http.go

/*
Copyright 2022 The Flux authors

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

/*
This was inspired and contains part of:
https://github.com/libgit2/git2go/blob/eae00773cce87d5282a8ac7c10b5c1961ee6f9cb/http.go

The MIT License

Copyright (c) 2013 The git2go contributors

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/

package managed

import (
	"bytes"
	"context"
	"crypto/tls"
	"crypto/x509"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strings"
	"sync"

	"github.com/fluxcd/pkg/runtime/logger"
	pool "github.com/fluxcd/source-controller/internal/transport"
	"github.com/fluxcd/source-controller/pkg/git"
	"github.com/go-logr/logr"
	git2go "github.com/libgit2/git2go/v33"
	ctrl "sigs.k8s.io/controller-runtime"
)

var actionSuffixes = []string{
	"/info/refs?service=git-upload-pack",
	"/git-upload-pack",
	"/info/refs?service=git-receive-pack",
	"/git-receive-pack",
}

// registerManagedHTTP registers a Go-native implementation of an
// HTTP(S) transport that doesn't rely on any lower-level libraries
// such as OpenSSL.
func registerManagedHTTP() error {
	for _, protocol := range []string{"http", "https"} {
		_, err := git2go.NewRegisteredSmartTransport(protocol, true, httpSmartSubtransportFactory)
		if err != nil {
			return fmt.Errorf("failed to register transport for %q: %v", protocol, err)
		}
	}
	return nil
}

func httpSmartSubtransportFactory(remote *git2go.Remote, transport *git2go.Transport) (git2go.SmartSubtransport, error) {
	sst := &httpSmartSubtransport{
		transport:     transport,
		httpTransport: pool.NewOrIdle(nil),
		ctx:           context.Background(),
		logger:        logr.Discard(),
	}

	return sst, nil
}

type httpSmartSubtransport struct {
	transport     *git2go.Transport
	httpTransport *http.Transport

	// once is used to ensure that logger and ctx is set only once,
	// on the initial (or only) Action call. Without this a mutex must
	// be applied to ensure that ctx won't be changed, as this would be
	// prone to race conditions in the stdout processing goroutine.
	once sync.Once
	// ctx defines the context to be used across long-running or
	// cancellable operations.
	// Defaults to context.Background().
	ctx context.Context
	// logger keeps a Logger instance for logging. This was preferred
	// due to the need to have a correlation ID and URL set and
	// reused across all log calls.
	// If context is not set, this defaults to logr.Discard().
	logger logr.Logger
}

func (t *httpSmartSubtransport) Action(transportOptionsURL string, action git2go.SmartServiceAction) (git2go.SmartSubtransportStream, error) {
	opts, found := getTransportOptions(transportOptionsURL)

	if !found {
		return nil, fmt.Errorf("failed to create client: could not find transport options for the object: %s", transportOptionsURL)
	}
	targetURL := opts.TargetURL

	if targetURL == "" {
		return nil, fmt.Errorf("repository URL cannot be empty")
	}

	if len(targetURL) > URLMaxLength {
		return nil, fmt.Errorf("URL exceeds the max length (%d)", URLMaxLength)
	}

	var proxyFn func(*http.Request) (*url.URL, error)
	proxyOpts := opts.ProxyOptions
	if proxyOpts != nil {
		switch proxyOpts.Type {
		case git2go.ProxyTypeNone:
			proxyFn = nil
		case git2go.ProxyTypeAuto:
			proxyFn = http.ProxyFromEnvironment
		case git2go.ProxyTypeSpecified:
			parsedUrl, err := url.Parse(proxyOpts.Url)
			if err != nil {
				return nil, err
			}
			proxyFn = http.ProxyURL(parsedUrl)
		}
		t.httpTransport.Proxy = proxyFn
		t.httpTransport.ProxyConnectHeader = map[string][]string{}
	} else {
		t.httpTransport.Proxy = nil
	}
	t.httpTransport.DisableCompression = false

	t.once.Do(func() {
		if opts.Context != nil {
			t.ctx = opts.Context
			t.logger = ctrl.LoggerFrom(t.ctx,
				"transportType", "http",
				"url", opts.TargetURL)
		}
	})

	client, req, err := createClientRequest(targetURL, action, t.httpTransport, opts.AuthOpts)
	if err != nil {
		return nil, err
	}

	stream := newManagedHttpStream(t, req, client)
	if req.Method == "POST" {
		stream.recvReply.Add(1)
		stream.sendRequestBackground()
	}

	client.CheckRedirect = func(req *http.Request, via []*http.Request) error {
		if len(via) >= 3 {
			return fmt.Errorf("too many redirects")
		}

