[Backport release-3_10] [DelimitedText provider] Fix performance issue with files with Unix end-of-line characters

src/providers/delimitedtext/qgsdelimitedtextfile.cpp

@@ -583,40 +583,63 @@ QgsDelimitedTextFile::Status QgsDelimitedTextFile::nextLine( QString &buffer, bo
     // Identify position of \r , \n or \r\n
     // We should rather use mStream->readLine(), but it fails to detect \r
     // line endings.
-    int eolPos = mBuffer.indexOf( '\r', mPosInBuffer );
-    int nextPos = 0;
-    if ( eolPos >= 0 )
+    int eolPos = -1;
     {
-      nextPos = eolPos + 1;
-      // Check if there is a \n just afterwards
-      if ( eolPos + 1 < mBuffer.size() )
+      if ( mLineNumber == 0 )
       {
-        if ( mBuffer[eolPos + 1] == '\n' )
+        // For the first line we don't know yet the end of line character, so
+        // manually scan for the first we find
+        const QChar *charBuffer = mBuffer.constData();
+        const int bufferSize = mBuffer.size();
+        for ( int pos = mPosInBuffer; pos < bufferSize; ++pos )
         {
-          nextPos = eolPos + 2;
+          if ( charBuffer[pos] == '\r' || charBuffer[pos] == '\n' )
+          {
+            mFirstEOLChar = charBuffer[pos];
+            eolPos = pos;
+            break;
+          }
         }
       }
       else
       {
-        // If we are just at the end of the buffer, read an extra character
-        // from the stream
-        QString newChar = mStream->read( 1 );
-        mBuffer += newChar;
-        if ( newChar == '\n' )
-        {
-          nextPos = eolPos + 2;
-        }
+        // Once we know the end of line character, use optimized indexOf()
+        eolPos = mBuffer.indexOf( mFirstEOLChar, mPosInBuffer );
       }
     }
-    else
+    if ( eolPos >= 0 )
     {
-      eolPos = mBuffer.indexOf( '\n', mPosInBuffer );
-      if ( eolPos >= 0 )
+      int nextPos = eolPos + 1;
+      if ( mBuffer[eolPos] == '\r' )
       {
-        nextPos = eolPos + 1;
+        // Check if there is a \n just afterwards
+        if ( eolPos + 1 < mBuffer.size() )
+        {
+          if ( mBuffer[eolPos + 1] == '\n' )
+          {
+            nextPos = eolPos + 2;
+          }
+        }
+        else
+        {
+          // If we are just at the end of the buffer, read an extra character
+          // from the stream
+          QString newChar = mStream->read( 1 );
+          mBuffer += newChar;
+          if ( newChar == '\n' )
+          {
+            nextPos = eolPos + 2;
+          }
+        }
       }
+
+      // Extract the current line from the buffer
+      buffer = mBuffer.mid( mPosInBuffer, eolPos - mPosInBuffer );
+      // Update current position in buffer to be the one next to the end of
+      // line character(s)
+      mPosInBuffer = nextPos;
     }
-    if ( eolPos < 0 )
+    else
     {
       if ( mPosInBuffer == 0 )
       {
@@ -637,14 +660,6 @@ QgsDelimitedTextFile::Status QgsDelimitedTextFile::nextLine( QString &buffer, bo
         continue;
       }
     }
-    else
-    {
-      // Extract the current line from the buffer
-      buffer = mBuffer.mid( mPosInBuffer, eolPos - mPosInBuffer );
-      // Update current position in buffer to be the one next to the end of
-      // line character(s)
-      mPosInBuffer = nextPos;
-    }
     mLineNumber++;
     if ( skipBlank && buffer.isEmpty() ) continue;
     return RecordOk;

src/providers/delimitedtext/qgsdelimitedtextfile.h

@@ -431,6 +431,7 @@ class QgsDelimitedTextFile : public QObject
     QString mBuffer;
     int mPosInBuffer = 0;
     int mMaxBufferSize = 0;
+    QChar mFirstEOLChar = 0; // '\r' if EOL is "\r" or "\r\n", or `\n' if EOL is "\n"
     QStringList mCurrentRecord;
     bool mHoldCurrentRecord = false;
     // Maximum number of record (ie maximum record number visited)