fix(server): fall back to text/plain; charset=utf-8 when MIME type is unknown in artifact server

server/artifacts/artifact_server.go

@@ -544,7 +544,14 @@ func (a *ArtifactServer) returnArtifact(ctx context.Context, w http.ResponseWrit
 
 	key, _ := art.GetKey()
 	w.Header().Add("Content-Disposition", fmt.Sprintf(`filename="%s"`, path.Base(key)))
-	w.Header().Add("Content-Type", mime.TypeByExtension(path.Ext(key)))
+	// mime.TypeByExtension relies on the system MIME database, which may not exist in
+	// minimal container images such as distroless. Fall back to "text/plain; charset=utf-8" so that
+	// unrecognized extensions (e.g. ".log") are still served with a valid Content-Type.
+	contentType := mime.TypeByExtension(path.Ext(key))
+	if contentType == "" {
+		contentType = "text/plain; charset=utf-8"
+	}
+	w.Header().Add("Content-Type", contentType)
 	a.setSecurityHeaders(w)
 
 	_, err = io.Copy(w, stream)

server/artifacts/artifact_server_test.go

@@ -65,6 +65,7 @@ var bucketsOfKeys = map[string][]string{
 		"my-wf/my-node-1/my-gcs-artifact.tgz",
 		"my-wf/my-node-1/my-oss-artifact.zip",
 		"my-wf/my-node-1/my-s3-artifact.tgz",
+		"my-wf/my-node-1/main.log",
 		"my-wf/my-node-inline/main.log",
 	},
 	"my-bucket-2": {
@@ -264,6 +265,18 @@ func newServer(t *testing.T) *ArtifactServer {
 									},
 								},
 							},
+							{
+								// Log artifact created when archiveLogs is enabled
+								// (see workflow/executor/executor.go:saveContainerLogs).
+								// The key ends with ".log", which is not in the MIME database
+								// on minimal container images (e.g. distroless).
+								Name: "main-logs",
+								ArtifactLocation: wfv1.ArtifactLocation{
+									S3: &wfv1.S3Artifact{
+										Key: "my-wf/my-node-1/main.log",
+									},
+								},
+							},
 						},
 					},
 				},
@@ -474,6 +487,16 @@ func TestArtifactServer_GetArtifactFile(t *testing.T) {
 			statusCode:  200,
 			isDirectory: false,
 		},
+		{
+			path:        "/artifact-files/my-ns/workflows/my-wf/my-node-1/outputs/main-logs",
+			statusCode:  200,
+			isDirectory: false,
+			// Verify that .log artifacts are served with a non-empty Content-Type.
+			// The ".log" extension may not be in the system MIME database on minimal
+			// container images (e.g. distroless), causing mime.TypeByExtension to
+			// return "". The fallback in returnArtifact ensures "text/plain; charset=utf-8"
+			// is used instead.
+		},
 	}
 
 	for _, tt := range tests {
@@ -502,6 +525,7 @@ func TestArtifactServer_GetArtifactFile(t *testing.T) {
 					}
 				} else {
 					assert.Equal(t, "my-data", string(all))
+					assert.NotEmpty(t, recorder.Header().Get("Content-Type"), "Content-Type header must not be empty")
 				}
 			}
 		})