istio.io/istio@v0.0.0-20240520182934-d79c90f27776/pkg/config/validation/header_value_validator.go (about)

     1  // Copyright Istio Authors
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package validation
    16  
    17  import (
    18  	"errors"
    19  	"fmt"
    20  )
    21  
    22  type ParserState int32
    23  
    24  const (
    25  	LiteralParserState                   ParserState = iota // processing literal data
    26  	VariableNameParserState                                 // consuming a %VAR% name
    27  	ExpectArrayParserState                                  // expect starting [ in %VAR([...])%
    28  	ExpectStringParserState                                 // expect starting " in array of strings
    29  	StringParserState                                       // consuming an array element string
    30  	ExpectArrayDelimiterOrEndParserState                    // expect array delimiter (,) or end of array (])
    31  	ExpectArgsEndParserState                                // expect closing ) in %VAR(...)%
    32  	ExpectVariableEndParserState                            // expect closing % in %VAR(...)%
    33  )
    34  
    35  // validateHeaderValue is golang port version of
    36  // https://github.com/envoyproxy/envoy/blob/master/source/common/router/header_parser.cc#L73
    37  func validateHeaderValue(headerValue string) error {
    38  	if headerValue == "" {
    39  		return nil
    40  	}
    41  
    42  	var (
    43  		pos   = 0
    44  		state = LiteralParserState
    45  	)
    46  
    47  	for pos < len(headerValue) {
    48  		ch := headerValue[pos]
    49  		hasNextCh := (pos + 1) < len(headerValue)
    50  
    51  		switch state {
    52  		case LiteralParserState:
    53  			// Searching for start of %VARIABLE% expression.
    54  			if ch != '%' {
    55  				break
    56  			}
    57  
    58  			if !hasNextCh {
    59  				return errors.New("invalid header configuration. Un-escaped %")
    60  			}
    61  
    62  			if headerValue[pos+1] == '%' {
    63  				// Escaped %, skip next character.
    64  				pos++
    65  				break
    66  			}
    67  
    68  			// Un-escaped %: start of variable name. Create a formatter for preceding characters, if any.
    69  			state = VariableNameParserState
    70  
    71  		case VariableNameParserState:
    72  			// Consume "VAR" from "%VAR%" or "%VAR(...)%"
    73  			if ch == '%' {
    74  				state = LiteralParserState
    75  				break
    76  			}
    77  
    78  			if ch == '(' {
    79  				// Variable with arguments, search for start of arg array.
    80  				state = ExpectArrayParserState
    81  			}
    82  
    83  		case ExpectArrayParserState:
    84  			// Skip over whitespace searching for the start of JSON array args.
    85  			if ch == '[' {
    86  				// Search for first argument string
    87  				state = ExpectStringParserState
    88  			} else if !isSpace(ch) {
    89  				// Consume it as a string argument.
    90  				state = StringParserState
    91  			}
    92  
    93  		case ExpectArrayDelimiterOrEndParserState:
    94  			// Skip over whitespace searching for a comma or close bracket.
    95  			if ch == ',' {
    96  				state = ExpectStringParserState
    97  			} else if ch == ']' {
    98  				state = ExpectArgsEndParserState
    99  			} else if !isSpace(ch) {
   100  				return errors.New("invalid header configuration. Expecting ',', ']', or whitespace")
   101  			}
   102  
   103  		case ExpectStringParserState:
   104  			// Skip over whitespace looking for the starting quote of a JSON string.
   105  			if ch == '"' {
   106  				state = StringParserState
   107  			} else if !isSpace(ch) {
   108  				return errors.New("invalid header configuration. Expecting '\"'")
   109  			}
   110  
   111  		case StringParserState:
   112  			// Consume a JSON string (ignoring backslash-escaped chars).
   113  			if ch == '\\' {
   114  				if !hasNextCh {
   115  					return errors.New("invalid header configuration. Un-terminated backslash in JSON string")
   116  				}
   117  
   118  				// Skip escaped char.
   119  				pos++
   120  			} else if ch == ')' {
   121  				state = ExpectVariableEndParserState
   122  			} else if ch == '"' {
   123  				state = ExpectArrayDelimiterOrEndParserState
   124  			}
   125  
   126  		case ExpectArgsEndParserState:
   127  			// Search for the closing paren of a %VAR(...)% expression.
   128  			if ch == ')' {
   129  				state = ExpectVariableEndParserState
   130  			} else if !isSpace(ch) {
   131  				return errors.New("invalid header configuration. Expecting ')' or whitespace after '{}', but found '{}'")
   132  			}
   133  
   134  		case ExpectVariableEndParserState:
   135  			// Search for closing % of a %VAR(...)% expression
   136  			if ch == '%' {
   137  				state = LiteralParserState
   138  				break
   139  			}
   140  
   141  			if !isSpace(ch) {
   142  				return errors.New("invalid header configuration. Expecting '%' or whitespace after")
   143  			}
   144  		}
   145  
   146  		pos++
   147  	}
   148  
   149  	if state != LiteralParserState {
   150  		// Parsing terminated mid-variable.
   151  		return fmt.Errorf("invalid header configuration. Un-terminated variable expression '%s'", headerValue)
   152  	}
   153  
   154  	return nil
   155  }
   156  
   157  func isSpace(chr byte) bool {
   158  	return chr == ' '
   159  }