feat: add internal/bucket/cors CORS config type and matching

Signed-off-by: h5vx <h5v@protonmail.com>

internal/bucket/cors/cors.go

@@ -0,0 +1,150 @@
+// Copyright (c) 2015-2021 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 implements the S3 per-bucket CORS configuration type,
+// its validation, and origin/method/header matching helpers.
+package cors
+
+import (
+	"encoding/xml"
+	"errors"
+	"io"
+	"strings"
+
+	"github.com/minio/pkg/v3/wildcard"
+)
+
+// maxCORSRules is the maximum number of rules allowed per bucket (AWS S3 limit).
+const maxCORSRules = 100
+
+// supportedMethods are the HTTP methods permitted in an AllowedMethod element.
+var supportedMethods = map[string]bool{
+	"GET":    true,
+	"PUT":    true,
+	"HEAD":   true,
+	"POST":   true,
+	"DELETE": true,
+}
+
+// Config is the S3 <CORSConfiguration> document.
+type Config struct {
+	XMLName   xml.Name `xml:"CORSConfiguration"`
+	CORSRules []Rule   `xml:"CORSRule"`
+}
+
+// Rule is a single <CORSRule>.
+type Rule struct {
+	ID             string   `xml:"ID,omitempty"`
+	AllowedHeaders []string `xml:"AllowedHeader"`
+	AllowedMethods []string `xml:"AllowedMethod"`
+	AllowedOrigins []string `xml:"AllowedOrigin"`
+	ExposeHeaders  []string `xml:"ExposeHeader"`
+	MaxAgeSeconds  int      `xml:"MaxAgeSeconds"`
+}
+
+// ParseBucketCorsConfig parses a CORS configuration from the given reader.
+func ParseBucketCorsConfig(r io.Reader) (*Config, error) {
+	var c Config
+	if err := xml.NewDecoder(r).Decode(&c); err != nil {
+		return nil, err
+	}
+	return &c, nil
+}
+
+// Validate checks the config against the S3 constraints.
+func (c *Config) Validate() error {
+	if len(c.CORSRules) == 0 {
+		return errors.New("CORSConfiguration must contain at least one rule")
+	}
+	if len(c.CORSRules) > maxCORSRules {
+		return errors.New("CORSConfiguration exceeds the maximum number of rules")
+	}
+	for _, r := range c.CORSRules {
+		if len(r.AllowedOrigins) == 0 {
+			return errors.New("CORSRule must contain at least one AllowedOrigin")
+		}
+		if len(r.AllowedMethods) == 0 {
+			return errors.New("CORSRule must contain at least one AllowedMethod")
+		}
+		for _, m := range r.AllowedMethods {
+			if !supportedMethods[strings.ToUpper(m)] {
+				return errors.New("unsupported method in CORSRule: " + m)
+			}
+		}
+		if r.MaxAgeSeconds < 0 {
+			return errors.New("MaxAgeSeconds must not be negative")
+		}
+	}
+	return nil
+}
+
+// HasAllowedOrigin reports whether the rule allows the given origin.
+func (r Rule) HasAllowedOrigin(origin string) bool {
+	for _, o := range r.AllowedOrigins {
+		if o == "*" || wildcard.MatchSimple(o, origin) {
+			return true
+		}
+	}
+	return false
+}
+
+// HasAllowedMethod reports whether the rule allows the given HTTP method.
+func (r Rule) HasAllowedMethod(method string) bool {
+	for _, m := range r.AllowedMethods {
+		if strings.EqualFold(m, method) {
+			return true
+		}
+	}
+	return false
+}
+
+// FilterAllowedHeaders returns the subset of reqHeaders permitted by the rule
+// and whether every requested header was allowed.
+func (r Rule) FilterAllowedHeaders(reqHeaders []string) ([]string, bool) {
+	var allowed []string
+	for _, h := range reqHeaders {
+		h = strings.TrimSpace(h)
+		if h == "" {
+			continue
+		}
+		if !r.headerAllowed(h) {
+			return nil, false
+		}
+		allowed = append(allowed, h)
+	}
+	return allowed, true
+}
+
+func (r Rule) headerAllowed(header string) bool {
+	for _, h := range r.AllowedHeaders {
+		if h == "*" || wildcard.MatchSimple(strings.ToLower(h), strings.ToLower(header)) {
+			return true
+		}
+	}
+	return false
+}
+
+// MatchRule returns the first rule whose origin and method both match.
+func (c *Config) MatchRule(origin, method string) (*Rule, bool) {
+	for i := range c.CORSRules {
+		r := &c.CORSRules[i]
+		if r.HasAllowedOrigin(origin) && r.HasAllowedMethod(method) {
+			return r, true
+		}
+	}
+	return nil, false
+}

