I'm trying to understand how to organize my golang project using go1.11 modules. I tried several options, but none of them worked.
I have some code in the main package under the application folder and a local package that the main package uses.
$GOPATH
+ src
+ application/
+ main/
+ main.go
+ otherFileUnderMainPackage.go
+ aLocalPackage/
+ someCode.go
+ someCode_test.go
+ someMoreCode.go
+ someMoreCode_test.go
Files in the main package, imports ../aLocalPackage. When I compile by go build main/*.go it's working.
Then, I ran go mod init application: V.0.9.9 and got the go.mod file, but the build always fails. I always get error about not finding the local package: build application:V0.9.9/main: cannot find module for path _/.../src/application/aLocalPackage. I also tried to place the local package right under src/, place it under main/ etc. but none of these methods worked for me.
What is the way to use modules and local packages?
Thanks.
Relative import paths are not supported in module mode. You will need to update your import statements to use a full (absolute) import path.
You should also choose a module name other than application. Your module path should generally begin with a URL prefix that you control — either your own domain name, or a unique path such as github.com/$USER/$REPO.
I had some problems working with local packages myself.
There are two tricks to make it work:
you run "go build" in the package directory
This compiles the package and places it in the build cache.
This link about code organisation in go explains more.
You can identify where the cache is using:
>go env GOCACHE
/home/<user>/.cache/go-build
Import using a path relative to the project
I puzzled loads over what the correct import path was and finally discovered that go doc or go list will tell you.
>go doc
package docs // import "tools/src/hello/docs"
>go list
tools/src/hello/docs
For example. I have a hello world API project and was using swaggo to generate documentation which it does in a docs sub-directory.
To use it I add an import:
_ "tools/src/hello/docs"
For my case the _ is important as docs is not used directly but we its init() function to be invoked.
Now in hello/main.go I can add "tools/src/hello/docs" and it will import the correct package.
The path is relative to the location of go.mod if you have one.
I have tools/ here as I have a go.mod declaring "modules tools".
Modules are a different kettle of fish - see https://github.com/golang/go/wiki/Modules.
Recent versions of go (1.11 and later) can create a go.mod file which you may use to fix the version of a module that is used and avoid go's crazy default behaviour of just downloading the latest version of any package you import.
I have written a blogpost on how to start your first Go project using modules.
https://marcofranssen.nl/start-on-your-first-golang-project/
In general it boils down to just create a new folder somewhere on your system (doesn't have to be in GOPATH).
mkdir my-project
cd my-project
go mod init github.com/you-user/my-project
This will create the go.mod file. Now you can simply create your project layout and start building whatever you like.
Maybe one of my other blogs can inspire you a bit more on how to do things.
https://marcofranssen.nl/categories/software-development/golang/
Related
Not so familiar with Golang, it's probably a stupid mistake I made... But still, I can't for the life of me figure it out.
So, I got a proto3 file (let's call it file.proto), whose header is as follows:
syntax = "proto3";
package [package_name];
option go_package = "github.com/[user]/[repository]";
And I use protoc:
protoc --go_out=$GOPATH/src --go-grpc_out=$GOPATH/src file.proto
So far so good, I end up with two generated files (file.pb.go and file_grpc.pb.go) inside /go/src/github.com/[user]/[repository]/, and they are defined inside the package [package_name].
Then, the code I'm trying to build has the following import:
import (
"github.com/[user]/[repository]/[package_name]"
)
And I naively thought it would work. However, it produces the following error when running go mod tidy:
go: downloading github.com/[user]/[repository] v0.0.0-20211105185458-d7aab96b7629
go: finding module for package github.com/[user]/[repository]/[package_name]
example/xxx imports
github.com/[user]/[repository]/[package_name]: module github.com/[user]/[repository]#latest found (v0.0.0-20211105185458-d7aab96b7629), but does not contain package github.com/[user]/[repository]/[package_name]
Any idea what I'm doing wrong here? Go version is go1.19 linux/amd64 within Docker (golang:1.19-alpine).
Note: I also tried to only import github.com/[user]/[repository], same issue obviously.
UPDATE:
OK so what I do is that I get the proto file from the git repository that only contains the proto file:
wget https://raw.githubusercontent.com/[user]/[repository]/file.proto
Then I generate go files from that file with protoc:
protoc --go_out=. --go-grpc_out=. file.proto
Right now, in current directory, it looks like:
- directory
| - process.go
| - file.proto
| - github.com
| - [user]
| - [repository]
| - file.pb.go
| - file_grpc.pb.go
In that same directory, I run:
go mod init xxx
go mod tidy
CGO_ENABLED=0 go build process.go
The import directive in process.go is as follows:
import (
"xxx/github.com/[user]/[repository]"
)
Now it looks like it finds it, but still getting a gRPC error, which is weird because nothing changed. I still have to figure out if it comes from the issue above or not. Thanks!
Your question is really a number of questions in one; I'll try to provide some info that will help. The initial issue you had was because
At least one file with the .go extension must be present in a directory for it to be considered a package.
