 + start + b->blen;
	}
	if(start <= 0) {
		start = 1;
	}

	if(end < 0) {
		end = 1 + end + b->blen;
	}

	if(end > (long)b->blen) {
		end = b->blen;
	}
	if(start < 1) {
		start = 1;
	}

	if(start > end) {
		return 0;
	}

	start = start - 1;

	if(!wrap_pos(b, start, out_start)) {
		return 0;
	}
	if(!wrap_pos(b, end, out_end)) {
		return 0;
	}

	return 1;
}

static void writechar(ringbuffer *b, char c) {
	b->blen++;
	b->buffer[(b->wpos++) % b->alen] = c;
}

/* make sure position counters stay within the allocation */
static void modpos(ringbuffer *b) {
	b->rpos = b->rpos % b->alen;
	b->wpos = b->wpos % b->alen;
}

static int find(ringbuffer *b, const char *s, size_t l) {
	size_t i, j;
	int m;

	if(b->rpos == b->wpos) { /* empty */
		return 0;
	}

	/* look for a matching first byte */
	for(i = 0; i <= b->blen - l; i++) {
		if(b->buffer[(b->rpos + i) % b->alen] == *s) {
			m = 1;

			/* check if the following byte also match */
			for(j = 1; j < l; j++)
				if(b->buffer[(b->rpos + i + j) % b->alen] != s[j]) {
					m = 0;
					break;
				}

			if(m) {
				return i + l;
			}
		}
	}

	return 0;
}

/*
 * Find first position of a substring in buffer
 * (buffer, string) -> number
 */
static int rb_find(lua_State *L) {
	size_t l, m;
	ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt");
	const char *s = luaL_checklstring(L, 2, &l);
	m = find(b, s, l);

	if(m > 0) {
		lua_pushinteger(L, m);
		return 1;
	}

	return 0;
}

/*
 * Move read position forward without returning the data
 * (buffer, number) -> boolean
 */
static int rb_discard(lua_State *L) {
	ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt");
	size_t r = luaL_checkinteger(L, 2);

	if(r > b->blen) {
		lua_pushboolean(L, 0);
		return 1;
	}

	b->blen -= r;
	b->rpos += r;
	modpos(b);

	lua_pushboolean(L, 1);
	return 1;
}

/*
 * Read bytes from buffer
 * (buffer, number, boolean?) -> string
 */
static int rb_read(lua_State *L) {
	ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt");
	size_t r = luaL_checkinteger(L, 2);
	int peek = lua_toboolean(L, 3);

	if(r > b->blen) {
		luaL_pushfail(L);
		return 1;
	}

	if((b->rpos + r) > b->alen) {
		/* Substring wraps around to the beginning of the buffer */
		lua_pushlstring(L, &b->buffer[b->rpos], b->alen - b->rpos);
		lua_pushlstring(L, b->buffer, r - (b->alen - b->rpos));
		lua_concat(L, 2);
	} else {
		lua_pushlstring(L, &b->buffer[b->rpos], r);
	}

	if(!peek) {
		b->blen -= r;
		b->rpos += r;
		modpos(b);
	}

	return 1;
}

/*
 * Read buffer until first occurrence of a substring
 * (buffer, string) -> string
 */
static int rb_readuntil(lua_State *L) {
	size_t l, m;
	ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt");
	const char *s = luaL_checklstring(L, 2, &l);
	m = find(b, s, l);

	if(m > 0) {
		lua_settop(L, 1);
		lua_pushinteger(L, m);
		return rb_read(L);
	}

	return 0;
}

/*
 * Write bytes into the buffer
 * (buffer, string) -> integer
 */
static int rb_write(lua_State *L) {
	size_t l, w = 0;
	ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt");
	const char *s = luaL_checklstring(L, 2, &l);

