core: add two new unit file settings: StandardInputData= + StandardInputText=

Both permit configuring data to pass through STDIN to an invoked
process. StandardInputText= accepts a line of text (possibly with
embedded C-style escapes as well as unit specifiers), which is appended
to the buffer to pass as stdin, followed by a single newline.
StandardInputData= is similar, but accepts arbitrary base64 encoded
data, and will not resolve specifiers or C-style escapes, nor append
newlines.

This may be used to pass input/configuration data to services, directly
in-line from unit files, either in a cooked or in a more raw format.

src/systemctl/systemctl.c

@@ -55,6 +55,7 @@
 #include "fs-util.h"
 #include "glob-util.h"
 #include "hostname-util.h"
+#include "hexdecoct.h"
 #include "initreq.h"
 #include "install.h"
 #include "io-util.h"
@@ -4977,6 +4978,24 @@ static int print_property(const char *name, sd_bus_message *m, const char *conte
                                 return bus_log_parse_error(r);
 
                         return 0;
+
+                } else if (contents[1] == SD_BUS_TYPE_BYTE && streq(name, "StandardInputData")) {
+                        _cleanup_free_ char *h = NULL;
+                        const void *p;
+                        size_t sz;
+                        ssize_t n;
+
+                        r = sd_bus_message_read_array(m, 'y', &p, &sz);
+                        if (r < 0)
+                                return bus_log_parse_error(r);
+
+                        n = base64mem(p, sz, &h);
+                        if (n < 0)
+                                return log_oom();
+
+                        print_prop(name, "%s", h);
+
+                        return 0;
                 }
 
                 break;