1 files changed, 127 insertions, 0 deletions
diff --git a/pdf/pdf_loop_detect.c b/pdf/pdf_loop_detect.c
new file mode 100644
index 00000000..7d08b182
--- /dev/null
+++ b/pdf/pdf_loop_detect.c
@@ -0,0 +1,127 @@
+/* Copyright (C) 2018-2021 Artifex Software, Inc.
+   All Rights Reserved.
+
+   This software is provided AS-IS with no warranty, either express or
+   implied.
+
+   This software is distributed under license and may not be copied,
+   modified or distributed except as expressly authorized under the terms
+   of the license contained in the file LICENSE in this distribution.
+
+   Refer to licensing information at http://www.artifex.com or contact
+   Artifex Software, Inc.,  1305 Grant Avenue - Suite 200, Novato,
+   CA 94945, U.S.A., +1(415)492-9861, for further information.
+*/
+
+/* code for handling circular references */
+
+#include "pdf_int.h"
+#include "pdf_loop_detect.h"
+
+static int pdfi_init_loop_detector(pdf_context *ctx)
+{
+    if (ctx->loop_detection) {
+        dbgmprintf(ctx->memory, "Attempt to initialise loop detector while one is in operation\n");
+        return_error(gs_error_unknownerror);
+    }
+
+    ctx->loop_detection = (uint64_t *)gs_alloc_bytes(ctx->memory, INITIAL_LOOP_TRACKER_SIZE * sizeof (uint64_t), "allocate loop tracking array");
+    if (ctx->loop_detection == NULL)
+        return_error(gs_error_VMerror);
+
+    ctx->loop_detection_entries = 0;
+    ctx->loop_detection_size = INITIAL_LOOP_TRACKER_SIZE;
+    return 0;
+}
+
+static int pdfi_free_loop_detector(pdf_context *ctx)
+{
+    if (ctx->loop_detection == NULL) {
+        dbgmprintf(ctx->memory, "Attempt to free loop detector without initialising it\n");
+        return 0;
+    }
+    if (ctx->loop_detection != NULL)
+        gs_free_object(ctx->memory, ctx->loop_detection, "Free array for loop tracking");
+    ctx->loop_detection_entries = 0;
+    ctx->loop_detection_size = 0;
+    ctx->loop_detection = NULL;
+
+    return 0;
+}
+
+int pdfi_loop_detector_add_object(pdf_context *ctx, uint64_t object)
+{
+    if (ctx->loop_detection == NULL) {
+        dbgmprintf(ctx->memory, "Attempt to use loop detector without initialising it\n");
+        return 0;
+    }
+
+    if (ctx->loop_detection_entries == ctx->loop_detection_size) {
+        uint64_t *New;
+
+        New = (uint64_t *)gs_alloc_bytes(ctx->memory, (ctx->loop_detection_size + INITIAL_LOOP_TRACKER_SIZE) * sizeof (uint64_t), "re-allocate loop tracking array");
+        if (New == NULL) {
+            return_error(gs_error_VMerror);
+        }
+        memcpy(New, ctx->loop_detection, ctx->loop_detection_entries * sizeof(uint64_t));
+        gs_free_object(ctx->memory, ctx->loop_detection, "Free array for loop tracking");
+        ctx->loop_detection_size += INITIAL_LOOP_TRACKER_SIZE;
+        ctx->loop_detection = New;
+    }
+    ctx->loop_detection[ctx->loop_detection_entries++] = object;
+    return 0;
+}
+
+bool pdfi_loop_detector_check_object(pdf_context *ctx, uint64_t object)
+{
+    int i = 0;
+
+    if (ctx->loop_detection == NULL) {
+        dbgmprintf(ctx->memory, "Attempt to use loop detector without initialising it\n");
+        return 0;
+    }
+
+    for (i=0;i < ctx->loop_detection_entries;i++) {
+        if (ctx->loop_detection[i] == object) {
+            char info_string[256];
+            gs_sprintf(info_string, "Error! circular reference to object %"PRIu64" detected.\n", object);
+            pdfi_set_error(ctx, 0, NULL, E_PDF_CIRCULARREF, "pdfi_loop_detector_check_object", info_string);
+            return true;
+        }
+    }
+    return false;
+}
+
+int pdfi_loop_detector_mark(pdf_context *ctx)
+{
+    int code = 0;
+
+    if (ctx->loop_detection == NULL) {
+        code = pdfi_init_loop_detector(ctx);
+        if (code < 0)
+            return code;
+    }
+
+    return pdfi_loop_detector_add_object(ctx, 0);
+}
+
+int pdfi_loop_detector_cleartomark(pdf_context *ctx)
+{
+    if (ctx->loop_detection == NULL) {
+        dbgmprintf(ctx->memory, "Attempt to use loop detector without initialising it\n");
+        return 0;
+    }
+
+    while (ctx->loop_detection[--ctx->loop_detection_entries] != 0) {
+        ctx->loop_detection[ctx->loop_detection_entries] = 0;
+    }
+    /* FIXME - potential optimisation
+     * Instead of freeing the loop detection array every tiome we are done with it
+     * and then reallocating a new one next time we need one, we could just keep
+     * the existing (empty) array. I suspect this would provide a small performance
+     * improvement.
+     */
+    if (ctx->loop_detection_entries == 0)
+        pdfi_free_loop_detector(ctx);
+    return 0;
+}