feat: Add support for hard links

docs/API.md

@@ -77,7 +77,9 @@ This enum lists all supported file types:
 
 `MTAR_SYMLINK`: Symbolic links
 
-Other file types supported in tar archives, such as block/character devices, FIFOs, or hard links, are not supported and minitar will throw an error when encountering one of them. This behavior can be controlled by passing `-DMINITAR_IGNORE_UNSUPPORTED_TYPES=ON` to CMake when configuring, which will make minitar silently ignore such entries instead of panicking.
+`MTAR_HARDLINK`: Hard links
+
+Other file types supported in tar archives, such as block/character devices or FIFOs, are not supported and minitar will throw an error when encountering one of them. This behavior can be controlled by passing `-DMINITAR_IGNORE_UNSUPPORTED_TYPES=ON` to CMake when configuring, which will make minitar silently ignore such entries instead of panicking.
 
 ### minitar_entry_metadata
 `struct minitar_entry_metadata`
@@ -88,7 +90,7 @@ This structure represents an entry's metadata, with the following fields:
 
 `name`: A string representing the base name of the entry (the last component of its path). (`char[]`)
 
-`link`: A string representing the file being linked to. (Only applies to symlinks) (`char[]`)
+`link`: A string representing the file being linked to. (Only applies to symlinks/hard links) (`char[]`)
 
 `mode`: An integer representing the permissions of the entry. (`mode_t`)
 

examples/untar.c

@@ -98,6 +98,18 @@ int main(int argc, char** argv)
 
                 printf("symlink %s -> %s\n", entry.metadata.path, entry.metadata.link);
             }
+            else if (entry.metadata.type == MTAR_HARDLINK)
+            {
+                int status = link(entry.metadata.link, entry.metadata.path);
+
+                if (status != 0)
+                {
+                    fprintf(stderr, "Failed to create hard link %s: %s\n", entry.metadata.path, strerror(errno));
+                    break;
+                }
+
+                printf("link %s -> %s\n", entry.metadata.path, entry.metadata.link);
+            }
         }
         else
             break;

minitar.h

@@ -21,7 +21,8 @@ enum minitar_file_type
 {
     MTAR_REGULAR,
     MTAR_DIRECTORY,
-    MTAR_SYMLINK
+    MTAR_SYMLINK,
+    MTAR_HARDLINK,
 };
 
 struct minitar_entry_internal

src/util.c

@@ -174,6 +174,8 @@ void minitar_parse_metadata_from_tar_header(const struct tar_header* hdr, struct
     metadata->uid = (uid_t)minitar_parse_octal(hdr->uid);
     metadata->gid = (gid_t)minitar_parse_octal(hdr->gid);
 
+    // These two fields aren't null-terminated.
+
     char* sizeptr = minitar_static_dup(hdr->size, 12);
     metadata->size = (size_t)minitar_parse_octal(sizeptr);
 
@@ -186,12 +188,13 @@ void minitar_parse_metadata_from_tar_header(const struct tar_header* hdr, struct
     {
     case '\0':
     case '0': metadata->type = MTAR_REGULAR; break;
-    case '1': minitar_handle_panic("Links to other files within a tar archive are unsupported");
+    case '1': metadata->type = MTAR_HARDLINK; break;
     case '2': metadata->type = MTAR_SYMLINK; break;
     case '3': minitar_handle_panic("Character devices are unsupported");
     case '4': minitar_handle_panic("Block devices are unsupported");
     case '5': metadata->type = MTAR_DIRECTORY; break;
     case '6': minitar_handle_panic("FIFOs are unsupported");
+    // This case should have been previously handled by minitar_validate_header().
     default: minitar_handle_panic("Unknown entry type in tar header");
     }
 
@@ -228,7 +231,9 @@ uint32_t minitar_checksum_header(const struct tar_header* hdr)
 int minitar_validate_header(const struct tar_header* hdr)
 {
 #ifdef MINITAR_IGNORE_UNSUPPORTED_TYPES
-    if (hdr->typeflag != '\0' && hdr->typeflag != '0' && hdr->typeflag != '2' && hdr->typeflag != '5') return 0;
+    if (hdr->typeflag != '\0' && hdr->typeflag != '0' && hdr->typeflag != '1' && hdr->typeflag != '2' &&
+        hdr->typeflag != '5')
+        return 0;
 #else
     if (hdr->typeflag != '\0' && hdr->typeflag != '0' && hdr->typeflag != '1' && hdr->typeflag != '2' &&
         hdr->typeflag != '3' && hdr->typeflag != '4' && hdr->typeflag != '5' && hdr->typeflag != '6')