[c-lightning] plugin development

Sat Dec 15 05:04:59 AEDT 2018

Notice that this is already partially documented in the plugins.md file
[1]. I say partially because it's missing the "configuration" key. I have a
commit in my next PR that addresses this and adds documentation for the
JSON-RPC passthrough.

[1]
https://github.com/ElementsProject/lightning/blob/master/doc/plugins.md#the-init-method

On Fri, Dec 14, 2018 at 7:00 PM Richard Bondi <socketexception at gmail.com>
wrote:

> Logs would help, so I created my own log to file and here is what the
> issue was
>
> the "init" message looks like this
>
> {  "jsonrpc": "2.0",   "method": "init",   "id": 1,   "params": {
> "options": {      "greeting": "greeting"    },     "configuration": {
>     "lightning-dir": "/home/richard/.lightning",       "rpc-file":
> "lightning-rpc"    }  }}
>
> I was not expecting the "params" to be an object and the plugin was
> crashing because of this, I was always trying to read as array of
> strings, for the hello response and never imagined.  I am sure this
> will lead me to a fix for the go version also.
>
> I think it would be good to document the the expected requests, I will
> make a PR.
>
> Thank you both for your time and responses.
> On Sun, Dec 9, 2018 at 10:48 PM Rusty Russell <rusty at rustcorp.com.au>
> wrote:
> >
> > Pretty sure Christian is right, you need to flush in your plugin, *or*
> > you're not closing your JSON reply.  Both will give you hangs like this
> > as c-lightning waits for the complete response.
> >
> > We should do I/O logging on plugins so that this kind of thing can be
> > diagnosed more easily.
> >
> > Cheers,
> > Rusty.
> >
> > Richard Bondi <socketexception at gmail.com> writes:
> > > Additional info, it hangs here
> > >
> https://github.com/ElementsProject/lightning/blob/8238fe6acfc7db9e397ecac21e9e82cdc25c40be/cli/lightning-cli.c#L322
> > >
> > > the `cmd` variable = 0x55555577d868 "{ \\"method\\" : \\"hello\\",
> > > \\"id\\" : \\"lightning-cli-10719\\", \\"params\\" : [ \\"fred\\"] }"
> > >
> > > also, when I follow the `read` function in my ide, it takes me to
> > > cli/test/run-large-input.c which does not look right, and I never seem
> > > to hit a breakpoint there, what other info could I provide that would
> > > be useful?
> > > On Sat, Dec 8, 2018 at 11:53 AM Richard Bondi <
> socketexception at gmail.com> wrote:
> > >>
> > >> Thanks Christian,
> > >>
> > >> This is exactly the approach I took, except with formatted json
> > >> response, but I updated to unformatted and the results I get are as
> > >> expected from the shell, so it seems my assumptions were correct.
> > >>
> > >> However, I still have the issue as described.
> > >>
> > >> I created a repository
> > >>
> https://github.com/rsbondi/clightning-dotnet-plugin/tree/9b0e73fa77691a40e3f2a010c8b8bff0deeb861a
> > >>
> > >> This shows in the gifs that in shell I get the responses expected, but
> > >> when running clightning and calling commands from the cli, the result
> > >> is not as expected
> > >>
> > >> > The JSON you posted got mangled somewhere, i.e., it's missing the
> > >> > quotes. I think this might actually be the shell doing random things
> > >> > with quotes. And testing with escaping or single-quoting the
> parameter
> > >> > seems to work:
> > >>
> > >> My intention here was only to show that the plugin was registered and
> > >> responding to the command, but only on errors(mangled json), not on
> > >> valid input `lightning-cli hello fred`.
> > >> On Sat, Dec 8, 2018 at 2:38 AM Christian Decker
> > >> <decker.christian at gmail.com> wrote:
> > >> >
> > >> > Hi Richard,
> > >> >
> > >> > the plugins being simple executables that communicate over stdin and
> > >> > stdout should be able to be started directly from the shell and you
> > >> > should also be able to interact with the from there. So you can try
> > >> > starting your plugin and issuing some JSON-RPC requests and see how
> it
> > >> > reacts. For the initialization you should be able to do the
> following
> > >> > (taking the helloworld.py plugin as an example:
> > >> >
> > >> > ```
