Add tell/seek methods to CsvReader

Sming/Core/Data/CsvReader.cpp

@@ -13,16 +13,34 @@
 #include "CsvReader.h"
 #include <debug_progmem.h>
 
-void CsvReader::reset()
+CsvReader::CsvReader(IDataSourceStream* source, char fieldSeparator, const CStringArray& headings, size_t maxLineLength)
+	: source(source), maxLineLength(maxLineLength), headings(headings), fieldSeparator(fieldSeparator)
 {
-	if(source) {
-		source->seekFrom(0, SeekOrigin::Start);
-		if(!userHeadingsProvided) {
-			readRow();
-			headings = row;
-		}
+	if(source && !headings) {
+		readRow();
+		this->headings = std::move(row);
+		start = cursor;
 	}
+	cursor = BOF;
+}
+
+bool CsvReader::seek(int cursor)
+{
 	row = nullptr;
+	if(!source) {
+		return false;
+	}
+	auto newpos = std::max(cursor, int(start));
+	int pos = source->seekFrom(newpos, SeekOrigin::Start);
+	if(pos != newpos) {
+		return false;
+	}
+	this->cursor = cursor;
+	if(cursor < int(start)) {
+		// Before first record has been read
+		return true;
+	}
+	return readRow();
 }
 
 bool CsvReader::readRow()
@@ -46,6 +64,8 @@ bool CsvReader::readRow()
 	char lc{'\0'};
 	unsigned writepos{0};
 
+	cursor = source->seekFrom(0, SeekOrigin::Current);
+
 	while(true) {
 		if(buffer.length() == maxLineLength) {
 			debug_w("[CSV] Line buffer limit reached %u", maxLineLength);
@@ -58,6 +78,7 @@ bool CsvReader::readRow()
 		}
 		auto len = source->readBytes(buffer.begin() + writepos, buflen - writepos);
 		if(len == 0) {
+			// End of input
 			if(writepos == 0) {
 				return false;
 			}

Sming/Core/Data/CsvReader.h

@@ -40,29 +40,28 @@ class CsvReader
 public:
 	/**
 	 * @brief Construct a CSV reader
-	 * @param source Stream to read CSV text from
+	 * @param source Stream to read CSV text from. Must support random seeking.
 	 * @param fieldSeparator
 	 * @param headings Required if source data does not contain field headings as first row
 	 * @param maxLineLength Limit size of buffer to guard against malformed data
 	 */
 	CsvReader(IDataSourceStream* source, char fieldSeparator = ',', const CStringArray& headings = nullptr,
-			  size_t maxLineLength = 2048)
-		: source(source), fieldSeparator(fieldSeparator), userHeadingsProvided(headings), maxLineLength(maxLineLength),
-		  headings(headings)
-	{
-		reset();
-	}
+			  size_t maxLineLength = 2048);
 
 	/**
 	 * @brief Reset reader to start of CSV file
 	 *
 	 * Cursor is set to 'before start'.
 	 * Call 'next()' to fetch first record.
 	 */
-	void reset();
+	void reset()
+	{
+		seek(start);
+	}
 
 	/**
 	 * @brief Seek to next record
+	 * @retval bool true on success, false if there are no more records
 	 */
 	bool next()
 	{
@@ -131,13 +130,39 @@ class CsvReader
 		return row;
 	}
 
+	/**
+	 * @brief Get cursor position for current row
+	 *
+	 * The returned value indicates source stream offset for start of current row.
+	 * After construction cursor is set to -1. This indicates 'Before first record' (BOF).
+	 */
+	int tell() const
+	{
+		return cursor;
+	}
+
+	/**
+	 * @brief Set reader to previously noted position
+	 * @param cursor Value obtained via `tell()`
+	 * @retval bool true on success, false on failure or end of records
+	 *
+	 * If cursor is BOF then there will be no current record until `next()` is called.
+	 * This is the same as if `next()` were called.
+	 *
+	 * Otherwise the corresponding row will be available via `getRow()`.
+	 */
+	bool seek(int cursor);
+
 private:
 	bool readRow();
 
