Version 1.6

The "--preserve-symlinks" option preserves the symlink target instead of
deriving absolute/relative-paths from it. If archived symlinks are
absolute-paths, then it is NOT recommended to use this option as the
symlinks can be clobbered on extraction (unless if "--no-safe-links" is
specified on extraction).

Changelog.md

@@ -2,6 +2,18 @@
 
 ## Upcoming Changes
 
+## Version 1.6
+
+Enforce "safe-links" on extraction by ensuring every extracted symlink actually
+points to a file in the archive. Additionally any extracted symlinks that don't
+point to a valid destination is removed. This "enforce safe-links on extract"
+can be disabled with the "--no-safe-links" option.
+
+Add "--preserve-symlinks" option that will verbatim store the symlinks' target.
+Not recommended if symlinks are pointing to absolute paths, which will be
+clobbered on extraction to a different directory unless if "--no-safe-links" is
+specified on extraction.
+
 ## Version 1.5
 
 Previous file-format-v1 implementation of "safe links" still created a symlink

README.md

@@ -27,6 +27,7 @@ API calls.
     --overwrite-create : allows overwriting an archive file
     --overwrite-extract : allows overwriting when extracting
     --no-abs-symlink : do not store absolute paths for symlinks
+    --preserve-symlinks : preserve the symlink's path on archive creation instead of deriving abs/relative paths, ignores "--no-abs-symlink" (It is not recommended to use this option, as absolute-path-symlinks may be clobbered on extraction)
     --no-safe-links : keep symlinks that link to outside archive contents
     --temp-files-dir <dir> : where to store temporary files created when compressing (defaults to current working directory)
     --write-version <version> : Force write version file format (default 1)

src/archiver.c

@@ -759,13 +759,28 @@ int write_files_fn(void *data, void *ud) {
     // Get absolute path.
     __attribute__((cleanup(
         simple_archiver_helper_cleanup_malloced))) void *abs_path = NULL;
-#if SIMPLE_ARCHIVER_PLATFORM == SIMPLE_ARCHIVER_PLATFORM_COSMOPOLITAN || \
-    SIMPLE_ARCHIVER_PLATFORM == SIMPLE_ARCHIVER_PLATFORM_MAC ||          \
-    SIMPLE_ARCHIVER_PLATFORM == SIMPLE_ARCHIVER_PLATFORM_LINUX
-    abs_path = realpath(file_info->filename, NULL);
-#endif
     __attribute__((cleanup(
         simple_archiver_helper_cleanup_malloced))) void *rel_path = NULL;
+
+    if ((state->parsed->flags & 0x100) != 0) {
+      // Preserve symlink target.
+      char *path_buf = malloc(1024);
+      ssize_t ret = readlink(file_info->filename, path_buf, 1023);
+      if (ret == -1) {
+        fprintf(stderr, "WARNING: Failed to get symlink's target!\n");
+        free(path_buf);
+        ((uint8_t *)temp_to_write->buf)[1] |= 0x8;
+      } else {
+        path_buf[ret] = 0;
+        if (path_buf[0] == '/') {
+          abs_path = path_buf;
+          ((uint8_t *)temp_to_write->buf)[1] |= 0x4;
+        } else {
+          rel_path = path_buf;
+        }
+      }
+    } else {
+      abs_path = realpath(file_info->filename, NULL);
       if (abs_path) {
         // Get relative path.
         // First get absolute path of link.
@@ -778,13 +793,15 @@ int write_files_fn(void *data, void *ud) {
           // fprintf(stderr, "DEBUG: abs_path: %s\nDEBUG: link_abs_path: %s\n",
           //                 (char*)abs_path, (char*)link_abs_path);
 
-        rel_path =
-            simple_archiver_filenames_to_relative_path(link_abs_path, abs_path);
+          rel_path = simple_archiver_filenames_to_relative_path(link_abs_path,
+                                                                abs_path);
+        }
       }
     }
 
