Update Changelog.md

Tweaked the default hash function and hash-map-bucket-size.

CMakeLists.txt

@@ -1,7 +1,7 @@
-cmake_minimum_required(VERSION 3.7)
+cmake_minimum_required(VERSION 3.10)
 project(SimpleArchiver C)
 
-set(SimpleArchiver_VERSION 1.0)
+set(SimpleArchiver_VERSION 1.7)
 
 set(SimpleArchiver_SOURCES
     src/main.c

Changelog.md

@@ -2,6 +2,44 @@
 
 ## Upcoming Changes
 
+## Version 1.7
+
+Refactor the internal hash-map data structure.
+
+Minor update to CMakeLists.txt.
+
+## 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
+if a relative or absolute link existed in the file. This version fixes this, and
+prevents invalid symlinks from being created. (This check is only done if the
+bit-flag is set in the file as mentioned in the file-format spec for v1 files.)
+
+## Version 1.4
+
+Do "safe links" behavior by default: symlinks pointing to outside of archived
+files (or invalid symlinks) should not be included in the archive, unless if the
+option "--no-safe-links" is specified. This is supported in both v0 and v1 file
+formats.
+
+## Version 1.3
+
+Prevent `simplearchiver` from busy-waiting during non-blocking IO by sleeping
+in "EWOULDBLOCK" conditions. This results in less consumed cpu time by the
+process, especially during compression.
+
 ## Version 1.2
 
 Proper handling of Ctrl+C (SIGINT). This prevents temporary files from

README.md

@@ -27,6 +27,8 @@ 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)
     --chunk-min-size <bytes> : v1 file format minimum chunk size (default 4194304 or 4MiB)
@@ -38,6 +40,11 @@ API calls.
 Note that `--compressor` and `--decompressor` cmds must accept data from stdin
 and return processed data to stdout.
 
+## Using the Cosmopolitan-Compiled Version
+
+Note that on Linux, the `actually_portable_simplearchiver` binaries may attempt
+to open via Wine (if Wine is installed). [A workaround is mentioned here.](https://github.com/jart/cosmopolitan/blob/master/README.md#linux)
+
 ## Changes
 
 See the [Changelog](https://git.seodisparate.com/stephenseo/SimpleArchiver/src/branch/main/Changelog.md).

file_format.md

@@ -57,6 +57,11 @@ Following the file-count bytes, the following bytes are added for each file:
         2. The second bit is "other execute permission".
         3. The third bit is UNSET if relative links are preferred, and is SET
            if absolute links are preferred.
+        4. The fourth bit is set if this file/symlink-entry is invalid and must
+           be skipped. Ignore following bytes after these 4 bytes bit-flags in
+           this specification and skip to the next entry; if marked invalid,
+           the following specification bytes for this file/symlink entry must
+           not exist.
     3. The third byte.
         1. Currently unused.
     4. The fourth byte.
@@ -128,6 +133,9 @@ Following the link-count bytes, the following bytes are added for each symlink:
     2. The second byte.
         1. The first bit is "other write permission".
         2. The second bit is "other execute permission".
+        3. If this bit is set, then this entry is marked invalid. The link name
+           will be preserved in this entry, but the following link target paths
+           will be set to zero-length and will not be stored.
 2. 2 bytes 16-bit unsigned integer "link name" in big-endian. This does not
    include the NULL at the end of the string. Must not be zero.
 3. X bytes of link-name (length defined by previous value). Is a NULL-terminated

src/archiver.c

@@ -64,6 +64,8 @@ void handle_sig_int(int sig) {
     is_sig_int_occurred = 1;
   }
 }
+
+const struct timespec nonblock_sleep = {.tv_sec = 0, .tv_nsec = 1000000};
 #endif
 
 typedef struct SDArchiverInternalToWrite {
@@ -112,6 +114,20 @@ void cleanup_temp_filename_delete(void ***ptrs_array) {
 #endif
 }
 