This makes sense because importing github.com/[user]/[repository] would be fairly pointless if that repository does not contain any .go files (i.e. the go compiler could not really do anything with the files).
Your options are:
Copy the output from protoc directly into your project folder and change the package declarations to match your package. If you do this there is no need for any imports.
Copy (or set go_out argument to protoc) the output from protoc into a subfolder of your project. The import path will then be the value of the module declaration in your go.mod plus the path from the folder that the go.mod is in (this is what you have done).
Store the files in a repo (on github or somewhere else). This does not need to be the same repo as your .proto files if you "want it to be agnostic" (note that 2 & 3 can be combined if the generated files will only be used within one code base or the repo is accessible to all users).
Option 1 is simple but its often beneficial to keep the generated code separate (makes it clear what you should not edit and improves editor autocomplete etc).
Option 2 is OK (especially if protoc writes the files directly and you set go_package appropriately). However issues may arise when the generated files will be used in multiple modules (e.g. as part of your customers code) and your repo is private. They will need to change go_package before running protoc (or search/replace the package declarations) and importing other .proto files may not work well.
Option 3 is probably the best approach in most situations because this works with the go tooling. You can create github.com/[user]/goproto (or similar) and put all of your generated code in there. To use this your customers just need to import github.com/[user]/goproto (no need to run protoc etc).
Go Modules/package intro
The go spec does not detail the format of import paths, leaving it up to the implementation:
The interpretation of the ImportPath is implementation-dependent but it is typically a substring of the full file name of the compiled package and may be relative to a repository of installed packages.
As you are using go modules (pretty much the default now) the implementations rules for resolving package paths (synonym of import path) can be summarised as:
Each package within a module is a collection of source files in the same directory that are compiled together. A package path is the module path joined with the subdirectory containing the package (relative to the module root). For example, the module "golang.org/x/net" contains a package in the directory "html". That package’s path is "golang.org/x/net/html".
So if your "module path" (generally the top line in a go.mod) is set to xxx (go mod init xxx) then you would import the package in subfolder github.com/[user]/[repository] with import xxx/github.com/[user]/[repository] (as you have found). If you got rid of the intervening folders and put the files into the [repository] subfolder (directly off your main folder) then it would be import xxx/[repository]
You will note in the examples above that the module names I used are paths to repo (as opposed to the xxx you used in go mod init xxx). This is intentional because it allows the go tooling to find the package when you import it from a different module. For example if you had used go mod init github.com/[user]/[repository] and option go_package = "github.com/[user]/[repository]/myproto";" then the generated files should go into the myproto folder in your project and you import them with import github.com/[user]/[repository]/myproto.
While you do not have to follow this approach I'd highly recommend it (it will save you from a lot of pain!). It can take a while to understand the go way of doing this, but once you do, it works well and makes it very clear where a package is hosted.
I have my projects that have many packages which import each other and import outside packages. When I make a change to one of my low lever packages, and then push it to git it is fine and works in that section. When I go get it for use in another project that was working perfectly I now get this go get this error:
module declares its path as: github.com/xdg-go/scram
but was required as: github.com/xdg/scram
None of my code uses either of those directly. It looks like it automatically updated some lower external packages and broke things the used to then old import.
How do I either find out the package that is importing the wrong name or stop all auto-updates?
The go.mod file at github.com/xdg/scram declares itself as github.com/xdg-go/scram:
module github.com/xdg-go/scram
go 1.11
require (
github.com/xdg-go/stringprep v1.0.2
golang.org/x/crypto v0.0.0-20210322153248-0c34fe9e7dc2
)
The go.mod file should be updated to reflect the correct import path.
Unfortunately if this module is for you an indirect dependency, the best fix possible is to update whatever project you import that is directly importing it.
When that is not an option, a solution to this error is to clone the problematic repository locally and use the replace directive in your go.mod file:
module mymodule
replace github.com/xdg/stringprep => ../strprep
go 1.16.2
require (
github.com/divjotarora/mgo v0.0.0-20190308170442-1d451d2a3149
)
where ../strprep is where the code of the required module exists in your local machine, relative to the go.mod file of your project.
The downside of this of course is that you have to replicate this palliative fix wherever you plan to go get your modules.
Note also:
divjotarora/mgo is just a random example of a project that imports one of those packages using their old import path.
I'm using xdg/stringprep as an example because I can't find modules that import xdg/scram instead, but apparently it suffers from the same issue
Beside, you can use:
go mod why <package> to find out why a certain package is listed as a dependency of your project
go mod graph to show the full dependency graph. The output is in <package> <requirement> format
I can not find a way to factor out some code from main.go into a local package when using Go modules (go version >= 1.11) outside of $GOPATH.
I am not importing any external dependencies that need to be included into go.mod, I am just trying to organize locally the source code of this Go module.