     // Check if absolute path refers to one of the filenames.
     if (abs_path && (state->parsed->flags & 0x20) == 0 &&
+        (state->parsed->flags & 0x100) == 0 &&
         !simple_archiver_hash_map_get(state->map, abs_path,
                                       strlen(abs_path) + 1)) {
       // Is not a filename being archived.
@@ -804,6 +821,43 @@ int write_files_fn(void *data, void *ud) {
                 file_info->filename);
         ((uint8_t *)temp_to_write->buf)[1] |= 0x8;
       }
+    } else if ((state->parsed->flags & 0x100) != 0 &&
+               (state->parsed->flags & 0x80) == 0 &&
+               (((uint8_t *)temp_to_write->buf)[1] & 0x8) == 0) {
+      __attribute__((cleanup(
+          simple_archiver_helper_cleanup_c_string))) char *resolved_path = NULL;
+      if (abs_path || rel_path) {
+        resolved_path = realpath(file_info->filename, NULL);
+        if (!resolved_path) {
+          fprintf(stderr,
+                  "WARNING: Symlink \"%s\" is invalid, will not be stored!  "
+                  "(Use \"--no-safe-links\" to disable this behavior)\n",
+                  file_info->filename);
+          ((uint8_t *)temp_to_write->buf)[1] |= 0x8;
+        } else if (!simple_archiver_hash_map_get(state->map, resolved_path,
+                                                 strlen(resolved_path) + 1)) {
+          fprintf(stderr,
+                  "WARNING: Symlink \"%s\" points to outside archive contents, "
+                  "will not be stored! (Use \"--no-safe-links\" to disable "
+                  "this behavior)\n",
+                  file_info->filename);
+          ((uint8_t *)temp_to_write->buf)[1] |= 0x8;
+        }
+      } else {
+        fprintf(stderr,
+                "WARNING: Unable to get target path from symlink \"%s\"!\n",
+                file_info->filename);
+        ((uint8_t *)temp_to_write->buf)[1] |= 0x8;
+      }
+    }
+
+    if (!abs_path && !rel_path) {
+      // No valid paths, set as invalid.
+      fprintf(stderr,
+              "WARNING: Could not get valid abs/rel path for symlink \"%s\" "
+              "(invalid symlink)!\n",
+              file_info->filename);
+      ((uint8_t *)temp_to_write->buf)[1] |= 0x8;
     }
 
     // Store the 4 byte bit-flags for file.
@@ -822,8 +876,10 @@ int write_files_fn(void *data, void *ud) {
 
     // Store the absolute and relative paths.
     if (!abs_path) {
+      if ((state->parsed->flags & 0x100) == 0) {
         fprintf(stderr,
                 "WARNING: Failed to get absolute path of link destination!\n");
+      }
       temp_to_write = malloc(sizeof(SDArchiverInternalToWrite));
       temp_to_write->buf = malloc(2);
       temp_to_write->size = 2;
@@ -896,9 +952,17 @@ int write_files_fn(void *data, void *ud) {
     // Write all previously set data.
     fprintf(stderr, "Writing symlink info: %s\n", file_info->filename);
     if ((state->parsed->flags & 0x20) == 0) {
+      if (abs_path) {
         fprintf(stderr, "  abs path: %s\n", (char *)abs_path);
+      } else {
+        fprintf(stderr, "  abs path is NOT set\n");
       }
+    }
+    if (rel_path) {
       fprintf(stderr, "  rel path: %s\n", (char *)rel_path);
+    } else {
+      fprintf(stderr, "  rel path is NOT set\n");
+    }
     simple_archiver_list_get(to_write, write_list_datas_fn, state->out_f);
     simple_archiver_list_free(&to_write);
   }
@@ -974,10 +1038,15 @@ int filenames_to_abs_map_fn(void *data, void *ud) {
       char *fullpath_dirname_copy = malloc(strlen(fullpath_dirname) + 1);
       strncpy(fullpath_dirname_copy, fullpath_dirname,
               strlen(fullpath_dirname) + 1);
+      if (!simple_archiver_hash_map_get(abs_filenames, fullpath_dirname_copy,
+                                        strlen(fullpath_dirname_copy) + 1)) {
         simple_archiver_hash_map_insert(
             abs_filenames, fullpath_dirname_copy, fullpath_dirname_copy,
             strlen(fullpath_dirname_copy) + 1,
             simple_archiver_helper_datastructure_cleanup_nop, NULL);
+      } else {
+        free(fullpath_dirname_copy);
+      }
     }
     prev = fullpath_dirname;
   }
@@ -1680,6 +1749,29 @@ int files_to_chunk_count(void *data, void *ud) {
 
