Github user paul-rogers commented on a diff in the pull request:
https://github.com/apache/drill/pull/830#discussion_r117382558
--- Diff:
exec/java-exec/src/main/java/org/apache/drill/exec/store/easy/text/compliant/HeaderBuilder.java
---
@@ -0,0 +1,249 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you 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 org.apache.drill.exec.store.easy.text.compliant;
+
+import java.nio.BufferOverflowException;
+import java.nio.ByteBuffer;
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+import com.google.common.base.Charsets;
+
+/**
+ * Text output that implements a header reader/parser.
+ * The caller parses out the characters of each header;
+ * this class assembles UTF-8 bytes into Unicode characters,
+ * fixes invalid characters (those not legal for SQL symbols),
+ * and maps duplicate names to unique names.
+ * <p>
+ * That is, this class is as permissive as possible with file
+ * headers to avoid spurious query failures for trivial reasons.
+ */
+
+// Note: this class uses Java heap strings and the usual Java
+// convenience classes. Since we do heavy Unicode string operations,
+// and read a single row, there is no good reason to try to use
+// value vectors and direct memory for this task.
+
+public class HeaderBuilder extends TextOutput {
+
+ /**
+ * Maximum Drill symbol length, as enforced for headers.
+ * @see <a
href="https://drill.apache.org/docs/lexical-structure/#identifier";>
+ * identifier documentation</a>
+ */
+ // TODO: Replace with the proper constant, if available
+ public static final int MAX_HEADER_LEN = 1024;
+
+ /**
+ * Exception that reports header errors. Is an unchecked exception
+ * to avoid cluttering the normal field reader interface.
+ */
+ public static class HeaderError extends RuntimeException {
+
+ private static final long serialVersionUID = 1L;
+
+ public HeaderError(String msg) {
+ super(msg);
+ }
+
+ public HeaderError(int colIndex, String msg) {
+ super("Column " + (colIndex + 1) + ": " + msg);
+ }
+
+ }
+
+ public List<String> headers = new ArrayList<>();
+ public ByteBuffer currentField = ByteBuffer.allocate(MAX_HEADER_LEN);
+
+ @Override
+ public void startField(int index) {
+ currentField.clear();
+ }
+
+ @Override
+ public boolean endField() {
+ String header = new String(currentField.array(), 0,
currentField.position(), Charsets.UTF_8);
+ header = validateSymbol(header);
+ headers.add(header);
+ return true;
+ }
+
+ @Override
+ public boolean endEmptyField() {
+
+ // Empty header will be rewritten to "column<n>".
+
+ return endField();
+ }
+
+ /**
+ * Validate the header name according to the SQL lexical rules.
+ * @see <a
href="https://drill.apache.org/docs/lexical-structure/#identifier";>
+ * identifier documentation</a>
+ * @param header the header name to validate
+ */
+
+ // TODO: Replace with existing code, if any.
+ private String validateSymbol(String header) {
+ header = header.trim();
+
+ // To avoid unnecessary query failures, just make up a column name
+ // if the name is missing or all blanks.
+
+ if (header.isEmpty()) {
+ return "column_" + (headers.size() + 1);
+ }
+ if (! Character.isAlphabetic(header.charAt(0))) {
+ return rewriteHeader(header);
+ }
+ for (int i = 1; i < header.length(); i++) {
+ char ch = header.charAt(i);
+ if (! Character.isAlphabetic(ch) &&
+ ! Character.isDigit(ch) && ch != '_') {
+ return rewriteHeader(header);
+ }
+ }
+ return header;
+ }
+
+ /**
+ * Given an invalid header, rewrite it to replace illegal characters
+ * with valid ones. The header won't be what the user specified,
+ * but it will be a valid SQL identifier. This solution avoids failing
+ * queries due to corrupted of invalid header data.
+ *
+ * @param header the original header
+ * @return the rewritten header, valid for SQL
+ */
+
+ private String rewriteHeader(String header) {
+ StringBuilder buf = new StringBuilder();
+
+ // If starts with non-alphabetic, can't map the character to
+ // underscore, so just tack on a prefix.
+
+ char ch = header.charAt(0);
+ if (Character.isAlphabetic(ch)) {
+ buf.append(ch);
+ } else {
+ if (Character.isDigit(ch)) {
+ buf.append("col_");
+ buf.append(ch);
+ } else {
+
+ // For the strange case of only one character, format
+ // the same as an empty header.
+
+ if (header.length() == 1) {
+ return "column_" + (headers.size() + 1);
+ } else {
+ buf.append("col_");
+ }
+ }
+ }
+
+ // Convert all remaining invalid characters to underscores
+
+ for (int i = 1; i < header.length(); i++) {
+ ch = header.charAt(i);
+ if (Character.isAlphabetic(ch) ||
+ Character.isDigit(ch) || ch == '_') {
+ buf.append(ch);
+ } else {
+ buf.append("_");
+ }
+ }
+ return buf.toString();
+ }
+
+ @Override
+ public void append(byte data) {
+ try {
+ currentField.put(data);
+ } catch (BufferOverflowException e) {
+ throw new HeaderError(headers.size(), "Column exceeds maximum length
of " + MAX_HEADER_LEN);
+ }
+ }
+
+ @Override
+ public void finishRecord() {
+ if (headers.isEmpty()) {
+ throw new HeaderError("The file must define at least one header.");
+ }
+
+ // Force headers to be unique.
+
+ Set<String> idents = new HashSet<String>();
--- End diff --
Fixed.
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