		// golang will change POST to GET in case of redirects.
		if len(via) >= 0 && req.Method != via[0].Method {
			if via[0].URL.Scheme == "https" && req.URL.Scheme == "http" {
				return fmt.Errorf("downgrade from https to http is not allowed: from %q to %q", via[0].URL.String(), req.URL.String())
			}
			if via[0].URL.Host != req.URL.Host {
				return fmt.Errorf("cross hosts redirects are not allowed: from %s to %s", via[0].URL.Host, req.URL.Host)
			}

			return http.ErrUseLastResponse
		}

		// Some Git servers (i.e. Gitlab) only support redirection on the GET operations.
		// Therefore, on the initial GET operation we update the target URL to include the
		// new target, so the subsequent actions include the correct target URL.
		// Example of this is trying to access a Git repository without the .git suffix.
		if req.Response != nil {
			if newURL, err := req.Response.Location(); err == nil && newURL != nil {
				if strings.EqualFold(newURL.Host, req.URL.Host) && strings.EqualFold(newURL.Port(), req.URL.Port()) {
					opts, _ := getTransportOptions(transportOptionsURL)
					if opts == nil {
						opts = &TransportOptions{}
					}

					opts.TargetURL = trimActionSuffix(newURL.String())
					AddTransportOptions(transportOptionsURL, *opts)

					// show as info, as this should be visible regardless of the
					// chosen log-level.
					t.logger.Info("server responded with redirect",
						"newUrl", opts.TargetURL, "StatusCode", req.Response.StatusCode)
				}
			}
		}

		return nil
	}

	return stream, nil
}

func trimActionSuffix(url string) string {
	newUrl := url
	for _, s := range actionSuffixes {
		newUrl = strings.TrimSuffix(newUrl, s)
	}

	return newUrl
}

func createClientRequest(targetURL string, action git2go.SmartServiceAction,
	t *http.Transport, authOpts *git.AuthOptions) (*http.Client, *http.Request, error) {
	var req *http.Request
	var err error

	if t == nil {
		return nil, nil, fmt.Errorf("failed to create client: transport cannot be nil")
	}

	client := &http.Client{
		Transport: t,
		Timeout:   fullHttpClientTimeOut,
	}

	switch action {
	case git2go.SmartServiceActionUploadpackLs:
		req, err = http.NewRequest("GET", targetURL+"/info/refs?service=git-upload-pack", nil)

	case git2go.SmartServiceActionUploadpack:
		req, err = http.NewRequest("POST", targetURL+"/git-upload-pack", nil)
		if err != nil {
			break
		}
		req.Header.Set("Content-Type", "application/x-git-upload-pack-request")
		if t.Proxy != nil {
			t.ProxyConnectHeader.Set("Content-Type", "application/x-git-upload-pack-request")
		}

	case git2go.SmartServiceActionReceivepackLs:
		req, err = http.NewRequest("GET", targetURL+"/info/refs?service=git-receive-pack", nil)

	case git2go.SmartServiceActionReceivepack:
		req, err = http.NewRequest("POST", targetURL+"/git-receive-pack", nil)
		if err != nil {
			break
		}
		req.Header.Set("Content-Type", "application/x-git-receive-pack-request")
		if t.Proxy != nil {
			t.ProxyConnectHeader.Set("Content-Type", "application/x-git-receive-pack-request")
		}

	default:
		err = errors.New("unknown action")
	}

	if err != nil {
		return nil, nil, err
	}

	// Apply authentication and TLS settings to the HTTP transport.
	if authOpts != nil {
		if len(authOpts.Username) > 0 {
			req.SetBasicAuth(authOpts.Username, authOpts.Password)
		}
		if len(authOpts.CAFile) > 0 {
			certPool := x509.NewCertPool()
			if ok := certPool.AppendCertsFromPEM(authOpts.CAFile); !ok {
				return nil, nil, fmt.Errorf("PEM CA bundle could not be appended to x509 certificate pool")
			}
			t.TLSClientConfig = &tls.Config{
				RootCAs: certPool,
			}
		}
	}

	req.Header.Set("User-Agent", "git/2.0 (flux-libgit2)")
	if t.Proxy != nil {
		t.ProxyConnectHeader.Set("User-Agent", "git/2.0 (flux-libgit2)")
	}
	return client, req, nil
}

func (t *httpSmartSubtransport) Close() error {
	t.logger.V(logger.TraceLevel).Info("httpSmartSubtransport.Close()")
	return nil
}

func (t *httpSmartSubtransport) Free() {
	t.logger.V(logger.TraceLevel).Info("httpSmartSubtransport.Free()")

