Optional arguments

Some of the functions in the NEAT API, such as neat_open, neat_read and neat_write, take optional arguments. These are sometimes used to pass optional arguments to functions, and sometimes used to return additional values from the function. Optional arguments are passed as an array of the struct neat_tlv and an integer specifying the length of this array. neat_tlv is defined as follows:

struct neat_tlv {
    neat_tlv_tag  tag;
    neat_tlv_type type;

    union {
        int   integer;
        char *string;
        float real;
    } value;

An optional argument takes the form of a tag name, a type, and a value of either a string, integer or a floating point number. The tag specifies which optional argument the value belongs to, and the type asserts the type of the value passed as this argument. An error will be raised of the type is different than what the function expects.

You may either work with this struct directly, or you may use the preprocessor macros explained later in this document.

Specifying no optional arguments

To specify no optional arguments, simply pass NULL as the optargs parameter and 0 as the opt_count parameter of the function.

Optional argument macros

  • NEAT_OPTARGS_DECLARE(max) - Declare the necessary variables to use the rest of these macros. Allocates (on the stack) an array of length max and an integer for storing the number of optional arguments specified. NEAT_OPTARGS_MAX may be used as the default array size.
  • NEAT_OPTARGS_INIT() - Initializes the variables declared by NEAT_OPTARGS_DECLARE. May also be used to reset the (number of) optional arguments back to 0.
  • NEAT_OPTARG_INT(tag,value) - Specify the tag and the value of an optional argument that takes an integer.
  • NEAT_OPTARG_FLOAT(tag,value) - Specify the tag and the value of an optional argument that takes a floating point number.
  • NEAT_OPTARG_STRING(tag,value) - Specify the tag and the value of an optional argument that takes a string.
  • NEAT_OPTARGS - Represents the array of optional arguments. Specify this macro as the optarg parameter.
  • NEAT_OPTARG_COUNT - Stores the number of the optional arguments specified so far with NEAT_OPTARG_INT, NEAT_OPTARG_FLOAT or NEAT_OPTARG_STRING. This count is reset by NEAT_OPTARGS_INIT(). Specify this macro as the opt_count argument.

Optional argument tags

  • NEAT_TAG_STREAM_ID (integer) - Specifies the ID of the stream which the data should be written to, or which stream the data was read from.
  • NEAT_TAG_STREAM_COUNT (integer) - Specifies the number of stream to create. Only used with protocols that support multiple streams.
  • NEAT_TAG_FLOW_GROUP (int) - Specifies the flow group this flow belongs to.
  • NEAT_TAG_PRIORITY (float) - Specifies the priority of this flow relative to other flows in the flow group.
  • NEAT_TAG_CC_ALGORITHM (string) - Speficies the name of the (TCP) congestion control algorithm that will be used by this flow. A system default will be used if the specified algorithm is not available.

Currently unused tags:



    neat_open(ctx, flow, "", 8000, NEAT_OPTARGS, NEAT_OPTARGS_COUNT);