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daml/daml-lf/archive/README.md
Robert Autenrieth e2c79b27cf Fix broken link (#530) 
* Fix broken link

* remove old daml-lf spec
2019-04-16 16:14:43 +02:00

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DAML-LF archive

This component contains the .proto definitions specifying the format in which DAML-LF packages are stored -- the DAML-LF archive.

The entry point definition is Archive in da/daml_lf.proto. Archive contains some metadata about the actual archive (currently the hashing function and the hash), and then a binary blob containing the archive. The binary blob must be an ArchivePayload -- we keep it in binary form to facilitate hashing, signing, etc. The encoding and decoding of the payload is handled by Haskell and Java libraries in daml-core-package, so that consumers and producers do not really need to worry about it.

ArchivePayload is a sum type containing the various DAML-LF versions supported by the DAML-LF archive. Currently we have two versions:

Building

It produces two libraries containing code to encode / decode such definition, a Haskell one and a Java one:

$ bazel build //daml-lf/archive:daml_lf_haskell_proto
$ bazel build //daml-lf/archive:daml_lf_java_proto

Editing the .proto definitions

When editing the proto definitions, you must make sure to not change them in a backwards-incompatible way. To make sure this doesn't happen:

  • DO NOT delete message fields;
  • DO NOT change the number of a message field or an enum value;
  • DO NOT change the type of a message field;

Note that "fields" include oneof fields. Also note that the "don't delete fields" rule is there not because they introduce a backwards incompatible change, but rather because after a field has been deleted another commiter might redefine it with a different type without realizing.

What is OK is renaming message fields while keeping the number and semantics unchanged. For example, if you have

message Foo {
  bytes blah = 1;
}

it's OK to change it to

message Foo {
  // this field is deprecated -- use baz instead!
  bytes blah_deprecated = 1;
  string baz = 2;
}

Conversion from the .proto to AST

The .proto definitions contain the serialized format for DAML-LF packages, however the code to convert from the .proto definitions to the actual AST lives elsewhere.