+void cleanup_overwrite_filename_delete_simple(char **filename) {
+  if (filename && *filename) {
+    if ((*filename)[0] != 0) {
+#if SIMPLE_ARCHIVER_PLATFORM == SIMPLE_ARCHIVER_PLATFORM_COSMOPOLITAN || \
+    SIMPLE_ARCHIVER_PLATFORM == SIMPLE_ARCHIVER_PLATFORM_MAC ||          \
+    SIMPLE_ARCHIVER_PLATFORM == SIMPLE_ARCHIVER_PLATFORM_LINUX
+      unlink(*filename);
+#endif
+    }
+    free(*filename);
+    *filename = NULL;
+  }
+}
+
 int write_files_fn(void *data, void *ud) {
   if (is_sig_int_occurred) {
     return 1;
@@ -297,6 +313,7 @@ int write_files_fn(void *data, void *ud) {
             ret = write(pipe_into_cmd[1], write_buf, write_count);
             if (ret == -1) {
               if (errno == EAGAIN || errno == EWOULDBLOCK) {
+                nanosleep(&nonblock_sleep, NULL);
                 write_again = 1;
               } else {
                 // Error during write.
@@ -354,7 +371,7 @@ int write_files_fn(void *data, void *ud) {
             // fprintf(stderr, "read_done\n");
           } else if (ret == -1) {
             if (errno == EAGAIN || errno == EWOULDBLOCK) {
-              // Nop.
+              nanosleep(&nonblock_sleep, NULL);
             } else {
               // Read error.
               fprintf(stderr,
@@ -742,13 +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.
@@ -761,29 +793,93 @@ 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, set preference to absolute path.
-      fprintf(stderr,
+      // Is not a filename being archived.
+      if ((state->parsed->flags & 0x80) != 0) {
+        // No safe links, set preference to absolute path.
+        fprintf(
+            stderr,
             "NOTICE: abs_path exists, \"--no-abs-symlink\" not specified, "
             "and link refers to file NOT in archive; preferring abs_path.\n");
         ((uint8_t *)temp_to_write->buf)[1] |= 0x4;
+      } else {
+        // Safe links, do not store symlink!
+        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 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.
     simple_archiver_list_add(to_write, temp_to_write, free_internal_to_write);
 
+    if ((((uint8_t *)temp_to_write->buf)[1] & 0x8) != 0) {
+      // Skipped symlink.
+      simple_archiver_list_get(to_write, write_list_datas_fn, state->out_f);
+      simple_archiver_list_free(&to_write);
+      char format_str[64];
+      snprintf(format_str, 64, FILE_COUNTS_OUTPUT_FORMAT_STR_1, state->digits,
+               state->digits);
+      fprintf(stderr, format_str, ++(state->count), state->max);
+      return 0;
+    }
+
     // 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;
@@ -856,9 +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);
   }
@@ -934,10 +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;
   }
@@ -1171,6 +1280,7 @@ int read_decomp_to_out_file(const char *out_filename, int in_pipe,
       } else {
         if (errno == EAGAIN || errno == EWOULDBLOCK) {
           // Non-blocking read from pipe.
+          nanosleep(&nonblock_sleep, NULL);
           continue;
         } else {
           // Error.
@@ -1210,6 +1320,7 @@ int read_decomp_to_out_file(const char *out_filename, int in_pipe,
       } else {
         if (errno == EAGAIN || errno == EWOULDBLOCK) {
           // Non-blocking read from pipe.
+          nanosleep(&nonblock_sleep, NULL);
           continue;
         } else {
           // Error.
@@ -1638,6 +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:
@@ -2017,15 +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 =
@@ -2037,12 +2192,56 @@ int simple_archiver_write_v1(FILE *out_f, SDArchiverState *state,
                                                                   abs_path);
           }
         }
+      }
+
       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, set preference to absolute path.
+        // Is not a filename being archived.
+        if ((state->parsed->flags & 0x80) == 0) {
+          // Not a "safe link", mark invalid and continue.
+          is_invalid = 1;
+          fprintf(stderr,
+                  "WARNING: \"%s\" points to outside of archived files (or is "
+                  "invalid) and \"--no-safe-links\" not specified, will not "
+                  "store abs/rel-links to this entry!\n",
+                  (const char *)node->data);
+        } else {
+          // 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.
       struct stat stat_buf;
@@ -2084,6 +2283,11 @@ int simple_archiver_write_v1(FILE *out_f, SDArchiverState *state,
       buf[0] = 0xFE;
       buf[1] = 3;
 #endif
+
+      if (is_invalid) {
+        buf[1] |= 4;
+      }
+
       if (fwrite(buf, 1, 2, out_f) != 2) {
         return SDAS_FAILED_TO_WRITE;
       }
@@ -2104,7 +2308,7 @@ int simple_archiver_write_v1(FILE *out_f, SDArchiverState *state,
         return SDAS_FAILED_TO_WRITE;
       }
 
