Fix the problem of not using error template in theme (#3166)

#### What type of PR is this?

/kind bug
/area core

#### What this PR does / why we need it:

Currently, if there is no `error.html` error template in theme, but there is a `404.html` error template, this will not work correctly.

We always get rendering result from global error template `error.html`.

This PR mainly provides a `ThemeTemplateAvailabilityProvider` to check if the template is available in theme instead of in globally predefined templates.

#### Which issue(s) this PR fixes:

Fixes https://github.com/halo-dev/halo/issues/3062

#### Special notes for your reviewer:

1. Download and install any theme
2. Check the theme folder
3. Check folder `templates/error`
4. Try to remove `templates/error/error.html` template file
5. Create `templates/error/404.html`
6. Request a page which does not exist
7. See the result

#### Does this PR introduce a user-facing change?

```release-note
解决主题自定义错误模板不生效的问题。
```

src/main/java/run/halo/app/infra/exception/handlers/HaloErrorWebExceptionHandler.java

@@ -1,6 +1,7 @@
 package run.halo.app.infra.exception.handlers;
 
 import java.util.Map;
+import java.util.Optional;
 import org.springframework.boot.autoconfigure.web.ErrorProperties;
 import org.springframework.boot.autoconfigure.web.WebProperties;
 import org.springframework.boot.autoconfigure.web.reactive.error.DefaultErrorWebExceptionHandler;
@@ -11,9 +12,16 @@ import org.springframework.http.ProblemDetail;
 import org.springframework.web.reactive.function.server.ServerRequest;
 import org.springframework.web.reactive.function.server.ServerResponse;
 import reactor.core.publisher.Mono;
+import run.halo.app.theme.ThemeContext;
+import run.halo.app.theme.ThemeResolver;
+import run.halo.app.theme.engine.ThemeTemplateAvailabilityProvider;
 
 public class HaloErrorWebExceptionHandler extends DefaultErrorWebExceptionHandler {
 
+    private final ThemeTemplateAvailabilityProvider templateAvailabilityProvider;
+
+    private final ThemeResolver themeResolver;
+
     /**
      * Create a new {@code DefaultErrorWebExceptionHandler} instance.
      *
@@ -29,6 +37,9 @@ public class HaloErrorWebExceptionHandler extends DefaultErrorWebExceptionHandle
         ErrorProperties errorProperties,
         ApplicationContext applicationContext) {
         super(errorAttributes, resources, errorProperties, applicationContext);
+        this.templateAvailabilityProvider =
+            applicationContext.getBean(ThemeTemplateAvailabilityProvider.class);
+        this.themeResolver = applicationContext.getBean(ThemeResolver.class);
     }
 
     @Override
@@ -45,4 +56,24 @@ public class HaloErrorWebExceptionHandler extends DefaultErrorWebExceptionHandle
             .contentType(MediaType.APPLICATION_PROBLEM_JSON)
             .bodyValue(errorAttributes.get("error"));
     }
+
+    @Override
+    protected Mono<ServerResponse> renderErrorView(ServerRequest request) {
+        return themeResolver.getTheme(request.exchange().getRequest())
+            .flatMap(themeContext -> super.renderErrorView(request)
+                .contextWrite(context -> context.put(ThemeContext.class, themeContext)));
+    }
+
+    @Override
+    protected Mono<ServerResponse> renderErrorView(String viewName,
+        ServerResponse.BodyBuilder responseBody, Map<String, Object> error) {
+        return Mono.deferContextual(contextView -> {
+            Optional<ThemeContext> themeContext = contextView.getOrEmpty(ThemeContext.class);
+            if (themeContext.isPresent()
+                && templateAvailabilityProvider.isTemplateAvailable(themeContext.get(), viewName)) {
+                return responseBody.render(viewName, error);
+            }
+            return super.renderErrorView(viewName, responseBody, error);
+        });
+    }
 }

src/main/java/run/halo/app/infra/utils/FilePathUtils.java

@@ -1,25 +0,0 @@
-package run.halo.app.infra.utils;
-
-import java.nio.file.FileSystem;
-import java.nio.file.FileSystems;
-import java.nio.file.Path;
-import java.nio.file.Paths;
-import org.thymeleaf.util.StringUtils;
-
-/**
- * File system path utils.
- *
- * @author guqing
- * @since 2.0.0
- */
-public class FilePathUtils {
-    private FilePathUtils() {
-    }
-
-    public static Path combinePath(String first, String... more) {
-        FileSystem fileSystem = FileSystems.getDefault();
-        Path path = fileSystem.getPath(first, more);
-        String unixPath = StringUtils.replace(path.normalize(), "\\", "/");
-        return Paths.get(unixPath);
-    }
-}

