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gateway_createfromjson_requirements.md

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Gateway Requirements

Overview

This is the higher level API to create and manage a gateway via a JSON configuration file. Modules are added to the gateway, and communication "links" are established between modules via a message broker.

References

Parson

Third party C JSON library: https://github.com/kgabis/parson

JSON Structure

{
    "loaders" :
    [
        {
            "type" : "<loader type>",
            "name" : "<loader name>",
            "configuration" : ...
        }
    ]
    "modules" :
    [
        {
            "name" : "one",
            "loader" :
            {
                "name" : "<loader name>",
                "entrypoint" : ...
            },
            "args" : ...
        },
        {
            "name" : "two",
            "loader" :
            {
                "name" : "<loader name>",
                "entrypoint" : ...
            },
            "args" : ...
        }
    ],
    "links":
    [
        {
            "source": "one",
            "sink": "two"
        }
    ]
}

Exposed API

#ifdef __cplusplus
extern "C"
{
#endif

extern GATEWAY_HANDLE Gateway_CreateFromJson(const char* file_path);

#ifdef __cplusplus
}
#endif

##Gateway_CreateFromJson

extern GATEWAY_HANDLE Gateway_CreateFromJson(const char* file_path);

Gateway_CreateFromJson creates a new gateway using information contained within a well-formed JSON configuration file. The JSON string should be formatted as described above.

SRS_GATEWAY_JSON_14_001: [ If file_path is NULL the function shall return NULL. ]

SRS_GATEWAY_JSON_14_002: [ The function shall use parson to read the file and parse the JSON string to a parson JSON_Value structure. ]

SRS_GATEWAY_JSON_14_003: [ The function shall return NULL if the file contents could not be read and/or parsed to a JSON_Value. ]

SRS_GATEWAY_JSON_14_004: [ The function shall traverse the JSON_Value object to initialize a GATEWAY_PROPERTIES instance. ]

SRS_GATEWAY_JSON_17_005: [ The function shall initialize the default module loader list. ]

SRS_GATEWAY_JSON_17_012: [ This function shall return NULL if the module list is not initialized. ]

SRS_GATEWAY_JSON_17_006: [ Upon failure this function shall destroy the module loader list. ]

SRS_GATEWAY_JSON_17_007: [ The function shall parse the "loaders" JSON array and initialize new module loaders or update the existing default loaders. ]

SRS_GATEWAY_JSON_17_008: [ The function shall parse the "modules" JSON array for each module entry. ]

SRS_GATEWAY_JSON_17_013: [ The function shall parse each modules object for "loader.name" and "loader.entrypoint". ]

SRS_GATEWAY_JSON_13_001: [ If loader.name is not found in the JSON then the gateway assumes that the loader name is native. ]

SRS_GATEWAY_JSON_17_014: [ The function shall find the correct loader by "loader.name". ]

SRS_GATEWAY_JSON_17_010: [ If the module's loader is not found by name, the the function shall fail and return NULL. ]

SRS_GATEWAY_JSON_17_009: [ For each module, the function shall call the loader's ParseEntrypointFromJson function to parse the entrypoint JSON. ]

SRS_GATEWAY_JSON_17_011: [ The function shall the loader's BuildModuleConfiguration to construct module input from module's "args" and "loader.entrypoint". ]

SRS_GATEWAY_JSON_14_005: [ The function shall set the value of const void* module_configuration in the GATEWAY_PROPERTIES instance to a char* representing the serialized args value for the particular module. ]

SRS_GATEWAY_JSON_14_006: [ The function shall return NULL if the JSON_Value contains incomplete information. ]

SRS_GATEWAY_JSON_04_001: [ The function shall create a Vector to Store all links to this gateway. ]

SRS_GATEWAY_JSON_04_002: [ The function shall add all modules source and sink to GATEWAY_PROPERTIES inside gateway_links. ]

SRS_GATEWAY_JSON_14_007: [ The function shall use the GATEWAY_PROPERTIES instance to create and return a GATEWAY_HANDLE using the lower level API. ]

SRS_GATEWAY_JSON_17_004: [ The function shall set the module loader to the default dynamically linked library module loader. ]

SRS_GATEWAY_JSON_17_001: [ Upon successful creation, this function shall start the gateway. ]

SRS_GATEWAY_JSON_17_002: [ This function shall return NULL if starting the gateway fails. ]

SRS_GATEWAY_JSON_14_008: [ This function shall return NULL upon any memory allocation failure. ]