-      if (abs_path && (state->parsed->flags & 0x20) == 0) {
+      if (abs_path && (state->parsed->flags & 0x20) == 0 && !is_invalid) {
         len = strlen(abs_path);
         if (len >= 0xFFFF) {
           fprintf(stderr,
@@ -2128,7 +2332,7 @@ int simple_archiver_write_v1(FILE *out_f, SDArchiverState *state,
         }
       }
 
-      if (rel_path) {
+      if (rel_path && !is_invalid) {
         len = strlen(rel_path);
         if (len >= 0xFFFF) {
           fprintf(stderr,
@@ -2436,6 +2640,7 @@ int simple_archiver_write_v1(FILE *out_f, SDArchiverState *state,
                     // Non-blocking write.
                     has_hold = (int)fread_ret;
                     memcpy(hold_buf, buf, fread_ret);
+                    nanosleep(&nonblock_sleep, NULL);
                   } else {
                     fprintf(
                         stderr,
@@ -2462,6 +2667,7 @@ int simple_archiver_write_v1(FILE *out_f, SDArchiverState *state,
               if (write_ret < 0) {
                 if (errno == EAGAIN || errno == EWOULDBLOCK) {
                   // Non-blocking write.
+                  nanosleep(&nonblock_sleep, NULL);
                 } else {
                   return SDAS_INTERNAL_ERROR;
                 }
@@ -2484,6 +2690,7 @@ int simple_archiver_write_v1(FILE *out_f, SDArchiverState *state,
           if (read_ret < 0) {
             if (errno == EAGAIN || errno == EWOULDBLOCK) {
               // Non-blocking read.
+              nanosleep(&nonblock_sleep, NULL);
             } else {
               fprintf(stderr,
                       "ERROR: Reading from compressor, pipe read error!\n");
@@ -2518,6 +2725,7 @@ int simple_archiver_write_v1(FILE *out_f, SDArchiverState *state,
           if (read_ret < 0) {
             if (errno == EAGAIN || errno == EWOULDBLOCK) {
               // Non-blocking read.
+              nanosleep(&nonblock_sleep, NULL);
             } else {
               fprintf(stderr,
                       "ERROR: Reading from compressor, pipe read error!\n");
@@ -2777,6 +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;
@@ -2793,6 +3013,9 @@ int simple_archiver_parse_archive_version_0(FILE *in_f, int_fast8_t do_extract,
         simple_archiver_helper_cleanup_malloced))) void *out_f_name = NULL;
     __attribute__((cleanup(simple_archiver_helper_cleanup_FILE))) FILE *out_f =
         NULL;
+    __attribute__((cleanup(
+        cleanup_overwrite_filename_delete_simple))) char *to_overwrite_dest =
+        NULL;
     if (u16 < SIMPLE_ARCHIVER_BUFFER_SIZE) {
       if (fread(buf, 1, u16 + 1, in_f) != (size_t)u16 + 1) {
         return SDAS_INVALID_FILE;
@@ -2822,12 +3045,14 @@ int simple_archiver_parse_archive_version_0(FILE *in_f, int_fast8_t do_extract,
           if (fd == -1) {
             if (errno == ELOOP) {
               // Is an existing symbolic file.
-              unlink((const char *)buf);
+              // Defer deletion to after "is invalid" check.
+              to_overwrite_dest = strdup((const char *)buf);
             }
           } else {
             close(fd);
             // Is an existing file.
-            unlink((const char *)buf);
+            // Defer deletion to after "is invalid" check.
+            to_overwrite_dest = strdup((const char *)buf);
           }
         }
         if (!skip) {
@@ -2869,12 +3094,14 @@ int simple_archiver_parse_archive_version_0(FILE *in_f, int_fast8_t do_extract,
           if (fd == -1) {
             if (errno == ELOOP) {
               // Is an existing symbolic file.
-              unlink((const char *)uc_heap_buf);
+              // Defer deletion to after "is invalid" check.
+              to_overwrite_dest = strdup((const char *)uc_heap_buf);
             }
           } else {
             close(fd);
             // Is an existing file.
-            unlink((const char *)uc_heap_buf);
+            // Defer deletion to after "is invalid" check.
+            to_overwrite_dest = strdup((const char *)uc_heap_buf);
           }
         }
         if (!skip) {
@@ -2889,6 +3116,21 @@ int simple_archiver_parse_archive_version_0(FILE *in_f, int_fast8_t do_extract,
       return SDAS_INVALID_FILE;
     }
 
