1 files changed, 152 insertions, 0 deletions
diff --git a/src/blind-peek-head.c b/src/blind-peek-head.c
new file mode 100644
index 0000000..86c96b8
--- /dev/null
+++ b/src/blind-peek-head.c
@@ -0,0 +1,152 @@
+/* See LICENSE file for copyright and license details. */
+#include "common.h"
+
+USAGE("")
+
+static ssize_t
+peek_socket(char *buf, size_t n)
+{
+	ssize_t r = recv(STDIN_FILENO, buf, n, MSG_PEEK);
+	if (r < 0 && errno != ENOTSOCK)
+		eprintf("recv <stdin>:");
+	return r;
+}
+
+static ssize_t
+peek_regular(char *buf, size_t n)
+{
+	ssize_t r;
+	off_t pos = lseek(STDIN_FILENO, 0, SEEK_CUR);
+	if (pos < 0) {
+		if (errno != ESPIPE)
+			eprintf("lseek <stdin>:");
+		return -1;
+	}
+	r = pread(STDIN_FILENO, buf, n, pos);
+	if (r < 0 && errno != ESPIPE)
+		eprintf("pread <stdin>:");
+	return r;
+}
+
+#if defined(HAVE_TEE)
+static ssize_t
+peek_pipe(char *buf, size_t n)
+{
+	int rw[2];
+	ssize_t m;
+	size_t p;
+	if (pipe(rw))
+		eprintf("pipe");
+	m = tee(STDIN_FILENO, rw[1], n, 0);
+	if (m < 0) {
+		if (errno != EINVAL)
+			eprintf("tee <stdin>:");
+		return -1;
+	}
+	close(rw[1]);
+	p = ereadall(rw[0], buf, (size_t)m, "<pipe>");
+	close(rw[0]);
+	return (ssize_t)p;
+}
+#endif
+
+static size_t
+peek(char *buf, size_t n)
+{
+	static int method = 0;
+	ssize_t r;
+	switch (method) {
+	case 0:
+		if ((r = peek_socket(buf, n)) >= 0)
+			return (size_t)r;
+		method++;
+		/* fall-through */
+	case 1:
+		if ((r = peek_regular(buf, n)) >= 0)
+			return (size_t)r;
+		method++;
+#if defined(HAVE_TEE)
+		/* fall-through */
+	default:
+		if ((r = peek_pipe(buf, n)) >= 0)
+			return (size_t)r;
+		eprintf("can only peek pipes, sockets, and regular files\n");
+#else
+		eprintf("can only peek sockets and regular files\n");
+#endif
+	}
+}
+
+int
+main(int argc, char *argv[])
+{
+	char buf[STREAM_HEAD_MAX], *p;
+	char magic[] = {'\0', 'u', 'i', 'v', 'f'};
+	size_t i, len = 0, last_len;
+#if defined(HAVE_EPOLL)
+	struct epoll_event ev;
+	int epfd, epr = 0;
+#endif
+
+	UNOFLAGS(argc);
+
+#if defined(HAVE_EPOLL)
+	epfd = epoll_create1(0);
+	if (epfd < 0)
+		eprintf("epoll_create1:");
+
+	memset(&ev, 0, sizeof(ev));
+	ev.events = EPOLLIN | EPOLLRDHUP | EPOLLET;
+	if (epoll_ctl(epfd, EPOLL_CTL_ADD, STDIN_FILENO, &ev))
+		eprintf("epoll_ctl EPOLL_CTL_ADD:");
+
+	do {
+		last_len = len;
+		len = peek(buf, sizeof(buf));
+		p = memchr(buf, '\n', len);
+		if (p && len >= (size_t)(++p - buf) + ELEMENTSOF(magic))
+			goto ready;
+	} while (len > last_len && (epr = epoll_wait(epfd, &ev, 1, -1)) >= 0);
+	if (epr < 0)
+		eprintf("epoll_wait:");
+#else
+	goto beginning;
+	do {
+		usleep(50000);
+	beginning:
+		last_len = len;
+		len = peek(buf, n);
+		p = memchr(buf, '\n', len);
+		if (p && len >= (size_t)(++p - buf) + ELEMENTSOF(magic))
+			goto ready;
+	} while (len > last_len);
+#endif
+	eprintf("could not read entire head\n");
+
+ready:
+	len = (size_t)(p - buf);
+	for (i = 0; i < ELEMENTSOF(magic); i++)
+		if (p[i] != magic[i])
+			goto bad_format;
+	p = buf;
+	for (i = 0; i < 3; i++) {
+		if (!isdigit(*p))
+			goto bad_format;
+		while (isdigit(*p)) p++;
+		if (*p++ != ' ')
+			goto bad_format;
+	}
+	while (isalnum(*p) || *p == ' ') {
+		if (p[0] == ' ' && p[-1] == ' ')
+			goto bad_format;
+		p++;
+	}
+	if (p[-1] == ' ' || p[0] != '\n')
+		goto bad_format;
+
+	ewriteall(STDOUT_FILENO, buf, len, "<stdout>");
+	return 0;
+
+bad_format:
+	eprintf("<stdin>: file format not supported\n");
+}