Init commit of jobs output/error message peek project.

src/frontend/apiserver/backend/clib.go

@@ -416,3 +416,41 @@ func signalNumber(signame string, action int) int {
 	}
 	return 15 // SIGTERM as safe default
 }
+
+// FetchFile fetches up to maxBytes of a job output file from offset via the
+// controller→worker chain. The filepath must be the fully resolved absolute
+// path on the exec host.
+func FetchFile(jobid uint64, filepath string, offset uint64, maxBytes uint32) (*FetchFileResult, error) {
+cFilepath := C.CString(filepath)
+defer C.free(unsafe.Pointer(cFilepath))
+
+msg := C.xce_fetchfile_t{
+jobid:     C.uint64_t(jobid),
+filepath:  cFilepath,
+offset:    C.uint64_t(offset),
+max_bytes: C.uint32_t(maxBytes),
+}
+
+var reply *C.xce_fetchfile_reply_t
+rc := C.xcecli_fetchfile(gCtx.ctx, &msg, &reply)
+if rc < 0 {
+return nil, fmt.Errorf("xcecli_fetchfile failed: %d", int(rc))
+}
+if reply == nil {
+return nil, fmt.Errorf("xcecli_fetchfile returned nil reply")
+}
+defer C.free(unsafe.Pointer(reply))
+
+if reply.error != 0 {
+return nil, fmt.Errorf("fetchfile remote error: %d", int(reply.error))
+}
+
+result := &FetchFileResult{
+FileSize:  uint64(reply.file_size),
+BytesRead: uint32(reply.bytes_read),
+}
+if reply.bytes_read > 0 && reply.content != nil {
+result.Content = C.GoBytes(unsafe.Pointer(reply.content), C.int(reply.bytes_read))
+}
+return result, nil
+}