+    // Check for "invalid entry" flag.
+    if ((buf[1] & 0x8) != 0) {
+      free(to_overwrite_dest);
+      to_overwrite_dest = NULL;
+      fprintf(stderr, "  This file entry was marked invalid, skipping...\n");
+      continue;
+    } else {
+      // Do deferred overwrite action: remove existing file/symlink.
+      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
@@ -3154,6 +3396,7 @@ int simple_archiver_parse_archive_version_0(FILE *in_f, int_fast8_t do_extract,
                   }
                 } else if (write_ret == -1) {
                   if (errno == EAGAIN || errno == EWOULDBLOCK) {
+                    nanosleep(&nonblock_sleep, NULL);
                     write_again = 1;
                   } else {
                     // Error.
@@ -3197,6 +3440,7 @@ int simple_archiver_parse_archive_version_0(FILE *in_f, int_fast8_t do_extract,
               } else if (read_ret == -1) {
                 if (errno == EAGAIN || errno == EWOULDBLOCK) {
                   // No bytes to read yet.
+                  nanosleep(&nonblock_sleep, NULL);
                 } else {
                   // Error.
                   fprintf(stderr,
@@ -3365,19 +3609,19 @@ int simple_archiver_parse_archive_version_0(FILE *in_f, int_fast8_t do_extract,
             if (ret == -1) {
               if (retry_symlink) {
                 fprintf(stderr,
-                        "WARNING: Failed to create symlink after removing "
+                        "  WARNING: Failed to create symlink after removing "
                         "existing symlink!\n");
                 goto V0_SYMLINK_CREATE_AFTER_0;
               } else if (errno == EEXIST) {
                 if ((state->parsed->flags & 8) == 0) {
                   fprintf(
                       stderr,
-                      "WARNING: Symlink already exists and "
+                      "  WARNING: Symlink already exists and "
                       "\"--overwrite-extract\" is not specified, skipping!\n");
                   goto V0_SYMLINK_CREATE_AFTER_0;
                 } else {
                   fprintf(stderr,
-                          "NOTICE: Symlink already exists and "
+                          "  NOTICE: Symlink already exists and "
                           "\"--overwrite-extract\" specified, attempting to "
                           "overwrite...\n");
                   unlink(out_f_name);
@@ -3388,16 +3632,20 @@ 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) {
               if (errno == EOPNOTSUPP) {
                 fprintf(stderr,
-                        "NOTICE: Setting permissions of symlink is not "
+                        "  NOTICE: Setting permissions of symlink is not "
                         "supported by FS/OS!\n");
               } else {
-                fprintf(stderr,
-                        "WARNING: Failed to set permissions of symlink (%d)!\n",
+                fprintf(
+                    stderr,
+                    "  WARNING: Failed to set permissions of symlink (%d)!\n",
                     errno);
               }
             }
@@ -3415,19 +3663,19 @@ int simple_archiver_parse_archive_version_0(FILE *in_f, int_fast8_t do_extract,
             if (ret == -1) {
               if (retry_symlink) {
                 fprintf(stderr,
-                        "WARNING: Failed to create symlink after removing "
+                        "  WARNING: Failed to create symlink after removing "
                         "existing symlink!\n");
                 goto V0_SYMLINK_CREATE_AFTER_1;
               } else if (errno == EEXIST) {
                 if ((state->parsed->flags & 8) == 0) {
                   fprintf(
                       stderr,
-                      "WARNING: Symlink already exists and "
+                      "  WARNING: Symlink already exists and "
                       "\"--overwrite-extract\" is not specified, skipping!\n");
                   goto V0_SYMLINK_CREATE_AFTER_1;
                 } else {
                   fprintf(stderr,
-                          "NOTICE: Symlink already exists and "
+                          "  NOTICE: Symlink already exists and "
                           "\"--overwrite-extract\" specified, attempting to "
                           "overwrite...\n");
                   unlink(out_f_name);
@@ -3438,16 +3686,20 @@ 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) {
               if (errno == EOPNOTSUPP) {
                 fprintf(stderr,
-                        "NOTICE: Setting permissions of symlink is not "
+                        "  NOTICE: Setting permissions of symlink is not "
                         "supported by FS/OS!\n");
               } else {
-                fprintf(stderr,
-                        "WARNING: Failed to set permissions of symlink (%d)!\n",
+                fprintf(
+                    stderr,
+                    "  WARNING: Failed to set permissions of symlink (%d)!\n",
                     errno);
               }
             }
@@ -3463,16 +3715,20 @@ 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,
-                      "NOTICE: Setting permissions of symlink is not supported "
+              fprintf(
+                  stderr,
+                  "  NOTICE: Setting permissions of symlink is not supported "
                   "by FS/OS!\n");
             } else {
               fprintf(stderr,
-                      "WARNING: Failed to set permissions of symlink (%d)!\n",
+                      "  WARNING: Failed to set permissions of symlink (%d)!\n",
                       errno);
             }
           }
@@ -3485,16 +3741,20 @@ 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,
-                      "NOTICE: Setting permissions of symlink is not supported "
+              fprintf(
+                  stderr,
+                  "  NOTICE: Setting permissions of symlink is not supported "
                   "by FS/OS!\n");
             } else {
               fprintf(stderr,
-                      "WARNING: Failed to set permissions of symlink (%d)!\n",
+                      "  WARNING: Failed to set permissions of symlink (%d)!\n",
                       errno);
             }
           }
@@ -3502,12 +3762,16 @@ int simple_archiver_parse_archive_version_0(FILE *in_f, int_fast8_t do_extract,
         } else {
           fprintf(
               stderr,
-              "WARNING: Symlink entry in archive has no paths to link to!\n");
+              "  WARNING: Symlink entry in archive has no paths to link to!\n");
         }
       }
     }
   }
 
