add_tracks_to_playlist() fails when uris has length 1.

[jonathan-g]

Trying to add tracks to a playlist, I get an error:

auth <- get_spotify_authorization_code(scope = c("playlist-modify-public"))

# This fails
add_tracks_to_playlist(playlist_id, track, 0, authorization = auth)
#> Request failed [400]. Retrying in 1 seconds...
#> Request failed [400]. Retrying in 1 seconds...
#> Error in add_tracks_to_playlist(playlist_id, track, 0, authorization = auth): Bad Request (HTTP 400).

# This succeeds
add_tracks_to_playlist(playlist_id, c(track, track), 0, authorization = auth)
#> $snapshot_id
#> [1] "<snapshot id>"

To get more information about the problem, I look at

library(tidyverse)
library(httr)
base_url <- "https://api.spotify.com/v1/playlists"
url <- str_glue("{base_url}/{playlist_id}/tracks")
params <- list(position = 0, uris = track)
res <- POST(url, body = params, config(token = auth), encode = "json")
res
#>   Response [https://api.spotify.com/v1/playlists/7uRhAIgNZNwsPaYfCaQJRW/tracks]
#>   Date: 2023-05-16 00:32
#>   Status: 400
#>   Content-Type: application/json; charset=utf-8
#>   Size: 79 B
#> {
#>   "error" : {
#>     "status" : 400,
#>     "message" : "Error parsing JSON."
#>   }

I think the issue is that the POST body is incorrectly encoded into JSON if there is only one element in the character vector uris.

Session info

sessioninfo::session_info()
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#> ─ Packages ───────────────────────────────────────────────────────────────────
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#> ──────────────────────────────────────────────────────────────────────────────

[enricotonini]

Hi, I've just found exactly the same problem. Since it seems a low-level issue not trivial to be solved, I tentatively decided to create a wrapper of add_tracks_to_playlist(), that, if length(uris) = 1 it adds together with the desired track another track which I would never add to my Spotify library and then immediately removes it. This is a trick that forces the function to add at least two songs in any case.