Injecting structured json logs into journald - systemd

Question

I get the impression that there might be a way to write to the systemd journal, json data directly without first converting it to the format the sd_journal* functions expect. Is this possible or not?
My suspicion is because of some comments about an inbuilt json parser. However the man pages suggest otherwise.
Also, I note that if your write to stdout in the format
<priority> message
The priority will end up in the PRIORITY="priority" field and message will end up in MESSAGE="message" field. But can other structured field data be input?
Note: The man pages do not talk about the last feature I mention. So I wouldn't be surprised if they are slightly out of date which is why I am asking.

Answer 1

journald doesn't accept arbitary JSON. Just Key/Value pairs. So it's not possible to send nested data structures. You can send data directly via the Unix Domain socket:
echo -e "MESSAGE=Hello\nFOO=BAR\nMY_ID=12345\n" |socat - UNIX-SENDTO:/run/systemd/journal/socket
results in:
{
"__CURSOR" : "s=46dc1bd66d0e4a48a6809e45228511e2;i=84cc;b=fd9144999d6846c8827d58f56c2635db;m=850161136;t=55669a307fdd6;x=887a021a37840789",
"__REALTIME_TIMESTAMP" : "1502386590318038",
"__MONOTONIC_TIMESTAMP" : "35703361846",
"_BOOT_ID" : "fd9144999d6846c8827d58f56c2635db",
"_TRANSPORT" : "journal",
"_UID" : "1001",
"_GID" : "1001",
"_CAP_EFFECTIVE" : "0",
"_SYSTEMD_OWNER_UID" : "1001",
"_SYSTEMD_SLICE" : "user-1001.slice",
"_SYSTEMD_USER_SLICE" : "-.slice",
"_MACHINE_ID" : "6e7b40640bf6473189165f19f8be2536",
"_HOSTNAME" : "samson",
"_SYSTEMD_UNIT" : "user#1001.service",
"_SYSTEMD_INVOCATION_ID" : "e5ed32fbb1004545b1ddf73a0d928d87",
"_SYSTEMD_CGROUP" : "/user.slice/user-1001.slice/user#1001.service/gnome-terminal-server.service",
"_SYSTEMD_USER_UNIT" : "gnome-terminal-server.service",
"_COMM" : "socat",
"_EXE" : "/usr/bin/socat",
"_CMDLINE" : "socat - UNIX-SENDTO:/run/systemd/journal/socket",
"FOO" : "BAR",
"MESSAGE" : "Hello",
"MY_ID" : "12345",
"_PID" : "19868",
"_SOURCE_REALTIME_TIMESTAMP" : "1502386590317991"
}