feat: Allow websocket subscription with PAK/PAT

backend/api/src/main/kotlin/io/tolgee/api/v2/controllers/batch/V2ExportController.kt

@@ -2,6 +2,7 @@ package io.tolgee.api.v2.controllers.batch
 
 import io.swagger.v3.oas.annotations.Operation
 import io.swagger.v3.oas.annotations.tags.Tag
+import io.tolgee.component.ProjectLastModifiedManager
 import io.tolgee.constants.Message
 import io.tolgee.dtos.request.export.ExportParams
 import io.tolgee.exceptions.BadRequestException
@@ -28,6 +29,7 @@ import org.springframework.web.bind.annotation.PostMapping
 import org.springframework.web.bind.annotation.RequestBody
 import org.springframework.web.bind.annotation.RequestMapping
 import org.springframework.web.bind.annotation.RestController
+import org.springframework.web.context.request.WebRequest
 import org.springframework.web.servlet.mvc.method.annotation.StreamingResponseBody
 import java.io.InputStream
 import java.io.OutputStream
@@ -46,39 +48,86 @@ class V2ExportController(
   private val languageService: LanguageService,
   private val authenticationFacade: AuthenticationFacade,
   private val streamingResponseBodyProvider: StreamingResponseBodyProvider,
+  private val projectLastModifiedManager: ProjectLastModifiedManager,
 ) {
   @GetMapping(value = [""])
-  @Operation(summary = "Export data")
+  @Operation(
+    summary = "Export data",
+    description = """
+      Exports project data in various formats (JSON, properties, YAML, etc.).
+
+      ## HTTP Conditional Requests Support
+
+      This endpoint supports HTTP conditional requests using the If-Modified-Since header:
+
+      - **If-Modified-Since header provided**: The server checks if the project data has been modified since the specified date
+      - **Data not modified**: Returns HTTP 304 Not Modified with empty body
+      - **Data modified or no header**: Returns HTTP 200 OK with the exported data and Last-Modified header
+
+      The Last-Modified header in the response contains the timestamp of the last project modification, 
+      which can be used for subsequent conditional requests to avoid unnecessary data transfer when the 
+      project hasn't changed.
+
+      Cache-Control header is set to max-age=0 to ensure validation on each request.
+    """,
+  )
   @RequiresProjectPermissions([Scope.TRANSLATIONS_VIEW])
   @AllowApiAccess
   @ExportApiResponse
   fun exportData(
     @ParameterObject params: ExportParams,
-  ): ResponseEntity<StreamingResponseBody> {
-    params.languages =
-      languageService
-        .getLanguagesForExport(params.languages, projectHolder.project.id, authenticationFacade.authenticatedUser.id)
-        .toList()
-        .map { language -> language.tag }
-        .toSet()
-    val exported = exportService.export(projectHolder.project.id, params)
-    checkExportNotEmpty(exported)
-    return getExportResponse(params, exported)
+    request: WebRequest,
+  ): ResponseEntity<StreamingResponseBody>? {
+    return projectLastModifiedManager.onlyWhenProjectDataChanged(request) { headersBuilder ->
+      params.languages =
+        languageService
+          .getLanguagesForExport(params.languages, projectHolder.project.id, authenticationFacade.authenticatedUser.id)
+          .toList()
+          .map { language -> language.tag }
+          .toSet()
+      val exported = exportService.export(projectHolder.project.id, params)
+      checkExportNotEmpty(exported)
+      val responseEntity = getExportResponse(params, exported)
+      headersBuilder.headers(responseEntity.headers)
+      responseEntity.body
+    }
   }
 
