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// re2c $INPUT -o $OUTPUT -f #include <assert.h> #include <stdio.h> #include <string.h> #define DEBUG 0 #define LOG(...) if (DEBUG) fprintf(stderr, __VA_ARGS__); // Use a small buffer to cover the case when a lexeme doesn't fit. // In real world use a larger buffer. #define BUFSIZE 10 struct State { FILE *file; char buf[BUFSIZE + 1], *lim, *cur, *mar, *tok; int state; }; typedef enum {END, READY, WAITING, BAD_PACKET, BIG_PACKET} Status; static Status fill(State &st) { const size_t shift = st.tok - st.buf; const size_t used = st.lim - st.tok; const size_t free = BUFSIZE - used; // Error: no space. In real life can reallocate a larger buffer. if (free < 1) return BIG_PACKET; // Shift buffer contents (discard already processed data). memmove(st.buf, st.tok, used); st.lim -= shift; st.cur -= shift; st.mar -= shift; st.tok -= shift; // Fill free space at the end of buffer with new data. const size_t read = fread(st.lim, 1, free, st.file); st.lim += read; st.lim[0] = 0; // append sentinel symbol return READY; } static Status lex(State &st, unsigned int *recv) { char yych; /*!getstate:re2c*/ for (;;) { st.tok = st.cur; /*!re2c re2c:api:style = free-form; re2c:define:YYCTYPE = "char"; re2c:define:YYCURSOR = "st.cur"; re2c:define:YYMARKER = "st.mar"; re2c:define:YYLIMIT = "st.lim"; re2c:define:YYGETSTATE = "st.state"; re2c:define:YYSETSTATE = "st.state = @@;"; re2c:define:YYFILL = "return WAITING;"; re2c:eof = 0; packet = [a-z]+[;]; * { return BAD_PACKET; } $ { return END; } packet { *recv = *recv + 1; continue; } */ } } void test(const char **packets, Status expect) { // Create a "socket" (open the same file for reading and writing). const char *fname = "pipe"; FILE *fw = fopen(fname, "w"); FILE *fr = fopen(fname, "r"); setvbuf(fw, NULL, _IONBF, 0); setvbuf(fr, NULL, _IONBF, 0); // Initialize lexer state: `state` value is -1, all pointers are at the end // of buffer. State st; st.file = fr; st.cur = st.mar = st.tok = st.lim = st.buf + BUFSIZE; // Sentinel (at YYLIMIT pointer) is set to zero, which triggers YYFILL. st.lim[0] = 0; st.state = -1; // Main loop. The buffer contains incomplete data which appears packet by // packet. When the lexer needs more input it saves its internal state and // returns to the caller which should provide more input and resume lexing. Status status; unsigned int send = 0, recv = 0; for (;;) { status = lex(st, &recv); if (status == END) { LOG("done: got %u packets\n", recv); break; } else if (status == WAITING) { LOG("waiting...\n"); if (*packets) { LOG("sent packet %u\n", send); fprintf(fw, "%s", *packets++); ++send; } status = fill(st); LOG("queue: '%s'\n", st.buf); if (status == BIG_PACKET) { LOG("error: packet too big\n"); break; } assert(status == READY); } else { assert(status == BAD_PACKET); LOG("error: ill-formed packet\n"); break; } } // Check results. assert(status == expect); if (status == END) assert(recv == send); // Cleanup: remove input file. fclose(fw); fclose(fr); remove(fname); } int main() { const char *packets1[] = {0}; const char *packets2[] = {"zero;", "one;", "two;", "three;", "four;", 0}; const char *packets3[] = {"zer0;", 0}; const char *packets4[] = {"looooooooooong;", 0}; test(packets1, END); test(packets2, END); test(packets3, BAD_PACKET); test(packets4, BIG_PACKET); return 0; }