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fifolog.c
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fifolog.c
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#include <assert.h>
#include <errno.h>
#include <unistd.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define OUTBUFSZ PIPE_BUF
// Return 1 when we are ready to flush the buffer, else 0.
int
feed(char c, int *noutbuf, char outbuf[])
{
if (c == '\n') {
outbuf[(*noutbuf)++] = c;
return 1;
}
if (*noutbuf == OUTBUFSZ-1) {
return 0;
}
outbuf[(*noutbuf)++] = c;
return 0;
}
int
main(int argc, char **argv) {
char *prefix;
char inbuf[PIPE_BUF];
char outbuf[OUTBUFSZ];
int noutbuf = 0;
if (argc != 2) {
fprintf(stderr, "%s PREFIX\n", argv[0]);
exit(1);
}
prefix = argv[1];
int prefixlen = strlen(prefix);
int truncprefixlen = (prefixlen > 510) ? 510 : prefixlen;
// We must have enough space for the prefix, one char and a new line.
assert(truncprefixlen + 2 <= sizeof(outbuf));
memcpy(outbuf, prefix, truncprefixlen);
noutbuf += truncprefixlen;
while (1) {
int nread = read(STDIN_FILENO, inbuf, sizeof(inbuf));
if (nread < 0) {
perror("error reading data");
exit(1);
}
if (nread == 0) {
break;
}
for (int i = 0; i < nread; i++) {
if (feed(inbuf[i], &noutbuf, outbuf)) {
if (write(STDOUT_FILENO, outbuf, noutbuf) < 0) {
perror("error writing output");
exit(1);
}
noutbuf = truncprefixlen;
}
}
}
if (!feed('\n', &noutbuf, outbuf)) {
assert(0 || "unexpected error");
}
if (noutbuf > truncprefixlen + 1) {
if (write(STDOUT_FILENO, outbuf, noutbuf) < 0) {
perror("error writing output");
exit(1);
}
}
return 0;
}