   @PostMapping(value = [""])
   @Operation(
     summary = "Export data (post)",
-    description = """Exports data (post). Useful when exceeding allowed URL size.""",
+    description = """
+      Exports project data in various formats (JSON, properties, YAML, etc.). 
+      Useful when exceeding allowed URL size with GET requests.
+
+      ## HTTP Conditional Requests Support
+
+      This endpoint supports HTTP conditional requests using the If-Modified-Since header:
+
+      - **If-Modified-Since header provided**: The server checks if the project data has been modified since the specified date
+      - **Data not modified**: Returns HTTP 412 Precondition Failed with empty body (as per HTTP specification for POST requests)
+      - **Data modified or no header**: Returns HTTP 200 OK with the exported data and Last-Modified header
+
+      Note: Unlike GET requests which return 304 Not Modified, POST requests return 412 Precondition Failed 
+      when the If-Modified-Since condition is not met, as POST is considered a modifying method according 
+      to HTTP specifications.
+
+      The Last-Modified header in the response contains the timestamp of the last project modification, 
+      which can be used for subsequent conditional requests to avoid unnecessary data transfer when the 
+      project hasn't changed.
+
+      Cache-Control header is set to max-age=0 to ensure validation on each request.
+    """,
   )
   @ReadOnlyOperation
   @RequiresProjectPermissions([Scope.TRANSLATIONS_VIEW])
   @AllowApiAccess
   @ExportApiResponse
   fun exportPost(
     @RequestBody params: ExportParams,
-  ): ResponseEntity<StreamingResponseBody> {
-    return exportData(params)
+    request: WebRequest,
+  ): ResponseEntity<StreamingResponseBody>? {
+    return exportData(params, request)
   }
 
   private fun getZipHeaders(projectName: String): HttpHeaders {

backend/api/src/main/kotlin/io/tolgee/api/v2/controllers/translation/TranslationsController.kt

@@ -15,6 +15,7 @@ import io.tolgee.activity.ActivityService
 import io.tolgee.activity.RequestActivity
 import io.tolgee.activity.data.ActivityType
 import io.tolgee.api.v2.controllers.IController
+import io.tolgee.component.ProjectLastModifiedManager
 import io.tolgee.component.ProjectTranslationLastModifiedManager
 import io.tolgee.constants.Message
 import io.tolgee.dtos.queryResults.TranslationHistoryView
@@ -57,7 +58,6 @@ import org.springframework.data.domain.Sort
 import org.springframework.data.web.PagedResourcesAssembler
 import org.springframework.data.web.SortDefault
 import org.springframework.hateoas.PagedModel
-import org.springframework.http.CacheControl
 import org.springframework.http.ResponseEntity
 import org.springframework.transaction.annotation.Transactional
 import org.springframework.web.bind.WebDataBinder
@@ -73,7 +73,6 @@ import org.springframework.web.bind.annotation.RequestMapping
 import org.springframework.web.bind.annotation.RequestParam
 import org.springframework.web.bind.annotation.RestController
 import org.springframework.web.context.request.WebRequest
-import java.util.concurrent.TimeUnit
 
 @Suppress("MVCPathVariableInspection", "SpringJavaInjectionPointsAutowiringInspection")
 @RestController
@@ -106,6 +105,7 @@ class TranslationsController(
   private val createOrUpdateTranslationsFacade: CreateOrUpdateTranslationsFacade,
   private val taskService: ITaskService,
   private val translationSuggestionService: TranslationSuggestionService,
+  private val projectLastModifiedManager: ProjectLastModifiedManager,
 ) : IController {
   @GetMapping(value = ["/{languages}"])
   @Operation(
@@ -162,32 +162,19 @@ When null, resulting file will be a flat key-value object.
     filterTag: List<String>? = null,
     request: WebRequest,
   ): ResponseEntity<Map<String, Any>>? {
-    val lastModified: Long = projectTranslationLastModifiedManager.getLastModified(projectHolder.project.id)
+    return projectLastModifiedManager.onlyWhenProjectDataChanged(request) {
+      val permittedTags =
+        securityService
+          .filterViewPermissionByTag(projectId = projectHolder.project.id, languageTags = languages)
 
