Pact Request and Response Matching

This library implements the core matching logic required for matching HTTP requests and responses. It is based on the V3 pact specification.

Online rust docs

To use it

To use it, add it to your dependencies in your cargo manifest:

[dependencies]
pact_matching = "1.1"

This crate provides three functions: match_request, match_response and match_message. These functions take an expected and actual request, response or message model from the pact_models crate, and return a vector of mismatches.

To compare any incoming request, it first needs to be converted to a pact_models::Request and then can be compared. Same for any response.

Crate features

All features are enabled by default

• datetime: Enables support of date and time expressions and generators. This will add the chronos crate as a dependency.
• xml: Enables support for parsing XML documents. This feature will add the sxd-document crate as a dependency.
• plugins: Enables support for using plugins. This feature will add the pact-plugin-driver crate as a dependency.
• multipart: Enables support for MIME multipart bodies. This feature will add the multer crate as a dependency.

Reading and writing Pact files

The Pact struct in the pact_models crate has methods to read and write pact JSON files. It supports all the specification versions up to V4, but will convert a V1, V1.1 and V2 spec file to the V3 format.

Matching request and response parts

V3 specification matching is supported for both JSON and XML bodies, headers, query strings and request paths.

To understand the basic rules of matching, see Gotchas. For example test cases for matching, see the Pact Specification Project, version 3.

By default, Pact will use string equality matching following Postel's Law. This means that for an actual value to match an expected one, they both must consist of the same sequence of characters. For collections (basically Maps and Lists), they must have the same elements that match in the same sequence, with cases where the additional elements in an actual Map are ignored.

Matching rules can be defined for both request and response elements based on a pseudo JSON-Path syntax.

Matching Bodies

For the most part, matching involves matching request and response bodies in JSON or XML format. Other formats will either have their own matching rules, or will follow the JSON one.

JSON body matching rules

Bodies consist of Objects (Maps of Key-Value pairs), Arrays (Lists) and values (Strings, Numbers, true, false, null). Body matching rules are prefixed with $..

The following method is used to determine if two bodies match:

1. If both the actual body and expected body are empty, the bodies match.
2. If the actual body is non-empty, and the expected body empty, the bodies match.
3. If the actual body is empty, and the expected body non-empty, the bodies don't match.
4. Otherwise do a comparison on the contents of the bodies.

For the body contents comparison:

1. If the actual and expected values are both Objects, compare as Maps.
2. If the actual and expected values are both Arrays, compare as Lists.
3. If the expected value is an Object, and the actual is not, they don't match.
4. If the expected value is an Array, and the actual is not, they don't match.
5. Otherwise, compare the values

For comparing Maps

1. If the actual map is non-empty while the expected is empty, they don't match.
2. If we allow unexpected keys, and the number of expected keys is greater than the actual keys, they don't match.
3. If we don't allow unexpected keys, and the expected and actual maps don't have the same number of keys, they don't match.
4. Otherwise, for each expected key and value pair:
   1. if the actual map contains the key, compare the values
   2. otherwise they don't match

Postel's law governs if we allow unexpected keys or not.

For comparing lists

1. If there is a body matcher defined that matches the path to the list, default to that matcher and then compare the list contents.
2. If the expected list is empty and the actual one is not, the lists don't match.
3. Otherwise
   1. compare the list sizes
   2. compare the list contents

For comparing list contents

1. For each value in the expected list:
   1. If the index of the value is less than the actual list's size, compare the value with the actual value at the same index using the method for comparing values.
   2. Otherwise the value doesn't match

For comparing values

1. If there is a matcher defined that matches the path to the value, default to that matcher
2. Otherwise compare the values using equality.

XML body matching rules

Bodies consist of a root element, Elements (Lists with children), Attributes (Maps) and values (Strings). Body matching rules are prefixed with $..

The following method is used to determine if two bodies match:

1. If both the actual body and expected body are empty, the bodies match.
2. If the actual body is non-empty, and the expected body empty, the bodies match.
3. If the actual body is empty, and the expected body non-empty, the bodies don't match.
4. Otherwise do a comparison on the contents of the bodies.

