From 7f32943dd8f11c1a17d602566437e196817acaa1 Mon Sep 17 00:00:00 2001
From: Adam Eijdenberg <adam.eijdenberg@defence.gov.au>
Date: Tue, 2 Apr 2024 10:52:40 +1100
Subject: [PATCH] fix: return ErrMessageSizeTooLarge when message is too large

For most of this library's existence it has returned ErrMessageSizeTooLarge
when the message exceeded the configured size.

For a short period in 2019 this error was renamed (#1218) but shortly
revered back (#1262). Later in 2023 this error was changed to a
ConfigurationError (#2628) to fix #2137, however this has caused issues
with clients who rely on the previous error code being distinct from
other ConfigurationError conditions (#2655).

This commit reverts to previous behaviour, and adds a test to pickup if
this changes again in the future.

Signed-off-by: Adam Eijdenberg <adam.eijdenberg@defence.gov.au>
---
 async_producer.go     |  5 ++---
 sync_producer_test.go | 29 +++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/async_producer.go b/async_producer.go
index f629a6a2e..8843a29fb 100644
--- a/async_producer.go
+++ b/async_producer.go
@@ -450,9 +450,8 @@ func (p *asyncProducer) dispatcher() {
 			continue
 		}
 
-		size := msg.ByteSize(version)
-		if size > p.conf.Producer.MaxMessageBytes {
-			p.returnError(msg, ConfigurationError(fmt.Sprintf("Attempt to produce message larger than configured Producer.MaxMessageBytes: %d > %d", size, p.conf.Producer.MaxMessageBytes)))
+		if msg.ByteSize(version) > p.conf.Producer.MaxMessageBytes {
+			p.returnError(msg, ErrMessageSizeTooLarge)
 			continue
 		}
 
diff --git a/sync_producer_test.go b/sync_producer_test.go
index 776ae5f69..99c542b4c 100644
--- a/sync_producer_test.go
+++ b/sync_producer_test.go
@@ -52,6 +52,35 @@ func TestSyncProducer(t *testing.T) {
 		}
 	}
 
+	// try to send a message too large
+	_, _, err = producer.SendMessage(&ProducerMessage{
+		Topic:    "my_topic",
+		Value:    ByteEncoder(make([]byte, config.Producer.MaxMessageBytes+1)), // will exceed default max size, e.g. configuration side
+		Metadata: "test",
+	})
+	if err != ErrMessageSizeTooLarge {
+		t.Error("expected err to be ErrMessageSizeTooLarge - many people rely on this, please do not change with searching for previous discussions")
+	}
+
+	// try to send small message the server rejects because too large
+	leader.Returns(&ProduceResponse{
+		Blocks: map[string]map[int32]*ProduceResponseBlock{
+			"my_topic": {
+				0: &ProduceResponseBlock{
+					Err: ErrMessageSizeTooLarge,
+				},
+			},
+		},
+	})
+	_, _, err = producer.SendMessage(&ProducerMessage{
+		Topic:    "my_topic",
+		Value:    StringEncoder(TestMessage),
+		Metadata: "test",
+	})
+	if err != ErrMessageSizeTooLarge {
+		t.Error("expected err to be ErrMessageSizeTooLarge - many people rely on this, please do not change with searching for previous discussions")
+	}
+
 	safeClose(t, producer)
 	leader.Close()
 	seedBroker.Close()