[API-84] Add track /stream /download /inspect (#57)

A bit more of a pain than I wanted
Tried to keep flow linear but with same behavior as python

Tested=
```
make test
```
api diff not super useful for these.

here's the response from inspect

<img width="329" alt="image"
src="https://github.com/user-attachments/assets/29ee0a6f-3087-4352-aa24-cc964505c468"
/>

Author: raymondjacobson

api/dbv1/full_tracks.go

@@ -80,14 +80,23 @@ func (q *Queries) FullTracksKeyed(ctx context.Context, arg GetTracksParams) (map
 		// Collect media links
 		// TODO(API-49): support self-access via grants
 		// see https://github.com/AudiusProject/audius-protocol/blob/4bd9fe80d8cca519844596061505ad8737579019/packages/discovery-provider/src/queries/query_helpers.py#L905
-		stream := mediaLink(track.TrackCid.String, track.TrackID, arg.MyID.(int32))
+		stream, err := mediaLink(track.TrackCid.String, track.TrackID, arg.MyID.(int32))
+		if err != nil {
+			return nil, err
+		}
 		var download *MediaLink
 		if track.IsDownloadable {
-			download = mediaLink(track.OrigFileCid.String, track.TrackID, arg.MyID.(int32))
+			download, err = mediaLink(track.OrigFileCid.String, track.TrackID, arg.MyID.(int32))
+			if err != nil {
+				return nil, err
+			}
 		}
 		var preview *MediaLink
 		if track.PreviewCid.String != "" {
-			preview = mediaLink(track.PreviewCid.String, track.TrackID, arg.MyID.(int32))
+			preview, err = mediaLink(track.PreviewCid.String, track.TrackID, arg.MyID.(int32))
+			if err != nil {
+				return nil, err
+			}
 		}
 
 		if track.FieldVisibility == nil || string(track.FieldVisibility) == "null" {

api/dbv1/media_link.go

@@ -19,7 +19,7 @@ type MediaLink struct {
 	Mirrors []string `json:"mirrors"`
 }
 
-func mediaLink(cid string, trackId int32, userId int32) *MediaLink {
+func mediaLink(cid string, trackId int32, userId int32) (*MediaLink, error) {
 	first, rest := rendezvous.GlobalHasher.ReplicaSet3(cid)
 
 	timestamp := time.Now().Unix() * 1000
@@ -32,7 +32,7 @@ func mediaLink(cid string, trackId int32, userId int32) *MediaLink {
 
 	signature, err := generateSignature(data)
 	if err != nil {
-		return nil
+		return nil, err
 	}
 
 	// Convert the data map to a JSON string
@@ -52,7 +52,7 @@ func mediaLink(cid string, trackId int32, userId int32) *MediaLink {
 	return &MediaLink{
 		Url:     fmt.Sprintf("%s/%s", first, path),
 		Mirrors: rest,
-	}
+	}, nil
 }
 
 func generateSignature(data map[string]interface{}) (string, error) {

api/server.go

@@ -228,21 +228,25 @@ func NewApiServer(config config.Config) *ApiServer {
 		g.Get("/tracks/trending", app.v1TracksTrending)
 		g.Get("/tracks/trending/ids", app.v1TracksTrendingIds)
 		g.Get("/tracks/recommended", app.v1TracksTrending)
+		g.Get("/tracks/inspect", app.v1TracksInspect)
 
 		g.Use("/tracks/:trackId", app.requireTrackIdMiddleware)
 		g.Get("/tracks/:trackId", app.v1Track)
-		g.Get("/tracks/:trackId/reposts", app.v1TracksReposts)
-		g.Get("/tracks/:trackId/favorites", app.v1TracksFavorites)
-		g.Get("/tracks/:trackId/comments", app.v1TracksComments)
+		g.Get("/tracks/:trackId/stream", app.v1TrackStream)
+		g.Get("/tracks/:trackId/download", app.v1TrackDownload)
+		g.Get("/tracks/:trackId/inspect", app.v1TrackInspect)
+		g.Get("/tracks/:trackId/reposts", app.v1TrackReposts)
+		g.Get("/tracks/:trackId/favorites", app.v1TrackFavorites)
+		g.Get("/tracks/:trackId/comments", app.v1TrackComments)
 
