From 89bc9907251bbadae9eb67b7472d41f538ff7a2c Mon Sep 17 00:00:00 2001
From: apio <blobs.trading@gmail.com>
Date: Sun, 25 Dec 2022 13:31:11 +0100
Subject: [PATCH] More optimization and heap elimination

---
 README.md  |  4 +---
 src/util.c | 34 +++++++++++++---------------------
 2 files changed, 14 insertions(+), 24 deletions(-)

diff --git a/README.md b/README.md
index cde98f3..9310a3d 100644
--- a/README.md
+++ b/README.md
@@ -4,9 +4,7 @@ Tiny and easy-to-use C library to parse tar (specifically, the newer [USTAR](htt
 
 No third-party dependencies, only a minimally capable standard C library (file IO, number parsing, malloc() and friends, string functions). 
 
-Aims to be as portable between systems as possible (has its own implementation of some non-standard functions, such as [strlcpy](https://linux.die.net/man/3/strlcpy), [strndup](https://linux.die.net/man/3/strndup) or [basename](https://linux.die.net/man/3/basename)).
-
-Very minimal and bloat-free, currently less than 500 lines :)
+Aims to be bloat-free (currently less than 500 LoC), fast and optimized, and as portable between systems as possible (has its own implementation of some non-standard functions, such as [strlcpy](https://linux.die.net/man/3/strlcpy) or [basename](https://linux.die.net/man/3/basename)).
 
 Does not include support for compressed archives. You'll have to pass those through another program or library to decompress them before minitar can handle them.
 
diff --git a/src/util.c b/src/util.c
index 8cbc51b..15be7c5 100644
--- a/src/util.c
+++ b/src/util.c
@@ -45,19 +45,6 @@ static size_t minitar_strlcpy(char* dest, const char* src, size_t size)
     return full_len;
 }
 
-// strdup() but copies at most max bytes of orig, always null-terminating the result. This function is non-standard and
-// as such, we provide our own implementation, to be as portable as possible.
-// https://linux.die.net/man/3/strndup
-static char* minitar_strndup(const char* orig, size_t max)
-{
-    size_t len = strnlen(orig, max);
-    char* ptr =
-        calloc(len + 1, 1); // Use calloc so everything is automatically zeroed and we get a null-terminator for free :)
-    if (!ptr) return NULL;
-    for (size_t i = 0; i < len; ++i) { *(ptr + i) = *(orig + i); }
-    return ptr;
-}
-
 static char dot[] = ".";
 
 // POSIX function to extract the basename from a path. Not present on non-POSIX, but since paths inside a tar archive
@@ -101,6 +88,17 @@ static size_t minitar_align_down_to_block_size(size_t size)
     return size - (size % 512);
 }
 
+// Return a static string formed by 'size' bytes copied from str, and a null terminator. This function is useful for
+// when you have a fixed-size field without a null-terminator, and you need a null-terminated string to pass to a
+// library function. The pointer returned WILL be overwritten by subsequent calls to this function.
+static char* minitar_static_dup(const char* str, size_t size)
+{
+    static char result[1024];
+    memcpy(result, str, size);
+    result[size] = 0;
+    return result;
+}
+
 size_t minitar_align_up_to_block_size(size_t size)
 {
     return minitar_is_aligned_to_block_size(size) ? size : minitar_align_down_to_block_size(size) + 512;
@@ -144,17 +142,11 @@ void minitar_parse_metadata_from_tar_header(const struct tar_header* hdr, struct
 
     // FIXME: Maybe avoid heap allocations (strndup) for simply parsing non-null-terminated fields?
 
-    char* sizeptr = minitar_strndup(
-        hdr->size, 12); // The hdr->size field is not null-terminated, yet strndup returns a null-terminated string.
-    if (!sizeptr) minitar_panic("Failed to allocate memory");
+    char* sizeptr = minitar_static_dup(hdr->size, 12);
     metadata->size = (size_t)strtoull(sizeptr, NULL, 8);
-    free(sizeptr);
 
-    char* timeptr = minitar_strndup(
-        hdr->mtime, 12); // The hdr->mtime field is not null-terminated, yet strndup returns a null-terminated string.
-    if (!timeptr) minitar_panic("Failed to allocate memory");
+    char* timeptr = minitar_static_dup(hdr->mtime, 12);
     metadata->mtime = (time_t)strtoull(timeptr, NULL, 8);
-    free(timeptr);
 
     // The type is stored as a character instead of an integer.