Add test for fopen_packed()

src/fs.c

@@ -1,4 +1,65 @@
 #include "fs.h"
 
-// FILE *fopen_packed(const char *path, const char *mode) {
-//}
+struct packed_file {
+  const char *data;
+  size_t size;
+  size_t pos;
+};
+
+const char *unpack(const char *, size_t *) WEAK;
+const char *unpack(const char *path, size_t *size) {
+  (void) path, (void) size;
+  return NULL;
+}
+
+#if defined(__linux__) && defined(GCC)
+ssize_t packed_read(void *cookie, char *buf, size_t size) {
+  struct packed_file *fp = (struct packed_file *) cookie;
+  if (size > fp->size - fp->pos) size = fp->size - fp->pos;
+  memcpy(buf, &fp->data[fp->pos], size);
+  fp->pos += size;
+  return (ssize_t) size;
+}
+
+ssize_t packed_write(void *cookie, const char *buf, size_t size) {
+  (void) cookie, (void) buf, (void) size;
+  return -1;
+}
+
+int packed_seek(void *cookie, off64_t *offset, int whence) {
+  struct packed_file *fp = (struct packed_file *) cookie;
+  if (whence == SEEK_SET) fp->pos = (size_t) *offset;
+  if (whence == SEEK_END) fp->pos = (size_t)((off64_t) fp->size + *offset);
+  if (whence == SEEK_CUR) fp->pos = (size_t)((off64_t) fp->pos + *offset);
+  if (fp->pos > fp->size) fp->pos = fp->size;
+  *offset = (off64_t) fp->pos;
+  return 0;
+}
+
+int packed_close(void *cookie) {
+  free(cookie);
+  return 0;
+}
+
+FILE *fopen_packed(const char *path, const char *mode) {
+  cookie_io_functions_t funcs = {
+      .read = packed_read,
+      .write = packed_write,
+      .seek = packed_seek,
+      .close = packed_close,
+  };
+  struct packed_file *cookie = NULL;
+  size_t size = 0;
+  const char *data = unpack(path, &size);
+  if (data == NULL) return NULL;
+  if ((cookie = calloc(1, sizeof(*cookie))) == NULL) return NULL;
+  cookie->data = data;
+  cookie->size = size;
+  return fopencookie(cookie, mode, funcs);
+}
+#else
+FILE *fopen_packed(const char *path, const char *mode) {
+  (void) path, (void) mode;
+  return NULL;
+}
+#endif