	/* Does `l` bytes fit? */
	if((l + b->blen) > b->alen) {
		luaL_pushfail(L);
		return 1;
	}

	while(l-- > 0) {
		writechar(b, *s++);
		w++;
	}

	modpos(b);

	lua_pushinteger(L, w);

	return 1;
}

static int rb_tostring(lua_State *L) {
	ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt");
	lua_pushfstring(L, "ringbuffer: %p %d/%d", b, b->blen, b->alen);
	return 1;
}

static int rb_sub(lua_State *L) {
	ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt");

	long start = luaL_checkinteger(L, 2);
	long end = luaL_optinteger(L, 3, -1);

	long wrapped_start, wrapped_end;
	if(!calc_splice_positions(b, start, end, &wrapped_start, &wrapped_end)) {
		lua_pushstring(L, "");
	} else if(wrapped_end <= wrapped_start) {
		lua_pushlstring(L, &b->buffer[wrapped_start], b->alen - wrapped_start);
		lua_pushlstring(L, b->buffer, wrapped_end);
		lua_concat(L, 2);
	} else {
		lua_pushlstring(L, &b->buffer[wrapped_start], (wrapped_end - wrapped_start));
	}

	return 1;
}

static int rb_byte(lua_State *L) {
	ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt");

	long start = luaL_optinteger(L, 2, 1);
	long end = luaL_optinteger(L, 3, start);

	long i;

	long wrapped_start, wrapped_end;
	if(calc_splice_positions(b, start, end, &wrapped_start, &wrapped_end)) {
		if(wrapped_end <= wrapped_start) {
			for(i = wrapped_start; i < (long)b->alen; i++) {
				lua_pushinteger(L, (unsigned char)b->buffer[i]);
			}
			for(i = 0; i < wrapped_end; i++) {
				lua_pushinteger(L, (unsigned char)b->buffer[i]);
			}
			return wrapped_end + (b->alen - wrapped_start);
		} else {
			for(i = wrapped_start; i < wrapped_end; i++) {
				lua_pushinteger(L, (unsigned char)b->buffer[i]);
			}
			return wrapped_end - wrapped_start;
		}
	}

	return 0;
}

static int rb_length(lua_State *L) {
	ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt");
	lua_pushinteger(L, b->blen);
	return 1;
}

static int rb_size(lua_State *L) {
	ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt");
	lua_pushinteger(L, b->alen);
	return 1;
}

static int rb_free(lua_State *L) {
	ringbuffer *b = luaL_checkudata(L, 1, "ringbuffer_mt");
	lua_pushinteger(L, b->alen - b->blen);
	return 1;
}

static int rb_new(lua_State *L) {
	lua_Integer size = luaL_optinteger(L, 1, sysconf(_SC_PAGESIZE));
	luaL_argcheck(L, size > 0, 1, "positive integer expected");
	ringbuffer *b = lua_newuserdata(L, sizeof(ringbuffer) + size);

	b->rpos = 0;
	b->wpos = 0;
	b->alen = size;
	b->blen = 0;

	luaL_getmetatable(L, "ringbuffer_mt");
	lua_setmetatable(L, -2);

	return 1;
}

int luaopen_util_ringbuffer(lua_State *L) {
	luaL_checkversion(L);

	if(luaL_newmetatable(L, "ringbuffer_mt")) {
		lua_pushcfunction(L, rb_tostring);
		lua_setfield(L, -2, "__tostring");
		lua_pushcfunction(L, rb_length);
		lua_setfield(L, -2, "__len");

		lua_createtable(L, 0, 7); /* __index */
		{
			lua_pushcfunction(L, rb_find);
			lua_setfield(L, -2, "find");
			lua_pushcfunction(L, rb_discard);
			lua_setfield(L, -2, "discard");
			lua_pushcfunction(L, rb_read);
			lua_setfield(L, -2, "read");
			lua_pushcfunction(L, rb_readuntil);
			lua_setfield(L, -2, "readuntil");
			lua_pushcfunction(L, rb_write);
			lua_setfield(L, -2, "write");
			lua_pushcfunction(L, rb_size);
			lua_setfield(L, -2, "size");
			lua_pushcfunction(L, rb_length);
			lua_setfield(L, -2, "length");
			lua_pushcfunction(L, rb_sub);
			lua_setfield(L, -2, "sub");
			lua_pushcfunction(L, rb_byte);
			lua_setfield(L, -2, "byte");
			lua_pushcfunction(L, rb_free);
			lua_setfield(L, -2, "free");
		}
		lua_setfield(L, -2, "__index");
	}

	lua_createtable(L, 0, 1);
	lua_pushcfunction(L, rb_new);
	lua_setfield(L, -2, "new");
	return 1;
}