> > >> > {"jsonrpc":"2.0", "id":1, "method":"getmanifest", "params":[]}
> > >> > {"jsonrpc": "2.0", "result": {"options": [{"name": "greeting",
> "type": "string", "default": "World", "description": "What name should I
> call you?"}], "rpcmethods": [{"name": "hello", "description": "Returns a
> personalized greeting for {name}"}, {"name": "fail", "description": "Always
> returns a failure for testing"}]}, "id": 1}
> > >> > ```
> > >> >
> > >> > The first line is what you send, the second is the reply from the
> > >> > plugin. After that you can issue the `init` call:
> > >> >
> > >> > ```
> > >> > {"jsonrpc":"2.0", "id":2, "method":"init", "params": {"options":
> {"greeting": "Richard"}}}
> > >> > {"jsonrpc": "2.0", "result": "ok", "id": 2}
> > >> > ```
> > >> >
> > >> > And from hereon the plugin is registered and can start doing its
> > >> > magic.
> > >> >
> > >> > > When I call the plugin it just hangs.  I have tried just ignoring
> all
> > >> > > input and returning the same response as the init and getmanifest,
> > >> > > still hangs.  It seems the passthrough is taking place, if I put
> in a
> > >> > > command like
> > >> >
> > >> > This could have something to do with buffering, since some languages
> > >> > will buffer output. Notice that the python3 plugin always adds
> newlines
> > >> > and flushes to make sure it clears buffers. Not sure how the
> situation
> > >> > is with C#, but python2 was acting up as well.
> > >> >
> > >> > > cli/lightning-cli hello {"greeting":"fred"}
> > >> > >
> > >> > > I get a response
> > >> > >
> > >> > > Invalid token in json input: '{ "method" : "hello", "id" :
> > >> > > "lightning-cli-25109", "params" : [ {greeting:fred}] }'
> > >> > >
> > >> > > which make sense, if I do an echo passing the same json I get the
> > >> > > broken json
> > >> >
> > >> >
> > >> > The JSON you posted got mangled somewhere, i.e., it's missing the
> > >> > quotes. I think this might actually be the shell doing random things
> > >> > with quotes. And testing with escaping or single-quoting the
> parameter
> > >> > seems to work:
> > >> >
> > >> > ```
> > >> > lightning-cli hello '{"greeting":"fred"}'
> > >> > "Hello {'greeting': 'fred'}"
> > >> > ```
> > >> >
> > >> > > what I expect to happen is, when I type in
> > >> > >
> > >> > > cli/lightning-cli hello fred
> > >> > >
> > >> > > I expect my message with "fred" substituted in or I expect the
> command
> > >> > > that I look for in code to be
> > >> > >
> > >> > > { "method" : "hello", "id" : "lightning-cli-25109", "params" :
> ["fred"] }
> > >> >
> > >> > The reason you get the full quoted text back is because
> `lightning-cli`
> > >> > takes that first argument (the JSON serialized object) and passes
> it in
> > >> > as the first positional parameter, and doesn't use the entire
> object as
> > >> > the params (i.e., it doesn't unpack). So to get `Hello fred` you'd
> have
> > >> > to run `lightning-cli hello fred` instead.
> > >> >
> > >> > > The other issue is when I try to do in go, it seems to call
> > >> > > `plugin_read_json_one` more than once for the same plugin's
> > >> > > getmanifest and I get the "Received a JSON-RPC response for
> > >> > > non-existent request" error.  It seems to have the same buffer
> value,
> > >> > > but no request.  I have gone as far in my code to remove
> getmanifest
> > >> > > from the map so there is no way it could erroneously send the
> request
> > >> > > a second time.
> > >> >
> > >> > This could happen in a couple of different ways: the plugin code
> issues
> > >> > the request twice (this would be a lightningd bug), the plugin
> responds
> > >> > multiple times (bug in the plugin), the plugin code doesn't clear
> the
> > >> > buffer inbetween responses (lightningd issue).
> > >> >
> > >> > We can easily eliminate the second case by running the plugin from
> the
> > >> > command line like explained above, and go from there.
> > >> >
> > >> > HTH,
> > >> > Christian
> > > --
> > > c-lightning mailing list
> > > c-lightning at lists.ozlabs.org
> > > https://lists.ozlabs.org/listinfo/c-lightning
>
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