docs: Presentation Exchange - adds samples

Signed-off-by: Andrii Soluk <isoluchok@gmail.com>

pkg/doc/presexch/README.md

@@ -0,0 +1,104 @@
+# Presentation Exchange
+
+This document shows how to use [Presentation Exchange](https://identity.foundation/presentation-exchange) by examples.
+Code examples can be found [here](example_test.go).
+
+1. This example demonstrates `predicate` and `limit_disclosure` usage.
+   The `presentation definition` below requires field `age` to be greater or equal to 18.
+   Also, we have `limit_disclosure=true` which requires that output data is limited to the entries specified in the `fields` property.
+   The `predicate` means that the result should be expressed as a boolean value.
+```json
+{
+  "id": "31e2f0f1-6b70-411d-b239-56aed5321884",
+  "purpose": "To sell you a drink we need to know that you are an adult.",
+  "input_descriptors": [
+    {
+      "id": "867bfe7a-5b91-46b2-9ba4-70028b8d9cc8",
+      "purpose": "Your age should be greater or equal to 18.",
+      "schema": [
+        {
+          "uri": "https://www.w3.org/TR/vc-data-model/#types"
+        }
+      ],
+      "constraints": {
+        "limit_disclosure": true,
+        "fields": [
+          {
+            "path": [
+              "$.age"
+            ],
+            "filter": {
+              "type": "integer",
+              "minimum": 18
+            },
+            "predicate": "required"
+          }
+        ]
+      }
+    }
+  ]
+}
+```
+Let's say we have such a credential in our database.
+```json
+{
+  "@context": [
+    "https://www.w3.org/2018/credentials/v1"
+  ],
+  "age": 21,
+  "credentialSchema": [
+    {
+      "id": "https://www.w3.org/TR/vc-data-model/#types"
+    }
+  ],
+  "first_name": "Jesse",
+  "id": "2dc74354-e965-4883-be5e-bfec48bf60c7",
+  "issuer": "",
+  "last_name": "Pinkman",
+  "type": "VerifiableCredential"
+}
+```
+As a result, we will have the following `verifiable presentation`:
+```json
+{
+  "@context": [
+    "https://www.w3.org/2018/credentials/v1",
+    "https://identity.foundation/presentation-exchange/submission/v1"
+  ],
+  "presentation_submission": {
+    "id": "accd5adf-1dbf-4ed9-9ba2-d687476126cb",
+    "definition_id": "31e2f0f1-6b70-411d-b239-56aed5321884",
+    "descriptor_map": [
+      {
+        "id": "867bfe7a-5b91-46b2-9ba4-70028b8d9cc8",
+        "format": "ldp_vp",
+        "path": "$.verifiableCredential[0]"
+      }
+    ]
+  },
+  "type": [
+    "VerifiablePresentation",
+    "PresentationSubmission"
+  ],
+  "verifiableCredential": [
+    {
+      "@context": [
+        "https://www.w3.org/2018/credentials/v1"
+      ],
+      "age": true,
+      "credentialSchema": [
+        {
+          "id": "https://www.w3.org/TR/vc-data-model/#types"
+        }
+      ],
+      "credentialSubject": null,
+      "id": "2dc74354-e965-4883-be5e-bfec48bf60c7",
+      "issuer": "",
+      "type": "VerifiableCredential"
+    }
+  ]
+}
+```
+
+As you can see the VP has a credential without `first_name` and `last_name` (because of `limit_disclosure`).
+Also, instead of `age`, we have a boolean value (because of `predicate`).

pkg/doc/presexch/api_test.go

@@ -4,7 +4,7 @@ Copyright SecureKey Technologies Inc. All Rights Reserved.
 SPDX-License-Identifier: Apache-2.0
 */
 
-package presexch
+package presexch_test
 
 import (
 	"encoding/json"
@@ -17,6 +17,7 @@ import (
 	"github.com/piprate/json-gold/ld"
 	"github.com/stretchr/testify/require"
 
+	. "github.com/hyperledger/aries-framework-go/pkg/doc/presexch"
 	"github.com/hyperledger/aries-framework-go/pkg/doc/util"
 	"github.com/hyperledger/aries-framework-go/pkg/doc/verifiable"
 )

pkg/doc/presexch/definition.go

@@ -11,6 +11,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"sort"
 	"strings"
 
 	"github.com/PaesslerAG/jsonpath"
@@ -33,6 +34,8 @@ const (
 	Required Preference = "required"
 	// Preferred predicate`s value.
 	Preferred Preference = "preferred"
+
+	tmpEnding = "tmp_unique_id_"
 )
 
 // nolint: gochecknoglobals
@@ -318,7 +321,7 @@ func (pd *PresentationDefinition) CreateVP(credentials ...*verifiable.Credential
 
 	credentials, descriptors := merge(result)
 	vp.CustomFields = verifiable.CustomFields{
-		submissionProperty: PresentationSubmission{
+		submissionProperty: &PresentationSubmission{
 			ID:            uuid.New().String(),
 			DefinitionID:  pd.ID,
 			DescriptorMap: descriptors,
@@ -530,7 +533,7 @@ func filterConstraints(constraints *Constraints, creds []*verifiable.Credential)
 
 			if constraints.LimitDisclosure {
 				template, err = json.Marshal(map[string]interface{}{
-					"id":                credential.ID,
+					"id":                tmpID(credential.ID),
 					"credentialSchema":  credential.Schemas,
 					"type":              credential.Types,
 					"@context":          credential.Context,
@@ -557,6 +560,19 @@ func filterConstraints(constraints *Constraints, creds []*verifiable.Credential)
 	return result, nil
 }
 
+func tmpID(id string) string {
+	return id + tmpEnding + uuid.New().String()
+}
+
+func trimTmpID(id string) string {
+	idx := strings.Index(id, tmpEnding)
+	if idx == -1 {
+		return id
+	}
+
+	return id[:idx]
+}
+
 func createNewCredential(fs []*Field, src, limitedCred []byte) (*verifiable.Credential, error) {
 	for _, f := range fs {
 		paths, err := jsonpathkeys.ParsePaths(f.Path...)
@@ -676,9 +692,19 @@ func merge(setOfCredentials map[string][]*verifiable.Credential) ([]*verifiable.
 		descriptors []*InputDescriptorMapping
 	)
 
-	for descriptorID, credentials := range setOfCredentials {
+	keys := make([]string, 0, len(setOfCredentials))
+	for k := range setOfCredentials {
+		keys = append(keys, k)
+	}
+
+	sort.Strings(keys)
+
+	for _, descriptorID := range keys {
+		credentials := setOfCredentials[descriptorID]
+
 		for _, credential := range credentials {
 			if _, ok := setOfCreds[credential.ID]; !ok {
+				credential.ID = trimTmpID(credential.ID)
 				result = append(result, credential)
 				setOfCreds[credential.ID] = len(descriptors)
 			}
@@ -694,9 +720,17 @@ func merge(setOfCredentials map[string][]*verifiable.Credential) ([]*verifiable.
 		}
 	}
 
+	sort.Sort(byID(descriptors))
+
 	return result, descriptors
 }
 
+type byID []*InputDescriptorMapping
+
+func (a byID) Len() int           { return len(a) }
+func (a byID) Less(i, j int) bool { return a[i].ID < a[j].ID }
+func (a byID) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+
 func credentialsToInterface(credentials []*verifiable.Credential) []interface{} {
 	var result []interface{}
 	for i := range credentials {