	if t.httpTransport != nil {
		t.logger.V(logger.TraceLevel).Info("release http transport back to pool")

		pool.Release(t.httpTransport)
		t.httpTransport = nil
	}
}

type httpSmartSubtransportStream struct {
	owner       *httpSmartSubtransport
	client      *http.Client
	req         *http.Request
	resp        *http.Response
	reader      *io.PipeReader
	writer      *io.PipeWriter
	sentRequest bool
	recvReply   sync.WaitGroup
	httpError   error
	m           sync.RWMutex
}

func newManagedHttpStream(owner *httpSmartSubtransport, req *http.Request, client *http.Client) *httpSmartSubtransportStream {
	r, w := io.Pipe()
	return &httpSmartSubtransportStream{
		owner:  owner,
		client: client,
		req:    req,
		reader: r,
		writer: w,
	}
}

func (self *httpSmartSubtransportStream) Read(buf []byte) (int, error) {
	if !self.sentRequest {
		self.recvReply.Add(1)
		if err := self.sendRequest(); err != nil {
			return 0, err
		}
	}

	if err := self.writer.Close(); err != nil {
		return 0, err
	}

	self.recvReply.Wait()

	self.m.RLock()
	err := self.httpError
	self.m.RUnlock()

	if err != nil {
		return 0, self.httpError
	}
	return self.resp.Body.Read(buf)
}

func (self *httpSmartSubtransportStream) Write(buf []byte) (int, error) {
	self.m.RLock()
	err := self.httpError
	self.m.RUnlock()

	if err != nil {
		return 0, self.httpError
	}
	return self.writer.Write(buf)
}

func (self *httpSmartSubtransportStream) Free() {
	if self.resp != nil {
		self.owner.logger.V(logger.TraceLevel).Info("httpSmartSubtransportStream.Free()")

		if self.resp.Body != nil {
			// ensure body is fully processed and closed
			// for increased likelihood of transport reuse in HTTP/1.x.
			// it should not be a problem to do this more than once.
			if _, err := io.Copy(io.Discard, self.resp.Body); err != nil {
				self.owner.logger.V(logger.TraceLevel).Error(err, "cannot discard response body")
			}

			if err := self.resp.Body.Close(); err != nil {
				self.owner.logger.V(logger.TraceLevel).Error(err, "cannot close response body")
			}
		}
	}
}

func (self *httpSmartSubtransportStream) sendRequestBackground() {
	go func() {
		err := self.sendRequest()

		self.m.Lock()
		self.httpError = err
		self.m.Unlock()
	}()
	self.sentRequest = true
}

func (self *httpSmartSubtransportStream) sendRequest() error {
	defer self.recvReply.Done()
	self.resp = nil

	var resp *http.Response
	var err error
	var content []byte

	for {
		req := &http.Request{
			Method: self.req.Method,
			URL:    self.req.URL,
			Header: self.req.Header,
		}
		if req.Method == "POST" {
			if len(content) == 0 {
				// a copy of the request body needs to be saved so
				// it can be reused in case of redirects.
				if content, err = io.ReadAll(self.reader); err != nil {
					return err
				}
			}
			req.Body = io.NopCloser(bytes.NewReader(content))
			req.ContentLength = -1
		}

		self.owner.logger.V(logger.TraceLevel).Info("new request", "method", req.Method, "postUrl", req.URL)
		resp, err = self.client.Do(req)
		if err != nil {
			return err
		}

		// GET requests will be automatically redirected.
		// POST require the new destination, and also the body content.
		if req.Method == "POST" && resp.StatusCode >= 301 && resp.StatusCode <= 308 {
			// ensure body is fully processed and closed
			// for increased likelihood of transport reuse in HTTP/1.x.
			_, _ = io.Copy(io.Discard, resp.Body) // errors can be safely ignored

			if err := resp.Body.Close(); err != nil {
				return err
			}

			// The next try will go against the new destination
			self.req.URL, err = resp.Location()
			if err != nil {
				return err
			}

			continue
		}

		// for HTTP 200, the response will be cleared up by Free()
		if resp.StatusCode == http.StatusOK {
			break
		}

		// ensure body is fully processed and closed
		// for increased likelihood of transport reuse in HTTP/1.x.
		_, _ = io.Copy(io.Discard, resp.Body) // errors can be safely ignored
		if err := resp.Body.Close(); err != nil {
			return err
		}

		return fmt.Errorf("unhandled HTTP error %s", resp.Status)
	}

	self.resp = resp
	self.sentRequest = true
	return nil
}