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|
package httprc
import (
"context"
"fmt"
"net/http"
"sync"
)
type fetchRequest struct {
mu sync.RWMutex
// client contains the HTTP Client that can be used to make a
// request. By setting a custom *http.Client, you can for example
// provide a custom http.Transport
//
// If not specified, http.DefaultClient will be used.
client HTTPClient
wl Whitelist
// u contains the URL to be fetched
url string
// reply is a field that is only used by the internals of the fetcher
// it is used to return the result of fetching
reply chan *fetchResult
}
type fetchResult struct {
mu sync.RWMutex
res *http.Response
err error
}
func (fr *fetchResult) reply(ctx context.Context, reply chan *fetchResult) error {
select {
case <-ctx.Done():
return ctx.Err()
case reply <- fr:
}
close(reply)
return nil
}
type fetcher struct {
requests chan *fetchRequest
}
type Fetcher interface {
Fetch(context.Context, string, ...FetchOption) (*http.Response, error)
fetch(context.Context, *fetchRequest) (*http.Response, error)
}
func NewFetcher(ctx context.Context, options ...FetcherOption) Fetcher {
var nworkers int
var wl Whitelist
for _, option := range options {
//nolint:forcetypeassert
switch option.Ident() {
case identFetcherWorkerCount{}:
nworkers = option.Value().(int)
case identWhitelist{}:
wl = option.Value().(Whitelist)
}
}
if nworkers < 1 {
nworkers = 3
}
incoming := make(chan *fetchRequest)
for i := 0; i < nworkers; i++ {
go runFetchWorker(ctx, incoming, wl)
}
return &fetcher{
requests: incoming,
}
}
func (f *fetcher) Fetch(ctx context.Context, u string, options ...FetchOption) (*http.Response, error) {
var client HTTPClient
var wl Whitelist
for _, option := range options {
//nolint:forcetypeassert
switch option.Ident() {
case identHTTPClient{}:
client = option.Value().(HTTPClient)
case identWhitelist{}:
wl = option.Value().(Whitelist)
}
}
req := fetchRequest{
client: client,
url: u,
wl: wl,
}
return f.fetch(ctx, &req)
}
// fetch (unexported) is the main fetching implemntation.
// it allows the caller to reuse the same *fetchRequest object
func (f *fetcher) fetch(ctx context.Context, req *fetchRequest) (*http.Response, error) {
reply := make(chan *fetchResult, 1)
req.mu.Lock()
req.reply = reply
req.mu.Unlock()
// Send a request to the backend
select {
case <-ctx.Done():
return nil, ctx.Err()
case f.requests <- req:
}
// wait until we get a reply
select {
case <-ctx.Done():
return nil, ctx.Err()
case fr := <-reply:
fr.mu.RLock()
res := fr.res
err := fr.err
fr.mu.RUnlock()
return res, err
}
}
func runFetchWorker(ctx context.Context, incoming chan *fetchRequest, wl Whitelist) {
LOOP:
for {
select {
case <-ctx.Done():
break LOOP
case req := <-incoming:
req.mu.RLock()
reply := req.reply
client := req.client
if client == nil {
client = http.DefaultClient
}
url := req.url
reqwl := req.wl
req.mu.RUnlock()
var wls []Whitelist
for _, v := range []Whitelist{wl, reqwl} {
if v != nil {
wls = append(wls, v)
}
}
if len(wls) > 0 {
for _, wl := range wls {
if !wl.IsAllowed(url) {
r := &fetchResult{
err: fmt.Errorf(`fetching url %q rejected by whitelist`, url),
}
if err := r.reply(ctx, reply); err != nil {
break LOOP
}
continue LOOP
}
}
}
// The body is handled by the consumer of the fetcher
//nolint:bodyclose
res, err := client.Get(url)
r := &fetchResult{
res: res,
err: err,
}
if err := r.reply(ctx, reply); err != nil {
break LOOP
}
}
}
}
|
