Replace getdelim to make swaybar work on FreeBSD

This commit fixes a segfault in swaybar on FreeBSD that was caused by
using getdelim with EOF as delimiter on an infinite stream. The FreeBSD
implementation handles the "no more data, delimiter not found, and EOF
not reached" scenario as an error, so it can't be used to read the
output of status command. This commit replaces the getline/getdelim
calls with reading all available data from the stream in one go.

swaybar/status_line.c

@@ -1,5 +1,6 @@
 #define _POSIX_C_SOURCE 200809L
 #include <fcntl.h>
+#include <sys/ioctl.h>
 #include <json-c/json.h>
 #include <stdlib.h>
 #include <string.h>
@@ -34,18 +35,35 @@ bool status_handle_readable(struct status_line *status) {
 	switch (status->protocol) {
 	case PROTOCOL_UNDEF:
 		errno = 0;
-		read_bytes = getline(&status->buffer,
-				&status->buffer_size, status->read);
-		if (errno == EAGAIN) {
-			clearerr(status->read);
-		} else if (errno) {
+		int available_bytes;
+		if (ioctl(status->read_fd, FIONREAD, &available_bytes) == -1) {
+			wlr_log(WLR_ERROR, "Unable to read status command output size");
+			status_error(status, "[error reading from status command]");
+			return true;
+		}
+
+		if ((size_t)available_bytes + 1 > status->buffer_size) {
+			// need room for leading '\0' too
+			status->buffer_size = available_bytes + 1;
+			status->buffer = realloc(status->buffer, status->buffer_size);
+		}
+		if (status->buffer == NULL) {
+			wlr_log_errno(WLR_ERROR, "Unable to read status line");
+			status_error(status, "[error reading from status command]");
+			return true;
+		}
+
+		read_bytes = read(status->read_fd, status->buffer, available_bytes);
+		if (read_bytes != available_bytes) {
 			status_error(status, "[error reading from status command]");
 			return true;
 		}
+		status->buffer[available_bytes] = 0;
 
 		// the header must be sent completely the first time round
+		char *newline = strchr(status->buffer, '\n');
 		json_object *header, *version;
-		if (status->buffer[read_bytes - 1] == '\n'
+		if (newline != NULL
 				&& (header = json_tokener_parse(status->buffer))
 				&& json_object_object_get_ex(header, "version", &version)
 				&& json_object_get_int(version) == 1) {
@@ -67,13 +85,9 @@ bool status_handle_readable(struct status_line *status) {
 
 			wl_list_init(&status->blocks);
 			status->tokener = json_tokener_new();
-			read_bytes = getdelim(&status->buffer, &status->buffer_size, EOF, status->read);
-			if (read_bytes > 0) {
-				status->buffer_index = read_bytes;
+			status->buffer_index = strlen(newline + 1);
+			memmove(status->buffer, newline + 1, status->buffer_index + 1);
 			return i3bar_handle_readable(status);
-			} else {
-				return false;
-			}
 		}
 
 		wlr_log(WLR_DEBUG, "Using text protocol.");