The checks

A diagnosis runs the checks of a mode, which is a bit set, and the mode is turned into a plan you can read before anything is probed.

The checks

the check	Rust	Swift	shared Kotlin	Android	C
ping	NetCheckType::PingCheck	.ping	Check.Ping	0	MarsSdtCheckPing
dns	NetCheckType::DnsCheck	.dns	Check.Dns	1	MarsSdtCheckDns
dns against another server, to compare with	NetCheckType::NewDnsCheck	.newDns	Check.NewDns	2	MarsSdtCheckNewDns
tcp	NetCheckType::TcpCheck	.tcp	Check.Tcp	3	MarsSdtCheckTcp
http	NetCheckType::HttpCheck	.http	Check.Http	4	MarsSdtCheckHttp
traceroute — planned, no probe asked for it yet	NetCheckType::TracerouteCheck	.traceroute	Check.Traceroute	—	MarsSdtCheckTraceroute
the request's own buffer — same	NetCheckType::ReqBufCheck	.reqBuf	Check.ReqBuf	—	MarsSdtCheckReqBuf

The bits the mode is made of

the bit	Rust	shared Kotlin, Android	Swift	C	what it puts in the plan
NET_CHECK_BASIC	NET_CHECK_BASIC	CheckMode.K_BASIC	.basic	NET_CHECK_BASIC	a ping and a dns check — the two the C++ starts with
NET_CHECK_LONG	NET_CHECK_LONG	K_LONG	.long	NET_CHECK_LONG	a tcp check: a noop out to the long link's hosts
NET_CHECK_SHORT	NET_CHECK_SHORT	K_SHORT	.short	NET_CHECK_SHORT	an http check: the net-check CGI, and the short link's hosts

They OR together — NET_CHECK_BASIC | NET_CHECK_LONG is a run of three checks — and 0 is no checks at all, and no seam runs it: a mode with none of the three bits in it is refused everywhere — Rust and the shared Kotlin answer false, Android through the same call, the C ABI MARS_SDT_ERR_BAD_ARG. What an app gets for 0 is a start that did not happen and no report at all, and not an empty one. It is not "run everything", which is 1 | 2 | 4 — Mode.all in Swift.

Swift takes them as a set, mode: [.basic, .long], and Objective-C keeps the integer: mode: NET_CHECK_BASIC | NET_CHECK_LONG.

NET_CHECK_SHORT is the one that needs its hosts: that bit with a shortLink of nothing is a plan of an http check with nothing to check, and a run whose report says nothing about the short link.

Reading the plan first

what	Rust	Swift	shared Kotlin, Android	C
the plan, in the order the checks will run	sdt.plan()	MarsSdt.plan	SdtLogic.plan()	mars_sdt_plan

The shared Kotlin hands it back as Checks and Android as the integers themselves, and the integers of the plan are the detectType of every entry of the report — so one vocabulary names both.

Where to go next

• The probes — what each check asks the app for, and what an answer is made of.
• Getting started — the dependency and a whole diagnosis, on every platform that carries SDT.