feat: Add Support for Proxy with Interceptor (#77)

proxy/interceptor.go

@@ -0,0 +1,78 @@
+package proxy
+
+import (
+	"net/http"
+	"net/url"
+	"time"
+)
+
+// ResponseAction determines how the proxy should handle a request
+type ResponseAction int
+
+const (
+	// ActionAllow forwards the request unchanged
+	ActionAllow ResponseAction = iota
+
+	// ActionBlock blocks the request with an error response
+	ActionBlock
+
+	// ActionModifyRequest modifies the request before forwarding
+	ActionModifyRequest
+
+	// ActionModifyResponse modifies the response after receiving
+	ActionModifyResponse
+)
+
+// RequestContext provides request information to interceptors
+// This is passed to ShouldIntercept and HandleRequest methods
+type RequestContext struct {
+	URL     *url.URL
+	Method  string
+	Headers http.Header
+
+	// Body is not currently used by the interceptors, but it is here for future use
+	Body []byte
+
+	Hostname  string
+	RequestID string
+	StartTime time.Time
+
+	// Interceptor can store custom data
+	Data map[string]interface{}
+}
+
+// InterceptorResponse defines how the proxy should handle the request
+type InterceptorResponse struct {
+	// Action to take
+	Action ResponseAction
+
+	// For Action = Block: error message to return
+	BlockMessage string
+	BlockCode    int
+
+	// For Action = ModifyRequest: modified headers/body
+	ModifiedHeaders http.Header
+
+	// ModifiedBody is not currently used by the interceptors, but it is here for future use
+	ModifiedBody []byte
+
+	// For Action = ModifyResponse: response modification function
+	ResponseModifier ResponseModifierFunc
+}
+
+// ResponseModifierFunc modifies HTTP response
+// It receives the status code, headers, and body, and returns modified versions
+type ResponseModifierFunc func(statusCode int, headers http.Header, body []byte) (int, http.Header, []byte, error)
+
+// Interceptor processes HTTP/HTTPS requests and can modify or block them
+type Interceptor interface {
+	// Name returns the interceptor name for logging
+	Name() string
+
+	// ShouldIntercept determines if this interceptor handles the given request
+	ShouldIntercept(ctx *RequestContext) bool
+
+	// HandleRequest processes the request and returns response action
+	// Called for each request matching ShouldIntercept
+	HandleRequest(ctx *RequestContext) (*InterceptorResponse, error)
+}