The Resources screen discovered and substituted template variables with a
bare `/\{(\w+)\}/g` regex, which is wrong two ways: it cannot see an
expression carrying an operator, so `foobar://events{?topic}` rendered no
input at all; and it splices the raw value in, so a `/`, `?`, `#`, `%`,
space or non-ASCII character in a simple `{topic}` landed unencoded and
changed the URI's structure -- `foo/bar` produced an extra path segment
that a conforming matcher rejects with `-32602 Resource not found`.
Delegate expansion to the SDK's `UriTemplate`, the same implementation
`InspectorClient.readResourceFromTemplate` (and so the TUI) already
expands through, so the two clients cannot disagree about what a template
means. The new `utils/uriTemplate` supplies only what that class does
not: which variables to render an input for, which of them a read cannot
proceed without, and a partially-expanded preview.
Required-ness follows the operator. Under `?`, `&`, `.` or `/` the whole
expression is omitted when the variable is undefined, so those fields are
marked Optional and reading with them blank is a legitimate request for
the unfiltered resource; under `""`, `+` or `#` the variable sits mid-URI,
so it stays required. Blank fields are dropped before expanding so an
untouched optional field reads as undefined rather than as the empty
string, which would expand to a valueless `?topic=`.
Adds the `rfc6570_templates` preset and a `rfc6570-templates-http.json`
showcase server serving the two templates from the issue.
Closes#1919
Signed-off-by: cliffhall <cliff@futurescale.com>