+  if (do_extract && links_list && files_map) {
+    simple_archiver_safe_links_enforce(links_list, files_map);
+  }
+
   if (is_sig_int_occurred) {
     return SDAS_SIGINT;
   }
@@ -3552,6 +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(
@@ -3616,6 +3895,11 @@ int simple_archiver_parse_archive_version_1(FILE *in_f, int_fast8_t do_extract,
       return SDAS_INVALID_FILE;
     }
     const uint_fast8_t absolute_preferred = (buf[0] & 1) ? 1 : 0;
+    const uint_fast8_t is_invalid = (buf[1] & 4) ? 1 : 0;
+
+    if (is_invalid) {
+      fprintf(stderr, "  WARNING: This symlink entry was marked invalid!\n");
+    }
 
 #if SIMPLE_ARCHIVER_PLATFORM == SIMPLE_ARCHIVER_PLATFORM_COSMOPOLITAN || \
     SIMPLE_ARCHIVER_PLATFORM == SIMPLE_ARCHIVER_PLATFORM_MAC ||          \
@@ -3625,7 +3909,7 @@ int simple_archiver_parse_archive_version_1(FILE *in_f, int_fast8_t do_extract,
 
     uint_fast8_t link_extracted = 0;
     uint_fast8_t skip_due_to_map = 0;
-    uint_fast8_t skip_due_to_invalid = 0;
+    uint_fast8_t skip_due_to_invalid = is_invalid ? 1 : 0;
 
