Add special formatting for CIDs and Multiaddrs

Cid objects always serialize to JSON as `{"/": "<cid string>"}` (https://github.com/ipfs/go-cid/blob/078355866b1dda1658b5fdc5496ed7e25fdcf883/cid.go#L407-L415). There's no obvious way to detect what any type's serialization behavior might be, so we need a special case explicitly for CIDs here.

Also specially calls out Multiaddrs. It doesn't appear that we have any other interfaces or pointer types besides these two that wind up in response schemas. I don't know that string checking on the type is really the best way to do this, but it seemed expendient and avoids needing to depend on CID and Multiaddr packages and make sure they stay in sync with the version of IPFS we are working against.

There is also some discussion here (ipfs/kubo#5077) on whether this is the right formatting for CIDs. For now, I'm including it here because I heard plenty of complaints about the usefulness and accuracy of these docs from users. The output of this tool is preceived as documentation and not a spec, so I think it's right that it shows what IPFS actually *does,* not just what we think it *ought* to. (If we wanted this to be more like a spec, we need a way to annotate it for users to explain the difference between implementation and spec.)

License: MIT
Signed-off-by: Rob Brackett <[email protected]>

endpoints.go

@@ -154,12 +154,22 @@ func interfaceToJsonish(t reflect.Type, i int) string {
 	case reflect.Invalid:
 		result.WriteString("null\n")
 	case reflect.Interface:
-		result.WriteString(insertIndent(i) + "\"<object>\"\n")
+		description := "\"<object>\""
+		// Handle types that should be called out specially
+		if t.String() == "multiaddr.Multiaddr" {
+			description = "\"<multiaddr-string>\""
+		}
+		result.WriteString(fmt.Sprintf("%s%s\n", insertIndent(i), description))
 	case reflect.Ptr:
-		if _, ok := t.MethodByName("String"); ok && countExported(t.Elem()) == 0 {
+		// CIDs have specialized JSON marshaling, see:
+		// https://github.com/ipfs/go-cid/blob/078355866b1dda1658b5fdc5496ed7e25fdcf883/cid.go#L407-L415
+		if t.String() == "*cid.Cid" {
+			result.WriteString(insertIndent(i) + "{ \"/\": \"<cid-string>\" }\n")
+		} else if _, ok := t.MethodByName("String"); ok && countExported(t.Elem()) == 0 {
 			return interfaceToJsonish(reflect.TypeOf(""), i)
+		} else {
+			return interfaceToJsonish(t.Elem(), i)
 		}
-		return interfaceToJsonish(t.Elem(), i)
 	case reflect.Map:
 		result.WriteString(insertIndent(i) + "{\n")
 		result.WriteString(insertIndent(i+IndentLevel) + fmt.Sprintf(`"<%s>": `, t.Key().Kind()))