Specify format for PackManifest files

[flyingzumwalt]

In order to implement pack make, which generates a PackManifest file, we need to know how PackManifest files should be formatted.

Some references:

• bagit payload manifests -- extremely similar to what we need
• data packages format -- this json format is designed to capture metadata about a dataset. Not likely to be included in PackManifest, but could be included in the pack's contents... (if you have ideas around this, please create issues in this repo to discuss)

From the spec

> cat PackManifest
QmVP2aaAWFe21QjUujMw5hwYRKD1eGx3yYWEBbMtuxpqXs <fmtstr> moreData/0
QmV7eDE2WXuwQnvccsoXSzK5CQGXdFfay1LSadZCwyfbDV <fmtstr> moreData/1
QmaMY7h9pmTcA5w9S2dsQT5eGLEQ1CwYQ32HwMTXAev5gQ <fmtstr> moreData/2
QmQjYU5PscpCHadDbL1fDvTK4P9eXirSwD8hzJbAyrd5mf <fmtstr> moreData/3
QmRErwActoLmffucXq7HPtefBC19MjWUcj1DdBoaAnMm6p <fmtstr> moreData/4
QmeWvL929Tdhzw27CS5ZVHD73NQ9TT1xvLvCaXCgi7a9YB <fmtstr> moreData/5
QmXbzZeh44jJEUueWjFxEiLcfAfzoaKYEy1fMHygkSD3hm <fmtstr> moreData/6
QmYL17nYZrZsAhJut5v7ooD9hmz2rBotC1tqC9ZPxzCfer <fmtstr> moreData/7
QmPKkidoUYX12PyCuKzehQuhEJofUJ9PPaX2Gc2iYd4GRs <fmtstr> moreData/8
QmQAubXA3Gji5v5oaJhMbvmbGbiuwDf1u9sYsN125mcqrn <fmtstr> moreData/9
QmYbYduoHMZAUMB5mjHoJHgJ9WndrdWkTCzuQ6yHkbgqkU <fmtstr> someJSON.json
QmeWiZD5cdyiJoS3b7h87Cs9G21uQ1sLmeKrunTae9h5qG <fmtstr> someXML.xml
QmVizQ5fUceForgWogbb2m2v5RRrE8xEm8uSkbkyNB4Rdm <fmtstr> moreData
QmZ7iEGqahTHdUWGGZMUxYRXPwSM3UjBouneLcCmj9e6q6 <fmtstr> .

[whyrusleeping]

curious what we think the fmtstr should look like

[jbenet]

curious what we think the fmtstr should look like

@whyrusleeping it's what we discussed in ipfs/notes#216

[flyingzumwalt]

@jbenet @whyrusleeping I need you to update the spec.md to document the fmtstr. Currently the only documentation for that string is this issue.

From ipfs/notes#216:

• importer fmt string like <mbp><fmt-string-version-varint><mcp-code-for-importer><importer-args>
  • where <importer-args> can be like <hash-fn-multihash-code><dag-layout><chunker><chunk-size>

[flyingzumwalt]

Need to add this info to the spec with definitions for:

• mbp
• fmt-string-version-varint
• mcp-code-for-importer
• hash-fn-multihash-code
• dag-layout
• chunker
• etc.

[flyingzumwalt]

It's not clear how much of this info is in the PackManifest fmtstr and how much of this info is elsewhere in the .ipfs-pack repo. Is there info about chunking in the fmtstr in the PackManifest? Why is it there instead of in the object store?

[whyrusleeping]

The fmtstr contains information about the chunker, layout, and importer type. This should be sufficient for most use cases (and extensible in others)