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and last but not least: document the new InLength<> feature. :-)

JSON-93
Roker 4 years ago
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@ -363,6 +363,60 @@ bitfield, so they can be combined:
More flags will be added when different semantics will be needed.
### Automatic parameter value generation
For some parameters or parameter combinations the JSON Server Adapter is
able to generate the values automatically either from the environment or
from other parameters.
These automatic parameter value generators are supported at the moment:
#### InLength
For functions that have a string parameter of type `const char*` followed by
a `size_t` that specifies the length of the string, the JSON Adapter can
calculate the value of that length parameter automatically because in the
JSON API the lengths of strings are always known.
Moreover, the "length" that has to be given here means the length of the
string seen by the C API side, after processing of all JSON escaping
mechanisms, so it might be difficult to calculate that value at client side.
Example:
```
// C function declaration:
char* tohex(const char* input, size_t length);
// API definition:
// with implicit length parameter, with dummy JSON parameter
FP( "tohex", new Func<char*, In<c_string>, InLength<>>( &tohex ))
```
To be compatible with previous API versions the `InLength` parameter still
needs a dummy placeholder in the JSON interface, but its value is no longer
relevant:
```
{"jsonrpc":"2.0", "id":28,
"method":"tohex", "params":["some string","dummy_parameter"]
}
```
It is possible to specifiy `InLength<ParamFlag::NoInput>` so no
parameter is exposed to the JSON API anymore:
```
FP( "tohex", new Func<char*, In<c_string>, InLength<ParamFlag::NoInput>>( &tohex ))
```
Now the 2nd parameter is omitted:
```
{"jsonrpc":"2.0", "id":28,
"method":"tohex", "params":["some string"]
}
```
## TODOs
The following issues are planned but not yet implemented.


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