Proposal: Add SetString.srv to std_srvs

[Navifra-Henry]

Proposal: Add SetString.srv to std_srvs

Summary

I would like to propose adding a simple SetString.srv definition to the std_srvs package, similar in spirit to the existing SetBool.srv.

Motivation

std_srvs/SetBool provides a minimal and widely reusable pattern for simple command-style services:

bool data
---
bool success
string message

In practice, many systems require a similar pattern but with a string payload instead of a bool. A common example is mode switching, command dispatching, or passing standardized string-based instructions (e.g., from external protocols or industrial specifications).

Currently, developers must repeatedly define custom services such as:

string data
---
bool success
string message

across multiple packages and projects. This leads to unnecessary duplication of identical interface definitions and reduces interoperability.

Use Cases

Typical use cases include:

• Setting a mode by name (e.g., "AUTO", "MANUAL", "PAUSE")
• Forwarding externally defined string commands
• Bridging industrial communication standards that rely on string-based command semantics
• Rapid prototyping and testing via CLI tools

In many real-world integrations (especially when ROS 2 is used as an interface layer rather than a full application framework), a generic SetString service would reduce friction and boilerplate.

Proposed Definition

string data
---
bool success
string message

This mirrors the structure and philosophy of SetBool, maintaining consistency within std_srvs.

I appreciate any feedback from maintainers and the community.