 int greater_fn(int64_t a, int64_t b) { return a > b; }
 
+void simple_archiver_internal_paths_to_files_map(SDArchiverHashMap *files_map,
+                                                 const char *filename) {
+  simple_archiver_hash_map_insert(
+      files_map, (void *)1, strdup((const char *)filename),
+      strlen((const char *)filename) + 1,
+      simple_archiver_helper_datastructure_cleanup_nop, NULL);
+  __attribute__((
+      cleanup(simple_archiver_helper_cleanup_c_string))) char *filename_copy =
+      strdup(filename);
+  char *filename_dirname = dirname(filename_copy);
+
+  while (strcmp(filename_dirname, ".") != 0) {
+    if (!simple_archiver_hash_map_get(files_map, filename_dirname,
+                                      strlen(filename_dirname) + 1)) {
+      simple_archiver_hash_map_insert(
+          files_map, (void *)1, strdup(filename_dirname),
+          strlen(filename_dirname) + 1,
+          simple_archiver_helper_datastructure_cleanup_nop, NULL);
+    }
+    filename_dirname = dirname(filename_dirname);
+  }
+}
+
 char *simple_archiver_error_to_string(enum SDArchiverStateReturns error) {
   switch (error) {
     case SDAS_SUCCESS:
@@ -2059,15 +2151,36 @@ int simple_archiver_write_v1(FILE *out_f, SDArchiverState *state,
       node = node->next;
       ++u32;
       memset(buf, 0, 2);
+
+      uint_fast8_t is_invalid = 0;
+
 #if SIMPLE_ARCHIVER_PLATFORM == SIMPLE_ARCHIVER_PLATFORM_COSMOPOLITAN || \
     SIMPLE_ARCHIVER_PLATFORM == SIMPLE_ARCHIVER_PLATFORM_MAC ||          \
     SIMPLE_ARCHIVER_PLATFORM == SIMPLE_ARCHIVER_PLATFORM_LINUX
-      // Check if symlink points to thing to be stored into archive.
-      __attribute__((
-          cleanup(simple_archiver_helper_cleanup_malloced))) void *abs_path =
-          realpath(node->data, NULL);
+      __attribute__((cleanup(
+          simple_archiver_helper_cleanup_malloced))) void *abs_path = NULL;
       __attribute__((cleanup(
           simple_archiver_helper_cleanup_malloced))) void *rel_path = NULL;
+      if ((state->parsed->flags & 0x100) != 0) {
+        // Preserve symlink target.
+        char *path_buf = malloc(1024);
+        ssize_t ret = readlink(node->data, path_buf, 1023);
+        if (ret == -1) {
+          fprintf(stderr, "WARNING: Failed to get symlink's target!\n");
+          free(path_buf);
+          is_invalid = 1;
+        } else {
+          path_buf[ret] = 0;
+          if (path_buf[0] == '/') {
+            abs_path = path_buf;
+            buf[0] |= 1;
+          } else {
+            rel_path = path_buf;
+          }
+        }
+      } else {
+        abs_path = realpath(node->data, NULL);
+        // Check if symlink points to thing to be stored into archive.
         if (abs_path) {
           __attribute__((cleanup(
               simple_archiver_helper_cleanup_malloced))) void *link_abs_path =
@@ -2079,10 +2192,10 @@ int simple_archiver_write_v1(FILE *out_f, SDArchiverState *state,
                                                                   abs_path);
           }
         }
-
-      uint_fast8_t is_invalid = 0;
+      }
 
