mshow: actually filter the parts

1 files changed, 124 insertions, 0 deletions

diff --git a/filter.c b/filter.c
new file mode 100644
index 0000000..3996dfd
--- /dev/null
+++ b/filter.c
@@ -0,0 +1,124 @@
+#include <poll.h>            
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+int
+filter(char *input, size_t inlen, char *cmd, char **outputo, size_t *outleno)
+{
+	char *output;
+	size_t outlen;
+	ssize_t outalloc = 4096;
+	pid_t pid;
+	
+	output = malloc(outalloc);
+	outlen = 0;
+
+	int pipe0[2];
+	int pipe1[2];
+
+	if (pipe(pipe0) != 0 || pipe(pipe1) != 0)
+		goto fail;
+
+	char *argv[] = { "/bin/sh", "-c", cmd, (char *)0 };
+
+	if (!(pid = fork())) {
+		dup2(pipe0[0], 0);
+		close(pipe0[1]);
+		close(pipe0[0]);
+
+		dup2(pipe1[1], 1);
+		close(pipe1[0]);
+		close(pipe1[1]);
+
+		execvp(argv[0], argv);
+		exit(-1);
+	}
+	close(pipe0[0]);
+	close(pipe1[1]);
+	
+	if (pid < 0) {
+		close(pipe0[1]);
+		close(pipe1[0]);
+		goto fail;
+	}
+
+	struct pollfd fds[2];
+
+	fds[0].fd = pipe1[0];
+	fds[0].events = POLLIN;
+	fds[1].fd = pipe0[1];
+	fds[1].events = POLLOUT;
+
+	while ((fds[0].fd >= 0 || fds[1].fd >= 0) &&
+	    poll(fds, sizeof fds / sizeof fds[0], -1) >= 0) {
+		if (fds[0].revents & POLLIN) {
+			if (outlen + 512 > outalloc) {
+				outalloc *= 2;
+				if (outalloc < 0)
+					exit(-1);
+				output = realloc(output, outalloc);
+				if (!output)
+					exit(-1);
+			}
+			ssize_t ret = read(fds[0].fd, output + outlen, 512);
+			if (ret > 0)
+				outlen += ret;
+			else if (ret < 0)
+				close(fds[0].fd);
+		} else if (fds[0].revents & (POLLERR | POLLHUP | POLLNVAL)) {
+			fds[0].fd = -1;
+		}
+		
+		if (fds[1].revents & POLLOUT) {
+			ssize_t ret = write(fds[1].fd, input, inlen);
+			if (ret > 0) {
+				input += ret;
+				inlen -= ret;
+			}
+			if (ret <= 0 || inlen == 0)
+				close(fds[1].fd);
+		} else if (fds[1].revents & (POLLERR | POLLHUP | POLLNVAL)) {
+			fds[1].fd = -1;
+		}
+	}
+
+	// ok to fail when closed already
+        close(pipe0[1]);
+        close(pipe1[0]);
+
+	int status;
+        waitpid(pid, &status, 0);
+
+	*outputo = output;
+	*outleno = outlen;
+
+	return WEXITSTATUS(status);
+
+fail:
+	*outputo = 0;
+	*outleno = 0;
+
+	return -1;
+}
+
+#ifdef TEST
+int
+main()
+{
+	char *input = "foo\nbar\nbaz";
+	int e;
+
+	char *output;
+	size_t outlen;
+
+	e = filter(input, strlen(input), "rev;exit 2", &output, &outlen);
+
+	fwrite(output, 1, outlen, stdout);
+	printf("%ld -> %d\n", outlen, e);
+
+	return 0;
+}
+#endif