-    if (request.checkNotModified(lastModified)) {
-      return null
-    }
-
-    val permittedTags =
-      securityService
-        .filterViewPermissionByTag(projectId = projectHolder.project.id, languageTags = languages)
-
-    val response =
       translationService.getTranslations(
         languageTags = permittedTags,
         namespace = ns,
         projectId = projectHolder.project.id,
         structureDelimiter = request.getStructureDelimiter(),
         filterTag = filterTag,
       )
-
-    return ResponseEntity
-      .ok()
-      .lastModified(lastModified)
-      .cacheControl(CacheControl.maxAge(0, TimeUnit.SECONDS))
-      .body(
-        response,
-      )
+    }
   }
 
   @PutMapping("")

backend/api/src/main/kotlin/io/tolgee/component/ProjectLastModifiedManager.kt

@@ -0,0 +1,74 @@
+package io.tolgee.component
+
+import io.tolgee.security.ProjectHolder
+import org.springframework.http.CacheControl
+import org.springframework.http.ResponseEntity
+import org.springframework.stereotype.Component
+import org.springframework.web.context.request.WebRequest
+import java.util.concurrent.TimeUnit
+
+/**
+ * Component responsible for managing HTTP conditional requests based on project data modifications.
+ *
+ * This manager implements the HTTP conditional request mechanism (If-Modified-Since/Last-Modified headers)
+ * to enable efficient caching of project-related data. It helps reduce unnecessary data transfer and
+ * processing by allowing clients to cache responses and only receive new data when the project has
+ * actually been modified.
+ */
+@Component
+class ProjectLastModifiedManager(
+  private val projectTranslationLastModifiedManager: ProjectTranslationLastModifiedManager,
+  private val projectHolder: ProjectHolder,
+) {
+  /**
+   * Executes a function only when the project data has been modified since the client's last request.
+   *
+   * This method implements HTTP conditional request handling by:
+   * 1. Retrieving the last modification timestamp of the current project
+   * 2. Checking if the client's If-Modified-Since header indicates the data is still current
+   * 3. If data hasn't changed, returning null
+   *    (which translates to HTTP 304 Not Modified / or HTTP 412 when the method is POST)
+   * 4. If data has changed, executing the provided function and wrapping the result in a ResponseEntity
+   *    with appropriate cache control headers
+   *
+   * The response includes:
+   * - Last-Modified header set to the project's modification timestamp
+   * - Cache-Control header set to max-age=0 to ensure validation on each request
+   *
+   * This mechanism helps optimize performance by preventing export data computation and loading from the database when
+   * not modified.
+   *
+   */
+  fun <T> onlyWhenProjectDataChanged(
+    request: WebRequest,
+    fn: (
+      /**
+       * Enables setting of additional headers on the response.
+       */
+      headersBuilder: ResponseEntity.HeadersBuilder<*>,
+    ) -> T?,
+  ): ResponseEntity<T>? {
+    val lastModified: Long = projectTranslationLastModifiedManager.getLastModified(projectHolder.project.id)
+
+    if (request.checkNotModified(lastModified)) {
+      return null
+    }
+
+    val headersBuilder =
+      ResponseEntity
+        .ok()
+        .lastModified(lastModified)
+        .cacheControl(DEFAULT_CACHE_CONTROL_HEADER)
+
+    val response = fn(headersBuilder)
+
+    return headersBuilder
+      .body(
+        response,
+      )
+  }
+
+  companion object {
+    val DEFAULT_CACHE_CONTROL_HEADER = CacheControl.maxAge(0, TimeUnit.SECONDS)
+  }
+}

