Warn on partial UDP send failure, raise SendError when all fail

spec/sparoid_spec.cr

@@ -142,3 +142,20 @@ describe Sparoid::Server do
     s.try &.close
   end
 end
+
+describe Sparoid::Client do
+  describe ".format_send_errors" do
+    it "joins host, address and message for each error" do
+      ip1 = Socket::IPAddress.new("1.1.1.1", 1)
+      ip2 = Socket::IPAddress.new("2.2.2.2", 2)
+      errors = [
+        {ip1, Exception.new("no route")},
+        {ip2, Exception.new("network down")},
+      ]
+      msg = Sparoid::Client.format_send_errors("example.com", errors)
+      msg.should contain("example.com")
+      msg.should contain("1.1.1.1:1: no route")
+      msg.should contain("2.2.2.2:2: network down")
+    end
+  end
+end

src/client-cli.cr

@@ -1,7 +1,11 @@
+require "log"
 require "option_parser"
 require "./client"
 require "./version"
 
+# Route logs to STDERR (in :connect mode STDOUT is the unix-domain socket used for FD passing).
+Log.setup_from_env(default_level: :info, backend: Log::IOBackend.new(STDERR))
+
 subcommand = :none
 host = "0.0.0.0"
 port = 8484

src/client.cr

@@ -1,3 +1,4 @@
+require "log"
 require "socket"
 require "random/secure"
 require "openssl/cipher"
@@ -11,6 +12,10 @@ require "wait_group"
 
 module Sparoid
   class Client
+    Log = ::Log.for(self)
+
+    class SendError < Exception; end
+
     def self.new(config_path = "~/.sparoid.ini")
       key = ENV.fetch("SPAROID_KEY", "")
       hmac_key = ENV.fetch("SPAROID_HMAC_KEY", "")
@@ -70,25 +75,41 @@ module Sparoid
       exit 1 # only if all connects fails
     end
 
-    # Send to all resolved IPs for the hostname
+    # Send to all resolved IPs for the hostname.
+    # Per-address failures are logged as warnings if at least one address succeeded.
+    # If every address fails, raises SendError.
     private def self.udp_send(host, port, key : String, hmac_key : String, public_ip : String? = nil) : Array(String)
       host_addresses = Socket::Addrinfo.udp(host, port)
+      errors = [] of {Socket::IPAddress, Exception}
+      successes = 0
       host_addresses.each do |addrinfo|
         packages = generate_messages(addrinfo.ip_address, public_ip).map { |message| generate_package(key, hmac_key, message) }
         socket = UDPSocket.new(addrinfo.family)
         begin
           packages.each do |data|
             socket.send data, to: addrinfo.ip_address
           end
+          successes += 1
         rescue ex
-          STDERR << "Sparoid error sending " << ex.inspect << "\n"
+          errors << {addrinfo.ip_address, ex}
         ensure
           socket.close
         end
       end
+      if successes.zero? && !errors.empty?
+        raise SendError.new(format_send_errors(host, errors))
+      end
+      errors.each do |ip, ex|
+        Log.warn { "skip #{host} (#{ip}): #{ex.message}" }
+      end
       host_addresses.map &.ip_address.address
     end
 
+    def self.format_send_errors(host : String, errors : Array({Socket::IPAddress, Exception})) : String
+      details = errors.map { |ip, ex| "#{ip}: #{ex.message}" }.join("; ")
+      "Sparoid: failed to send to any address for #{host}: #{details}"
+    end
+
     private def self.encrypt(key, hmac_key, data) : Bytes
       cipher = OpenSSL::Cipher.new("aes-256-cbc")
       cipher.encrypt