Fix artifact v4 upload above 8MB (#31664)

Multiple chunks are uploaded with type "block" without using
"appendBlock" and eventually out of order for bigger uploads.
8MB seems to be the chunk size

This change parses the blockList uploaded after all blocks to get the
final artifact size and order them correctly before calculating the
sha256 checksum over all blocks

Fixes #31354

(cherry picked from commit b594cec2bda6f861effedb2e8e0a7ebba191c0e9)

Conflicts:
	routers/api/actions/artifactsv4.go
  conflict because of Refactor AppURL usage (#30885) 67c1a07285008cc00036a87cef966c3bd519a50c
    that was not cherry-picked in Forgejo
    the resolution consist of removing the extra ctx argument

routers/api/actions/artifacts_chunks.go

@@ -123,6 +123,54 @@ func listChunksByRunID(st storage.ObjectStorage, runID int64) (map[int64][]*chun
 	return chunksMap, nil
 }
 
+func listChunksByRunIDV4(st storage.ObjectStorage, runID, artifactID int64, blist *BlockList) ([]*chunkFileItem, error) {
+	storageDir := fmt.Sprintf("tmpv4%d", runID)
+	var chunks []*chunkFileItem
+	chunkMap := map[string]*chunkFileItem{}
+	dummy := &chunkFileItem{}
+	for _, name := range blist.Latest {
+		chunkMap[name] = dummy
+	}
+	if err := st.IterateObjects(storageDir, func(fpath string, obj storage.Object) error {
+		baseName := filepath.Base(fpath)
+		if !strings.HasPrefix(baseName, "block-") {
+			return nil
+		}
+		// when read chunks from storage, it only contains storage dir and basename,
+		// no matter the subdirectory setting in storage config
+		item := chunkFileItem{Path: storageDir + "/" + baseName, ArtifactID: artifactID}
+		var size int64
+		var b64chunkName string
+		if _, err := fmt.Sscanf(baseName, "block-%d-%d-%s", &item.RunID, &size, &b64chunkName); err != nil {
+			return fmt.Errorf("parse content range error: %v", err)
+		}
+		rchunkName, err := base64.URLEncoding.DecodeString(b64chunkName)
+		if err != nil {
+			return fmt.Errorf("failed to parse chunkName: %v", err)
+		}
+		chunkName := string(rchunkName)
+		item.End = item.Start + size - 1
+		if _, ok := chunkMap[chunkName]; ok {
+			chunkMap[chunkName] = &item
+		}
+		return nil
+	}); err != nil {
+		return nil, err
+	}
+	for i, name := range blist.Latest {
+		chunk, ok := chunkMap[name]
+		if !ok || chunk.Path == "" {
+			return nil, fmt.Errorf("missing Chunk (%d/%d): %s", i, len(blist.Latest), name)
+		}
+		chunks = append(chunks, chunk)
+		if i > 0 {
+			chunk.Start = chunkMap[blist.Latest[i-1]].End + 1
+			chunk.End += chunk.Start
+		}
+	}
+	return chunks, nil
+}
+
 func mergeChunksForRun(ctx *ArtifactContext, st storage.ObjectStorage, runID int64, artifactName string) error {
 	// read all db artifacts by name
 	artifacts, err := db.Find[actions.ActionArtifact](ctx, actions.FindArtifactsOptions{
@@ -230,7 +278,7 @@ func mergeChunksForArtifact(ctx *ArtifactContext, chunks []*chunkFileItem, st st
 		rawChecksum := hash.Sum(nil)
 		actualChecksum := hex.EncodeToString(rawChecksum)
 		if !strings.HasSuffix(checksum, actualChecksum) {
-			return fmt.Errorf("update artifact error checksum is invalid")
+			return fmt.Errorf("update artifact error checksum is invalid %v vs %v", checksum, actualChecksum)
 		}
 	}