     if (fread(buf, 1, 2, in_f) != 2) {
       return SDAS_INVALID_FILE;
@@ -3697,21 +3981,22 @@ 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,
-                    "WARNING: Failed to create symlink after removing existing "
+            fprintf(
+                stderr,
+                "  WARNING: Failed to create symlink after removing existing "
                 "symlink!\n");
             goto V1_SYMLINK_CREATE_AFTER_0;
           } else if (errno == EEXIST) {
             if ((state->parsed->flags & 8) == 0) {
               fprintf(stderr,
-                      "WARNING: Symlink already exists and "
+                      "  WARNING: Symlink already exists and "
                       "\"--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;
@@ -3723,11 +4008,11 @@ int simple_archiver_parse_archive_version_1(FILE *in_f, int_fast8_t do_extract,
         if (ret == -1) {
           if (errno == EOPNOTSUPP) {
             fprintf(stderr,
-                    "NOTICE: Setting permissions of symlink is not supported "
+                    "  NOTICE: Setting permissions of symlink is not supported "
                     "by FS/OS!\n");
           } else {
             fprintf(stderr,
-                    "WARNING: Failed to set permissions of symlink (%d)!\n",
+                    "  WARNING: Failed to set permissions of symlink (%d)!\n",
                     errno);
           }
         }
@@ -3736,7 +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) {
@@ -3769,21 +4054,22 @@ 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,
-                    "WARNING: Failed to create symlink after removing existing "
+            fprintf(
+                stderr,
+                "  WARNING: Failed to create symlink after removing existing "
                 "symlink!\n");
             goto V1_SYMLINK_CREATE_AFTER_1;
           } else if (errno == EEXIST) {
             if ((state->parsed->flags & 8) == 0) {
               fprintf(stderr,
-                      "WARNING: Symlink already exists and "
+                      "  WARNING: Symlink already exists and "
                       "\"--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;
@@ -3795,11 +4081,11 @@ int simple_archiver_parse_archive_version_1(FILE *in_f, int_fast8_t do_extract,
         if (ret == -1) {
           if (errno == EOPNOTSUPP) {
             fprintf(stderr,
-                    "NOTICE: Setting permissions of symlink is not supported "
+                    "  NOTICE: Setting permissions of symlink is not supported "
                     "by FS/OS!\n");
           } else {
             fprintf(stderr,
-                    "WARNING: Failed to set permissions of symlink (%d)!\n",
+                    "  WARNING: Failed to set permissions of symlink (%d)!\n",
                     errno);
           }
         }
@@ -3808,7 +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) {
@@ -3819,6 +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);
     }
   }
 
@@ -3919,6 +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;
@@ -4248,6 +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;
 }
 
@@ -4431,3 +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/data_structures/hash_map.c

@@ -76,19 +76,17 @@ int simple_archiver_hash_map_internal_pick_in_list(void *data, void *ud) {
 
 uint64_t simple_archiver_hash_default_fn(const void *key, size_t key_size) {
   uint64_t seed = 0;
-  uint64_t temp = 0;
-  size_t count = 0;
+  uint64_t temp;
   for (size_t idx = 0; idx < key_size; ++idx) {
-    temp |= ((uint64_t) * ((uint8_t *)key + idx)) << (8 * count);
-    ++count;
-    if (count >= 8) {
-      count = 0;
-      seed += temp;
-      temp = 0;
+    temp = (uint64_t)(((uint8_t*)key)[idx]) + seed;
+    if (idx % 3 == 0) {
+      temp ^= 0xA5A538A5A9B5A5A5;
+    } else if (idx % 3 == 1) {
+      temp ^= 0xD7A58BD7A58BD7AA;
+    } else {
+      temp ^= 0x8B7A8B8B87CB8B84;
     }
-  }
-  if (temp != 0) {
-    seed += temp;
+    seed += simple_archiver_algo_lcg_defaults(temp);
   }
 
   return simple_archiver_algo_lcg_defaults(seed);
@@ -106,7 +104,7 @@ int simple_archiver_hash_map_internal_rehash(SDArchiverHashMap *hash_map) {
   }
   SDArchiverHashMap new_hash_map;
   new_hash_map.hash_fn = hash_map->hash_fn;
-  new_hash_map.buckets_size = hash_map->buckets_size * 2;
+  new_hash_map.buckets_size = (hash_map->buckets_size - 1) * 2 + 1;
   // Pointers have the same size (at least on the same machine), so
   // sizeof(void*) should be ok.
   new_hash_map.buckets = malloc(sizeof(void *) * new_hash_map.buckets_size);
@@ -154,7 +152,7 @@ SDArchiverHashMap *simple_archiver_hash_map_init_custom_hasher(
     uint64_t (*hash_fn)(const void *, size_t)) {
   SDArchiverHashMap *hash_map = malloc(sizeof(SDArchiverHashMap));
   hash_map->hash_fn = hash_fn;
-  hash_map->buckets_size = SC_SA_DS_HASH_MAP_START_BUCKET_SIZE;
+  hash_map->buckets_size = SC_SA_DS_HASH_MAP_START_BUCKET_SIZE + 1;
   // Pointers have the same size (at least on the same machine), so
   // sizeof(void*) should be ok.
   hash_map->buckets = malloc(sizeof(void *) * hash_map->buckets_size);

src/data_structures/test.c

@@ -219,6 +219,59 @@ int main(void) {
     simple_archiver_hash_map_free(&hash_map);
   }
 
