github.com/dolthub/dolt/go@v0.40.5-0.20240520175717-68db7794bea6/libraries/doltcore/mvdata/channel_row_source.go (about)

     1  // Copyright 2020-2021 Dolthub, Inc.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package mvdata
    16  
    17  import (
    18  	"io"
    19  
    20  	"github.com/dolthub/go-mysql-server/sql"
    21  )
    22  
    23  // ChannelRowSource is a sql.Node that wraps a channel as a sql.RowIter.
    24  type ChannelRowSource struct {
    25  	schema     sql.Schema
    26  	rowChannel chan sql.Row
    27  }
    28  
    29  var _ sql.ExecSourceRel = (*ChannelRowSource)(nil)
    30  
    31  // NewChannelRowSource returns a ChannelRowSource object.
    32  func NewChannelRowSource(schema sql.Schema, rowChannel chan sql.Row) *ChannelRowSource {
    33  	return &ChannelRowSource{schema: schema, rowChannel: rowChannel}
    34  }
    35  
    36  var _ sql.Node = (*ChannelRowSource)(nil)
    37  
    38  // Resolved implements the sql.Node interface.
    39  func (c *ChannelRowSource) Resolved() bool {
    40  	return true
    41  }
    42  
    43  func (c *ChannelRowSource) IsReadOnly() bool {
    44  	return true
    45  }
    46  
    47  // String implements the sql.Node interface.
    48  func (c *ChannelRowSource) String() string {
    49  	return "ChannelRowSource()"
    50  }
    51  
    52  // Schema implements the sql.Node interface.
    53  func (c *ChannelRowSource) Schema() sql.Schema {
    54  	return c.schema
    55  }
    56  
    57  // Children implements the sql.Node interface.
    58  func (c *ChannelRowSource) Children() []sql.Node {
    59  	return nil
    60  }
    61  
    62  // RowIter implements the sql.Node interface.
    63  func (c *ChannelRowSource) RowIter(ctx *sql.Context, row sql.Row) (sql.RowIter, error) {
    64  	return &channelRowIter{
    65  		rowChannel: c.rowChannel,
    66  	}, nil
    67  }
    68  
    69  // WithChildren implements the sql.Node interface.
    70  func (c *ChannelRowSource) WithChildren(children ...sql.Node) (sql.Node, error) {
    71  	if len(children) != 0 {
    72  		return nil, sql.ErrInvalidChildrenNumber.New(c, len(children), 0)
    73  	}
    74  
    75  	return c, nil
    76  }
    77  
    78  // CheckPrivileges implements the sql.Node interface.
    79  func (c *ChannelRowSource) CheckPrivileges(ctx *sql.Context, opChecker sql.PrivilegedOperationChecker) bool {
    80  	return true
    81  }
    82  
    83  // channelRowIter wraps the channel under the sql.RowIter interface
    84  type channelRowIter struct {
    85  	rowChannel chan sql.Row
    86  }
    87  
    88  var _ sql.RowIter = (*channelRowIter)(nil)
    89  
    90  // Next implements the sql.RowIter interface.
    91  func (c *channelRowIter) Next(ctx *sql.Context) (sql.Row, error) {
    92  	for r := range c.rowChannel {
    93  		select {
    94  		case <-ctx.Done():
    95  			return nil, io.EOF
    96  		default:
    97  			return r, nil
    98  		}
    99  	}
   100  	return nil, io.EOF
   101  }
   102  
   103  // Close implements the sql.RowIter interface.
   104  func (c *channelRowIter) Close(context *sql.Context) error {
   105  	return nil
   106  }