internal/bucket/cors/cors_test.go

@@ -0,0 +1,91 @@
+// Copyright (c) 2015-2021 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 (
+	"strings"
+	"testing"
+)
+
+const sampleCORS = `<CORSConfiguration>
+  <CORSRule>
+    <ID>rule1</ID>
+    <AllowedOrigin>http://www.example.com</AllowedOrigin>
+    <AllowedOrigin>https://*.example.org</AllowedOrigin>
+    <AllowedMethod>GET</AllowedMethod>
+    <AllowedMethod>PUT</AllowedMethod>
+    <AllowedHeader>x-amz-*</AllowedHeader>
+    <ExposeHeader>ETag</ExposeHeader>
+    <MaxAgeSeconds>3000</MaxAgeSeconds>
+  </CORSRule>
+</CORSConfiguration>`
+
+func TestParseAndValidate(t *testing.T) {
+	c, err := ParseBucketCorsConfig(strings.NewReader(sampleCORS))
+	if err != nil {
+		t.Fatalf("parse failed: %v", err)
+	}
+	if err := c.Validate(); err != nil {
+		t.Fatalf("validate failed: %v", err)
+	}
+	if len(c.CORSRules) != 1 {
+		t.Fatalf("expected 1 rule, got %d", len(c.CORSRules))
+	}
+	if c.CORSRules[0].MaxAgeSeconds != 3000 {
+		t.Fatalf("MaxAgeSeconds mismatch: %d", c.CORSRules[0].MaxAgeSeconds)
+	}
+}
+
+func TestValidateRejections(t *testing.T) {
+	cases := map[string]string{
+		"bad method":    `<CORSConfiguration><CORSRule><AllowedOrigin>*</AllowedOrigin><AllowedMethod>TRACE</AllowedMethod></CORSRule></CORSConfiguration>`,
+		"no origin":     `<CORSConfiguration><CORSRule><AllowedMethod>GET</AllowedMethod></CORSRule></CORSConfiguration>`,
+		"no method":     `<CORSConfiguration><CORSRule><AllowedOrigin>*</AllowedOrigin></CORSRule></CORSConfiguration>`,
+		"negative age":  `<CORSConfiguration><CORSRule><AllowedOrigin>*</AllowedOrigin><AllowedMethod>GET</AllowedMethod><MaxAgeSeconds>-1</MaxAgeSeconds></CORSRule></CORSConfiguration>`,
+	}
+	for name, doc := range cases {
+		c, err := ParseBucketCorsConfig(strings.NewReader(doc))
+		if err != nil {
+			continue // parse-level rejection is acceptable
+		}
+		if err := c.Validate(); err == nil {
+			t.Errorf("%s: expected validation error, got nil", name)
+		}
+	}
+}
+
+func TestMatching(t *testing.T) {
+	c, _ := ParseBucketCorsConfig(strings.NewReader(sampleCORS))
+	rule, ok := c.MatchRule("https://api.example.org", "GET")
+	if !ok {
+		t.Fatal("expected origin+method to match")
+	}
+	if _, ok := c.MatchRule("http://evil.com", "GET"); ok {
+		t.Fatal("did not expect match for disallowed origin")
+	}
+	if _, ok := c.MatchRule("http://www.example.com", "DELETE"); ok {
+		t.Fatal("did not expect match for disallowed method")
+	}
+	allowed, ok := rule.FilterAllowedHeaders([]string{"x-amz-date", "x-amz-content-sha256"})
+	if !ok || len(allowed) != 2 {
+		t.Fatalf("expected both headers allowed via wildcard, got %v ok=%v", allowed, ok)
+	}
+	if _, ok := rule.FilterAllowedHeaders([]string{"authorization"}); ok {
+		t.Fatal("did not expect authorization to be allowed")
+	}
+}