+  // Test hashing.
+  //{
+  //  printf("Distribution of 13 over 33...\n");
+  //  unsigned int counts[33];
+  //  memset(counts, 0, sizeof(unsigned int) * 33);
+
+  //  uint64_t hash;
+
+  //  hash = simple_archiver_hash_default_fn("/", 2);
+  //  printf("%s in bucket %lu (%lu)\n", "/", hash % 33, hash);
+  //  counts[hash % 33] += 1;
+  //  hash = simple_archiver_hash_default_fn("/faq", 5);
+  //  printf("%s in bucket %lu (%lu)\n", "/faq", hash % 33, hash);
+  //  counts[hash % 33] += 1;
+  //  hash = simple_archiver_hash_default_fn("/FAQ", 5);
+  //  printf("%s in bucket %lu (%lu)\n", "/FAQ", hash % 33, hash);
+  //  counts[hash % 33] += 1;
+  //  hash = simple_archiver_hash_default_fn("/url", 5);
+  //  printf("%s in bucket %lu (%lu)\n", "/url", hash % 33, hash);
+  //  counts[hash % 33] += 1;
+  //  hash = simple_archiver_hash_default_fn("/home", 6);
+  //  printf("%s in bucket %lu (%lu)\n", "/home", hash % 33, hash);
+  //  counts[hash % 33] += 1;
+  //  hash = simple_archiver_hash_default_fn("/blog", 6);
+  //  printf("%s in bucket %lu (%lu)\n", "/blog", hash % 33, hash);
+  //  counts[hash % 33] += 1;
+  //  hash = simple_archiver_hash_default_fn("/test", 6);
+  //  printf("%s in bucket %lu (%lu)\n", "/test", hash % 33, hash);
+  //  counts[hash % 33] += 1;
+  //  hash = simple_archiver_hash_default_fn("/menu", 6);
+  //  printf("%s in bucket %lu (%lu)\n", "/menu", hash % 33, hash);
+  //  counts[hash % 33] += 1;
+  //  hash = simple_archiver_hash_default_fn("/posts", 7);
+  //  printf("%s in bucket %lu (%lu)\n", "/posts", hash % 33, hash);
+  //  counts[hash % 33] += 1;
+  //  hash = simple_archiver_hash_default_fn("/about", 7);
+  //  printf("%s in bucket %lu (%lu)\n", "/about", hash % 33, hash);
+  //  counts[hash % 33] += 1;
+  //  hash = simple_archiver_hash_default_fn("/media", 7);
+  //  printf("%s in bucket %lu (%lu)\n", "/media", hash % 33, hash);
+  //  counts[hash % 33] += 1;
+  //  hash = simple_archiver_hash_default_fn("/social", 8);
+  //  printf("%s in bucket %lu (%lu)\n", "/social", hash % 33, hash);
+  //  counts[hash % 33] += 1;
+  //  hash = simple_archiver_hash_default_fn("/projects", 10);
+  //  printf("%s in bucket %lu (%lu)\n", "/projects", hash % 33, hash);
+  //  counts[hash % 33] += 1;
+
+  //  for (unsigned int idx = 0; idx < 33; ++idx) {
+  //    printf("Bucket %u: %u\n", idx, counts[idx]);
+  //  }
+  //}
+
   // Test PriorityHeap.
   {
     SDArchiverPHeap *priority_heap = simple_archiver_priority_heap_init();

src/parser.c

@@ -168,6 +168,15 @@ 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");
   fprintf(stderr,
           "--temp-files-dir <dir> : where to store temporary files created "
           "when compressing (defaults to current working directory)\n");
@@ -303,6 +312,13 @@ 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,
+                "NOTICE: Disabling safe-links, symlinks that point to outside "
+                "archived files will be preserved!\n");
       } else if (strcmp(argv[0], "--temp-files-dir") == 0) {
         if (argc < 2) {
           fprintf(stderr, "ERROR: --temp-files-dir is missing an argument!\n");

src/parser.h

@@ -36,6 +36,8 @@ typedef struct SDArchiverParsed {
   /// 0b xxx1 xxxx - Create archive to stdout or read archive from stdin.
   /// 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"));