[Rust] Handle messages with blockLength > fixed field size

Author: Vadim Platonov

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/rust/RustCodecType.java

@@ -44,12 +44,18 @@ void appendDirectCodeMethods(
             final String methodName,
             final String representationType,
             final String nextCoderType,
-            final int numBytes) throws IOException
+            final int numBytes,
+            final int trailingBytes) throws IOException
         {
             indent(appendable, 1, "pub fn %s(mut self) -> CodecResult<(&%s %s, %s)> {\n",
                 methodName, DATA_LIFETIME, representationType, RustGenerator.withLifetime(nextCoderType));
             indent(appendable, 2, "let v = self.%s.read_type::<%s>(%s)?;\n",
                 RustCodecType.Decoder.scratchProperty(), representationType, numBytes);
+            if (trailingBytes > 0)
+            {
+                indent(appendable, 2, "self.%s.skip_bytes(%s)?;\n",
+                        RustCodecType.Decoder.scratchProperty(), trailingBytes);
+            }
             indent(appendable, 2, "Ok((v, %s::wrap(self.%s)))\n",
                 nextCoderType, RustCodecType.Decoder.scratchProperty());
             indent(appendable).append("}\n");
@@ -78,15 +84,20 @@ void appendDirectCodeMethods(
             final String methodName,
             final String representationType,
             final String nextCoderType,
-            final int numBytes) throws IOException
+            final int numBytes,
+            final int trailingBytes) throws IOException
         {
             indent(appendable, 1, "\n/// Create a mutable struct reference overlaid atop the data buffer\n");
             indent(appendable, 1, "/// such that changes to the struct directly edit the buffer. \n");
             indent(appendable, 1, "/// Note that the initial content of the struct's fields may be garbage.\n");
             indent(appendable, 1, "pub fn %s(mut self) -> CodecResult<(&%s mut %s, %s)> {\n",
                 methodName, DATA_LIFETIME, representationType, RustGenerator.withLifetime(nextCoderType));
-            indent(appendable, 2, "let v = self.%s.writable_overlay::<%s>(%s)?;\n",
-                RustCodecType.Encoder.scratchProperty(), representationType, numBytes);
+            if (trailingBytes > 0)
+            {
+                indent(appendable, 2, "// add trailing bytes to extend the end position of the scratch buffer\n");
+            }
+            indent(appendable, 2, "let v = self.%s.writable_overlay::<%s>(%s+%s)?;\n",
+                RustCodecType.Encoder.scratchProperty(), representationType, numBytes, trailingBytes);
             indent(appendable, 2, "Ok((v, %s::wrap(self.%s)))\n",
                 nextCoderType, RustCodecType.Encoder.scratchProperty());
             indent(appendable).append("}\n\n");
@@ -97,6 +108,12 @@ void appendDirectCodeMethods(
             indent(appendable, 2)
                 .append(format("self.%s.write_type::<%s>(t, %s)?;\n",
                 RustCodecType.Encoder.scratchProperty(), representationType, numBytes));
+            if (trailingBytes > 0)
+            {
+                indent(appendable, 2, "// fixed message length > sum of field lengths\n");
+                indent(appendable, 2, "self.%s.skip_bytes(%s)?;\n",
+                        RustCodecType.Decoder.scratchProperty(), trailingBytes);
+            }
             indent(appendable, 2).append(format("Ok(%s::wrap(self.%s))\n",
                 nextCoderType, RustCodecType.Encoder.scratchProperty()));
             indent(appendable).append("}\n");
@@ -125,7 +142,8 @@ abstract void appendDirectCodeMethods(
         String methodName,
         String representationType,
         String nextCoderType,
-        int numBytes) throws IOException;
+        int numBytes,
+        int trailingBytes) throws IOException;
 
     abstract String gerund();
 
@@ -175,7 +193,7 @@ String generateMessageHeaderCoder(
             appendScratchWrappingStruct(writer, headerCoderType);
             RustGenerator.appendImplWithLifetimeHeader(writer, headerCoderType);
             appendWrapMethod(writer, headerCoderType);
-            appendDirectCodeMethods(writer, "header", messageHeaderRepresentation, topType, headerSize);
+            appendDirectCodeMethods(writer, "header", messageHeaderRepresentation, topType, headerSize, 0);
             writer.append("}\n");
         }
 

