elm-call-rpc

Basic shape

Each RPC (protos/rellm.proto's service Rellm) has a generated Grpc.Rpc req res value in Proto.Rellm.Rellm (e.g. Rellm.updatePost, Rellm.createPost, Rellm.getPosts), from the anmolitor/elm-grpc package (Grpc module).

Grpc.new Rellm.updatePost requestValue
    |> Grpc.setHost (AccountsPanel.serverUrl server)
    |> Grpc.addHeader "authorization" token   -- only for authenticated calls
    |> Grpc.toTask                            -- : Task Grpc.Error res

Use Grpc.toTask when chaining (Task.andThen) or Task.attempting yourself; Grpc.toCmd if you just want a Cmd msg directly.

Many RPCs (CreatePost, UpdatePost, ...) take/return the whole resource message directly (Post -> Post), not a separate FooRequest/FooResponse pair — check the actual rpc line in the .proto file rather than assuming a request wrapper exists.

Auth / token refresh: use Shared.MaybeAccountRequest

Don't call Grpc.addHeader "authorization" with a token you're holding onto — it may have expired. Instead:

• MaybeAccountRequest.perform : connection -> Maybe Account -> (Maybe String -> Task Grpc.Error b) -> Task Grpc.Error ( Maybe Account, b ) — anonymous if given Nothing, otherwise refreshes the access token first if expired/expiring (via the AccessToken RPC), then calls your req with the current token. Returns the (possibly-refreshed) Account back so you can persist it.
• MaybeAccountRequest.performWithAccount — same, but takes/returns a concrete Account (not Maybe) — use once you've already confirmed a signed-in account exists (e.g. after your own permission check), so you're not re-handling Nothing at the call site.
• Always propagate the refreshed account back, e.g. Effect.fromShared (Shared.AccountsPanelMsg (AccountsPanel.AccountRefreshed account)) from a page, or as the Maybe AccountsPanel.Msg a Shared-level panel's update returns. Skipping this silently drops a rotated refresh token, breaking future requests once the old one expires. Grep any existing fetchX/GotXResult handler (Components/Posts.elm, Shared/StarredPostsPanel.elm, Shared/MarkdownPanel.elm) for the pattern.
• connection is { host : String, port_ : Int, tls : Bool }, built from a Server as { host = server.backendHost, port_ = server.port_, tls = server.tls } — backendHost, not frontendHost (the latter is the public-facing name; the gRPC API actually lives at backendHost, often a CDN).

Read-modify-write safety

Some RPCs take and unconditionally apply a whole record server-side — e.g. UpdatePost (backend/src/rpcs/posts/update_post.rs) overwrites visibility/media/embed_link/shareable/etc. from whatever Post you send, not just the field you intended to change. If you're changing one field of something fetched a while ago (user was editing in a text box, a panel sat open, etc.), re-fetch it fresh immediately before submitting and overlay only your change onto that fresh copy — don't resubmit a possibly-stale in-hand snapshot. See Shared/MarkdownPanel.elm's saveTask (Task.andThens a fresh GetPosts into the eventual UpdatePost) for the pattern. Check the corresponding backend/src/rpcs/**/*.rs handler when in doubt about which fields get blindly overwritten vs. merged.

Errors

AccountsPanel.grpcErrorToString : Grpc.Error -> String is the shared formatter (Grpc.BadUrl/Timeout/NetworkError/BadStatus { errMessage }/BadBody) used for displaying RPC failures — use it instead of writing a new Grpc.Error -> String case expression.