Added ability to declare empty directory (#86)

* Added an ability to declare empty directories

* Added test cases to cover packaging of empty directories

README.markdown

@@ -44,13 +44,18 @@ and is what will be extracted from the ZIP file. Example:
 
     1034ab38 428    /foo.txt   My Document1.txt
     83e8110b 100339 /bar.txt   My Other Document1.txt
+    0        0      @directory My empty directory
 
 Files are retrieved and encoded in order. If a file cannot be found or the file
 request returns any sort of error, the download is aborted.
 
 The CRC-32 is optional. Put "-" if you don't know the CRC-32; note that in this
 case mod_zip will disable support for the `Range` header.
 
+A special URL marker `@directory` can be used to declare a directory entry
+within an archive. This is very convenient when you have to package a tree of
+files, including some empty directories. As they have to be declared explicitly.
+
 
 Re-encoding filenames
 ---

ngx_http_zip_file.c

@@ -390,7 +390,7 @@ ngx_http_zip_generate_pieces(ngx_http_request_t *r, ngx_http_zip_ctx_t *ctx)
         header_piece->range.end = offset;
 
         file_piece = &ctx->pieces[piece_i++];
-        file_piece->type = zip_file_piece;
+        file_piece->type = file->is_directory ? zip_dir_piece : zip_file_piece;
         file_piece->file = file;
         file_piece->range.start = offset;
         file_piece->range.end = offset += file->size; //!note: (sizeless chunks): we need file size here / or mark it and modify ranges after
@@ -683,6 +683,11 @@ ngx_http_zip_write_central_directory_entry(u_char *p, ngx_http_zip_file_t *file,
     central_directory_file_header.version_made_by = htole16(central_directory_file_header.version_made_by);
     central_directory_file_header.version_needed = htole16(central_directory_file_header.version_needed);
     central_directory_file_header.flags = htole16(central_directory_file_header.flags);
+
+    if (file->is_directory) {
+        central_directory_file_header.attr_external = zip_directory_attr_external;
+    }
+
     central_directory_file_header.attr_external = htole32(central_directory_file_header.attr_external);
     central_directory_file_header.mtime = htole32(file->dos_time);
     central_directory_file_header.crc32 = htole32(file->crc32);

ngx_http_zip_file_format.h

@@ -9,6 +9,9 @@
 #define zip_version_zip64 45
 #define zip_utf8_flag 0x0800
 #define zip_missing_crc32_flag 0x08
+#define zip_directory_attr_external 0x41ED0010
+//                      Unix dir bit -^     ^- DOS dir bit
+//        Unix permission bits (0755) -^^^
 
 typedef struct {
     uint16_t   tag; //0x5455

ngx_http_zip_module.c

@@ -42,6 +42,8 @@ static ngx_int_t ngx_http_zip_send_header_piece(ngx_http_request_t *r,
         ngx_http_zip_ctx_t *ctx, ngx_http_zip_piece_t *piece, ngx_http_zip_range_t *req_range);
 static ngx_int_t ngx_http_zip_send_file_piece(ngx_http_request_t *r,
         ngx_http_zip_ctx_t *ctx, ngx_http_zip_piece_t *piece, ngx_http_zip_range_t *req_range);
+static ngx_int_t ngx_http_zip_send_directory_piece(ngx_http_request_t *r,
+        ngx_http_zip_ctx_t *ctx, ngx_http_zip_piece_t *piece, ngx_http_zip_range_t *req_range);
 static ngx_int_t ngx_http_zip_send_trailer_piece(ngx_http_request_t *r,
         ngx_http_zip_ctx_t *ctx, ngx_http_zip_piece_t *piece, ngx_http_zip_range_t *req_range);
 static ngx_int_t ngx_http_zip_send_central_directory_piece(ngx_http_request_t *r,
@@ -576,6 +578,13 @@ ngx_http_zip_send_file_piece(ngx_http_request_t *r, ngx_http_zip_ctx_t *ctx,
     return NGX_AGAIN;   // must be NGX_AGAIN
 }
 
+static ngx_int_t ngx_http_zip_send_directory_piece(ngx_http_request_t *r,
+        ngx_http_zip_ctx_t *ctx, ngx_http_zip_piece_t *piece, ngx_http_zip_range_t *req_range)
+{
+    // Directory has no data.
+    return NGX_OK;
+}
+
 static ngx_int_t
 ngx_http_zip_send_trailer_piece(ngx_http_request_t *r, ngx_http_zip_ctx_t *ctx,
         ngx_http_zip_piece_t *piece, ngx_http_zip_range_t *req_range)
@@ -621,6 +630,8 @@ ngx_http_zip_send_piece(ngx_http_request_t *r, ngx_http_zip_ctx_t *ctx,
         rc = ngx_http_zip_send_header_piece(r, ctx, piece, req_range);
     } else if (piece->type == zip_file_piece) {
         rc = ngx_http_zip_send_file_piece(r, ctx, piece, req_range);
+    } else if (piece->type == zip_dir_piece) {
+        rc = ngx_http_zip_send_directory_piece(r, ctx, piece, req_range);
     } else if (piece->type == zip_trailer_piece) {
         rc = ngx_http_zip_send_trailer_piece(r, ctx, piece, req_range);
     } else if (piece->type == zip_central_directory_piece) {

ngx_http_zip_module.h

@@ -28,6 +28,7 @@ typedef struct {
     unsigned    missing_crc32:1;
     unsigned    need_zip64:1;
     unsigned    need_zip64_offset:1;
+    unsigned    is_directory:1;
 } ngx_http_zip_file_t;
 
 typedef struct {
@@ -41,6 +42,7 @@ typedef struct {
 typedef enum {
     zip_header_piece, //local file header
     zip_file_piece, // file data
+    zip_dir_piece, // directory data
     zip_trailer_piece, // data descriptor (for files without CRC, exists if bit 3 of GP flag is set),
     zip_trailer_piece64, // the same but for zip64 (if zip64 extended information extra field is in file header)
     zip_central_directory_piece,