Raise useful Horizon errors

sdk/lib/stellar-sdk.rb

@@ -6,6 +6,7 @@ module Stellar
   autoload :Amount
   autoload :Client
   autoload :SEP10
+  autoload :HorizonError
 
   module Horizon
     extend ActiveSupport::Autoload

sdk/lib/stellar/client.rb

@@ -200,6 +200,9 @@ def submit_transaction(tx_envelope:, options: {skip_memo_required_check: false})
         check_memo_required(tx_envelope)
       end
       @horizon.transactions._post(tx: tx_envelope.to_xdr(:base64))
+
+    rescue Faraday::BadRequestError => ex
+      raise HorizonError.make(ex.response[:body])
     end
 
     # Required by SEP-0029

sdk/lib/stellar/horizon_error.rb

@@ -0,0 +1,53 @@
+module Stellar
+  class HorizonError < StandardError
+    attr_reader :original_response, :extras
+
+    def self.make(original_response)
+      klass = class_for(original_response["title"])
+      klass.new(original_response)
+    end
+
+    # Uses specialized class if it is defined
+    def self.class_for(title)
+      const_get title.delete(" ").to_sym
+    rescue NameError
+      self
+    end
+
+    def initialize(original_response)
+      message = make_message(
+        detail: original_response["detail"],
+        title: original_response["title"]
+      )
+
+      # Superclass StandardError has different argument signature
+      super(message)
+
+      @original_response = original_response
+      @extras = original_response["extras"]
+    end
+
+    private
+
+    def make_message(detail:, title:)
+      # Include title only on generic class
+      # Condition passes only for child classes
+      if self.class != HorizonError
+        title = nil
+      end
+
+      [title, detail].compact.join(": ")
+    end
+
+    class TransactionFailed < self
+      def make_message(detail:)
+        detail.sub!(
+          "The `extras.result_codes` field on this response contains further details.",
+          "extras.result_codes contained: `#{hash.dig("extras", "result_codes")}`"
+        )
+      end
+    end
+
+    class TransactionMalformed < self; end
+  end
+end