For the body contents comparison:

Start by comparing the root element.

For comparing elements

1. If there is a body matcher defined that matches the path to the element, default to that matcher on the elements name or children.
2. Otherwise the elements match if they have the same name.

Then, if there are no mismatches:

1. compare the attributes of the element
2. compare the child elements
3. compare the text nodes

For comparing attributes

Attributes are treated as a map of key-value pairs.

1. If the actual map is non-empty while the expected is empty, they don't match.
2. If we allow unexpected keys, and the number of expected keys is greater than the actual keys, they don't match.
3. If we don't allow unexpected keys, and the expected and actual maps don't have the same number of keys, they don't match.

Then, for each expected key and value pair:

1. if the actual map contains the key, compare the values
2. otherwise they don't match

Postel's law governs if we allow unexpected keys or not. Note for matching paths, attribute names are prefixed with an @.

For comparing child elements

1. If there is a matcher defined for the path to the child elements, then pad out the expected child elements to have the same size as the actual child elements.
2. Otherwise
   1. If the actual children is non-empty while the expected is empty, they don't match.
   2. If we allow unexpected keys, and the number of expected children is greater than the actual children, they don't match.
   3. If we don't allow unexpected keys, and the expected and actual children don't have the same number of elements, they don't match.

Then, for each expected and actual element pair, compare them using the rules for comparing elements.

For comparing text nodes

Text nodes are combined into a single string and then compared as values.

1. If there is a matcher defined that matches the path to the text node (text node paths end with #text), default to that matcher
2. Otherwise compare the text using equality.

For comparing values

1. If there is a matcher defined that matches the path to the value, default to that matcher
2. Otherwise compare the values using equality.

Matching Paths

Paths are matched by the following:

1. If there is a matcher defined for path, default to that matcher.
2. Otherwise paths are compared as Strings

Matching Queries

1. If the actual and expected query strings are empty, they match.
2. If the actual is not empty while the expected is, they don't match.
3. If the actual is empty while the expected is not, they don't match.
4. Otherwise convert both into a Map of keys mapped to a list values, and compare those.

Matching Query Maps

Query strings are parsed into a Map of keys mapped to lists of values. Key value pairs can be in any order, but when the same key appears more than once the values are compared in the order they appear in the query string.

Matching Headers

1. Do a case-insensitive sort of the headers by keys
2. For each expected header in the sorted list:
   1. If the actual headers contain that key, compare the header values
   2. Otherwise the header does not match

For matching header values:

1. If there is a matcher defined for header.<HEADER_KEY>, default to that matcher
2. Otherwise strip all whitespace after commas and compare the resulting strings.

Matching Request Headers

Request headers are matched by excluding the cookie header.

Matching Request cookies

If the list of expected cookies contains all the actual cookies, the cookies match.

Matching Status Codes

Status codes are compared as integer values.

Matching HTTP Methods

The actual and expected methods are compared as case-insensitive strings.

Matching Rules

Pact supports extending the matching rules on each type of object (Request or Response) with a matchingRules element in the pact file. This is a map of JSON path strings to a matcher. When an item is being compared, if there is an entry in the matching rules that corresponds to the path to the item, the comparison will be delegated to the defined matcher. Note that the matching rules cascade, so a rule can be specified on a value and will apply to all children of that value.

Matcher Path expressions

Pact does not support the full JSON path expressions, only ones that match the following rules:

1. All paths start with a dollar ($), representing the root.
2. All path elements are separated by periods (.), except array indices which use square brackets ([]).
3. Path elements represent keys.
4. A star (*) can be used to match all keys of a map or all items of an array (one level only).

So the expression $.item1.level[2].id will match the highlighted item in the following body:

{
  "item1": {
    "level": [
      {
        "id": 100
      },
      {
        "id": 101
      },
      {
        "id": 102 // <---- $.item1.level[2].id
      },
      {
        "id": 103
      }
    ]
  }
}

while $.*.level[*].id will match all the ids of all the levels for all items.

