Implemented check sum field checks (#33)

Co-authored-by: Oleg Smirnov <smirnov_oleg96@mail.ru>

Author: Nikita-Smirnov-Exactpro

README.md

@@ -53,6 +53,7 @@ Component benchmark results available [here](docs/benchmarks/jmh-benchmark.md).
   + codec checks:
     + that tag value may not contain leading zeros.
     + BodyLength field.
+    * CheckSum filed.
 
 ### 0.1.3
 + Updated:

src/main/kotlin/com/exactpro/th2/codec/fixng/ByteBufUtil.kt

@@ -25,6 +25,10 @@ const val SEP_BYTE = '='.code.toByte()
 const val DIGIT_0 = '0'.code.toByte()
 const val DIGIT_9 = '9'.code.toByte()
 
+const val SOH_CHAR = '
'
+const val SOH_BYTE = SOH_CHAR.code.toByte()
+
+@Suppress("KotlinConstantConditions")
 private fun Int.getDigitCount(): Int = when {
     this < 10 -> 1
     this < 100 -> 2
@@ -140,11 +144,19 @@ fun ByteBuf.writeField(tag: Int, value: Any?, delimiter: Byte, charset: Charset)
     writeField(tag, value.toString(), delimiter, charset)
 
 fun ByteBuf.writeChecksum(delimiter: Byte) {
+    val checksum = calculateChecksum(delimiter)
+    writeTag(10).printInt(checksum, 3).writeByte(delimiter.toInt())
+}
+
+fun ByteBuf.calculateChecksum(delimiter: Byte): Int {
     val index = readerIndex()
     var checksum = 0
-    while (isReadable) checksum += readByte()
+    while (isReadable) {
+        val value = readByte()
+        checksum += if (value == delimiter) SOH_BYTE else value
+    }
     readerIndex(index)
-    writeTag(10).printInt(checksum % 256, 3).writeByte(delimiter.toInt())
+    return checksum % 256
 }
 
 fun ByteBuf.getLastTagIndex(delimiter: Byte): Int {

src/main/kotlin/com/exactpro/th2/codec/fixng/FixNgCodec.kt

@@ -162,6 +162,8 @@ class FixNgCodec(dictionary: IDictionaryStructure, settings: FixNgCodecSettings)
                 error(errorMessage)
             }
 
+            validateCheckSum(isDirty, context, buffer)
+
             header["BeginString"] = beginString
             header["BodyLength"] = if (isDecodeToStrings) bodyLengthString else bodyLength
             header["MsgType"] = msgType
@@ -182,6 +184,66 @@ class FixNgCodec(dictionary: IDictionaryStructure, settings: FixNgCodecSettings)
         return MessageGroup(messages)
     }
 
