Initialize reason and

Initialize reason and SQLState in PostgresqlServerErrorException.

Previously, the reason and SQLState properties of the R2dbcException type were
unspecified.  This change updates the code to provide these values from the
exception field payload.  This aligns the behavior with the JDBC driver that
populates SQLState and leaves errorCode empty.

[resolves #3, resolves #4]

src/main/java/io/r2dbc/postgresql/PostgresqlServerErrorException.java

@@ -97,29 +97,30 @@ public final class PostgresqlServerErrorException extends R2dbcException {
      * @throws NullPointerException if {@code fields} is {@code null}
      */
     public PostgresqlServerErrorException(List<Field> fields) {
-        Objects.requireNonNull(fields, "fields must not be null");
-
-        Map<FieldType, String> map = fields.stream()
-            .collect(Collectors.toMap(Field::getType, Field::getValue));
+        this(convertToMap(fields));
+    }
 
-        this.code = map.get(CODE);
-        this.columnName = map.get(COLUMN_NAME);
-        this.constraintName = map.get(CONSTRAINT_NAME);
-        this.dataTypeName = map.get(DATA_TYPE_NAME);
-        this.detail = map.get(DETAIL);
-        this.file = map.get(FILE);
-        this.hint = map.get(HINT);
-        this.internalPosition = map.get(INTERNAL_POSITION);
-        this.internalQuery = map.get(INTERNAL_QUERY);
-        this.line = map.get(LINE);
-        this.message = map.get(MESSAGE);
-        this.position = map.get(POSITION);
-        this.routine = map.get(ROUTINE);
-        this.schemaName = map.get(SCHEMA_NAME);
-        this.severityLocalized = map.get(SEVERITY_LOCALIZED);
-        this.severityNonLocalized = map.get(SEVERITY_NON_LOCALIZED);
-        this.tableName = map.get(TABLE_NAME);
-        this.where = map.get(WHERE);
+    private PostgresqlServerErrorException(Map<FieldType, String> fields) {
+        super(fields.get(MESSAGE), fields.get(CODE));
+
+        this.code = fields.get(CODE);
+        this.columnName = fields.get(COLUMN_NAME);
+        this.constraintName = fields.get(CONSTRAINT_NAME);
+        this.dataTypeName = fields.get(DATA_TYPE_NAME);
+        this.detail = fields.get(DETAIL);
+        this.file = fields.get(FILE);
+        this.hint = fields.get(HINT);
+        this.internalPosition = fields.get(INTERNAL_POSITION);
+        this.internalQuery = fields.get(INTERNAL_QUERY);
+        this.line = fields.get(LINE);
+        this.message = fields.get(MESSAGE);
+        this.position = fields.get(POSITION);
+        this.routine = fields.get(ROUTINE);
+        this.schemaName = fields.get(SCHEMA_NAME);
+        this.severityLocalized = fields.get(SEVERITY_LOCALIZED);
+        this.severityNonLocalized = fields.get(SEVERITY_NON_LOCALIZED);
+        this.tableName = fields.get(TABLE_NAME);
+        this.where = fields.get(WHERE);
     }
 
     @Override
@@ -352,6 +353,13 @@ static void handleErrorResponse(BackendMessage message, SynchronousSink<BackendM
         }
     }
 
+    private static Map<FieldType, String> convertToMap(List<Field> fields) {
+        Objects.requireNonNull(fields, "fields must not be null");
+
+        return fields.stream()
+            .collect(Collectors.toMap(Field::getType, Field::getValue));
+    }
+
     private static PostgresqlServerErrorException toException(ErrorResponse errorResponse) {
         Objects.requireNonNull(errorResponse, "errorResponse must not be null");
 

src/test/java/io/r2dbc/postgresql/PostgresqlServerErrorExceptionTest.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2017-2018 the original author or authors.
+ *
+ * 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 io.r2dbc.postgresql;
+
+import io.r2dbc.postgresql.message.backend.Field;
+import org.junit.jupiter.api.Test;
+
+import java.util.Collections;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+final class PostgresqlServerErrorExceptionTest {
+
+    @Test
+    void initializesReason() {
+        PostgresqlServerErrorException exception = new PostgresqlServerErrorException(Collections.singletonList(new Field(Field.FieldType.MESSAGE, "Duplicate")));
+
+        assertThat(exception.getMessage()).isEqualTo("Duplicate");
+    }
+
+    @Test
+    void initializesSqlState() {
+        PostgresqlServerErrorException exception = new PostgresqlServerErrorException(Collections.singletonList(new Field(Field.FieldType.CODE, "1234")));
+
+        assertThat(exception.getSqlState()).isEqualTo("1234");
+    }
+
+    @Test
+    void skipsInitializationWithEmptyFields() {
+        PostgresqlServerErrorException exception = new PostgresqlServerErrorException(Collections.emptyList());
+
+        assertThat(exception.getSqlState()).isNull();
+        assertThat(exception.getMessage()).isNull();
+    }
+}