       if (abs_path && (state->parsed->flags & 0x20) == 0 &&
+          (state->parsed->flags & 0x100) == 0 &&
           !simple_archiver_hash_map_get(abs_filenames, abs_path,
                                         strlen(abs_path) + 1)) {
         // Is not a filename being archived.
@@ -2098,6 +2211,36 @@ int simple_archiver_write_v1(FILE *out_f, SDArchiverState *state,
           // Safe links disabled, set preference to absolute path.
           buf[0] |= 1;
         }
+      } else if ((state->parsed->flags & 0x100) != 0 &&
+                 (state->parsed->flags & 0x80) == 0 && !is_invalid) {
+        __attribute__((cleanup(
+            simple_archiver_helper_cleanup_c_string))) char *target_realpath =
+            realpath(node->data, NULL);
+        if (!target_realpath) {
+          fprintf(
+              stderr,
+              "WARNING: \"%s\" is an invalid symlink and \"--no-safe-links\" "
+              "not specified, will skip this symlink!\n",
+              (const char *)node->data);
+          is_invalid = 1;
+        } else if (!simple_archiver_hash_map_get(abs_filenames, target_realpath,
+                                                 strlen(target_realpath) + 1)) {
+          fprintf(
+              stderr,
+              "WARNING: \"%s\" points to outside of archived files and "
+              "\"--no-safe-links\" not specified, will skip this symlink!\n",
+              (const char *)node->data);
+          is_invalid = 1;
+        }
+      }
+
+      if (!abs_path && !rel_path) {
+        // No valid paths, mark as invalid.
+        fprintf(stderr,
+                "WARNING: \"%s\" is an invalid symlink, will not store rel/abs "
+                "link paths!\n",
+                (const char *)node->data);
+        is_invalid = 1;
       }
 
       // Get symlink stats for permissions.
@@ -2842,6 +2985,18 @@ int simple_archiver_parse_archive_version_0(FILE *in_f, int_fast8_t do_extract,
       // fprintf(stderr, "\"%s\" put in map\n", key);
     }
   }
+
+  __attribute__((cleanup(simple_archiver_list_free)))
+  SDArchiverLinkedList *links_list =
+      state && state->parsed && state->parsed->flags & 0x80
+          ? NULL
+          : simple_archiver_list_init();
+  __attribute__((cleanup(simple_archiver_hash_map_free)))
+  SDArchiverHashMap *files_map =
+      state && state->parsed && state->parsed->flags & 0x80
+          ? NULL
+          : simple_archiver_hash_map_init();
+
   for (uint32_t idx = 0; idx < size; ++idx) {
     if (is_sig_int_occurred) {
       return SDAS_SIGINT;
@@ -2972,6 +3127,10 @@ int simple_archiver_parse_archive_version_0(FILE *in_f, int_fast8_t do_extract,
       cleanup_overwrite_filename_delete_simple(&to_overwrite_dest);
     }
 
