wehub-resource-sync
121 lines
3.4 KiB
Go
121 lines
3.4 KiB
Go
// Copyright 2024 Dolthub, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package main
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import "github.com/jackc/pgx/v5/pgproto3"
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// MessageReader acts like an iterator over a collection of messages.
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type MessageReader struct {
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messages []pgproto3.Message
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queue []pgproto3.Message
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idx int
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}
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// NewMessageReader returns a new *MessageReader.
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func NewMessageReader(messages []pgproto3.Message) *MessageReader {
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return &MessageReader{
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messages: messages,
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idx: 0,
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}
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}
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// Decrement sets the reader back a position, so that the next call to Next will return the previous message.
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func (mr *MessageReader) Decrement() {
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mr.idx--
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if mr.idx < 0 {
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mr.idx = 0
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}
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}
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// IsEmpty returns true when all messages have been returned.
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func (mr *MessageReader) IsEmpty() bool {
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return len(mr.queue) == 0 && mr.idx >= len(mr.messages)
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}
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// Next returns the next message, or nil if the reader has been exhausted.
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func (mr *MessageReader) Next() pgproto3.Message {
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if len(mr.queue) > 0 {
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if len(mr.queue) == 1 {
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m := mr.queue[0]
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mr.queue = nil
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return m
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} else {
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m := mr.queue[0]
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mr.queue = mr.queue[1:]
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return m
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}
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}
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if mr.idx >= len(mr.messages) {
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return nil
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}
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mr.idx++
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return mr.messages[mr.idx-1]
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}
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// Peek returns the next message without moving the reader forward, or nil if the reader has been exhausted.
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func (mr *MessageReader) Peek() pgproto3.Message {
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if len(mr.queue) > 0 {
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return mr.queue[0]
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}
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if mr.idx >= len(mr.messages) {
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return nil
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}
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return mr.messages[mr.idx]
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}
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// Previous returns the message that was last returned by Next. Returns nil if the reader is at the beginning message.
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func (mr *MessageReader) Previous() pgproto3.Message {
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if mr.idx <= 0 {
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return nil
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}
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return mr.messages[mr.idx-1]
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}
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// PushQueue adds the given messages to the queue, which will be returned when calling Next. Both Previous and Decrement
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// ignore the queue.
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func (mr *MessageReader) PushQueue(messages ...pgproto3.Message) {
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mr.queue = append(mr.queue, messages...)
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}
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// SurroundingMessages returns the messages that are surrounding the ones at the current index. This is primarily for
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// debugging, as it can be hard to locate messages when there are thousands in the reader, and you want to know which
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// messages surround the current one.
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func (mr *MessageReader) SurroundingMessages(amountBefore int, amountAfter int) []pgproto3.Message {
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amountBefore = mr.idx - amountBefore
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amountAfter = mr.idx + amountAfter
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if amountBefore < 0 {
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amountBefore = 0
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}
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if amountAfter > len(mr.messages) {
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amountAfter = len(mr.messages) - 1
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}
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return mr.messages[amountBefore:amountAfter]
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}
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// SyncToNextQuery advances the reader forward to the next query.
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func (mr *MessageReader) SyncToNextQuery() {
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for {
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switch mr.Next().(type) {
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case *pgproto3.ReadyForQuery:
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return
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case *pgproto3.Terminate:
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mr.Decrement()
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return
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case nil:
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return
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}
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}
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}
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