Supporting code for bucket-level CORS configuration settings

cors/cors.go

@@ -0,0 +1,179 @@
+// Copyright (c) 2015-2024 MinIO, Inc.
+//
+// # This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package cors
+
+import (
+	"encoding/xml"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+
+	"github.com/minio/pkg/v3/wildcard"
+)
+
+const defaultXMLNS = "http://s3.amazonaws.com/doc/2006-03-01/"
+
+var allowedCORSRuleMethods = map[string]bool{
+	http.MethodGet:    true,
+	http.MethodPut:    true,
+	http.MethodPost:   true,
+	http.MethodDelete: true,
+	http.MethodHead:   true,
+}
+
+// Config is the container for a CORS configuration for a bucket.
+type Config struct {
+	XMLNS     string   `xml:"xmlns,attr,omitempty"`
+	XMLName   xml.Name `xml:"CORSConfiguration"`
+	CORSRules []Rule   `xml:"CORSRule"`
+}
+
+// Rule is a single rule in a CORS configuration.
+type Rule struct {
+	AllowedHeader []string `xml:"AllowedHeader,omitempty"`
+	AllowedMethod []string `xml:"AllowedMethod,omitempty"`
+	AllowedOrigin []string `xml:"AllowedOrigin,omitempty"`
+	ExposeHeader  []string `xml:"ExposeHeader,omitempty"`
+	ID            string   `xml:"ID,omitempty"`
+	MaxAgeSeconds int      `xml:"MaxAgeSeconds,omitempty"`
+}
+
+// Validate checks the CORS configuration is valid. This has been implemented to return errors that can be transformed
+// to match the S3 API externally, while being slightly more informative internally using wrapping.
+// Validate copies S3 behavior, and validates one rule at a time, erroring on the first invalid one found.
+func (c *Config) Validate() error {
+	if len(c.CORSRules) == 0 {
+		return fmt.Errorf("no CORS rules found, %w", ErrMalformedXML{})
+	}
+	if len(c.CORSRules) > 100 {
+		return fmt.Errorf("too many CORS rules, max 100 allowed, got: %d, %w", len(c.CORSRules), ErrTooManyRules{})
+	}
+	for _, rule := range c.CORSRules {
+		// Origin validation
+		if len(rule.AllowedOrigin) == 0 {
+			return fmt.Errorf("no AllowedOrigin found in CORS rule, id: %s, %w", rule.ID, ErrMalformedXML{})
+		}
+		for _, origin := range rule.AllowedOrigin {
+			if strings.Count(origin, "*") > 1 {
+				return fmt.Errorf("origin %s in CORS rule, id: %s, %w", origin, rule.ID, ErrAllowedOriginWildcards{Origin: origin})
+			}
+		}
+
+		// Methods validation
+		if len(rule.AllowedMethod) == 0 {
+			return fmt.Errorf("no AllowedMethod found in CORS rule, id: %s, %w", rule.ID, ErrMalformedXML{})
+		}
+		for _, method := range rule.AllowedMethod {
+			if !allowedCORSRuleMethods[method] {
+				return fmt.Errorf("method %s in CORS rule, id: %s, %w", method, rule.ID, ErrInvalidMethod{Method: method})
+			}
+		}
+
+		// Headers validation
+		for _, header := range rule.AllowedHeader {
+			if strings.Count(header, "*") > 1 {
+				return fmt.Errorf("header %s in CORS rule, id: %s, %w", header, rule.ID, ErrAllowedHeaderWildcards{Header: header})
+			}
+		}
+	}
+
+	return nil
+}
+
+// HasAllowedOrigin returns true if the given origin is allowed by the CORS rule
+func (c *Rule) HasAllowedOrigin(origin string) bool {
+	// See "AllowedOrigin element" in https://docs.aws.amazon.com/AmazonS3/latest/userguide/ManageCorsUsing.html
+	for _, allowedOrigin := range c.AllowedOrigin {
+		if wildcard.Match(allowedOrigin, origin) {
+			// Only one wildcard character (*) is allowed by S3 spec, but Match does
+			// not enforce that, it's done by Validate() function.
+			// Origins are case sensitive
+			return true
+		}
+	}
+	return false
+}
+
+// HasAllowedMethod returns true if the given method is contained in the CORS rule.
+func (c *Rule) HasAllowedMethod(method string) bool {
+	// See "AllowedMethod element" in https://docs.aws.amazon.com/AmazonS3/latest/userguide/ManageCorsUsing.html
+	for _, allowedMethod := range c.AllowedMethod {
+		if allowedMethod == method {
+			// Methods are always uppercase, enforced by Validate() function.
+			return true
+		}
+	}
+	return false
+}
+
+// FilterAllowedHeaders returns the headers that are allowed by the rule, and a boolean indicating if all headers are allowed.
+func (c *Rule) FilterAllowedHeaders(headers []string) ([]string, bool) {
+	// See "AllowedHeader element" in https://docs.aws.amazon.com/AmazonS3/latest/userguide/ManageCorsUsing.html
+	// It's inefficient to store the CORS config verbatim and run ToLower here, but S3 essentially
+	// behaves this way, and will return the XML config verbatim when you GET it.
+	filtered := []string{}
+	for _, header := range headers {
+		header = strings.ToLower(header)
+		found := false
+		for _, allowedHeader := range c.AllowedHeader {
+			// Case insensitive comparison for headers
+			if wildcard.Match(strings.ToLower(allowedHeader), header) {
+				// Only one wildcard character (*) is allowed by S3 spec, but Match does
+				// not enforce that, it's done by rule.Validate() function.
+				filtered = append(filtered, header)
+				found = true
+				break
+			}
+		}
+		if !found {
+			return nil, false
+		}
+	}
+	return filtered, true
+}
+
+// ParseBucketCorsConfig parses a CORS configuration in XML from an io.Reader.
+func ParseBucketCorsConfig(reader io.Reader) (*Config, error) {
+	var c Config
+	err := xml.NewDecoder(reader).Decode(&c)
+	if err != nil {
+		return nil, fmt.Errorf("decoding xml: %w", err)
+	}
+	if c.XMLNS == "" {
+		c.XMLNS = defaultXMLNS
+	}
+	for i, rule := range c.CORSRules {
+		for j, method := range rule.AllowedMethod {
+			c.CORSRules[i].AllowedMethod[j] = strings.ToUpper(method)
+		}
+	}
+	return &c, nil
+}
+
+// ToXML marshals the CORS configuration to XML.
+func (c Config) ToXML() ([]byte, error) {
+	if c.XMLNS == "" {
+		c.XMLNS = defaultXMLNS
+	}
+	data, err := xml.Marshal(&c)
+	if err != nil {
+		return nil, fmt.Errorf("marshaling xml: %w", err)
+	}
+	return append([]byte(xml.Header), data...), nil
+}