src/main/java/run/halo/app/theme/TemplateEngineManager.java

@@ -100,7 +100,7 @@ public class TemplateEngineManager {
             thymeleafProperties.isRenderHiddenMarkersBeforeCheckboxes());
 
         var mainResolver = haloTemplateResolver();
-        mainResolver.setPrefix(theme.getPath() + "/templates/");
+        mainResolver.setPrefix(theme.getPath().resolve("templates") + "/");
         engine.addTemplateResolver(mainResolver);
         // replace StandardDialect with SpringStandardDialect
         engine.setDialect(new SpringStandardDialect() {

src/main/java/run/halo/app/theme/ThemeConfiguration.java

@@ -7,6 +7,7 @@ import static org.springframework.web.reactive.function.server.RouterFunctions.r
 import java.io.IOException;
 import java.nio.file.Path;
 import java.time.Instant;
+import org.apache.commons.lang3.StringUtils;
 import org.springframework.boot.autoconfigure.web.WebProperties;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
@@ -18,8 +19,7 @@ import org.springframework.web.reactive.function.server.RouterFunction;
 import org.springframework.web.reactive.function.server.ServerResponse;
 import org.thymeleaf.extras.springsecurity6.dialect.SpringSecurityDialect;
 import reactor.core.publisher.Mono;
-import run.halo.app.infra.properties.HaloProperties;
-import run.halo.app.infra.utils.FilePathUtils;
+import run.halo.app.infra.ThemeRootGetter;
 import run.halo.app.theme.dialect.HaloSpringSecurityDialect;
 import run.halo.app.theme.dialect.LinkExpressionObjectDialect;
 
@@ -29,10 +29,11 @@ import run.halo.app.theme.dialect.LinkExpressionObjectDialect;
  */
 @Configuration
 public class ThemeConfiguration {
-    private final HaloProperties haloProperties;
 
-    public ThemeConfiguration(HaloProperties haloProperties) {
-        this.haloProperties = haloProperties;
+    private final ThemeRootGetter themeRoot;
+
+    public ThemeConfiguration(ThemeRootGetter themeRoot) {
+        this.themeRoot = themeRoot;
     }
 
     @Bean
@@ -43,6 +44,7 @@ public class ThemeConfiguration {
             request -> {
                 var themeName = request.pathVariable("themeName");
                 var resource = request.pathVariable("resource");
+                resource = StringUtils.removeStart(resource, "/");
                 var fsRes = new FileSystemResource(getThemeAssetsPath(themeName, resource));
                 var bodyBuilder = ServerResponse.ok()
                     .cacheControl(cacheProperties.getCachecontrol().toHttpCacheControl());
@@ -61,8 +63,11 @@ public class ThemeConfiguration {
     }
 
     private Path getThemeAssetsPath(String themeName, String resource) {
-        return FilePathUtils.combinePath(haloProperties.getWorkDir().toString(),
-            "themes", themeName, "templates", "assets", resource);
+        return themeRoot.get()
+            .resolve(themeName)
+            .resolve("templates")
+            .resolve("assets")
+            .resolve(resource);
     }
 
     @Bean

src/main/java/run/halo/app/theme/ThemeResolver.java

@@ -1,17 +1,14 @@
 package run.halo.app.theme;
 
-import java.nio.file.Files;
 import lombok.AllArgsConstructor;
 import org.apache.commons.lang3.StringUtils;
-import org.springframework.boot.autoconfigure.thymeleaf.ThymeleafProperties;
 import org.springframework.http.server.reactive.ServerHttpRequest;
 import org.springframework.stereotype.Component;
 import org.springframework.util.Assert;
 import reactor.core.publisher.Mono;
 import run.halo.app.infra.SystemConfigurableEnvironmentFetcher;
 import run.halo.app.infra.SystemSetting.Theme;
-import run.halo.app.infra.properties.HaloProperties;
-import run.halo.app.infra.utils.FilePathUtils;
+import run.halo.app.infra.ThemeRootGetter;
 
 /**
  * @author johnniang
@@ -20,17 +17,14 @@ import run.halo.app.infra.utils.FilePathUtils;
 @Component
 @AllArgsConstructor
 public class ThemeResolver {
-    private static final String THEME_WORK_DIR = "themes";
+
     private final SystemConfigurableEnvironmentFetcher environmentFetcher;
 