 		// Playlists
 		g.Get("/playlists", app.v1playlists)
 		g.Get("/playlists/unclaimed_id", app.v1PlaylistsUnclaimedId)
 
 		g.Use("/playlists/:playlistId", app.requirePlaylistIdMiddleware)
 		g.Get("/playlists/:playlistId", app.v1Playlist)
-		g.Get("/playlists/:playlistId/reposts", app.v1PlaylistsReposts)
-		g.Get("/playlists/:playlistId/favorites", app.v1PlaylistsFavorites)
+		g.Get("/playlists/:playlistId/reposts", app.v1PlaylistReposts)
+		g.Get("/playlists/:playlistId/favorites", app.v1PlaylistFavorites)
 
 		// Developer Apps
 		g.Get("/developer_apps/:address", app.v1DeveloperApps)

api/stream_util.go

@@ -0,0 +1,57 @@
+package api
+
+import (
+	"net/http"
+	"net/url"
+	"time"
+
+	"bridgerton.audius.co/api/dbv1"
+)
+
+// tryFindWorkingUrl attempts to validate a media link by checking if it can serve content.
+// It tries the primary URL first, then falls back to mirrors if needed.
+// Returns the first valid URL found or the main URL if nothing works.
+func tryFindWorkingUrl(mediaLink *dbv1.MediaLink) *url.URL {
+	mainURL, err := url.Parse(mediaLink.Url)
+	if err != nil {
+		return nil
+	}
+
+	// Construct all URLs to try
+	urls := make([]*url.URL, 0, len(mediaLink.Mirrors)+1)
+	urls = append(urls, mainURL)
+	for _, mirror := range mediaLink.Mirrors {
+		mirrorURL := *mainURL
+		mirrorURL.Host = mirror
+		urls = append(urls, &mirrorURL)
+	}
+
+	client := &http.Client{
+		Timeout: 5 * time.Second,
+	}
+	for _, u := range urls {
+		q := u.Query()
+		q.Set("skip_play_count", "true")
+		u.RawQuery = q.Encode()
+
+		req, err := http.NewRequest("GET", u.String(), nil)
+		if err != nil {
+			continue
+		}
+		req.Header.Set("Range", "bytes=0-1")
+
+		resp, err := client.Do(req)
+		if err != nil {
+			continue
+		}
+		resp.Body.Close()
+
+		if resp.StatusCode == http.StatusPartialContent ||
+			resp.StatusCode == http.StatusOK ||
+			resp.StatusCode == http.StatusNoContent {
+			return u
+		}
+	}
+
+	return mainURL
+}

api/testdata/track_fixtures.csv

@@ -1,12 +1,12 @@
-track_id,genre,owner_id,title,is_unlisted,stream_conditions,download_conditions
-100,Electronic,1,T1,f,,
-101,Alternative,1,T2,f,,
-200,Electronic,2,Culca Canyon,f,,
-201,Alternative,2,Turkey Time DEMO,t,,
-202,Alternative,2,Turkey Time (live),f,,
-300,Electronic,3,Follow Gated Download,f,,"{""follow_user_id"": 3}"
-301,Electronic,3,Pay Gated Download,f,,"{""usdc_purchase"": {""price"": 135, ""splits"": [{""user_id"": 3, ""percentage"": 100.0}]}}"
-302,Electronic,3,Tip Gated Stream,f,"{""tip_user_id"": 3}","{""tip_user_id"": 3}"
-303,Electronic,3,Pay Gated Stream,f,"{""usdc_purchase"": {""price"": 135, ""splits"": [{""user_id"": 3, ""percentage"": 100.0}]}}",
-400,Folk,5,Trending Month Folk,f,,
-500,Experimental,6,track by permalink,f,,
+track_id,genre,owner_id,title,is_unlisted,stream_conditions,download_conditions,is_downloadable
+100,Electronic,1,T1,f,,,t
+101,Alternative,1,T2,f,,,f
+200,Electronic,2,Culca Canyon,f,,,f
+201,Alternative,2,Turkey Time DEMO,t,,,f
+202,Alternative,2,Turkey Time (live),f,,,f
+300,Electronic,3,Follow Gated Download,f,,"{""follow_user_id"": 3}",t
+301,Electronic,3,Pay Gated Download,f,,"{""usdc_purchase"": {""price"": 135, ""splits"": [{""user_id"": 3, ""percentage"": 100.0}]}}",t
+302,Electronic,3,Tip Gated Stream,f,"{""tip_user_id"": 3}","{""tip_user_id"": 3}",f
+303,Electronic,3,Pay Gated Stream,f,"{""usdc_purchase"": {""price"": 135, ""splits"": [{""user_id"": 3, ""percentage"": 100.0}]}}",,f
+400,Folk,5,Trending Month Folk,f,,,f
+500,Experimental,6,track by permalink,f,,,f

