mime: parse media types that contain braces

This CL fixes a bug introduced by CL 666655: isTokenChar would no longer
(but should) report true for '{' and '}'.

Fixes #76236

Change-Id: Ifc0953c30d7cae7bfba9bc4b6bb6951a83c52576
GitHub-Last-Rev: c91a75c
GitHub-Pull-Request: #76243
Reviewed-on: https://go-review.googlesource.com/c/go/+/719380
Reviewed-by: Sean Liao <[email protected]>
Reviewed-by: Jorropo <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>
Reviewed-by: Damien Neil <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: jub0bs

src/mime/grammar.go

@@ -62,7 +62,9 @@ func isTokenChar(c byte) bool {
 		1<<'^' |
 		1<<'_' |
 		1<<'`' |
+		1<<'{' |
 		1<<'|' |
+		1<<'}' |
 		1<<'~'
 	return ((uint64(1)<<c)&(mask&(1<<64-1)) |
 		(uint64(1)<<(c-64))&(mask>>64)) != 0

src/mime/mediatype_test.go

@@ -413,6 +413,9 @@ func init() {
 		// Issue #48866: duplicate parameters containing equal values should be allowed
 		{`text; charset=utf-8; charset=utf-8; format=fixed`, "text", m("charset", "utf-8", "format", "fixed")},
 		{`text; charset=utf-8; format=flowed; charset=utf-8`, "text", m("charset", "utf-8", "format", "flowed")},
+
+		// Issue #76236: '{' and '}' are token chars.
+		{"attachment; filename={file}.png", "attachment", m("filename", "{file}.png")},
 	}
 }