NEP: NEO Executable Format (NEF)

nep-16.mediawiki

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+<pre>
+  NEP: 16
+  Title: NEO Executable Format (NEF)
+  Author: Fernando Díaz Toledano <shargon@gmail.com>, Erik Zhang <erik@neo.org>, Igor Machado Coelho <igormachado@gmail.com>, Li Jianying <lightsever@hotmail.com>, Vitor Nazário Coelho <vncoelho@gmail.com>
+  Type: Standard
+  Status: Accepted
+  Created: 2020-03-31
+</pre>
+
+==Abstract==
+
+A <code>NefFile</code> is a file meeting the standard format for a valid NEO executable file. It provides the basic information about the script, including the compiler and version.
+
+This NEP describes the NEF standard for NEO smart contracts.
+
+==Motivation==
+
+Although we use neo-vm as the virtual machine currently, we should have other scripts in the future. A standard definition for the executable file format can guarantee both the feasibility of other vm code and the validity of the script file.
+
+==Specification==
+
+In the field definitions below, we provide both the definitions of the fields as well as the corresponding functions.
+
+==NefFile Structure==
+
+A <code>nef</code> file consists of a stream of 8-bit bytes. Multibyte data items are always stored in little-endian order, where the low bytes come first. Its structure is described further below.
+
+{| class="wikitable sortable" style="width: auto; text-align: center; font-size: smaller; table-layout: fixed;"
+!<nowiki>#</nowiki>
+!size
+!item
+|-
+| 1
+| 4 bytes
+| magic
+|-
+| 2
+| 32 bytes
+| compiler
+|-
+| 3
+| 32 bytes
+| version
+|-
+| 4
+| 4 bytes
+| Reserve
+|-
+| 5
+| variable bytes
+| script
+|-
+| 6
+| 4 bytes
+| checksum
+|}
+
+===magic===
+
+The <code>magic</code> item supplies the magic number identifying the <code>NEF3</code> file format; it has the value <code>0x3346454E</code>.
+
+===compiler===
+
+The <code>compiler</code> is a UTF-8 encoded <code>string</code> representing the compiler used to create the data in the <code>script</code> item. It is a fixed-length item, which is padded to force alignment on 32-byte boundary.
+
+===version===
+
+The compiler <code>version</code> is represented using a 32-byte string encoded in UTF-8. It must be padded with padding bytes to make it up to the required length if shorter than 32 bytes.
+
+===reserve===
+
+All bits of the <code>reserve</code> item are reserved for future use. They should be set to zero in generated nef files and should be ignored by Neo Virtual Machine implementations.
+
+===script===
+
+The value of <code>script</code> stores the raw VM opcodes. The data should be serialised using the variable length format as described in the [https://docs.neo.org/developerguide/en/articles/conventions.html#variable-length-types documentation].
+
+===checksum===
+
+The <code>checksum</code> item is used not only to ensure a corrupt-free transmission, but also to ensure that the file has not been tampered with. It is computed by using the SHA256 algorithm to hash the serialised `NefFile` excluding `checksum` twice, and converting the result into a 32-bit unsigned integer.