Add support for multipart form data parsing

[outofcoffee]

Summary

This PR adds comprehensive support for parsing multipart form data (multipart/form-data) in addition to the existing URL-encoded form support. Previously, the application only handled application/x-www-form-urlencoded requests, which limited form parameter extraction in multipart scenarios.

Key Changes

• New utility functions in pkg/utils/http.go:

  • parseRequestForms(): Ensures both URL-encoded and multipart form bodies are parsed by explicitly calling ParseMultipartForm() when needed
  • isMultipartFormRequest(): Helper to detect multipart form requests
  • GetFormParams(): Returns a flat map of form parameters from both encoding types, handling only text fields and returning the first value for multi-valued parameters
  • GetFormValue(): Retrieves a single form parameter value, supporting both encoding types

• Updated form parameter handling across the codebase:

  • internal/steps/script/context.go: Replaced manual form parsing with utils.GetFormParams()
  • internal/capture/capture.go: Replaced manual form parsing with utils.GetFormValue()
  • internal/template/template.go: Replaced manual form parsing with utils.GetFormValue()

• Comprehensive test coverage:

  • Added unit tests for GetFormParams() and GetFormValue() covering URL-encoded, multipart, and empty body scenarios
  • Added integration tests in script execution, capture, and template processing to verify multipart form data works end-to-end

Implementation Details

The solution addresses a subtle issue with Go's http.Request.FormValue(): once ParseForm() is called (which handles URL-encoded data), the request's Form field becomes non-nil, preventing FormValue() from automatically calling ParseMultipartForm(). The parseRequestForms() helper explicitly calls both parsing methods to ensure all form data is available regardless of content type.

Form parameters are deduplicated (URL-encoded takes precedence) and only the first value is returned for multi-valued parameters, providing a simple string-based interface for template and script contexts.

https://claude.ai/code/session_014vwtKZV7ZX1YGGTzZ6UcMQ