fix: Trim extra spaces in signed header values (#1065)

Trim extra spaces in signed header values for creating canonical 
request string for v4 signature.

As per S3 spec:
https://docs.aws.amazon.com/general/latest/gr/sigv4-create-canonical-request.html

functional_tests.go

@@ -653,7 +653,8 @@ func testPutObjectWithMetadata() {
 	customContentType := "custom/contenttype"
 
 	args["metadata"] = map[string][]string{
-		"Content-Type": {customContentType},
+		"Content-Type":         {customContentType},
+		"X-Amz-Meta-CustomKey": {"extra  spaces  in   value"},
 	}
 
 	n, err := c.PutObject(bucketName, objectName, reader, int64(bufSize), minio.PutObjectOptions{

pkg/s3signer/request-signature-v4.go

@@ -151,7 +151,7 @@ func getCanonicalHeaders(req http.Request, ignoredHeaders map[string]bool) strin
 				if idx > 0 {
 					buf.WriteByte(',')
 				}
-				buf.WriteString(v)
+				buf.WriteString(signV4TrimAll(v))
 			}
 			buf.WriteByte('\n')
 		}

pkg/s3signer/utils.go

@@ -21,6 +21,7 @@ import (
 	"crypto/hmac"
 	"crypto/sha256"
 	"net/http"
+	"strings"
 )
 
 // unsignedPayload - value to be set to X-Amz-Content-Sha256 header when
@@ -47,3 +48,11 @@ func getHostAddr(req *http.Request) string {
 	}
 	return req.URL.Host
 }
+
+// Trim leading and trailing spaces and replace sequential spaces with one space, following Trimall()
+// in http://docs.aws.amazon.com/general/latest/gr/sigv4-create-canonical-request.html
+func signV4TrimAll(input string) string {
+	// Compress adjacent spaces (a space is determined by
+	// unicode.IsSpace() internally here) to one space and return
+	return strings.Join(strings.Fields(input), " ")
+}

pkg/s3signer/utils_test.go

@@ -84,3 +84,32 @@ func TestEncodeURL2Path(t *testing.T) {
 	}
 
 }
+
+// TestSignV4TrimAll - tests the logic of TrimAll() function
+func TestSignV4TrimAll(t *testing.T) {
+	testCases := []struct {
+		// Input.
+		inputStr string
+		// Expected result.
+		result string
+	}{
+		{"本語", "本語"},
+		{" abc ", "abc"},
+		{" a b ", "a b"},
+		{"a b ", "a b"},
+		{"a  b", "a b"},
+		{"a   b", "a b"},
+		{"   a   b  c   ", "a b c"},
+		{"a \t b  c   ", "a b c"},
+		{"\"a \t b  c   ", "\"a b c"},
+		{" \t\n\u000b\r\fa \t\n\u000b\r\f b \t\n\u000b\r\f c \t\n\u000b\r\f", "a b c"},
+	}
+
+	// Tests generated values from url encoded name.
+	for i, testCase := range testCases {
+		result := signV4TrimAll(testCase.inputStr)
+		if testCase.result != result {
+			t.Errorf("Test %d: Expected signV4TrimAll result to be \"%s\", but found it to be \"%s\" instead", i+1, testCase.result, result)
+		}
+	}
+}