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[Draft]Add structured parameter support #1254

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[Draft]Add structured parameter support #1254

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@Rahul-K-A Rahul-K-A commented Aug 30, 2025 •
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Description

Adds support for YAML structures as a parameter type. Original GSOC proposal here. Essentially with a YAML file such as

<node>:
  ros__parameters:
    passenger_size:
      min:
        x: 0.6
        y: 0.4
        z: 0.17
      max:
        x: 0.850
        y: 0.65
        z: 0.47

The user will now able to access min and max as individual parameters. These parameters will be available in rclcpp as a YAML::Node or as a dict() in Python. The rcl specific changes primarily include modifications to rcl parser that:

  1. Add support for strucrured yaml field in rcl_variant_t as a C string (char *)
  2. Modifies the YAML document parsing code to detect nesting
  3. If a nesting of parameters it detected, the parser will automatically write all subsequent events to the structured yaml events
  4. The parser uses the indentations (map_depth) to determine when to stop writing to the YAML structure

Support for namespaced existing namespaced parameters is not affected. If required users will still be able to access individual parameters such as passenger_size.min.x, passenger_size.max.x, etc.

Fixes # (issue)

Is this user-facing behavior change?

Somewhat(?). The new changes will allow the user to define use new parameter types. Old methods of getting parameters still work

Did you use Generative AI?

No.

Additional Information

  1. Companion rclcpp PR: [Draft]Add structured parameter support rclcpp#2944
  2. Companion rclpy PR: [Draft]Add structured parameter support rclpy#1494
  3. Compantion rcl_interfaces PR: Add structured parameter support  rcl_interfaces#183

Rahul-K-A and others added 18 commits July 22, 2025 20:13
@Rahul-K-A
feat: Add write_structured_parameter_to_string function and integra…
245dfe4 
…te it into the YAML parser

Signed-off-by: Rahul K.A <[email protected]>
@Rahul-K-A
chore: Adjust write_structured_parameter args
f9a58d2 
Signed-off-by: Rahul K.A <[email protected]>
@Rahul-K-A
chore: Add yaml type
9dc0ca6 
Signed-off-by: Rahul K.A <[email protected]>
@Rahul-K-A
chore: Add allocator and allocations to `write_structured_parameter_t…
5a91f64 
…o_string`

Signed-off-by: Rahul K.A <[email protected]>
@Rahul-K-A
chore: Clean up parse.c a bit. Other refactors still pending (see T…
88fa00f 
…ODOs)

Signed-off-by: Rahul K.A <[email protected]>
@Rahul-K-A
chore: Add copy and deallocation operations for the YAML field of `rc…
663eb4e 
…l_variant_t`

Signed-off-by: Rahul K.A <[email protected]>
@Rahul-K-A
chore: Remove redundant memset
446b443 
Signed-off-by: Rahul K.A <[email protected]>
@Rahul-K-A
chore: Refactor TODOs
786a711 
Signed-off-by: Rahul K.A <[email protected]>
@Rahul-K-A
Add function to copy and emit events
cecd979 
Signed-off-by: Rahul K.A <[email protected]>
@Rahul-K-A
chore: Remove unused printf
7d5ca80 
Signed-off-by: Rahul K.A <[email protected]>
@Rahul-K-A
chore: Add new functions to begin and end string
88612f0 
Signed-off-by: Rahul K.A <[email protected]>
@Rahul-K-A
chore: Add new parameters to parser functions
b15a3a5 
Signed-off-by: Rahul K.A <[email protected]>
@Rahul-K-A
chore: Add emitter and pass it as part of parser.c
7ca623f 
Signed-off-by: Rahul K.A <[email protected]>
@Rahul-K-A
Add structured yaml parameter parsing using counter method
610e56a 
Signed-off-by: Rahul K.A <[email protected]>
@Rahul-K-A
chore: Move to a depth-based structured yaml detection system
e945c48 
Signed-off-by: Rahul K.A <[email protected]>
@Rahul-K-A
chore: Remove volatile qualifier for written_size
240e2e8 
Signed-off-by: Rahul K.A <[email protected]>
@Rahul-K-A
chore: Apply ament_uncrustify
1587c65 
Signed-off-by: Rahul K.A <[email protected]>
@Rahul-K-A
Merge branch 'ros2:rolling' into add-structured-parameter-support
d6aab38
This was referenced Aug 30, 2025
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Tagging this as a draft, because Im yet to add in tests/ apply linter. Once done,will remove the draft tag. Maintainers are welcome to start reviewing it in the meantime

@Rahul-K-A Rahul-K-A mentioned this pull request Aug 30, 2025
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@asherikov
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  1. does this work?
<node>:
  ros__parameters:
    passenger_size:
       - x: 0.6
       - x: 0.850
  1. "The parser uses the indentations": do you mean nesting? yaml may be in compact form or JSON
  2. "automatically write all subsequent events to the structured yaml events": not clear, when the folowing is double and when it is yaml?
<node>:
  ros__parameters:
    passenger_size:
      min:
        x: 0.6

jmachowinski
jmachowinski suggested changes Sep 18, 2025
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Rough first pass, need to look at the code in more detail

rcl_yaml_param_parser/include/rcl_yaml_param_parser/types.h
int64_t * integer_value; ///< If integer, gets stored here
double * double_value; ///< If double, gets stored here
char * string_value; ///< If string, gets stored here
char * yaml_value; ///< If structured YAML, gets stored here -> Is this right?
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Suggested change
char * yaml_value; ///< If structured YAML, gets stored here -> Is this right?
char * yaml_value; ///< If structured YAML, gets stored here

rcl_yaml_param_parser/src/parse.c
}

// rahul-k-a: TODO Combine this with the parameter allocation part of
// `write_structured_parameter_to_string` and put everything in a seperate functiong
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is this todo solved or still relevant ?

rcl_yaml_param_parser/src/parse.c
// make sure that the parameter index of the yaml parameter is not overwritten
// By default, if a namespace is detected, then the parameter entry in the param
// table is replaced by its immediate chile
// This is done for optimization (?) - Rahul-K-A
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Suggested change
// This is done for optimization (?) - Rahul-K-A
// This is done for optimization

rcl_yaml_param_parser/src/parser.c
RCUTILS_SET_ERROR_MSG("Could not initialize the emitter");
}

size_t max_string_length = 100000;
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Suggested change
size_t max_string_length = 100000;
const size_t max_string_length = 100000;

rcl_yaml_param_parser/src/parser.c

size_t max_string_length = 100000;
size_t written_size = 0;
unsigned char nested_param_string_allocator[100000];
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Suggested change
unsigned char nested_param_string_allocator[100000];
unsigned char nested_param_string_allocator[max_string_length];

Or is this a cpp feature and does not work for C code ?

rcl_yaml_param_parser/test/test_parse.cpp
yaml_parser_delete(&parser);
});

size_t max_string_length = 100000;
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Suggested change
size_t max_string_length = 100000;
const size_t max_string_length = 100000;

rcl_yaml_param_parser/test/test_parse.cpp


size_t written_size = 0;
char nested_param_string_allocator[100000];
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Suggested change
char nested_param_string_allocator[100000];
char nested_param_string_allocator[max_string_length];

might not work in C

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@jmachowinski jmachowinski jmachowinski requested changes

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@Rahul-K-A @asherikov @jmachowinski @wjwwood