go-checksum

Simple tool to calc Golang module checksum of go.mod and module directory.

This README also describes how Golang go.sum calc hash from file conent.

Maybe this is the missing official doc for how Golang go.sum calc hash from file conent

Usage

Example Golang Module

• Github: https://github.com/gin-gonic/gin
• Example Version: v1.4.0
• CheckSum: https://sum.golang.org/lookup/github.com/gin-gonic/[email protected]

Clone and checkout a version

git clone https://github.com/gin-gonic/gin.git
git checkout v1.4.0

Install go-checksum

go get -u github.com/vikyd/go-checksum

Calc checksum of go.mod

go-checksum relOrAbsPathOfGinDir/go.mod

will print like:

file: /Users/viky/tmp/gin/go.mod
{
	"Hash": "b1946b355a09fedc3865073bbeb5214de686542bbeaea9e1bf83cb3a08f66b99",
	"HashBase64": "sZRrNVoJ/tw4ZQc7vrUhTeaGVCu+rqnhv4PLOgj2a5k=",
	"HashSynthesized": "396d84667dc33bc2e7f6820a3af33ef8b04efb950f1c92431fbdbfabfdeb65d3",
	"HashSynthesizedBase64": "OW2EZn3DO8Ln9oIKOvM++LBO+5UPHJJDH72/q/3rZdM=",
	"GoCheckSum": "h1:OW2EZn3DO8Ln9oIKOvM++LBO+5UPHJJDH72/q/3rZdM="
}

The output hash "GoCheckSum": "h1:OW2EZn3DO8Ln9oIKOvM++LBO+5UPHJJDH72/q/3rZdM="

is the same as

the online checksum: github.com/gin-gonic/gin v1.4.0/go.mod h1:OW2EZn3DO8Ln9oIKOvM++LBO+5UPHJJDH72/q/3rZdM=

(from here)

Calc checksum of module directory

go-checksum relOrAbsPathOfGinDir github.com/gin-gonic/[email protected]

• 1st param: module directory
  • no need to remove .git, will ignore
• 2nd param: module prefix with version
  • necessary for dir checksum

will print like:

directory: /Users/viky/tmp/gin
{
	"HashSynthesized": "ded3280827ccee9a6ab11d29b73ff08b58a6a4da53efff7042d319f25af59824",
	"HashSynthesizedBase64": "3tMoCCfM7ppqsR0ptz/wi1impNpT7/9wQtMZ8lr1mCQ=",
	"GoCheckSum": "h1:3tMoCCfM7ppqsR0ptz/wi1impNpT7/9wQtMZ8lr1mCQ="
}

The output hash "GoCheckSum": "h1:3tMoCCfM7ppqsR0ptz/wi1impNpT7/9wQtMZ8lr1mCQ="

is the same as

the online checksum: github.com/gin-gonic/gin v1.4.0 h1:3tMoCCfM7ppqsR0ptz/wi1impNpT7/9wQtMZ8lr1mCQ=

(from here)

Explain

How go.mod checksum works?

Steps:

• tell me the path of go.mod
• read content from go.mod, as variable content
• calc SHA256 hash from content, as variable hash
• mix some string with hash, as variable mixedHash

  • hash  go.mod\n
    

  • if hash is: CDa7N
  • then mixedHash is:

  • CDa7N  go.mod\n
    

  • yeah, that's a strange string
• calc SHA256 hash from mixedHash, as variable hashSynthesized
• calc Base64 from hashSynthesized, as variable hashSynthesizedBase64
• finally, in go.sum, the string is: h1:hashSynthesizedBase64, as variable GoCheckSum
  • if hashSynthesized is: CCfM7
  • then GoCheckSum is: h1:CCfM7
  • h1: The hash begins with an algorithm prefix of the form "h<N>:". The only defined algorithm prefix is "h1:", which uses SHA-256.
  • h: hash

How module direcory checksum works?

Steps:

• tell me the path of module's dir and module's prefix (also named import path)
  • module's prefix is used to calc hash, as part of the content string
• clean the dir path, to remove duplicate path seperator etc.
• loop each file in module's dir
  • only consider file, not dir
  • find the relative path of the file (relative to module's dir)
  • join file relative path with module's prefix, as variable fileImportPath
  • example:
    • one file in gin project: gin.go
    • its module's dir: /dir01/dir02/gin
    • its absolute path: /dir01/dir02/gin/gin.go
    • its relative path: gin.go
    • final string fileImportPath: github.com/gin-gonic/[email protected]/gin.go
• after the loop, we got a list fileImportPath of all files, as variable files
  • except files in .git
• sort files as string in increasion order
• then begin hash steps
• loop sorted files
  • read content from a file of files, as variable content
  • calc SHA256 hash from content, as variable hash
  • mix some string with hash, as variable mixedHash

    • hash  fileImportPath\n
      

    • if hash is: CDa7N
    • if fileImportPath is: github.com/gin-gonic/[email protected]/gin.go
    • then mixedHash is:

    • CDa7N  github.com/gin-gonic/[email protected]/gin.go\n
      

    • yeah, that's a strange string
• after this loop, we can get a single long string joined by all files' mixedHash, as variable mixedHashAll
  • example:

  • CDa7N  github.com/gin-gonic/[email protected]/gin.go\nEFb8M  github.com/gin-gonic/[email protected]/context.go\n ...
    

• calc SHA256 hash from mixedHashAll, as variable hashSynthesized
• calc Base64 from hashSynthesized, as variable hashSynthesizedBase64
• finally, in go.sum, the string is: h1:hashSynthesizedBase64, as variable GoCheckSum
  • if hashSynthesized is: CCfM7
  • then GoCheckSum is: h1:CCfM7
  • h1: The hash begins with an algorithm prefix of the form "h<N>:". The only defined algorithm prefix is "h1:", which uses SHA-256.
  • h: hash

Ref

Golang source code about how to calc hash for modules: https://github.com/golang/mod/blob/release-branch.go1.15/sumdb/dirhash/hash.go