api/v1_playlists_favorites.go api/v1_playlist_favorites.goapi/v1_playlists_favorites.go renamed to api/v1_playlist_favorites.go

@@ -6,7 +6,7 @@ import (
 	"github.com/jackc/pgx/v5"
 )
 
-func (app *ApiServer) v1PlaylistsFavorites(c *fiber.Ctx) error {
+func (app *ApiServer) v1PlaylistFavorites(c *fiber.Ctx) error {
 	sql := `
 	SELECT user_id
 	FROM saves

api/v1_playlists_reposts.go api/v1_playlist_reposts.goapi/v1_playlists_reposts.go renamed to api/v1_playlist_reposts.go

@@ -6,7 +6,7 @@ import (
 	"github.com/jackc/pgx/v5"
 )
 
-func (app *ApiServer) v1PlaylistsReposts(c *fiber.Ctx) error {
+func (app *ApiServer) v1PlaylistReposts(c *fiber.Ctx) error {
 	sql := `
 	SELECT user_id
 	FROM reposts r

api/v1_tracks_comments.go api/v1_track_comments.goapi/v1_tracks_comments.go renamed to api/v1_track_comments.go

@@ -5,7 +5,7 @@ import (
 	"github.com/jackc/pgx/v5"
 )
 
-func (app *ApiServer) v1TracksComments(c *fiber.Ctx) error {
+func (app *ApiServer) v1TrackComments(c *fiber.Ctx) error {
 
 	sql := `
 	SELECT comment_id as id

api/v1_tracks_comments_test.go api/v1_track_comments_test.goapi/v1_tracks_comments_test.go renamed to api/v1_track_comments_test.go

@@ -0,0 +1,40 @@
+package api
+
+import (
+	"bridgerton.audius.co/api/dbv1"
+	"github.com/gofiber/fiber/v2"
+)
+
+func (app *ApiServer) v1TrackDownload(c *fiber.Ctx) error {
+	myId := app.getMyId(c)
+	trackId := c.Locals("trackId").(int)
+	filename := c.Query("filename")
+
+	tracks, err := app.queries.FullTracks(c.Context(), dbv1.GetTracksParams{
+		MyID: myId,
+		Ids:  []int32{int32(trackId)},
+	})
+	if err != nil {
+		return err
+	}
+
+	if len(tracks) == 0 {
+		return sendError(c, 404, "track not found")
+	}
+
+	track := tracks[0]
+	if !track.Access.Download {
+		return sendError(c, 403, "track not downloadable")
+	}
+
+	downloadUrl := tryFindWorkingUrl(track.Download)
+
+	q := downloadUrl.Query()
+	q.Set("skip_play_count", "true")
+	if filename != "" {
+		q.Set("filename", filename)
+	}
+	downloadUrl.RawQuery = q.Encode()
+
+	return c.Redirect(downloadUrl.String(), fiber.StatusFound)
+}