-    private final HaloProperties haloProperties;
-
-    private final ThymeleafProperties thymeleafProperties;
+    private final ThemeRootGetter themeRoot;
 
     public Mono<ThemeContext> getThemeContext(String themeName) {
         Assert.hasText(themeName, "Theme name cannot be empty");
-        var path = FilePathUtils.combinePath(haloProperties.getWorkDir().toString(),
-            THEME_WORK_DIR, themeName);
+        var path = themeRoot.get().resolve(themeName);
         return Mono.just(ThemeContext.builder().name(themeName).path(path))
             .flatMap(builder -> environmentFetcher.fetch(Theme.GROUP, Theme.class)
                 .mapNotNull(Theme::getActive)
@@ -55,8 +49,7 @@ public class ThemeResolver {
                     themeName = activatedTheme;
                 }
                 boolean active = StringUtils.equals(activatedTheme, themeName);
-                var path = FilePathUtils.combinePath(haloProperties.getWorkDir().toString(),
-                    THEME_WORK_DIR, themeName);
+                var path = themeRoot.get().resolve(themeName);
                 return builder.name(themeName)
                     .path(path)
                     .active(active)
@@ -64,22 +57,4 @@ public class ThemeResolver {
             });
     }
 
-    /**
-     * Check whether the template file exists.
-     *
-     * @param viewName view name must not be blank
-     * @return if exists return true, otherwise return false
-     */
-    public Mono<Boolean> isTemplateAvailable(ServerHttpRequest request, String viewName) {
-        return getTheme(request)
-            .map(themeContext -> {
-                String prefix = themeContext.getPath() + "/templates/";
-                String viewNameToUse = viewName;
-                if (!viewNameToUse.endsWith(thymeleafProperties.getSuffix())) {
-                    viewNameToUse = viewNameToUse + thymeleafProperties.getSuffix();
-                }
-                return Files.exists(FilePathUtils.combinePath(prefix, viewNameToUse));
-            })
-            .onErrorResume(e -> Mono.just(false));
-    }
 }

src/main/java/run/halo/app/theme/engine/DefaultThemeTemplateAvailabilityProvider.java

@@ -0,0 +1,25 @@
+package run.halo.app.theme.engine;
+
+import java.nio.file.Files;
+import org.springframework.boot.autoconfigure.thymeleaf.ThymeleafProperties;
+import org.springframework.stereotype.Component;
+import run.halo.app.theme.ThemeContext;
+
+@Component
+public class DefaultThemeTemplateAvailabilityProvider implements ThemeTemplateAvailabilityProvider {
+
+    private final ThymeleafProperties thymeleafProperties;
+
+    public DefaultThemeTemplateAvailabilityProvider(ThymeleafProperties thymeleafProperties) {
+        this.thymeleafProperties = thymeleafProperties;
+    }
+
+    @Override
+    public boolean isTemplateAvailable(ThemeContext themeContext, String viewName) {
+        var suffix = thymeleafProperties.getSuffix();
+        // Currently, we only support Path here.
+        var path = themeContext.getPath().resolve("templates").resolve(viewName + suffix);
+        return Files.exists(path);
+    }
+
+}

src/main/java/run/halo/app/theme/engine/ThemeTemplateAvailabilityProvider.java

@@ -0,0 +1,9 @@
+package run.halo.app.theme.engine;
+
+import run.halo.app.theme.ThemeContext;
+
+public interface ThemeTemplateAvailabilityProvider {
+
+    boolean isTemplateAvailable(ThemeContext themeContext, String viewName);
+
+}

src/test/java/run/halo/app/theme/engine/DefaultThemeTemplateAvailabilityProviderTest.java

@@ -0,0 +1,47 @@
+package run.halo.app.theme.engine;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.mockito.Mockito.when;
+
+import java.io.FileNotFoundException;
+import java.net.URISyntaxException;
+import java.nio.file.Path;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.InjectMocks;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+import org.springframework.boot.autoconfigure.thymeleaf.ThymeleafProperties;
+import org.springframework.util.ResourceUtils;
+import run.halo.app.theme.ThemeContext;
+
+@ExtendWith(MockitoExtension.class)
+class DefaultThemeTemplateAvailabilityProviderTest {
+
+    @InjectMocks
+    DefaultThemeTemplateAvailabilityProvider provider;
+
+    @Mock
+    ThymeleafProperties thymeleafProperties;
+
+    @Test
+    void templateAvailableTest() throws FileNotFoundException, URISyntaxException {
+        var themeUrl = ResourceUtils.getURL("classpath:themes/default");
+        var themePath = Path.of(themeUrl.toURI());
+
+        when(thymeleafProperties.getSuffix()).thenReturn(".html");
+        var themeContext = ThemeContext.builder()
+            .name("default")
+            .path(themePath)
+            .build();
+        boolean templateAvailable = provider.isTemplateAvailable(themeContext, "fake");
+        assertFalse(templateAvailable);
+
+        templateAvailable = provider.isTemplateAvailable(themeContext, "index");
+        assertTrue(templateAvailable);
+
+        templateAvailable = provider.isTemplateAvailable(themeContext, "timezone");
+        assertTrue(templateAvailable);
+    }
+}