+	static constexpr int BOF{-1}; ///< Indicates 'Before First Record'
+
 	std::unique_ptr<IDataSourceStream> source;
-	char fieldSeparator;
-	bool userHeadingsProvided;
 	size_t maxLineLength;
+	size_t start{0}; ///< Stream position of first record
+	int cursor{BOF}; ///< Stream position for start of current row
 	CStringArray headings;
 	CStringArray row;
+	char fieldSeparator;
 };

tests/HostTests/modules/CsvReader.cpp

@@ -3,9 +3,14 @@
 
 DEFINE_FSTR_LOCAL(
 	test1_csv, "\"field1\",field2,field3,\"field four\"\n"
-			   "Something \"awry\",\"datavalue 2\",\"where,are,\"\"the,bananas\",sausages abound,\"never surrender\"")
-DEFINE_FSTR_LOCAL(csv_headings, "field1;field2;field3;field four;")
-DEFINE_FSTR_LOCAL(csv_row1, "Something \"awry\";datavalue 2;where,are,\"the,bananas;sausages abound;never surrender;")
+			   "Something \"awry\",\"datavalue 2\",\"where,are,\"\"the,bananas\",sausages abound,\"never surrender\"\n"
+			   "one,two,three,four\n"
+			   "a,b,c,d,e,f")
+
+DEFINE_FSTR_LOCAL(csv_headings, "field1;field2;field3;field four")
+DEFINE_FSTR_LOCAL(csv_row1, "Something \"awry\";datavalue 2;where,are,\"the,bananas;sausages abound;never surrender")
+DEFINE_FSTR_LOCAL(csv_row2, "one;two;three;four")
+DEFINE_FSTR_LOCAL(csv_row3, "a;b;c;d;e;f")
 
 class CsvReaderTest : public TestGroup
 {
@@ -18,22 +23,59 @@ class CsvReaderTest : public TestGroup
 	{
 		TEST_CASE("Basic")
 		{
-			auto str = [](const CStringArray& cs) {
-				String s = reinterpret_cast<const String&>(cs);
-				s.replace('\0', ';');
-				return s;
-			};
-
-			CsvReader reader(new FSTR::Stream(test1_csv));
-			String headings = str(reader.getHeadings());
-			Serial.println(headings);
-			CHECK(reader.next());
-			String row1 = str(reader.getRow());
-			Serial.println(row1);
-			CHECK(!reader.next());
-
-			CHECK(csv_headings == headings);
-			CHECK(csv_row1 == row1);
+			CsvReader reader(new FSTR::Stream(test1_csv, ','));
+
+			const char* sep = ";";
+
+			Serial << "Cursor " << reader.tell() << endl;
+			auto headings = reader.getHeadings();
+			Serial.println(headings.join(sep));
+			CHECK(csv_headings == headings.join(sep));
+
+			REQUIRE(reader.next());
+			auto cursor1 = reader.tell();
+			Serial << "Cursor " << cursor1 << endl;
+			auto row = reader.getRow();
+			Serial.println(row.join(sep));
+			CHECK(csv_row1 == row.join(sep));
+
+			REQUIRE(reader.next());
+			auto cursor2 = reader.tell();
+			Serial << "Cursor " << cursor2 << endl;
+			row = reader.getRow();
+			REQUIRE(csv_row2 == row.join(sep));
+
+			REQUIRE(reader.next());
+			auto cursor3 = reader.tell();
+			Serial << "Cursor " << cursor3 << endl;
+			row = reader.getRow();
+			REQUIRE(csv_row3 == row.join(sep));
+
+			REQUIRE(!reader.next());
+			Serial << "Cursor " << reader.tell() << endl;
+
+			TEST_CASE("reset")
+			{
+				reader.reset();
+				REQUIRE(reader.next());
+				row = reader.getRow();
+				REQUIRE(csv_row1 == row.join(sep));
+			}
+
+			TEST_CASE("seek")
+			{
+				reader.seek(cursor2);
+				row = reader.getRow();
+				REQUIRE(csv_row2 == row.join(sep));
+
+				reader.seek(cursor1);
+				row = reader.getRow();
+				REQUIRE(csv_row1 == row.join(sep));
+
+				reader.seek(cursor3);
+				row = reader.getRow();
+				REQUIRE(csv_row3 == row.join(sep));
+			}
 		}
 	}
 };