+    if (files_map && !skip && out_f_name) {
+      simple_archiver_internal_paths_to_files_map(files_map, out_f_name);
+    }
+
 #if SIMPLE_ARCHIVER_PLATFORM == SIMPLE_ARCHIVER_PLATFORM_COSMOPOLITAN || \
     SIMPLE_ARCHIVER_PLATFORM == SIMPLE_ARCHIVER_PLATFORM_MAC ||          \
     SIMPLE_ARCHIVER_PLATFORM == SIMPLE_ARCHIVER_PLATFORM_LINUX
@@ -3473,6 +3632,9 @@ int simple_archiver_parse_archive_version_0(FILE *in_f, int_fast8_t do_extract,
                 return SDAS_FAILED_TO_EXTRACT_SYMLINK;
               }
             }
+            if (links_list) {
+              simple_archiver_list_add(links_list, strdup(out_f_name), NULL);
+            }
             ret = fchmodat(AT_FDCWD, out_f_name, permissions,
                            AT_SYMLINK_NOFOLLOW);
             if (ret == -1) {
@@ -3481,7 +3643,8 @@ int simple_archiver_parse_archive_version_0(FILE *in_f, int_fast8_t do_extract,
                         "  NOTICE: Setting permissions of symlink is not "
                         "supported by FS/OS!\n");
               } else {
-                fprintf(stderr,
+                fprintf(
+                    stderr,
                     "  WARNING: Failed to set permissions of symlink (%d)!\n",
                     errno);
               }
@@ -3523,6 +3686,9 @@ int simple_archiver_parse_archive_version_0(FILE *in_f, int_fast8_t do_extract,
                 return SDAS_FAILED_TO_EXTRACT_SYMLINK;
               }
             }
+            if (links_list) {
+              simple_archiver_list_add(links_list, strdup(out_f_name), NULL);
+            }
             ret = fchmodat(AT_FDCWD, out_f_name, permissions,
                            AT_SYMLINK_NOFOLLOW);
             if (ret == -1) {
@@ -3531,7 +3697,8 @@ int simple_archiver_parse_archive_version_0(FILE *in_f, int_fast8_t do_extract,
                         "  NOTICE: Setting permissions of symlink is not "
                         "supported by FS/OS!\n");
               } else {
-                fprintf(stderr,
+                fprintf(
+                    stderr,
                     "  WARNING: Failed to set permissions of symlink (%d)!\n",
                     errno);
               }
@@ -3548,11 +3715,15 @@ int simple_archiver_parse_archive_version_0(FILE *in_f, int_fast8_t do_extract,
           if (ret == -1) {
             return SDAS_FAILED_TO_EXTRACT_SYMLINK;
           }
+          if (links_list) {
+            simple_archiver_list_add(links_list, strdup(out_f_name), NULL);
+          }
           ret =
               fchmodat(AT_FDCWD, out_f_name, permissions, AT_SYMLINK_NOFOLLOW);
           if (ret == -1) {
             if (errno == EOPNOTSUPP) {
-              fprintf(stderr,
+              fprintf(
+                  stderr,
                   "  NOTICE: Setting permissions of symlink is not supported "
                   "by FS/OS!\n");
             } else {
@@ -3570,11 +3741,15 @@ int simple_archiver_parse_archive_version_0(FILE *in_f, int_fast8_t do_extract,
           if (ret == -1) {
             return SDAS_FAILED_TO_EXTRACT_SYMLINK;
           }
+          if (links_list) {
+            simple_archiver_list_add(links_list, strdup(out_f_name), NULL);
+          }
           ret =
               fchmodat(AT_FDCWD, out_f_name, permissions, AT_SYMLINK_NOFOLLOW);
           if (ret == -1) {
             if (errno == EOPNOTSUPP) {
-              fprintf(stderr,
+              fprintf(
+                  stderr,
                   "  NOTICE: Setting permissions of symlink is not supported "
                   "by FS/OS!\n");
             } else {
@@ -3593,6 +3768,10 @@ int simple_archiver_parse_archive_version_0(FILE *in_f, int_fast8_t do_extract,
     }
   }
 
+  if (do_extract && links_list && files_map) {
+    simple_archiver_safe_links_enforce(links_list, files_map);
+  }
+
   if (is_sig_int_occurred) {
     return SDAS_SIGINT;
   }
@@ -3637,6 +3816,21 @@ int simple_archiver_parse_archive_version_1(FILE *in_f, int_fast8_t do_extract,
 #endif
   }
 
