net/http: allow multiple spaces between method and path in mux patterns

Fixes #64910

Change-Id: I14fd1e35c95b14591e3ad7b889dc1ab19a008730
GitHub-Last-Rev: b8d436c
GitHub-Pull-Request: #65868
Reviewed-on: https://go-review.googlesource.com/c/go/+/565916
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Damien Neil <[email protected]>
Reviewed-by: Jonathan Amsterdam <[email protected]>

doc/next/6-stdlib/99-minor/net/http/64910.md

@@ -0,0 +1,2 @@
+The patterns used by [`net/http.ServeMux`](//net/http#ServeMux) allow
+multiple spaces matching regexp '[ \t]+'.

src/net/http/pattern.go

@@ -76,7 +76,7 @@ type segment struct {
 //     a literal or a wildcard of the form "{name}", "{name...}", or "{$}".
 //
 // METHOD, HOST and PATH are all optional; that is, the string can be "/".
-// If METHOD is present, it must be followed by a single space.
+// If METHOD is present, it must be followed by at least one space or tab.
 // Wildcard names must be valid Go identifiers.
 // The "{$}" and "{name...}" wildcard must occur at the end of PATH.
 // PATH may end with a '/'.
@@ -92,7 +92,10 @@ func parsePattern(s string) (_ *pattern, err error) {
 		}
 	}()
 
-	method, rest, found := strings.Cut(s, " ")
+	method, rest, found := s, "", false
+	if i := strings.IndexAny(s, " \t"); i >= 0 {
+		method, rest, found = s[:i], strings.TrimLeft(s[i+1:], " \t"), true
+	}
 	if !found {
 		rest = method
 		method = ""

src/net/http/pattern_test.go

@@ -98,6 +98,23 @@ func TestParsePattern(t *testing.T) {
 			"/%61%62/%7b/%",
 			pattern{segments: []segment{lit("ab"), lit("{"), lit("%")}},
 		},
+		// Allow multiple spaces matching regexp '[ \t]+' between method and path.
+		{
+			"GET\t  /",
+			pattern{method: "GET", segments: []segment{multi("")}},
+		},
+		{
+			"POST \t  example.com/foo/{w}",
+			pattern{
+				method:   "POST",
+				host:     "example.com",
+				segments: []segment{lit("foo"), wild("w")},
+			},
+		},
+		{
+			"DELETE    \texample.com/a/{foo12}/{$}",
+			pattern{method: "DELETE", host: "example.com", segments: []segment{lit("a"), wild("foo12"), lit("/")}},
+		},
 	} {
 		got := mustParsePattern(t, test.in)
 		if !got.equal(&test.want) {

src/net/http/server.go

@@ -2335,7 +2335,7 @@ func RedirectHandler(url string, code int) Handler {
 //	[METHOD ][HOST]/[PATH]
 //
 // All three parts are optional; "/" is a valid pattern.
-// If METHOD is present, it must be followed by a single space.
+// If METHOD is present, it must be followed by at least one space or tab.
 //
 // Literal (that is, non-wildcard) parts of a pattern match
 // the corresponding parts of a request case-sensitively.