From aa42b8a90a3a9d590f9bdc71984c405a71bd0842 Mon Sep 17 00:00:00 2001
From: Russ Smith <russ@bashme.org>
Date: Tue, 23 Jun 2026 14:11:36 -0700
Subject: [PATCH] Make Payload case-insensitive
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Crystal's JSON parsing is case-sensitive, so a payload like
`{"Command": "Subscribe"}` failed two ways:

1. `Payload.from_json` raised `Missing JSON attribute: command` because the
   key was `Command` rather than `command`.
2. Even once parsed, `Connection#receive` dispatched on `payload.command ==
   "subscribe"`, so a `Subscribe` value never matched.

Fix both:

- `Payload.from_json` normalizes the top-level keys (command/identifier/data)
  to lowercase before deserializing. Nested values — channel names and the
  identifier/data blobs — are left exactly as sent, since those stay
  case-sensitive.
- `Connection#receive` compares the command case-insensitively.

Adds a Payload unit spec for mixed-case top-level keys and an end-to-end
`#receive` spec exercising a `{"Command": "Subscribe", ...}` payload.

Fixes #108

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BMW1EsdCMExBhm3tg7TQhs
---
 spec/cable/connection_spec.cr | 12 ++++++++++++
 spec/cable/payload_spec.cr    | 14 ++++++++++++++
 src/cable/connection.cr       | 10 +++++++---
 src/cable/payload.cr          | 25 +++++++++++++++++++++++++
 4 files changed, 58 insertions(+), 3 deletions(-)

diff --git a/spec/cable/connection_spec.cr b/spec/cable/connection_spec.cr
index b56bc30..779102d 100644
--- a/spec/cable/connection_spec.cr
+++ b/spec/cable/connection_spec.cr
@@ -65,6 +65,18 @@ describe Cable::Connection do
       end
     end
 
+    it "accepts a case-insensitive command and keys (issue #108)" do
+      connect do |connection, socket|
+        connection.receive({"Command" => "Subscribe", "Identifier" => {channel: "ChatChannel", room: "1"}.to_json}.to_json)
+        sleep 100.milliseconds
+
+        socket.messages.should contain({"type" => "confirm_subscription", "identifier" => {channel: "ChatChannel", room: "1"}.to_json}.to_json)
+
+        connection.close
+        socket.close
+      end
+    end
+
     it "accepts without params hash key" do
       connect do |connection, socket|
         connection.receive({"command" => "subscribe", "identifier" => {channel: "AppearanceChannel"}.to_json}.to_json)
diff --git a/spec/cable/payload_spec.cr b/spec/cable/payload_spec.cr
index 785fde1..bcb2ed4 100644
--- a/spec/cable/payload_spec.cr
+++ b/spec/cable/payload_spec.cr
@@ -36,6 +36,20 @@ describe Cable::Payload do
     payload.action.should eq("invite")
   end
 
+  it "parses case-insensitive top-level keys (issue #108)" do
+    payload_json = {
+      "Command"    => "message",
+      "Identifier" => {channel: "ChatChannel"}.to_json,
+      "DATA"       => {invite_id: 3, action: "invite"}.to_json,
+    }.to_json
+
+    payload = Cable::Payload.from_json(payload_json)
+    payload.command.should eq("message")
+    payload.channel.should eq("ChatChannel")
+    payload.data.should eq({"invite_id" => 3})
+    payload.action.should eq("invite")
+  end
+
   it "raises a SerializableError when the identifier is not a string" do
     payload_json = {
       command:    "subscribe",
diff --git a/src/cable/connection.cr b/src/cable/connection.cr
index 25d4685..97807a4 100644
--- a/src/cable/connection.cr
+++ b/src/cable/connection.cr
@@ -123,9 +123,13 @@ module Cable
       return unless message.presence
       payload = Cable::Payload.from_json(message)
 
-      return subscribe(payload) if payload.command == "subscribe"
-      return unsubscribe(payload) if payload.command == "unsubscribe"
-      return message(payload) if payload.command == "message"
+      # Compare case-insensitively so a command like "Subscribe" still
+      # dispatches correctly (see issue #108).
+      case payload.command.downcase
+      when "subscribe"   then subscribe(payload)
+      when "unsubscribe" then unsubscribe(payload)
+      when "message"     then message(payload)
+      end
     end
 
     def subscribe(payload : Cable::Payload)
diff --git a/src/cable/payload.cr b/src/cable/payload.cr
index a87f5d3..2b78709 100644
--- a/src/cable/payload.cr
+++ b/src/cable/payload.cr
@@ -39,6 +39,31 @@ module Cable
     @[JSON::Field(ignore: true)]
     getter action : String = ""
 
+    # Crystal's JSON parsing is case-sensitive, but cable clients in the wild
+    # aren't always consistent about the casing of the top-level protocol keys.
+    # Normalize them to lowercase before deserializing so a payload such as
+    # `{"Command": "subscribe", ...}` is accepted instead of raising
+    # "Missing JSON attribute: command".
+    #
+    # Only the top-level keys (command/identifier/data) are touched; the nested
+    # values — channel names and the identifier/data blobs — are left exactly as
+    # sent, since those remain case-sensitive. See issue #108.
+    def self.from_json(string : String) : self
+      if object = JSON.parse(string).as_h?
+        string = String.build do |io|
+          JSON.build(io) do |json|
+            json.object do
+              object.each do |key, value|
+                json.field(key.downcase) { value.to_json(json) }
+              end
+            end
+          end
+        end
+      end
+
+      new(JSON::PullParser.new(string))
+    end
+
     # After the Payload is deserialized, parse the data.
     # This will ensure we know if it's an action.
     def after_initialize