| 1 | package tinygit |
| 2 | |
| 3 | import ( |
| 4 | "bufio" |
| 5 | "context" |
| 6 | "crypto/rand" |
| 7 | "crypto/subtle" |
| 8 | "encoding/base64" |
| 9 | "encoding/hex" |
| 10 | "errors" |
| 11 | "io" |
| 12 | "net" |
| 13 | "net/http" |
| 14 | "strings" |
| 15 | "sync" |
| 16 | "sync/atomic" |
| 17 | ) |
| 18 | |
| 19 | var errRepairByteLimit = errors.New("PR repair transfer exceeds byte limit" ) |
| 20 | |
| 21 | // A single budget covers every connection, ref and source in one repair. |
| 22 | // Counting tunneled TLS bytes also bounds HTTPS without terminating its TLS. |
| 23 | type byteBudget struct{ used atomic.Int64 } |
| 24 | |
| 25 | func (b *byteBudget) take(wanted, limit int64) int64 { |
| 26 | for { |
| 27 | old := b.used.Load() |
| 28 | allowed := min(wanted, max(0, limit-old)) |
| 29 | if b.used.CompareAndSwap(old, old+allowed) { |
| 30 | return allowed |
| 31 | } |
| 32 | } |
| 33 | } |
| 34 | |
| 35 | type repairProxy struct { |
| 36 | listener net.Listener |
| 37 | // credential is the Proxy-Authorization value Git presents. The listener |
| 38 | // is loopback only, but other local processes cannot borrow the tunnel. |
| 39 | credential string |
| 40 | url string |
| 41 | ctx context.Context |
| 42 | cancel context.CancelFunc |
| 43 | budget *byteBudget |
| 44 | limit int64 |
| 45 | targetIP string |
| 46 | targetHost string |
| 47 | targetPort string |
| 48 | mu sync.Mutex |
| 49 | connections map[net.Conn]struct{} |
| 50 | closeOnce sync.Once |
| 51 | } |
| 52 | |
| 53 | func newRepairProxy(ctx context.Context, targetIP, targetHost, targetPort string, budget *byteBudget, limit int64) (*repairProxy, error) { |
| 54 | listener, err := net.Listen("tcp" , "127.0.0.1:0" ) |
| 55 | if err != nil { |
| 56 | return nil, err |
| 57 | } |
| 58 | var secret [16]byte |
| 59 | if _, err := rand.Read(secret[:]); err != nil { |
| 60 | _ = listener.Close() |
| 61 | return nil, err |
| 62 | } |
| 63 | proxyCtx, cancel := context.WithCancel(ctx) |
| 64 | token := hex.EncodeToString(secret[:]) |
| 65 | credential := "Basic " + base64.StdEncoding.EncodeToString([]byte("tiny:" +token)) |
| 66 | p := &repairProxy{listener: listener, credential: credential, ctx: proxyCtx, cancel: cancel, budget: budget, limit: limit, targetIP: targetIP, targetHost: targetHost, targetPort: targetPort, connections: make(map[net.Conn]struct{})} |
| 67 | p.url = "http://tiny:" + token + "@" + listener.Addr().String() |
| 68 | context.AfterFunc(proxyCtx, func() { _ = p.Close() }) |
| 69 | go p.serve() |
| 70 | return p, nil |
| 71 | } |
| 72 | |
| 73 | func (p *repairProxy) URL() string { return p.url } |
| 74 | |
| 75 | func (p *repairProxy) Close() error { |
| 76 | p.closeOnce.Do(func() { |
| 77 | p.cancel() |
| 78 | _ = p.listener.Close() |
| 79 | p.mu.Lock() |
| 80 | defer p.mu.Unlock() |
| 81 | for conn := range p.connections { |
| 82 | _ = conn.Close() |
| 83 | } |
| 84 | }) |
| 85 | return nil |
| 86 | } |
| 87 | |
| 88 | func (p *repairProxy) track(conn net.Conn) bool { |
| 89 | p.mu.Lock() |
| 90 | defer p.mu.Unlock() |
| 91 | if p.ctx.Err() != nil { |
| 92 | _ = conn.Close() |
| 93 | return false |
| 94 | } |
| 95 | p.connections[conn] = struct{}{} |
| 96 | return true |
| 97 | } |
| 98 | |
| 99 | func (p *repairProxy) release(conn net.Conn) { |
| 100 | _ = conn.Close() |
| 101 | p.mu.Lock() |
