refactor(coverart/deezer): delegate HTTP plumbing to httpClient (C1 2/3)

internal/coverart/provider_deezer.go

@@ -2,14 +2,10 @@ package coverart
 
 import (
 	"context"
-	"encoding/json"
 	"fmt"
-	"io"
-	"math/rand"
 	"net/http"
 	"net/url"
 	"strings"
-	"sync"
 	"sync/atomic"
 	"time"
 )
@@ -30,18 +26,21 @@ const (
 
 // deezerProvider implements Provider, AlbumCoverProvider, and
 // ArtistArtProvider against Deezer's public read API. No API key
-// required. Safe for concurrent use; the internal mutex serialises
-// ALL HTTP calls so the rate limit applies uniformly.
+// required. Safe for concurrent use; the underlying httpClient
+// serialises calls so the rate limit applies uniformly.
 type deezerProvider struct {
-	enabled  atomic.Bool
-	mu       sync.Mutex
-	lastCall time.Time
-	client   *http.Client
+	enabled atomic.Bool
+	client  *httpClient
 }
 
 func init() {
 	Register(&deezerProvider{
-		client: &http.Client{Timeout: 30 * time.Second},
+		client: newHTTPClient(httpClientOptions{
+			Name:        "deezer",
+			HTTPClient:  &http.Client{Timeout: 30 * time.Second},
+			MinInterval: deezerMinPeriod,
+			MaxRetries:  deezerMaxRetries,
+		}),
 	})
 }
 