+    /**
+     * Information about 'CheckSum' field from FIX specification:
+     * Three byte, simple checksum (see Volume 2: "Checksum Calculation" for description).
+     * ALWAYS LAST FIELD IN MESSAGE; i.e. serves, with the trailing <SOH>, as the end-of-message delimiter.
+     * Always defined as three characters. (Always unencrypted)
+     */
+    private fun validateCheckSum(
+        isDirty: Boolean,
+        context: IReportingContext,
+        buffer: ByteBuf,
+    ) {
+        val index = buffer.readerIndex()
+        try {
+            val lastTagIndex = buffer.indexOf(buffer.writerIndex() - 1, 0, decodeDelimiter) + 1
+            buffer.readerIndex(lastTagIndex)
+            val lastTag = buffer.readTag { tag, warn -> { LOGGER.warn { "Tag ($tag) reading problem: $warn" } } }
+            if (lastTag != TAG_CHECKSUM) {
+                handleError(
+                    isDirty, context,
+                    "Message ends with $lastTag tag instead of CheckSum ($TAG_CHECKSUM)",
+                )
+                return
+            }
+            val value = buffer.readValue(decodeDelimiter, charset, isDirty)
+            val valueSize = value.toByteArray(charset).size
+            if (valueSize != 3) {
+                handleError(
+                    isDirty, context,
+                    "CheckSum ($TAG_CHECKSUM) field must have 3 bytes length, instead of size: $valueSize, value: '$value'",
+                )
+                return
+            }
+            val checksum = value.toIntOrNull()
+            if (checksum == null) {
+                handleError(
+                    isDirty, context,
+                    "CheckSum ($TAG_CHECKSUM) field value must consist of digits only instead of '$value'",
+                )
+                return
+            }
+            if (checksum !in 0..255) {
+                handleError(
+                    isDirty, context,
+                    "CheckSum ($TAG_CHECKSUM) field must have value from 0 to 255 included both limits instead of '$checksum' value"
+                )
+                return
+            }
+            val calculatedChecksum = buffer.slice(0, lastTagIndex)
+                .calculateChecksum(decodeDelimiter)
+            if (checksum != calculatedChecksum) {
+                handleError(
+                    isDirty, context,
+                    "CheckSum ($TAG_CHECKSUM) field has $checksum value which isn't matched to calculated value $calculatedChecksum"
+                )
+            }
+        } finally {
+            buffer.readerIndex(index)
+        }
+    }
+
     /**
      * Information about 'BodyLength' field from FIX specification:
      * Message length, in bytes, forward to the CheckSum field.
@@ -603,8 +665,6 @@ class FixNgCodec(dictionary: IDictionaryStructure, settings: FixNgCodecSettings)
 
     companion object {
         private val LOGGER = KotlinLogging.logger { }
-        const val SOH_CHAR = '
'
-        private const val SOH_BYTE = SOH_CHAR.code.toByte()
 
         private const val HEADER = "header"
         private const val TRAILER = "trailer"

src/main/kotlin/com/exactpro/th2/codec/fixng/FixNgCodecSettings.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2023-2024 Exactpro (Exactpro Systems Limited)
+ * Copyright 2023-2025 Exactpro (Exactpro Systems Limited)
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,7 +17,6 @@
 package com.exactpro.th2.codec.fixng
 
 import com.exactpro.th2.codec.api.IPipelineCodecSettings
-import com.exactpro.th2.codec.fixng.FixNgCodec.Companion.SOH_CHAR
 import com.fasterxml.jackson.core.JsonParser
 import com.fasterxml.jackson.databind.DeserializationContext
 import com.fasterxml.jackson.databind.JsonDeserializer

src/test/kotlin/com/exactpro/th2/codec/fixng/ByteBufUtilKtTest.kt

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2023-2025 Exactpro (Exactpro Systems Limited)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.exactpro.th2.codec.fixng
+
+import io.netty.buffer.Unpooled
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.params.ParameterizedTest
+import org.junit.jupiter.params.provider.ValueSource
+import kotlin.charArrayOf
+
+
+class ByteBufUtilKtTest {
+
+    @ParameterizedTest
+    @ValueSource(chars = ['
', '|'])
+    fun `calculate checksum test`(delimiter: Char) {
+        val actual = Unpooled.wrappedBuffer(MSG_CORRECT.dropLast(7).replaceSoh(delimiter).toByteArray(Charsets.US_ASCII)).calculateChecksum(
+            delimiter.code.toByte()
+        )
+        assertEquals(191, actual)
+    }
+
+    companion object {
+        private const val MSG_CORRECT = "8=FIXT.1.1
9=295
35=8
49=SENDER
56=RECEIVER
34=10947
52=20230419-10:36:07.415088
17=495504662
11=zSuNbrBIZyVljs
41=zSuNbrBIZyVljs
37=49415882
150=0
39=0
151=500
14=500
48=NWDR
22=8
453=2
448=NGALL1FX01
447=D
452=76
448=0
447=P
452=3
1=test
40=A
59=0
54=B
55=ABC
38=500
44=1000
47=500
60=20180205-10:38:08.000008
10=191
"
+    }
+}