Added a new method SetUserMetadata to the PostPolicy (#839)

docs/API.md

@@ -1349,6 +1349,9 @@ policy.SetContentType("image/png")
 // Only allow content size in range 1KB to 1MB.
 policy.SetContentLengthRange(1024, 1024*1024)
 
+// Add a user metadata using the key "custom" and value "user"
+policy.SetUserMetadata("custom", "user")
+
 // Get the POST form key/value object:
 
 url, formData, err := minioClient.PresignedPostPolicy(policy)

functional_tests.go

@@ -2053,6 +2053,8 @@ func testPresignedPostPolicy() {
 	defer reader.Close()
 
 	objectName := randString(60, rand.NewSource(time.Now().UnixNano()), "")
+	metadataKey := randString(60, rand.NewSource(time.Now().UnixNano()), "")
+	metadataValue := randString(60, rand.NewSource(time.Now().UnixNano()), "")
 
 	buf, err := ioutil.ReadAll(reader)
 	if err != nil {
@@ -2089,12 +2091,16 @@ func testPresignedPostPolicy() {
 	if err := policy.SetContentLengthRange(1024*1024, 1024); err == nil {
 		failureLog(function, args, startTime, "", "SetContentLengthRange did not fail for invalid conditions", err).Fatal()
 	}
+	if err := policy.SetUserMetadata("", ""); err == nil {
+		failureLog(function, args, startTime, "", "SetUserMetadata did not fail for invalid conditions", err).Fatal()
+	}
 
 	policy.SetBucket(bucketName)
 	policy.SetKey(objectName)
 	policy.SetExpires(time.Now().UTC().AddDate(0, 0, 10)) // expires in 10 days
 	policy.SetContentType("binary/octet-stream")
 	policy.SetContentLengthRange(10, 1024*1024)
+	policy.SetUserMetadata(metadataKey, metadataValue)
 	args["policy"] = policy.String()
 
 	presignedPostPolicyURL, formData, err := c.PresignedPostPolicy(policy)

post-policy.go

@@ -167,6 +167,28 @@ func (p *PostPolicy) SetSuccessStatusAction(status string) error {
 	return nil
 }
 
+// SetUserMetadata - Set user metadata as a key/value couple.
+// Can be retrieved through a HEAD request or an event.
+func (p *PostPolicy) SetUserMetadata(key string, value string) error {
+	if strings.TrimSpace(key) == "" || key == "" {
+		return ErrInvalidArgument("Key is empty")
+	}
+	if strings.TrimSpace(value) == "" || value == "" {
+		return ErrInvalidArgument("Value is empty")
+	}
+	headerName := fmt.Sprintf("x-amz-meta-%s", key)
+	policyCond := policyCondition{
+		matchType: "eq",
+		condition: fmt.Sprintf("$%s", headerName),
+		value:     value,
+	}
+	if err := p.addNewPolicy(policyCond); err != nil {
+		return err
+	}
+	p.formData[headerName] = value
+	return nil
+}
+
 // addNewPolicy - internal helper to validate adding new policies.
 func (p *PostPolicy) addNewPolicy(policyCond policyCondition) error {
 	if policyCond.matchType == "" || policyCond.condition == "" || policyCond.value == "" {