Ruby EventSource ignores newlines at the beginning of event data (#24)

* fix parser to respect leading newlines in event data

* more tests

Author: eli-darkly

lib/ld-eventsource/impl/event_parser.rb

@@ -53,15 +53,17 @@ def reset_buffers
         @id = nil
         @type = nil
         @data = ""
+        @have_data = false
       end
 
       def process_field(name, value)
         case name
           when "event"
             @type = value.to_sym
           when "data"
-            @data << "\n" if !@data.empty?
+            @data << "\n" if @have_data
             @data << value
+            @have_data = true
           when "id"
             @id = value
           when "retry"
@@ -73,7 +75,7 @@ def process_field(name, value)
       end
 
       def maybe_create_event
-        return nil if @data.empty?
+        return nil if !@have_data
         StreamEvent.new(@type || :message, @data, @id)
       end
     end

spec/event_parser_spec.rb

@@ -3,6 +3,12 @@
 describe SSE::Impl::EventParser do
   subject { SSE::Impl::EventParser }
 
+  def verify_parsed_events(lines:, expected_events:)
+    ep = subject.new(lines)
+    output = ep.items.to_a
+    expect(output).to eq(expected_events)
+  end
+
   it "parses an event with all fields" do
     lines = [
       "event: abc",
@@ -42,6 +48,67 @@
     expect(output).to eq([ expected_event ])
   end
 
+  it "parses an event with empty data" do
+    verify_parsed_events(
+      lines: [
+        "data:",
+        ""
+      ],
+      expected_events: [
+        SSE::StreamEvent.new(:message, "", nil)
+      ])
+  end
+
+  it "parses an event with a leading blank data line" do
+    verify_parsed_events(
+      lines: [
+        "data:",
+        "data: abc",
+        ""
+      ],
+      expected_events: [
+        SSE::StreamEvent.new(:message, "\nabc", nil)
+      ])
+  end
+
+  it "parses an event with multiple leading blank data lines" do
+    verify_parsed_events(
+      lines: [
+        "data:",
+        "data:",
+        "data: abc",
+        ""
+      ],
+      expected_events: [
+        SSE::StreamEvent.new(:message, "\n\nabc", nil)
+      ])
+  end
+
+  it "parses an event with a blank data line in the middle" do
+    verify_parsed_events(
+      lines: [
+        "data: abc",
+        "data:",
+        "data: def",
+        ""
+      ],
+      expected_events: [
+        SSE::StreamEvent.new(:message, "abc\n\ndef", nil)
+      ])
+  end
+
+  it "parses an event with a trailing blank data line" do
+    verify_parsed_events(
+      lines: [
+        "data: abc",
+        "data:",
+        ""
+      ],
+      expected_events: [
+        SSE::StreamEvent.new(:message, "abc\n", nil)
+      ])
+  end
+
   it "ignores comments" do
     lines = [
       ":",