backend/api/src/main/kotlin/io/tolgee/controllers/ExportController.kt

@@ -4,6 +4,7 @@ import com.fasterxml.jackson.module.kotlin.jacksonObjectMapper
 import io.swagger.v3.oas.annotations.Operation
 import io.swagger.v3.oas.annotations.tags.Tag
 import io.tolgee.api.v2.controllers.IController
+import io.tolgee.component.ProjectLastModifiedManager
 import io.tolgee.model.enums.Scope
 import io.tolgee.security.ProjectHolder
 import io.tolgee.security.authentication.AllowApiAccess
@@ -19,6 +20,7 @@ import org.springframework.web.bind.annotation.GetMapping
 import org.springframework.web.bind.annotation.PathVariable
 import org.springframework.web.bind.annotation.RequestMapping
 import org.springframework.web.bind.annotation.RestController
+import org.springframework.web.context.request.WebRequest
 import org.springframework.web.servlet.mvc.method.annotation.StreamingResponseBody
 import java.io.ByteArrayInputStream
 import java.io.OutputStream
@@ -40,6 +42,7 @@ class ExportController(
   private val projectHolder: ProjectHolder,
   private val authenticationFacade: AuthenticationFacade,
   private val streamingResponseBodyProvider: StreamingResponseBodyProvider,
+  private val projectLastModifiedManager: ProjectLastModifiedManager,
 ) : IController {
   @GetMapping(value = ["/jsonZip"], produces = ["application/zip"])
   @Operation(summary = "Export to ZIP of jsons", description = "Exports data as ZIP of jsons", deprecated = true)
@@ -48,38 +51,39 @@ class ExportController(
   @Deprecated("Use v2 export controller")
   fun doExportJsonZip(
     @PathVariable("projectId") projectId: Long?,
-  ): ResponseEntity<StreamingResponseBody> {
-    val allLanguages =
-      permissionService.getPermittedViewLanguages(
-        projectHolder.project.id,
-        authenticationFacade.authenticatedUser.id,
-      )
+    request: WebRequest,
+  ): ResponseEntity<StreamingResponseBody>? {
+    return projectLastModifiedManager.onlyWhenProjectDataChanged(request) { headersBuilder ->
+      val allLanguages =
+        permissionService.getPermittedViewLanguages(
+          projectHolder.project.id,
+          authenticationFacade.authenticatedUser.id,
+        )
 
-    return ResponseEntity
-      .ok()
-      .header(
+      headersBuilder.header(
         "Content-Disposition",
         String.format("attachment; filename=\"%s.zip\"", projectHolder.project.name),
-      ).body(
-        streamingResponseBodyProvider.createStreamingResponseBody { out: OutputStream ->
-          val zipOutputStream = ZipOutputStream(out)
-          val translations =
-            translationService.getTranslations(
-              allLanguages.map { it.tag }.toSet(),
-              null,
-              projectHolder.project.id,
-              '.',
-            )
-          for ((key, value) in translations) {
-            zipOutputStream.putNextEntry(ZipEntry(String.format("%s.json", key)))
-            val data = jacksonObjectMapper().writerWithDefaultPrettyPrinter().writeValueAsBytes(value)
-            val byteArrayInputStream = ByteArrayInputStream(data)
-            IOUtils.copy(byteArrayInputStream, zipOutputStream)
-            byteArrayInputStream.close()
-            zipOutputStream.closeEntry()
-          }
-          zipOutputStream.close()
-        },
       )
+
+      streamingResponseBodyProvider.createStreamingResponseBody { out: OutputStream ->
+        val zipOutputStream = ZipOutputStream(out)
+        val translations =
+          translationService.getTranslations(
+            allLanguages.map { it.tag }.toSet(),
+            null,
+            projectHolder.project.id,
+            '.',
+          )
+        for ((key, value) in translations) {
+          zipOutputStream.putNextEntry(ZipEntry(String.format("%s.json", key)))
+          val data = jacksonObjectMapper().writerWithDefaultPrettyPrinter().writeValueAsBytes(value)
+          val byteArrayInputStream = ByteArrayInputStream(data)
+          IOUtils.copy(byteArrayInputStream, zipOutputStream)
+          byteArrayInputStream.close()
+          zipOutputStream.closeEntry()
+        }
+        zipOutputStream.close()
+      }
+    }
   }
 }