@@ -84,7 +83,7 @@ func (p *deezerProvider) FetchArtistArt(ctx context.Context, ref ArtistRef) (thu
 			PictureBig string `json:"picture_big"`
 		} `json:"data"`
 	}
-	if err := p.getJSON(ctx, "/search/artist?"+q.Encode(), &resp); err != nil {
+	if err := p.client.getJSON(ctx, deezerBaseURL+"/search/artist?"+q.Encode(), &resp); err != nil {
 		return nil, nil, err
 	}
 	if len(resp.Data) == 0 {
@@ -101,7 +100,7 @@ func (p *deezerProvider) FetchArtistArt(ctx context.Context, ref ArtistRef) (thu
 	if imgURL == "" {
 		return nil, nil, ErrNotFound
 	}
-	img, ferr := p.getImage(ctx, imgURL)
+	img, ferr := p.client.getImage(ctx, imgURL)
 	if ferr != nil {
 		return nil, nil, ferr
 	}
@@ -133,7 +132,7 @@ func (p *deezerProvider) FetchAlbumCover(ctx context.Context, ref AlbumRef) ([]b
 			} `json:"artist"`
 		} `json:"data"`
 	}
-	if err := p.getJSON(ctx, "/search/album?"+q.Encode(), &resp); err != nil {
+	if err := p.client.getJSON(ctx, deezerBaseURL+"/search/album?"+q.Encode(), &resp); err != nil {
 		return nil, err
 	}
 	if len(resp.Data) == 0 {
@@ -150,137 +149,7 @@ func (p *deezerProvider) FetchAlbumCover(ctx context.Context, ref AlbumRef) ([]b
 	if imgURL == "" {
 		return nil, ErrNotFound
 	}
-	return p.getImage(ctx, imgURL)
-}
-
-// getJSON performs a rate-limited GET against Deezer's JSON API.
-// Retries on 429 / 5xx with exponential backoff up to deezerMaxRetries.
-func (p *deezerProvider) getJSON(ctx context.Context, path string, out any) error {
-	fullURL := deezerBaseURL + path
-	for attempt := 0; attempt <= deezerMaxRetries; attempt++ {
-		if err := p.rateLimitWait(ctx); err != nil {
-			return err
-		}
-		req, err := http.NewRequestWithContext(ctx, http.MethodGet, fullURL, nil)
-		if err != nil {
-			return fmt.Errorf("coverart deezer: build request: %w", err)
-		}
-		req.Header.Set("Accept", "application/json")
-
-		resp, err := p.client.Do(req)
-		if err != nil {
-			if attempt < deezerMaxRetries {
-				if waitErr := p.backoff(ctx, attempt); waitErr != nil {
-					return waitErr
-				}
-				continue
-			}
-			return fmt.Errorf("%w: %v", ErrTransient, err)
-		}
-
-		switch {
-		case resp.StatusCode == http.StatusNotFound:
-			_ = resp.Body.Close()
-			return ErrNotFound
-		case resp.StatusCode == http.StatusTooManyRequests || resp.StatusCode >= 500:
-			_ = resp.Body.Close()
-			if attempt < deezerMaxRetries {
-				if waitErr := p.backoff(ctx, attempt); waitErr != nil {
-					return waitErr
-				}
-				continue
-			}
-			return fmt.Errorf("%w: status %d", ErrTransient, resp.StatusCode)
-		case resp.StatusCode != http.StatusOK:
-			_ = resp.Body.Close()
-			return fmt.Errorf("%w: status %d", ErrTransient, resp.StatusCode)
-		}
-
-		body, err := io.ReadAll(io.LimitReader(resp.Body, 1*1024*1024))
-		_ = resp.Body.Close()
-		if err != nil {
-			return fmt.Errorf("%w: read body: %v", ErrTransient, err)
-		}
-		if err := json.Unmarshal(body, out); err != nil {
-			return fmt.Errorf("%w: decode body: %v", ErrTransient, err)
-		}
-		return nil
-	}
-	return fmt.Errorf("%w: exhausted retries", ErrTransient)
-}
-
-// getImage performs a rate-limited GET of an image URL. Same
-// 404/5xx/network handling as TheAudioDB's getImage.
-func (p *deezerProvider) getImage(ctx context.Context, imgURL string) ([]byte, error) {
-	if err := p.rateLimitWait(ctx); err != nil {
-		return nil, err
-	}
-	req, err := http.NewRequestWithContext(ctx, http.MethodGet, imgURL, nil)
-	if err != nil {
-		return nil, fmt.Errorf("coverart deezer: build request: %w", err)
-	}
-	req.Header.Set("Accept", "image/*")
-	resp, err := p.client.Do(req)
-	if err != nil {
-		return nil, fmt.Errorf("%w: %v", ErrTransient, err)
-	}
-	defer func() { _ = resp.Body.Close() }()
-
-	switch {
-	case resp.StatusCode == http.StatusNotFound:
-		return nil, ErrNotFound
-	case resp.StatusCode != http.StatusOK:
-		return nil, fmt.Errorf("%w: status %d", ErrTransient, resp.StatusCode)
-	}
-
-	body, err := io.ReadAll(io.LimitReader(resp.Body, 5*1024*1024))
-	if err != nil {
-		return nil, fmt.Errorf("%w: read body: %v", ErrTransient, err)
-	}
-	return body, nil
-}
-
-// rateLimitWait blocks until at least deezerMinPeriod has elapsed since
-// the last call, then claims the slot.
-func (p *deezerProvider) rateLimitWait(ctx context.Context) error {
-	p.mu.Lock()
-	wait := time.Until(p.lastCall.Add(deezerMinPeriod))
-	if wait > 0 {
-		timer := time.NewTimer(wait)
-		p.mu.Unlock()
-		select {
-		case <-ctx.Done():
-			timer.Stop()
-			return ctx.Err()
-		case <-timer.C:
-		}
-		p.mu.Lock()
-	}
-	p.lastCall = time.Now()
-	p.mu.Unlock()
-	return nil
-}
-
-// backoff sleeps for 2^attempt × 250ms ± 20% jitter.
-func (p *deezerProvider) backoff(ctx context.Context, attempt int) error {
-	base := time.Duration(250*(1<<attempt)) * time.Millisecond
-	jitterRange := int64(base) / 5
-	if jitterRange <= 0 {
-		jitterRange = 1
-	}
-	jitter := time.Duration(rand.Int63n(jitterRange))
-	if rand.Intn(2) == 0 {
-		jitter = -jitter
-	}
-	d := base + jitter
-	timer := time.NewTimer(d)
-	defer timer.Stop()
-	select {
-	case <-ctx.Done():
-		return ctx.Err()
-	case <-timer.C:
-		return nil
-	}
+	return p.client.getImage(ctx, imgURL)
 }
 
 // Compile-time check: the new provider implements both interfaces.