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/rust/RustGenerator.java

@@ -212,7 +212,7 @@ private static void generateMessageEncoder(
         String topType = codecType.generateDoneCoderType(outputManager, messageTypeName);
         topType = generateTopVarDataCoders(messageTypeName, components.varData, outputManager, topType, codecType);
         topType = generateGroupsCoders(groupTree, outputManager, topType, codecType);
-        topType = generateFixedFieldCoder(messageTypeName, outputManager, topType, fieldStruct, codecType);
+        topType = generateFixedFieldCoder(messageTypeName, msgToken.encodedLength(), outputManager, topType, fieldStruct, codecType);
         topType = codecType.generateMessageHeaderCoder(messageTypeName, outputManager, topType, headerSize);
         generateEntryPoint(messageTypeName, outputManager, topType, codecType);
     }
@@ -231,7 +231,7 @@ private static void generateMessageDecoder(
         String topType = codecType.generateDoneCoderType(outputManager, messageTypeName);
         topType = generateTopVarDataCoders(messageTypeName, components.varData, outputManager, topType, codecType);
         topType = generateGroupsCoders(groupTree, outputManager, topType, codecType);
-        topType = generateFixedFieldCoder(messageTypeName, outputManager, topType, fieldStruct, codecType);
+        topType = generateFixedFieldCoder(messageTypeName, msgToken.encodedLength(), outputManager, topType, fieldStruct, codecType);
         topType = codecType.generateMessageHeaderCoder(messageTypeName, outputManager, topType, headerSize);
         generateEntryPoint(messageTypeName, outputManager, topType, codecType);
     }
@@ -262,6 +262,7 @@ static String withLifetime(final String typeName)
 
     private static String generateFixedFieldCoder(
         final String messageTypeName,
+        final int messageEncodedLength,
         final OutputManager outputManager,
         final String topType,
         final RustStruct fieldStruct,
@@ -274,10 +275,9 @@ private static String generateFixedFieldCoder(
             appendImplWithLifetimeHeader(writer, decoderName);
             codecType.appendWrapMethod(writer, decoderName);
             codecType.appendDirectCodeMethods(writer, formatMethodName(messageTypeName) + "_fields",
-                    fieldStruct.name, topType, fieldStruct.sizeBytes());
+                    fieldStruct.name, topType, fieldStruct.sizeBytes(),
+                    messageEncodedLength - fieldStruct.sizeBytes());
             writer.append("}\n");
-            // TODO - Move read position further if in-message blockLength exceeds fixed fields representation size
-            // will require piping some data from the previously-read message header
             return decoderName;
         }
     }
@@ -1151,6 +1151,18 @@ static void generateEncoderScratchStruct(final Ir ir, final OutputManager output
             indent(writer, 2).append("}\n");
             indent(writer).append("}\n\n");
 
+            indent(writer, 1, "/// Advances the `pos` index by a set number of bytes.\n");
+            indent(writer).append("#[inline]\n");
+            indent(writer).append("fn skip_bytes(&mut self, num_bytes: usize) -> CodecResult<()> {\n");
+            indent(writer, 2).append("let end = self.pos + num_bytes;\n");
+            indent(writer, 2).append("if end <= self.data.len() {\n");
+            indent(writer, 3).append("self.pos = end;\n");
+            indent(writer, 3).append("Ok(())\n");
+            indent(writer, 2).append("} else {\n");
+            indent(writer, 3).append("Err(CodecErr::NotEnoughBytes)\n");
+            indent(writer, 2).append("}\n");
+            indent(writer).append("}\n\n");
+
             indent(writer, 1, "/// Create a struct reference overlaid atop the data buffer\n");
             indent(writer, 1, "/// such that changes to the struct directly edit the buffer. \n");
             indent(writer, 1, "/// Note that the initial content of the struct's fields may be garbage.\n");

sbe-tool/src/test/java/uk/co/real_logic/sbe/generation/rust/RustGeneratorTest.java

@@ -306,6 +306,17 @@ public void messageWithOffsets()
         assertContains(rust, expectedHeader);
     }
 
+    @Test
+    public void messageBlockLengthExceedingSumOfFieldLengths()
+    {
+        final String rust = fullGenerateForResource(outputManager, "message-block-length-test");
+        final String expectedEncoderSegment = "let v = self.scratch.writable_overlay::<MsgNameFields>(9+2)?;";
+        assertContains(rust, expectedEncoderSegment);
+        final String expectedDecoderSegment = "let v = self.scratch.read_type::<MsgNameFields>(9)?;\n" +
+                "    self.scratch.skip_bytes(2)?;";
+        assertContains(rust, expectedDecoderSegment);
+    }
+
     @Test
     public void constantEnumFields() throws IOException, InterruptedException
     {