Matcher selection algorithm

Due to the star notation, there can be multiple matcher paths defined that correspond to an item. The first, most specific expression is selected by assigning weightings to each path element and taking the product of the weightings. The matcher with the path with the largest weighting is used.

• The root node ($) is assigned the value 2.
• Any path element that does not match is assigned the value 0.
• Any property name that matches a path element is assigned the value 2.
• Any array index that matches a path element is assigned the value 2.
• Any star (*) that matches a property or array index is assigned the value 1.
• Everything else is assigned the value 0.

So for the body with highlighted item:

{
  "item1": {
    "level": [
      {
        "id": 100
      },
      {
        "id": 101
      },
      {
        "id": 102 // <--- Item under consideration
      },
      {
        "id": 103
      }
    ]
  }
}

The expressions will have the following weightings:

So for the item with id 102, the matcher with path $.item1.level[1].id and weighting 32 will be selected.

Supported matchers

The following matchers are supported:

Matching Rule Definition Language

The matching rule definition language is a text format to specify the matching rules to be applied to data formats from plugins. It allows the matching rules to be applied without having to specify the specifics of the data format.

For example, they can equally be applied to very different data formats like Protobuf and CSV.

CSV:

"column:Date", "matching(datetime, 'yyyy-MM-dd','2000-01-01')"

Protobuf:

"contents": {
    "contentType": "notEmpty('application/json')",
    "content": "matching(contentType, 'application/json', '{}')",
    "contentTypeHint": "matching(equalTo, 'TEXT')"
}

Matching Rule Definition

Each matching rule definition is a comma-separated list of functions with a number of arguments within brackets. Most of the time only a single definition is required for a value, but in they case were more than one is required, they just need to be separated by a comma.

Matching functions

The main function is the matching function. This creates a matching rule based on a type and a number of values. The values required are dependent on the type of the matching rule.

For example, matching with a regular expression: matching(regex, '\\$(\\.\\w+)+', '$.test.one')

equalTo

Specifies that the attribute/field must be equal to the example value.

Parameters:

• example (Primitive value)

Example:

matching(equalTo, 'TEXT')

type

Specifies that the attribute/field must have the same type as the example value.

Parameters:

• example (Primitive value)

Example:

matching(type, 100)

number types (number, integer, decimal)

Specifies that the attribute/field must be a number type. number will match any numeric value, integer will match numeric values with no decimals (no significant figures after the decimal point) and decimal will match numeric values that have decimals (at least one significant figure after the decimal point).

Parameters:

• example (integer or decimal value)

Example:

matching(integer, 100)
matching(decimal, 100.1234)

date and time matchers (datetime, date, time)

Specifies that the string representation of the attribute/field must match the format specifier. These are based on the Java DateTimeFormatter.

Parameters:

• format (string)
• example (string)

Example:

matching(datetime, 'yyyy-MM-dd HH:mm:ss', '2021-10-07 13:00:13')
matching(date, 'yyyy-MM-dd', '2021-10-07')
matching(time, 'HH:mm:ss', '13:00:13')

Regex

Specifies that the string representation of the attribute/field must match the provided regular expression.

Parameters:

• regex (string)
• example (string)

Example:

matching(regex, '\w+ \w+', 'Hello World')

Include

Specifies that the string representation of the attribute/field must include the given string.

Parameters:

• example (string)

Example:

matching(include, 'Hello World')

Boolean

Specifies that the attribute/field must be a boolean value or its string representation must be the strings true or false.

Parameters:

• example (boolean)

Example:

matching(boolean, false)

Semver

Specifies that the string representation of the attribute/field must be a valid semantic version as per the semver specification.

Parameters:

• example (string)

Example:

matching(semver, '1.0.0')

Content Type

Specifies that the byte string representation of the attribute/field must match the given content type using a magic file number check. This compares the first few bytes with a database of rules to determine the type of the contents.