+  __attribute__((cleanup(simple_archiver_list_free)))
+  SDArchiverLinkedList *links_list =
+      state && state->parsed && state->parsed->flags & 0x80
+          ? NULL
+          : simple_archiver_list_init();
+  __attribute__((cleanup(simple_archiver_hash_map_free)))
+  SDArchiverHashMap *files_map =
+      state && state->parsed && state->parsed->flags & 0x80
+          ? NULL
+          : simple_archiver_hash_map_init();
+
+  __attribute__((
+      cleanup(simple_archiver_helper_cleanup_c_string))) char *cwd_realpath =
+      realpath(".", NULL);
+
   const int_fast8_t is_compressed = (buf[0] & 1) ? 1 : 0;
 
   __attribute__((cleanup(
@@ -3704,9 +3898,7 @@ int simple_archiver_parse_archive_version_1(FILE *in_f, int_fast8_t do_extract,
     const uint_fast8_t is_invalid = (buf[1] & 4) ? 1 : 0;
 
     if (is_invalid) {
-      fprintf(stderr,
-              "  WARNING: This symlink entry was marked invalid (not a safe "
-              "link)!\n");
+      fprintf(stderr, "  WARNING: This symlink entry was marked invalid!\n");
     }
 
 #if SIMPLE_ARCHIVER_PLATFORM == SIMPLE_ARCHIVER_PLATFORM_COSMOPOLITAN || \
@@ -3789,7 +3981,8 @@ int simple_archiver_parse_archive_version_1(FILE *in_f, int_fast8_t do_extract,
         ret = symlink(path, link_name);
         if (ret == -1) {
           if (link_create_retry) {
-            fprintf(stderr,
+            fprintf(
+                stderr,
                 "  WARNING: Failed to create symlink after removing existing "
                 "symlink!\n");
             goto V1_SYMLINK_CREATE_AFTER_0;
@@ -3800,10 +3993,10 @@ int simple_archiver_parse_archive_version_1(FILE *in_f, int_fast8_t do_extract,
                       "\"--overwrite-extract\" is not specified, skipping!\n");
               goto V1_SYMLINK_CREATE_AFTER_0;
             } else {
-              fprintf(
-                  stderr,
-                  "NOTICE: Symlink already exists and \"--overwrite-extract\" "
-                  "specified, attempting to overwrite...\n");
+              fprintf(stderr,
+                      "  NOTICE: Symlink already exists and "
+                      "\"--overwrite-extract\" specified, attempting to "
+                      "overwrite...\n");
               unlink(link_name);
               link_create_retry = 1;
               goto V1_SYMLINK_CREATE_RETRY_0;
@@ -3828,7 +4021,7 @@ int simple_archiver_parse_archive_version_1(FILE *in_f, int_fast8_t do_extract,
       V1_SYMLINK_CREATE_AFTER_0:
         link_create_retry = 1;
 #endif
-      } else {
+      } else if (!do_extract) {
         fprintf(stderr, "  Abs path: %s\n", path);
       }
     } else if (!do_extract) {
@@ -3861,7 +4054,8 @@ int simple_archiver_parse_archive_version_1(FILE *in_f, int_fast8_t do_extract,
         ret = symlink(path, link_name);
         if (ret == -1) {
           if (link_create_retry) {
-            fprintf(stderr,
+            fprintf(
+                stderr,
                 "  WARNING: Failed to create symlink after removing existing "
                 "symlink!\n");
             goto V1_SYMLINK_CREATE_AFTER_1;
@@ -3872,10 +4066,10 @@ int simple_archiver_parse_archive_version_1(FILE *in_f, int_fast8_t do_extract,
                       "\"--overwrite-extract\" is not specified, skipping!\n");
               goto V1_SYMLINK_CREATE_AFTER_1;
             } else {
-              fprintf(
-                  stderr,
-                  "NOTICE: Symlink already exists and \"--overwrite-extract\" "
-                  "specified, attempting to overwrite...\n");
+              fprintf(stderr,
+                      "  NOTICE: Symlink already exists and "
+                      "\"--overwrite-extract\" specified, attempting to "
+                      "overwrite...\n");
               unlink(link_name);
               link_create_retry = 1;
               goto V1_SYMLINK_CREATE_RETRY_1;
@@ -3900,7 +4094,7 @@ int simple_archiver_parse_archive_version_1(FILE *in_f, int_fast8_t do_extract,
       V1_SYMLINK_CREATE_AFTER_1:
         link_create_retry = 1;
 #endif
-      } else {
+      } else if (!do_extract) {
         fprintf(stderr, "  Rel path: %s\n", path);
       }
     } else if (!do_extract) {
@@ -3911,6 +4105,9 @@ int simple_archiver_parse_archive_version_1(FILE *in_f, int_fast8_t do_extract,
         !skip_due_to_invalid) {
       fprintf(stderr, "  WARNING: Symlink \"%s\" was not created!\n",
               link_name);
+    } else if (do_extract && link_extracted && !skip_due_to_map &&
+               !skip_due_to_invalid && links_list) {
+      simple_archiver_list_add(links_list, strdup(link_name), NULL);
     }
   }
 
