mirror of
https://codeberg.org/scip/kleingebaeck.git
synced 2025-12-16 20:11:01 +01:00
130 lines
3.2 KiB
Go
130 lines
3.2 KiB
Go
/*
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Copyright © 2023-2024 Thomas von Dein
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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package main
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import (
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"bytes"
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"io"
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"log/slog"
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"math"
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"math/rand"
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"net/http"
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"time"
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)
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// I add an artificial "ID" to each HTTP request and the corresponding
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// respose for debugging purposes so that the pair of them can be
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// easier associated in debug output
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var letters = []rune("ABCDEF0123456789")
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func getid() string {
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b := make([]rune, 8)
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for i := range b {
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b[i] = letters[rand.Intn(len(letters))]
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}
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return string(b)
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}
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// retry after HTTP 50x errors or err!=nil
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const RetryCount = 3
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// used to inject debug log and implement retries
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type loggingTransport struct{}
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// escalating timeout, $retry^2 seconds
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func backoff(retries int) time.Duration {
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return time.Duration(math.Pow(2, float64(retries))) * time.Second
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}
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// only retry in case of errors or certain non 200 HTTP codes
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func shouldRetry(err error, resp *http.Response) bool {
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if err != nil {
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return true
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}
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if resp.StatusCode == http.StatusBadGateway ||
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resp.StatusCode == http.StatusServiceUnavailable ||
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resp.StatusCode == http.StatusGatewayTimeout {
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return true
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}
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return false
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}
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// Body needs to be drained, otherwise we can't reuse the http.Response
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func drainBody(resp *http.Response) {
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if resp != nil {
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if resp.Body != nil {
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_, err := io.Copy(io.Discard, resp.Body)
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if err != nil {
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// unable to copy data? uff!
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panic(err)
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}
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resp.Body.Close()
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}
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}
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}
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// the actual logging transport with retries
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func (t *loggingTransport) RoundTrip(req *http.Request) (*http.Response, error) {
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// just requred for debugging
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id := getid()
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// clone the request body, put into request on retry
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var bodyBytes []byte
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if req.Body != nil {
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bodyBytes, _ = io.ReadAll(req.Body)
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req.Body = io.NopCloser(bytes.NewBuffer(bodyBytes))
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}
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slog.Debug("REQUEST", "id", id, "uri", req.URL, "host", req.Host)
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// first try
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resp, err := http.DefaultTransport.RoundTrip(req)
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if err == nil {
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slog.Debug("RESPONSE", "id", id, "status", resp.StatusCode,
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"contentlength", resp.ContentLength)
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}
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// enter retry check and loop, if first req were successfull, leave loop immediately
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retries := 0
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for shouldRetry(err, resp) && retries < RetryCount {
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time.Sleep(backoff(retries))
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// consume any response to reuse the connection.
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drainBody(resp)
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// clone the request body again
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if req.Body != nil {
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req.Body = io.NopCloser(bytes.NewBuffer(bodyBytes))
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}
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// actual retry
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resp, err = http.DefaultTransport.RoundTrip(req)
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if err == nil {
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slog.Debug("RESPONSE", "id", id, "status", resp.StatusCode,
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"contentlength", resp.ContentLength, "retry", retries)
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}
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retries++
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}
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return resp, err
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}
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