github.com/psiphon-Labs/psiphon-tunnel-core@v2.0.28+incompatible/psiphon/common/parameters/frontingSpec.go (about)

     1  /*
     2   * Copyright (c) 2021, Psiphon Inc.
     3   * All rights reserved.
     4   *
     5   * This program is free software: you can redistribute it and/or modify
     6   * it under the terms of the GNU General Public License as published by
     7   * the Free Software Foundation, either version 3 of the License, or
     8   * (at your option) any later version.
     9   *
    10   * This program is distributed in the hope that it will be useful,
    11   * but WITHOUT ANY WARRANTY; without even the implied warranty of
    12   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    13   * GNU General Public License for more details.
    14   *
    15   * You should have received a copy of the GNU General Public License
    16   * along with this program.  If not, see <http://www.gnu.org/licenses/>.
    17   *
    18   */
    19  
    20  package parameters
    21  
    22  import (
    23  	"net"
    24  
    25  	"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/errors"
    26  	"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/prng"
    27  	regen "github.com/zach-klippenstein/goregen"
    28  )
    29  
    30  // FrontingSpecs is a list of domain fronting specs.
    31  type FrontingSpecs []*FrontingSpec
    32  
    33  // FrontingSpec specifies a domain fronting configuration, to be used with
    34  // MeekConn and MeekModePlaintextRoundTrip. In MeekModePlaintextRoundTrip, the
    35  // fronted origin is an arbitrary web server, not a Psiphon server. This
    36  // MeekConn mode requires HTTPS and server certificate validation:
    37  // VerifyServerName is required; VerifyPins is recommended. See also
    38  // psiphon.MeekConfig and psiphon.MeekConn.
    39  //
    40  // FrontingSpec.Addresses supports the functionality of both
    41  // ServerEntry.MeekFrontingAddressesRegex and
    42  // ServerEntry.MeekFrontingAddresses: multiple candidates are supported, and
    43  // each candidate may be a regex, or a static value (with regex syntax).
    44  type FrontingSpec struct {
    45  	FrontingProviderID string
    46  	Addresses          []string
    47  	DisableSNI         bool
    48  	VerifyServerName   string
    49  	VerifyPins         []string
    50  	Host               string
    51  }
    52  
    53  // SelectParameters selects fronting parameters from the given FrontingSpecs,
    54  // first selecting a spec at random. SelectParameters is similar to
    55  // psiphon.selectFrontingParameters, which operates on server entries.
    56  //
    57  // The return values are:
    58  // - Dial Address (domain or IP address)
    59  // - SNI (which may be transformed; unless it is "", which indicates omit SNI)
    60  // - VerifyServerName (see psiphon.CustomTLSConfig)
    61  // - VerifyPins (see psiphon.CustomTLSConfig)
    62  // - Host (Host header value)
    63  func (specs FrontingSpecs) SelectParameters() (
    64  	string, string, string, string, []string, string, error) {
    65  
    66  	if len(specs) == 0 {
    67  		return "", "", "", "", nil, "", errors.TraceNew("missing fronting spec")
    68  	}
    69  
    70  	spec := specs[prng.Intn(len(specs))]
    71  
    72  	if len(spec.Addresses) == 0 {
    73  		return "", "", "", "", nil, "", errors.TraceNew("missing fronting address")
    74  	}
    75  
    76  	frontingDialAddr, err := regen.Generate(
    77  		spec.Addresses[prng.Intn(len(spec.Addresses))])
    78  	if err != nil {
    79  		return "", "", "", "", nil, "", errors.Trace(err)
    80  	}
    81  
    82  	SNIServerName := frontingDialAddr
    83  	if spec.DisableSNI || net.ParseIP(frontingDialAddr) != nil {
    84  		SNIServerName = ""
    85  	}
    86  
    87  	return spec.FrontingProviderID,
    88  		frontingDialAddr,
    89  		SNIServerName,
    90  		spec.VerifyServerName,
    91  		spec.VerifyPins,
    92  		spec.Host,
    93  		nil
    94  }
    95  
    96  // Validate checks that the JSON values are well-formed.
    97  func (specs FrontingSpecs) Validate() error {
    98  
    99  	// An empty FrontingSpecs is allowed as a tactics setting, but
   100  	// SelectParameters will fail at runtime: code that uses FrontingSpecs must
   101  	// provide some mechanism -- or check for an empty FrontingSpecs -- to
   102  	// enable/disable features that use FrontingSpecs.
   103  
   104  	for _, spec := range specs {
   105  		if len(spec.FrontingProviderID) == 0 {
   106  			return errors.TraceNew("empty fronting provider ID")
   107  		}
   108  		if len(spec.Addresses) == 0 {
   109  			return errors.TraceNew("missing fronting addresses")
   110  		}
   111  		for _, addr := range spec.Addresses {
   112  			if len(addr) == 0 {
   113  				return errors.TraceNew("empty fronting address")
   114  			}
   115  		}
   116  		if len(spec.VerifyServerName) == 0 {
   117  			return errors.TraceNew("empty verify server name")
   118  		}
   119  		// An empty VerifyPins is allowed.
   120  		for _, pin := range spec.VerifyPins {
   121  			if len(pin) == 0 {
   122  				return errors.TraceNew("empty verify pin")
   123  			}
   124  		}
   125  		if len(spec.Host) == 0 {
   126  			return errors.TraceNew("empty fronting host")
   127  		}
   128  	}
   129  	return nil
   130  }