@@ -4011,6 +4208,11 @@ int simple_archiver_parse_archive_version_1(FILE *in_f, int_fast8_t do_extract,
       simple_archiver_helper_64_bit_be(&u64);
       file_info->file_size = u64;
 
+      if (files_map) {
+        simple_archiver_internal_paths_to_files_map(files_map,
+                                                    file_info->filename);
+      }
+
       simple_archiver_list_add(file_info_list, file_info,
                                free_internal_file_info);
       file_info = NULL;
@@ -4340,6 +4542,10 @@ int simple_archiver_parse_archive_version_1(FILE *in_f, int_fast8_t do_extract,
     }
   }
 
+  if (do_extract && links_list && files_map) {
+    simple_archiver_safe_links_enforce(links_list, files_map);
+  }
+
   return SDAS_SUCCESS;
 }
 
@@ -4523,3 +4729,69 @@ int simple_archiver_validate_file_path(const char *filepath) {
 
   return 0;
 }
+
+void simple_archiver_safe_links_enforce(SDArchiverLinkedList *links_list,
+                                        SDArchiverHashMap *files_map) {
+  uint_fast8_t need_to_print_note = 1;
+  // safe-links: Check that every link maps to a file in the files_map.
+  __attribute__((
+      cleanup(simple_archiver_helper_cleanup_c_string))) char *path_to_cwd =
+      realpath(".", NULL);
+
+  // Ensure path_to_cwd ends with '/'.
+  uint32_t idx = 0;
+  while (path_to_cwd[idx] != 0) {
+    ++idx;
+  }
+  if (path_to_cwd[idx - 1] != '/') {
+    char *temp = malloc(idx + 2);
+    memcpy(temp, path_to_cwd, idx);
+    temp[idx] = '/';
+    temp[idx + 1] = 0;
+    free(path_to_cwd);
+    path_to_cwd = temp;
+  }
+
+  // Check every link to make sure it points to an existing file.
+  SDArchiverLLNode *links_node = links_list->head;
+  while (links_node->next != links_list->tail) {
+    links_node = links_node->next;
+    __attribute__((
+        cleanup(simple_archiver_helper_cleanup_c_string))) char *link_realpath =
+        realpath(links_node->data, NULL);
+    if (link_realpath) {
+      // Get local path.
+      __attribute__((cleanup(
+          simple_archiver_helper_cleanup_c_string))) char *link_localpath =
+          simple_archiver_filenames_to_relative_path(path_to_cwd,
+                                                     link_realpath);
+      if (!simple_archiver_hash_map_get(files_map, link_localpath,
+                                        strlen(link_localpath) + 1)) {
+        // Invalid symlink.
+        fprintf(stderr,
+                "Symlink \"%s\" is invalid (not pointing to archived file), "
+                "removing...\n",
+                (const char *)links_node->data);
+        unlink(links_node->data);
+        if (need_to_print_note) {
+          fprintf(stderr,
+                  "NOTE: Disable this behavior with \"--no-safe-links\" if "
+                  "needed.\n");
+          need_to_print_note = 0;
+        }
+      }
+    } else {
+      // Invalid symlink.
+      fprintf(stderr,
+              "Symlink \"%s\" is invalid (failed to resolve), removing...\n",
+              (const char *)links_node->data);
+      unlink(links_node->data);
+      if (need_to_print_note) {
+        fprintf(stderr,
+                "NOTE: Disable this behavior with \"--no-safe-links\" if "
+                "needed.\n");
+        need_to_print_note = 0;
+      }
+    }
+  }
+}