Parameters:

• content type in MIME format (string)
• example (string)

Example:

matching(contentType, 'application/json', '{}')

Content Type - Detection Mechanisms for Binary Content

pact_matching currently performs the following for matching Binary content-types

1. Determines expected Content-Type header requested by user in test
2. Read content buffer with infer library, and guess Content-Type based on magic bytes
3. If unsuccessful
   1. Read content buffer with tree_magic_mini library, and guess Content-Type based on shared-mime-info DB
      1. MagicDB is not shipped with pact_matching, due to GPL restrictions, users can add manually
         1. Linux Alpine - apk add shared-mime-info
         2. MacOS brew install shared-mime-info
            1. arm64 MacOS requires tree_magic_mini fork
         3. Linux - Debianapt-get install -y shared-mime-info
4. If either result returns text/plain, then manually read bytes using detect_content_type_from_bytes function in pact_models
5. If all of 2, 3, or 4 fails, then throw error, otherwise return Ok

Rust libraries used:

• https://github.com/mbrubeck/tree_magic
• https://github.com/bojand/infer

Matching an example type by reference

Type matching can also be specified by a reference to an example. References are defined by a dollar ($) followed by a string value. The string value must be the attribute/field name that contains the example type.

Parameters:

• reference name

Example:

matching($'items') // where items is the name of the example to match the types against

NotEmpty

Specifies that the attribute field must be present and contain a value (not null or an empty string).

Parameters:

• example (primitive value)

Example:

notEmpty('DateTime')

EachKey

Allows a matching rule definition to be applied to the keys in a map.

Parameters:

• definition* (comma-separated list of matching rule definitions)

Example:

eachKey(matching(regex, '\\$(\\.\\w+)+', '$.test.one'))

EachValue

Allows a matching rule definition to be applied to the values in a collection (list/array or map form).

Parameters:

• definition* (comma-separated list of matching rule definitions)

Example:

eachValue(matching($'items'))

Grammar

The grammar for the Matching Rule Definition Language (ANTLR 4 format)

grammar MatcherDefinition;

matchingDefinition :
    matchingDefinitionExp  ( COMMA matchingDefinitionExp  )* EOF
    ;

matchingDefinitionExp :
    (
      'matching' LEFT_BRACKET matchingRule RIGHT_BRACKET 
      | 'notEmpty' LEFT_BRACKET primitiveValue RIGHT_BRACKET 
      | 'eachKey' LEFT_BRACKET matchingDefinitionExp RIGHT_BRACKET 
      | 'eachValue' LEFT_BRACKET matchingDefinitionExp RIGHT_BRACKET 
    )
    ;

matchingRule :
  (
    ( 'equalTo' | 'type' ) COMMA primitiveValue )
  | 'number' COMMA ( DECIMAL_LITERAL | INTEGER_LITERAL ) 
  | 'integer' COMMA INTEGER_LITERAL 
  | 'decimal' COMMA DECIMAL_LITERAL 
  | ( 'datetime' | 'date' | 'time' ) COMMA string COMMA string 
  | 'regex' COMMA string COMMA string 
  | 'include' COMMA string 
  | 'boolean' COMMA BOOLEAN_LITERAL 
  | 'semver' COMMA string 
  | 'contentType' COMMA string COMMA string 
  | DOLLAR string 
  ;

primitiveValue :
  string 
  | DECIMAL_LITERAL
  | INTEGER_LITERAL
  | BOOLEAN_LITERAL
  ;

string :
  STRING_LITERAL 
  | 'null'
  ;

INTEGER_LITERAL : '-'? DIGIT+ ;
DECIMAL_LITERAL : '-'? DIGIT+ '.' DIGIT+ ;
fragment DIGIT  : [0-9] ;

LEFT_BRACKET    : '(' ;
RIGHT_BRACKET   : ')' ;
STRING_LITERAL  : '\'' (~['])* '\'' ;
BOOLEAN_LITERAL : 'true' | 'false' ;
COMMA           : ',' ;
DOLLAR          : '$';

WS : [ \t\n\r] + -> skip ;