feat(chat_append): Return stream results as promise value

DESCRIPTION

@@ -20,6 +20,7 @@ Imports:
     bslib,
     coro,
     ellmer,
+    fastmap,
     htmltools,
     jsonlite,
     promises (>= 1.3.2),

NEWS.md

@@ -10,6 +10,8 @@
 
 * Added `chat_app()`, `chat_mod_ui()` and `chat_mod_server()`. `chat_app()` takes an `ellmer::Chat` client and launches a simple Shiny app interface with the chat. `chat_mod_ui()` and `chat_mod_server()` replicate the interface as a Shiny module, for easily adding a simple chat interface connected to a specific `ellmer::Chat` client. (#36)
 
+* The promise returned by `chat_append()` now resolves to the content streamed into the chat. (#49)
+
 ## Bug fixes
 
 * `chat_append()`, `chat_append_message()` and `chat_clear()` now all work in Shiny modules without needing to namespace the `id` of the Chat component. (#37)

R/chat.R

@@ -197,11 +197,12 @@ chat_ui <- function(
 #' @param role The role of the message (either "assistant" or "user"). Defaults
 #'   to "assistant".
 #' @param session The Shiny session object
-#' @returns Returns a promise. This promise resolves when the message has been
-#'   successfully sent to the client; note that it does not guarantee that the
-#'   message was actually received or rendered by the client. The promise
-#'   rejects if an error occurs while processing the response (see the "Error
-#'   handling" section).
+#'
+#' @returns Returns a promise that resolves to the contents of the stream, or an
+#'   error. This promise resolves when the message has been successfully sent to
+#'   the client; note that it does not guarantee that the message was actually
+#'   received or rendered by the client. The promise rejects if an error occurs
+#'   while processing the response (see the "Error handling" section).
 #'
 #' @examplesIf interactive()
 #' library(shiny)
@@ -460,13 +461,19 @@ rlang::on_load(
       chunk = "start",
       session = session
     )
+
+    res <- fastmap::fastqueue(200)
+
     for (msg in stream) {
       if (promises::is.promising(msg)) {
         msg <- await(msg)
       }
       if (coro::is_exhausted(msg)) {
         break
       }
+
+      res$add(msg)
+
       chat_append_message(
         id,
         list(role = role, content = msg),
@@ -475,13 +482,21 @@ rlang::on_load(
         session = session
       )
     }
+
     chat_append_message(
       id,
       list(role = role, content = ""),
       chunk = "end",
       operation = "append",
       session = session
     )
+
+    res <- res$as_list()
+    if (every(res, is.character)) {
+      paste(unlist(res), collapse = "")
+    } else {
+      res
+    }
   })
 )
 

R/shinychat-package.R

@@ -10,6 +10,7 @@ NULL
 
 ignore_unused_imports <- function() {
   jsonlite::fromJSON
+  fastmap::fastqueue
 }
 
 release_bullets <- function() {

tests/testthat/helper-sync.R

@@ -28,3 +28,14 @@ sync <- function(expr) {
     success
   }
 }
+
+expect_promise <- function(p, state = NULL) {
+  name <- deparse(substitute(p))
+  expect(
+    promises::is.promise(p),
+    sprintf("`%s` is not a promise", name)
+  )
+  if (!is.null(state)) {
+    expect_equal(attr(p, "promise_impl")$status(), state)
+  }
+}

tests/testthat/test-chat.R

@@ -42,6 +42,48 @@ test_that("Chat component markup", {
   # TODO: it'd be nice to mock the shinyChatMessage custom messages
 })
 
+test_that("chat_append_stream() returns the stream contents as string if all text", {
+  local_mocked_bindings(
+    chat_append_message = coro::async(function(...) invisible())
+  )
+
+  stream <- coro::async_generator(function() {
+    for (i in c("Hello", ",", " world", "!")) {
+      yield(i)
+    }
+  })
+
+  p <- chat_append_stream("chat", stream())
+  res <- sync(p)
+
+  expect_promise(p, "fulfilled")
+  expect_equal(res, "Hello, world!")
+})
+
+test_that("chat_append_stream() returns the stream contents as list if not all text", {
+  local_mocked_bindings(
+    chat_append_message = coro::async(function(...) invisible())
+  )
+
+  stream <- coro::async_generator(function() {
+    for (i in c("Hello", ",", " world", "!")) {
+      yield(ellmer::ContentText(i))
+    }
+  })
+
+  p <- chat_append_stream("chat", stream())
+  res <- sync(p)
+
+  expect_promise(p, "fulfilled")
+
+  expect_true(is.list(res))
+  expect_true(every(res, inherits, "ellmer::ContentText"))
+  expect_equal(
+    paste(map_chr(res, ellmer::contents_text), collapse = ""),
+    "Hello, world!"
+  )
+})
+
 test_that("chat_append_stream() handles errors in the stream", {
   local_mocked_bindings(
     chat_append_message = coro::async(function(...) invisible())
@@ -61,9 +103,7 @@ test_that("chat_append_stream() handles errors in the stream", {
       regexp = 'chat_append_stream'
     )
 
-    expect_s3_class(p, "promise")
-    expect_true(promises::is.promise(p))
-    expect_equal(attr(p, "promise_impl")$status(), "rejected")
+    expect_promise(p, "rejected")
 
     expect_s3_class(res, class = c("condition", "error"))
     expect_s3_class(res, class = "shiny.silent.error")