src/archiver.h

@@ -109,4 +109,9 @@ char *simple_archiver_file_abs_path(const char *filename);
 /// Returns 5 if "filepath" is NULL.
 int simple_archiver_validate_file_path(const char *filepath);
 
+/// Removes links from "links_list" in cwd if it is not valid or does not point
+/// to a file in "files_map".
+void simple_archiver_safe_links_enforce(SDArchiverLinkedList *links_list,
+                                        SDArchiverHashMap *files_map);
+
 #endif

src/parser.c

@@ -168,6 +168,12 @@ void simple_archiver_print_usage(void) {
   fprintf(stderr, "--overwrite-extract : allows overwriting when extracting\n");
   fprintf(stderr,
           "--no-abs-symlink : do not store absolute paths for symlinks\n");
+  fprintf(
+      stderr,
+      "--preserve-symlinks : preserve the symlink's path on archive creation "
+      "instead of deriving abs/relative paths, ignores \"--no-abs-symlink\" "
+      "(It is not recommended to use this option, as absolute-path-symlinks "
+      "may be clobbered on extraction)\n");
   fprintf(stderr,
           "--no-safe-links : keep symlinks that link to outside archive "
           "contents\n");
@@ -306,6 +312,8 @@ int simple_archiver_parse_args(int argc, const char **argv,
         out->flags |= 0x8;
       } else if (strcmp(argv[0], "--no-abs-symlink") == 0) {
         out->flags |= 0x20;
+      } else if (strcmp(argv[0], "--preserve-symlinks") == 0) {
+        out->flags |= 0x100;
       } else if (strcmp(argv[0], "--no-safe-links") == 0) {
         out->flags |= 0x80;
         fprintf(stderr,

src/parser.h

@@ -37,6 +37,7 @@ typedef struct SDArchiverParsed {
   /// 0b xx1x xxxx - Do not save absolute paths for symlinks.
   /// 0b x1xx xxxx - Sort files by size before archiving.
   /// 0b 1xxx xxxx - No safe links.
+  /// 0b xxxx xxx1 xxxx xxxx - Preserve symlink target.
   uint32_t flags;
   /// Null-terminated string.
   char *filename;

src/test.c

@@ -256,6 +256,11 @@ int main(void) {
     CHECK_STREQ(rel_path, "../other/dir/");
     simple_archiver_helper_cleanup_c_string(&rel_path);
 
+    rel_path = simple_archiver_filenames_to_relative_path(
+        "/one/two/three/", "/one/two/three/four");
+    CHECK_STREQ(rel_path, "four");
+    simple_archiver_helper_cleanup_c_string(&rel_path);
+
     CHECK_FALSE(simple_archiver_validate_file_path("Local/Path"));
     CHECK_TRUE(simple_archiver_validate_file_path("/Abs/Path"));
     CHECK_TRUE(simple_archiver_validate_file_path("Local/../../not/really"));