Fix seek for ColumnStream (#5224)

vonzshik · vonzshik · commit 60eeb0b42d3c · 2023-08-25T18:21:03.000+03:00
Fixes #5223 (cherry picked from commit 820cfcd)
diff --git a/src/Npgsql/Internal/NpgsqlReadBuffer.Stream.cs b/src/Npgsql/Internal/NpgsqlReadBuffer.Stream.cs
@@ -65,7 +65,7 @@ public override long Position
             {
                 if (value < 0)
                     throw new ArgumentOutOfRangeException(nameof(value), "Non - negative number required.");
-                Seek(_start + value, SeekOrigin.Begin);
+                Seek(value, SeekOrigin.Begin);
             }
         }
 
@@ -87,24 +87,27 @@ public override long Seek(long offset, SeekOrigin origin)
                 var tempPosition = unchecked(_start + (int)offset);
                 if (offset < 0 || tempPosition < _start)
                     throw new IOException(seekBeforeBegin);
-                _buf.ReadPosition = _start;
-                return tempPosition;
+                _buf.ReadPosition = tempPosition;
+                _read = (int)offset;
+                return _read;
             }
             case SeekOrigin.Current:
             {
                 var tempPosition = unchecked(_buf.ReadPosition + (int)offset);
                 if (unchecked(_buf.ReadPosition + offset) < _start || tempPosition < _start)
                     throw new IOException(seekBeforeBegin);
                 _buf.ReadPosition = tempPosition;
-                return tempPosition;
+                _read += (int)offset;
+                return _read;
             }
             case SeekOrigin.End:
             {
-                var tempPosition = unchecked(_len + (int)offset);
-                if (unchecked(_len + offset) < _start || tempPosition < _start)
+                var tempPosition = unchecked(_start + _len + (int)offset);
+                if (unchecked(_start + _len + offset) < _start || tempPosition < _start)
                     throw new IOException(seekBeforeBegin);
                 _buf.ReadPosition = tempPosition;
-                return tempPosition;
+                _read = _len + (int)offset;
+                return _read;
             }
             default:
                 throw new ArgumentOutOfRangeException(nameof(origin), "Invalid seek origin.");
@@ -238,4 +241,4 @@ static void ValidateArguments(byte[] buffer, int offset, int count)
         if (buffer.Length - offset < count)
             throw new ArgumentException("Offset and length were out of bounds for the array or count is greater than the number of elements from index to the end of the source collection.");
     }
-}
+}
diff --git a/test/Npgsql.Tests/ReaderTests.cs b/test/Npgsql.Tests/ReaderTests.cs
@@ -1471,6 +1471,50 @@ public async Task GetStream_in_middle_of_column_throws([Values] bool async)
             Assert.That(() => reader.GetStream(0), Throws.Exception.TypeOf<InvalidOperationException>());
     }
 
+    [Test, IssueLink("https://github.com/npgsql/npgsql/issues/5223")]
+    public async Task GetStream_seek()
+    {
+        // Sequential doesn't allow to seek
+        if (IsSequential)
+            return;
+
+        await using var conn = await OpenConnectionAsync();
+        await using var cmd = conn.CreateCommand();
+        cmd.CommandText = "SELECT 'abcdefgh'";
+        await using var reader = await cmd.ExecuteReaderAsync();
+        await reader.ReadAsync();
+
+        var buffer = new byte[4];
+
+        await using var stream = reader.GetStream(0);
+        Assert.IsTrue(stream.CanSeek);
+
+        var seekPosition = stream.Seek(-1, SeekOrigin.End);
+        Assert.That(seekPosition, Is.EqualTo(stream.Length - 1));
+        var read = stream.Read(buffer);
+        Assert.That(read, Is.EqualTo(1));
+        Assert.That(Encoding.ASCII.GetString(buffer, 0, 1), Is.EqualTo("h"));
+        read = stream.Read(buffer);
+        Assert.That(read, Is.EqualTo(0));
+
+        seekPosition = stream.Seek(2, SeekOrigin.Begin);
+        Assert.That(seekPosition, Is.EqualTo(2));
+        read = stream.Read(buffer);
+        Assert.That(read, Is.EqualTo(buffer.Length));
+        Assert.That(Encoding.ASCII.GetString(buffer), Is.EqualTo("cdef"));
+
+        seekPosition = stream.Seek(-3, SeekOrigin.Current);
+        Assert.That(seekPosition, Is.EqualTo(3));
+        read = stream.Read(buffer);
+        Assert.That(read, Is.EqualTo(buffer.Length));
+        Assert.That(Encoding.ASCII.GetString(buffer), Is.EqualTo("defg"));
+
+        stream.Position = 1;
+        read = stream.Read(buffer);
+        Assert.That(read, Is.EqualTo(buffer.Length));
+        Assert.That(Encoding.ASCII.GetString(buffer), Is.EqualTo("bcde"));
+    }
+
     #endregion GetBytes / GetStream
 
