Let's walk through your questions clearly, since you're trying to handle JSON schema changes without constant Rust code edits and want to weigh the tradeoffs:

Feasibility of Extracting Structs to a Configuration File #

Short answer: You can't load struct definitions directly from a config file at runtime (Rust is statically typed, so type information needs to exist at compile time). But you can automate the process of generating structs from an external schema:

• Define your JSON structure using a schema format (like JSON Schema) that the JSON team can edit.
• Use a code-generation tool (e.g., json-schema-to-rust or a custom script) to auto-generate the corresponding Rust structs with #[derive(Serialize, Deserialize, Debug)] attributes.
• When the JSON schema changes, run the generator to update the struct code, then recompile your Rust program.

If you want zero Rust code changes and no recompilation for JSON schema shifts, you'll need to use dynamic typing instead of static structs (more on that below).

Safety & Performance Tradeoffs of Decoupling Structs from .rs Files #

Safety #

• Code generation approach: This is as safe as writing structs manually, assuming your schema and generator are trusted. If an attacker tampers with the schema file, they could generate invalid structs (e.g., fields with unsafe types) that cause compile errors or runtime panics—but this is a supply chain risk, not a Rust memory safety issue.
• Dynamic typing approach (like serde_json::Value): You lose compile-time type checks, so invalid JSON (e.g., a string where a number should be) will cause runtime errors instead of compile errors. Malicious JSON could also trigger denial-of-service (DoS) attacks: think oversized arrays that consume all available memory, or deeply nested structures that crash your parser. You'll need to add manual validation (e.g., checking field types, limiting array sizes) to mitigate this.

Performance #

• Static structs: Serde optimizes serialization/deserialization at compile time, making it extremely fast with minimal memory overhead. The compiler knows exactly what fields to expect, so it can generate tight, efficient code.
• Dynamic types (serde_json::Value): Every JSON value is wrapped in an enum, which adds runtime type checking and memory overhead. Parsing and accessing fields is slower, especially for large or complex JSON documents, because the program has to traverse the dynamic structure at runtime instead of using direct compile-time offsets.

Anonymous/Unnamed Approaches to Adapt to JSON Changes #

The most common option here is serde_json::Value, which you mentioned. Let's address your concerns:

• Can it replace strong-typed structs? It depends on your use case:
  • If your program doesn't need to access specific fields (e.g., you're just passing the JSON through to another system), Value works perfectly.
  • If you do need to interact with fields, you'll have to manually check their existence and type (e.g., value["output"]["n_width"].as_u64()), which is error-prone compared to static structs where the compiler ensures fields exist and are the right type.
• Memory safety & malicious JSON: Rust's core memory safety guarantees still hold with Value (no dangling pointers, buffer overflows, etc.), but you need to defend against logical vulnerabilities. For example:
  • Use serde_json::StreamDeserializer to process large JSON incrementally instead of loading the whole thing into memory.
  • Add validation logic to reject JSON with unexpected fields, oversized values, or invalid types.
  • Use crates like validator to enforce schema rules even with dynamic values.

Other alternatives include using HashMap<String, serde_json::Value> for top-level fields, or serde::de::IgnoredAny to skip unknown fields if you only care about a subset of the JSON structure.

Scenario: JSON Team Manages Schema Without Rust Team Changes #

If your goal is to let the JSON team modify the schema without the Rust team touching code or recompiling, dynamic typing is your only option. Using serde_json::Value lets you parse any valid JSON, and if your program doesn't need to reference specific fields (like n_width), you won't have to make any code changes.

Just keep in mind that you'll need to add robust input validation to catch invalid or malicious JSON, since you're giving up the compile-time safety of static structs.

内容的提问来源于stack exchange，提问作者art vanderlay