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	blind-peek-head.c - blind - suckless command-line video editing utility
	git clone git://git.suckless.org/blind
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	blind-peek-head.c (3073B)
	---
	1 /* See LICENSE file for copyright and license details. */
	2 #include "common.h"
	3
	4 USAGE("")
	5
	6 static ssize_t
	7 peek_socket(char *buf, size_t n)
	8 {
	9 ssize_t r = recv(STDIN_FILENO, buf, n, MSG_PEEK);
	10 if (r < 0 && errno != ENOTSOCK)
	11 eprintf("recv <stdin>:");
	12 return r;
	13 }
	14
	15 static ssize_t
	16 peek_regular(char *buf, size_t n)
	17 {
	18 ssize_t r;
	19 off_t pos = lseek(STDIN_FILENO, 0, SEEK_CUR);
	20 if (pos < 0) {
	21 if (errno != ESPIPE)
	22 eprintf("lseek <stdin>:");
	23 return -1;
	24 }
	25 r = pread(STDIN_FILENO, buf, n, pos);
	26 if (r < 0 && errno != ESPIPE)
	27 eprintf("pread <stdin>:");
	28 return r;
	29 }
	30
	31 #if defined(HAVE_TEE)
	32 static ssize_t
	33 peek_pipe(char *buf, size_t n)
	34 {
	35 int rw[2];
	36 ssize_t m;
	37 size_t p;
	38 if (pipe(rw))
	39 eprintf("pipe");
	40 m = tee(STDIN_FILENO, rw[1], n, 0);
	41 if (m < 0) {
	42 if (errno != EINVAL)
	43 eprintf("tee <stdin>:");
	44 return -1;
	45 }
	46 close(rw[1]);
	47 p = ereadall(rw[0], buf, (size_t)m, "<pipe>");
	48 close(rw[0]);
	49 return (ssize_t)p;
	50 }
	51 #endif
	52
	53 static size_t
	54 peek(char *buf, size_t n)
	55 {
	56 static int method = 0;
	57 ssize_t r;
	58 switch (method) {
	59 case 0:
	60 if ((r = peek_socket(buf, n)) >= 0)
	61 return (size_t)r;
	62 method++;
	63 /* fall-through */
	64 case 1:
	65 if ((r = peek_regular(buf, n)) >= 0)
	66 return (size_t)r;
	67 method++;
	68 #if defined(HAVE_TEE)
	69 /* fall-through */
	70 default:
	71 if ((r = peek_pipe(buf, n)) >= 0)
	72 return (size_t)r;
	73 eprintf("can only peek pipes, sockets, and regular files…
	74 #else
	75 eprintf("can only peek sockets and regular files\n");
	76 #endif
	77 }
	78 }
	79
	80 int
	81 main(int argc, char *argv[])
	82 {
	83 char buf[STREAM_HEAD_MAX], *p;
	84 char magic[] = {'\0', 'u', 'i', 'v', 'f'};
	85 size_t i, len = 0, last_len;
	86 #if defined(HAVE_EPOLL)
	87 struct epoll_event ev;
	88 int epfd, epr = 0;
	89 #endif
	90
	91 UNOFLAGS(argc);
	92
	93 #if defined(HAVE_EPOLL)
	94 epfd = epoll_create1(0);
	95 if (epfd < 0)
	96 eprintf("epoll_create1:");
	97
	98 memset(&ev, 0, sizeof(ev));
	99 ev.events = EPOLLIN \| EPOLLRDHUP \| EPOLLET;
	100 if (epoll_ctl(epfd, EPOLL_CTL_ADD, STDIN_FILENO, &ev))
	101 eprintf("epoll_ctl EPOLL_CTL_ADD:");
	102
	103 do {
	104 last_len = len;
	105 len = peek(buf, sizeof(buf));
	106 p = memchr(buf, '\n', len);
	107 if (p && len >= (size_t)(++p - buf) + ELEMENTSOF(magic))
	108 goto ready;
	109 } while (len > last_len && (epr = epoll_wait(epfd, &ev, 1, -1)) …
	110 if (epr < 0)
	111 eprintf("epoll_wait:");
	112 #else
	113 goto beginning;
	114 do {
	115 usleep(50000);
	116 beginning:
	117 last_len = len;
	118 len = peek(buf, sizeof(buf));
	119 p = memchr(buf, '\n', len);
	120 if (p && len >= (size_t)(++p - buf) + ELEMENTSOF(magic))
	121 goto ready;
	122 } while (len > last_len);
	123 #endif
	124 eprintf("could not read entire head\n");
	125
	126 ready:
	127 len = (size_t)(p - buf);
	128 for (i = 0; i < ELEMENTSOF(magic); i++)
	129 if (p[i] != magic[i])
	130 goto bad_format;
	131 p = buf;
	132 for (i = 0; i < 3; i++) {
	133 if (!isdigit(*p))
	134 goto bad_format;
	135 while (isdigit(*p)) p++;
	136 if (*p++ != ' ')
	137 goto bad_format;
	138 }
	139 while (isalnum(p) \|\| p == ' ') {
	140 if (p[0] == ' ' && p[-1] == ' ')
	141 goto bad_format;
	142 p++;
	143 }
	144 if (p[-1] == ' ' \|\| p[0] != '\n')
	145 goto bad_format;
	146
	147 ewriteall(STDOUT_FILENO, buf, len, "<stdout>");
	148 return 0;
	149
	150 bad_format:
	151 eprintf("<stdin>: file format not supported\n");
	152 }