[c-lightning] plugin development

[Rusty Russell]

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
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