feat: Support dynamic query parameter on reconnect (#74)

Author: jsonbailey

.rubocop.yml

@@ -1,4 +1,4 @@
-require:
+plugins:
   - rubocop-performance
 
 AllCops:
@@ -289,7 +289,7 @@ Style/PerlBackrefs:
   StyleGuide: "https://github.com/bbatsov/ruby-style-guide#no-perl-regexp-last-matchers"
   Enabled: false
 
-Naming/PredicateName:
+Naming/PredicatePrefix:
   Description: "Check the names of predicate methods."
   StyleGuide: "https://github.com/bbatsov/ruby-style-guide#bool-methods-qmark"
   ForbiddenPrefixes:

lib/ld-eventsource/client.rb

@@ -164,6 +164,7 @@ def initialize(uri,
 
       @on = { event: ->(_) {}, error: ->(_) {} }
       @last_id = last_event_id
+      @query_params_callback = nil
 
       yield self if block_given?
 
@@ -206,6 +207,36 @@ def on_error(&action)
       @on[:error] = action
     end
 
+    #
+    # Specifies a block or Proc to generate query parameters dynamically. This will be called before
+    # each connection attempt (both initial connection and reconnections), allowing you to update
+    # query parameters based on the current client state.
+    #
+    # The block should return a Hash with string keys and string values, which will be merged with
+    # any existing query parameters in the base URI. If the callback raises an exception, it will be
+    # logged and the connection will proceed with the base URI's query parameters (or no query
+    # parameters if none were present).
+    #
+    # This is useful for scenarios where query parameters need to reflect the current state of the
+    # client, such as sending a "basis" parameter that represents what data the client already has.
+    #
+    # @example Using dynamic query parameters
+    #     client = SSE::Client.new(base_uri) do |c|
+    #       c.query_params do
+    #         {
+    #           "basis" => (selector.state if selector.defined?),
+    #           "filter" => filter_key
+    #         }.compact
+    #       end
+    #       c.on_event { |event| handle_event(event) }
+    #     end
+    #
+    # @yieldreturn [Hash<String, String>] a hash of query parameter names to values
+    #
+    def query_params(&action)
+      @query_params_callback = action
+    end
+
     #
     # Permanently shuts down the client and its connection. No further events will be dispatched. This
     # has no effect if called a second time.
@@ -289,8 +320,9 @@ def connect
         end
         cxn = nil
         begin
-          @logger.info { "Connecting to event stream at #{@uri}" }
-          cxn = @http_client.request(@method, @uri, build_opts)
+          uri = build_uri_with_query_params
+          @logger.info { "Connecting to event stream at #{uri}" }
+          cxn = @http_client.request(@method, uri, build_opts)
           if cxn.status.code == 200
             content_type = cxn.content_type.mime_type
             if content_type && content_type.start_with?("text/event-stream")
@@ -397,5 +429,27 @@ def build_opts
         {headers: build_headers, body: resolved_payload.to_s}
       end
     end
+
+    def build_uri_with_query_params
+      uri = @uri.dup
+
+      if @query_params_callback
+        begin
+          dynamic_params = @query_params_callback.call
+          if dynamic_params.is_a?(Hash) && !dynamic_params.empty?
+            existing_params = uri.query ? URI.decode_www_form(uri.query).to_h : {}
+            merged_params = existing_params.merge(dynamic_params)
+            uri.query = URI.encode_www_form(merged_params)
+          elsif !dynamic_params.is_a?(Hash)
+            @logger.warn { "query_params callback returned non-Hash value: #{dynamic_params.class}, ignoring" }
+          end
+        rescue StandardError => e
+          @logger.warn { "query_params callback raised an exception: #{e.inspect}, proceeding with base URI" }
+          @logger.debug { "Exception trace: #{e.backtrace}" }
+        end
+      end
+
+      uri
+    end
   end
 end