| 102 | delete(p.connections, conn) |
| 103 | p.mu.Unlock() |
| 104 | } |
| 105 | |
| 106 | func (p *repairProxy) serve() { |
| 107 | for { |
| 108 | conn, err := p.listener.Accept() |
| 109 | if err != nil { |
| 110 | return |
| 111 | } |
| 112 | if p.track(conn) { |
| 113 | go p.handle(conn) |
| 114 | } |
| 115 | } |
| 116 | } |
| 117 | |
| 118 | func (p *repairProxy) handle(client net.Conn) { |
| 119 | defer p.release(client) |
| 120 | reader := bufio.NewReader(client) |
| 121 | request, err := http.ReadRequest(reader) |
| 122 | if err != nil { |
| 123 | return |
| 124 | } |
| 125 | if request.Method != http.MethodConnect && request.Method != http.MethodGet && request.Method != http.MethodPost { |
| 126 | return |
| 127 | } |
| 128 | if subtle.ConstantTimeCompare([]byte(request.Header.Get("Proxy-Authorization" )), []byte(p.credential)) != 1 { |
| 129 | _, _ = io.WriteString(client, "HTTP/1.1 407 Proxy Authentication Required\r\nProxy-Authenticate: Basic realm=\"tiny\"\r\nContent-Length: 0\r\nConnection: close\r\n\r\n" ) |
| 130 | return |
| 131 | } |
| 132 | host := request.URL.Hostname() |
| 133 | port := request.URL.Port() |
| 134 | if port == "" { |
| 135 | port = "80" |
| 136 | if request.Method == http.MethodConnect || request.URL.Scheme == "https" { |
| 137 | port = "443" |
| 138 | } |
| 139 | } |
| 140 | if !strings.EqualFold(host, p.targetHost) || port != p.targetPort { |
| 141 | return |
| 142 | } |
| 143 | if p.budget.used.Load() >= p.limit { |
| 144 | return |
| 145 | } |
| 146 | // Dial only the already validated address. The proxy never resolves a |
| 147 | // host supplied by the client and never follows HTTP redirects. |
| 148 | upstream, err := (&net.Dialer{}).DialContext(p.ctx, "tcp" , net.JoinHostPort(p.targetIP, p.targetPort)) |
| 149 | if err != nil { |
| 150 | return |
| 151 | } |
| 152 | if !p.track(upstream) { |
| 153 | return |
| 154 | } |
| 155 | defer p.release(upstream) |
| 156 | if request.Method == http.MethodConnect { |
| 157 | if _, err := io.WriteString(repairBudgetWriter{p, client}, "HTTP/1.1 200 Connection Established\r\n\r\n" ); err != nil { |
| 158 | return |
| 159 | } |
| 160 | done := make(chan struct{}, 2) |
| 161 | go func() { _, _ = io.Copy(repairBudgetWriter{p, client}, upstream); done <- struct{}{} }() |
| 162 | // Keep bytes already buffered while reading CONNECT (e.g., a TLS |
| 163 | // handshake sent in the same write as the request). |
| 164 | go func() { _, _ = io.Copy(repairBudgetWriter{p, upstream}, reader); done <- struct{}{} }() |
| 165 | select { |
| 166 | case <-done: |
| 167 | case <-p.ctx.Done(): |
| 168 | } |
| 169 | return |
| 170 | } |
| 171 | request.RequestURI = "" |
| 172 | request.Close = true |
| 173 | if err := request.Write(repairBudgetWriter{p, upstream}); err != nil { |
| 174 | return |
| 175 | } |
| 176 | _, _ = io.Copy(repairBudgetWriter{p, client}, upstream) |
| 177 | } |
| 178 | |
| 179 | type repairBudgetWriter struct { |
| 180 | proxy *repairProxy |
| 181 | dst io.Writer |
| 182 | } |
| 183 | |
| 184 | func (w repairBudgetWriter) Write(data []byte) (int, error) { |
| 185 | allowed := w.proxy.budget.take(int64(len(data)), w.proxy.limit) |
| 186 | n, err := w.dst.Write(data[:allowed]) |
| 187 | if err == nil && allowed < int64(len(data)) { |
| 188 | err = errRepairByteLimit |
| 189 | } |
| 190 | return n, err |
| 191 | } |