SpecWeaver: End-to-End HTTP API Specification Inference across Multi-layer Routing in Production Web Services

HTTP API specifications are essential for modern web development, yet existing tools fail in production environments due to multi-layer routing. Production deployments employ infrastructure-level and framework-level routing that apply sequential rewrite and dispatch rules, creating a gap between client-visible external paths and internal paths. To address this challenge, we present SpecWeaver, the first tool to automatically extract and unify heterogeneous configuration-defined routing rules with code-level handlers. Our approach combines routing component information gathering, iterative configuration discovery using LLMs, and routing extraction from diverse configuration files to construct a routing graph representation that captures end-to-end routing relationships. Evaluated on 10 production applications, SpecWeaver extracts 36,361 rewrite rules and 48,394 dispatch rules with 99.44%/100% precision, materializes 8,288 external API paths, contributes 5,162 previously undocumented APIs with 160 unauthenticated endpoints, helps an existing testing tool improve testing coverage by 328.6% compared to the baseline, and discovers 305 bugs.