     #region GetChars / GetTextReader

Original file line number	Diff line number	Diff line change
`@@ -65,7 +65,7 @@ public override long Position`
`65`	`65`	`{`
`66`	`66`	`if (value < 0)`
`67`	`67`	`throw new ArgumentOutOfRangeException(nameof(value), "Non - negative number required.");`
`68`		`- Seek(_start + value, SeekOrigin.Begin);`
	`68`	`+ Seek(value, SeekOrigin.Begin);`
`69`	`69`	`}`
`70`	`70`	`}`
`71`	`71`
`@@ -87,24 +87,27 @@ public override long Seek(long offset, SeekOrigin origin)`
`87`	`87`	`var tempPosition = unchecked(_start + (int)offset);`
`88`	`88`	`if (offset < 0 \|\| tempPosition < _start)`
`89`	`89`	`throw new IOException(seekBeforeBegin);`
`90`		`- _buf.ReadPosition = _start;`
`91`		`- return tempPosition;`
	`90`	`+ _buf.ReadPosition = tempPosition;`
	`91`	`+ _read = (int)offset;`
	`92`	`+ return _read;`
`92`	`93`	`}`
`93`	`94`	`case SeekOrigin.Current:`
`94`	`95`	`{`
`95`	`96`	`var tempPosition = unchecked(_buf.ReadPosition + (int)offset);`
`96`	`97`	`if (unchecked(_buf.ReadPosition + offset) < _start \|\| tempPosition < _start)`
`97`	`98`	`throw new IOException(seekBeforeBegin);`
`98`	`99`	`_buf.ReadPosition = tempPosition;`
`99`		`- return tempPosition;`
	`100`	`+ _read += (int)offset;`
	`101`	`+ return _read;`
`100`	`102`	`}`
`101`	`103`	`case SeekOrigin.End:`
`102`	`104`	`{`
`103`		`- var tempPosition = unchecked(_len + (int)offset);`
`104`		`- if (unchecked(_len + offset) < _start \|\| tempPosition < _start)`
	`105`	`+ var tempPosition = unchecked(_start + _len + (int)offset);`
	`106`	`+ if (unchecked(_start + _len + offset) < _start \|\| tempPosition < _start)`
`105`	`107`	`throw new IOException(seekBeforeBegin);`
`106`	`108`	`_buf.ReadPosition = tempPosition;`
`107`		`- return tempPosition;`
	`109`	`+ _read = _len + (int)offset;`
	`110`	`+ return _read;`
`108`	`111`	`}`
`109`	`112`	`default:`
`110`	`113`	`throw new ArgumentOutOfRangeException(nameof(origin), "Invalid seek origin.");`
`@@ -238,4 +241,4 @@ static void ValidateArguments(byte[] buffer, int offset, int count)`
`238`	`241`	`if (buffer.Length - offset < count)`
`239`	`242`	`throw new ArgumentException("Offset and length were out of bounds for the array or count is greater than the number of elements from index to the end of the source collection.");`
`240`	`243`	`}`
`241`		`-}`
	`244`	`+}`