/embedded-data-parsing-libs

name: embedded-data-parsing-libs
description: Use when integrating, porting, configuring, or debugging embedded C data parsers such as cJSON, jsmn, or inih on MCU projects

Embedded Data Parsing Libs

Overview

Use this skill for small embedded data parsers where the main risks are memory allocation, input bounds, encoding assumptions, recursion, and callback handling. Cover `cJSON`, `jsmn`, and `inih` without copying their full APIs.

When To Use

Use this skill when:

• The user wants to parse JSON or INI on an MCU.
• The task mentions `cJSON`, `jsmn`, `inih`, config files, telemetry JSON, command payloads, or settings parsing.
• The issue involves parse failure, memory leak, heap exhaustion, malformed input, callback mapping, or stack/recursion limits.

Do not use this skill for binary protocols or large streaming parsers outside these small libraries.

First Questions

Ask for:

• Parser library: `cJSON`, `jsmn`, `inih`, or another small C parser.
• Input source and maximum input size.
• Runtime: bare metal, RTOS, Linux, bootloader, or shell command.
• Whether dynamic allocation is allowed.
• Expected schema and how malformed input should behave.
• Current error, sample input, and memory budget.

Library Checks

cJSON

• Decide whether heap allocation is acceptable.
• Provide custom malloc/free hooks if the project uses a custom allocator.
• Always delete parsed trees after use.
• Bound input size before parsing.
• Validate type before reading values.

jsmn

• Allocate enough tokens for the expected JSON shape.
• Handle `JSMN_ERROR_NOMEM`, `JSMN_ERROR_INVAL`, and `JSMN_ERROR_PART`.
• Remember that tokens reference the original input buffer.
• Validate string lengths and value types manually.

inih

• Implement the handler callback with strict section/key matching.
• Decide whether duplicate keys overwrite, error, or merge.
• Bound line length and input source.
• Validate converted numeric values and ranges.

Common Failures

• Heap fragmentation from repeated `cJSON_Parse` without hooks or cleanup.
• Token buffer too small for `jsmn`.
• Using JSON token pointers after the input buffer is freed.
• Accepting partial config and booting with unsafe defaults.
• Silent typo in INI key because handler ignores unknown fields.

Verification

Before claiming parser integration works:

• State parser, allocation policy, max input size, and schema assumptions.
• Test valid input, missing fields, wrong types, malformed input, and oversize input.
• Confirm memory is released or static buffers are bounded.
• Confirm unknown fields and duplicate keys behavior.

Example

User:

想用 cJSON 解析串口发来的配置。

Agent:

1. Asks for max payload size, schema, allocator policy, and malformed-input behavior. 1. Uses custom hooks if needed and validates each field type. 1. Tests good JSON, missing keys, bad types, and oversized payloads.