Extracts template variables from requests and responses using regex patterns.

This module scans specific parts of HTTP messages (URI, query params, body) to find values matching the configured patterns, returning them in a consistent order for positional template markers like {{var.0}}, {{var.1}}.

Extraction Scope

Patterns are applied to:

1. URI Path - The path component of the URL
2. Query Parameters - URL query string parameters (sorted)
3. Request/Response Bodies - The body content (text, JSON, or blob)

NOT scanned:

• Headers (to prevent accidental exposure of auth tokens)
• HTTP Method
• Status Code

Extraction Order

Values are extracted in this specific order to ensure predictable positional indexing:

1. URI path (left to right)
2. Query parameters (alphabetically sorted by key)
3. Request/response body (for JSON: depth-first traversal)

This ensures {{order_id.0}}, {{order_id.1}}, etc. map consistently.

Examples

# Basic extraction from request body
iex> patterns = %{sku: ~r/\d{4}-\d{4}/}
iex> request = %{
...>   "uri" => "https://api.example.com/products",
...>   "query_string" => "",
...>   "body" => "Get SKU 0234-3455 and SKU 0344-4456"
...> }
iex> extract_from_request(request, patterns)
%{sku: ["0234-3455", "0344-4456"]}

# Extraction from multiple scopes
iex> patterns = %{order_id: ~r/ORD-\d+/}
iex> request = %{
...>   "uri" => "https://api.example.com/orders/ORD-11111",
...>   "query_string" => "ref=ORD-22222",
...>   "body_json" => %{"related" => "ORD-33333"}
...> }
iex> extract_from_request(request, patterns)
%{order_id: ["ORD-11111", "ORD-22222", "ORD-33333"]}

# Multiple patterns
iex> patterns = %{
...>   sku: ~r/SKU-\d+/,
...>   order: ~r/ORD-\d+/
...> }
iex> request = %{
...>   "uri" => "https://api.example.com/orders/ORD-123",
...>   "query_string" => "",
...>   "body" => "SKU-456 for ORD-123"
...> }
iex> extract_from_request(request, patterns)
%{sku: ["SKU-456"], order: ["ORD-123", "ORD-123"]}

Response Scanning

The scan_response/2 function determines which request variables also appear in the response, so we know which ones to template:

iex> request_vars = %{sku: ["0234-3455", "0344-4456"]}
iex> response = %{"body_json" => %{"result" => "SKU 0234-3455 found"}}
iex> scan_response(response, request_vars)
MapSet.new(["sku.0"])

Pattern Overlap

When multiple patterns match the same text, the most specific (longest match) wins:

iex> patterns = %{
...>   id: ~r/\d+/,
...>   sku: ~r/SKU-\d{4}/
...> }
iex> extract_from_string("Item SKU-1234", patterns)
%{sku: ["SKU-1234"]}  # sku pattern wins over id