The file main.go:
package main
// this import does not work
import "./stuff"
func main() {
stuff.PrintBaz()
}
The file ./stuff/bar.go (pretending to be a local package):
package stuff
import "log"
type Bar struct {
Baz int
}
func PrintBaz() {
baz := Bar{42}
log.Printf("Bar struct: %v", baz)
}
The file go.mod (command go mod init foo):
module foo
go 1.12
When executing go run main.go:
If I import "./stuff", then I see build command-line-arguments: cannot find module for path _/home/<PATH_TO>/fooprj/stuff.
If I import "stuff", then I see build command-line-arguments: cannot load stuff: cannot find module providing package stuff.
If I import stuff "./stuff" with a package alias, then I see again: build command-line-arguments: cannot find module for path _/home/<PATH_TO>/fooprj/stuff.
I can not find a way to make local packages work with go modules.
What's wrong with the code above?
How can I import local packages into other Go code inside a project defined with Go modules (file go.mod)?
Module structure
The most common and easiest approach is:
Use a single go.mod per repository, and
Place the single go.mod file in the repository root, and
Use the repository name as the module path declared in the module line in the go.mod
(If you are using a custom import path such as me.io/mymod rather than using a VCS host based import path, then you would use the custom import path instead of the repository name in your go.mod).
For example, if your repo is github.com/my/repo, then you would place a single go.mod in the repo root, with the first line reading module github.com/my/repo. That can be created by cd'ing to the repo root and running go mod init github.com/my/repo. When working with the repo locally, the repo directory can be located wherever is convenient on your filesystem. (If you do not have a repo, see below).
Following this helps you stay on the happy path with modules, and it avoids multiple subtleties.
Russ Cox commented in #26664:
For all but power users, you probably want to adopt the usual convention that one repo = one module. It's important for long-term evolution of code storage options that a repo can contain multiple modules, but it's almost certainly not something you want to do by default.
There is much more about multi-module repositories in the "Multi-module Repositories" FAQ section on the modules wiki. Those 6 or so FAQs in that section should be read in their entirety by anyone considering veering off the recommendation above.
Arranging packages within a module
Once you have set up your go.mod, you can arrange your packages in directories however you see fit in directories underneath the directory containing the go.mod, as well as in the directory with the go.mod. Three good articles about how to arrange your code in packages:
https://rakyll.org/style-packages/
https://medium.com/#benbjohnson/standard-package-layout-7cdbc8391fc1#.ds38va3pp
https://www.goinggo.net/2017/02/design-philosophy-on-packaging.html
Those articles are classics that pre-date the introduction of modules, but the philosophies in them still apply to how to arrange your packages within a module.
Importing other packages in the same module
When importing another package with modules, you always use the full path including the module path. This is true even when importing another package in the same module. For example, if a module declared its identity in its go.mod as module github.com/my/repo, and you had this organization:
repo/
├── go.mod <<<<< Note go.mod is located in repo root
├── pkg1
│ └── pkg1.go
└── pkg2
└── pkg2.go
Then pkg1 would import its peer package as import "github.com/my/repo/pkg2". Note that you cannot use relative import paths like import "../pkg2" or import "./subpkg". (This is part of what OP hit above with import "./stuff").
Modules vs. repositories vs. packages vs. import paths
A Go module is a collection of related Go packages that are versioned together as a single unit. Modules record precise dependency requirements and create reproducible builds.
Summarizing the relationship between repositories, modules, and packages:
A repository contains one or more Go modules (most often exactly one module in the repository root).
Each module contains one or more Go packages.
Each package consists of one or more Go source files that all reside in a single directory.
Each Go source code file:
declares its own package with a package foo statement, which must be consistent for all Go files in a single package directory.
automatically has access to other Go source code in the same package, without explicitly importing its own package.
imports code from another package via an import path supplied in an import statement such as import "github.com/my/repo/pkg1". The import path always starts with the module path of that package, regardless of whether that package is in the same module or a different module.
A single module can be used to build multiple executable binaries, but the func main() {...} entry point for each binary must be in its own package main, with each package main in a distinct directory.
Local-only modules
You can create, build and run modules without ever publishing them or placing them on a VCS server.
A module is defined by a tree of Go source files with a go.mod file in the tree's root directory, so you can pick a directory on your local filesystem to serve as the root of your module and place your go.mod there. Everything described above still applies, except there does not need to be a repo.
For example:
some-directory/
├── go.mod <<<< go.mod at module root declaring 'module example.com/foo'
├── pkg1
│ └── pkg1.go
└── pkg2
└── pkg2.go
If the module path in the first line of that go.mod reads module example.com/foo, then pkg1 would import its peer package as import "example.com/foo/pkg2".
Of course, you can start with a local-only module without a repo, then later start tracking it in a local repo or publish it to a VCS server.
Even for local-only modules, it is a good idea to give the module a globally unique name, such as go mod init my.org/foo, or go mod init github.com/some/repo as if it will be published someday, even if that repo does not yet exist. (If you are in a hurry, it is possible to use a shorter module name without a dot or leading hostname component, such as go mod init temp or go mod init m, but it won’t be fetchable by the go command, and you run the risk of colliding with a current or future standard library package or otherwise seeing confusing error messages later).
If you have multiple local modules, you can point them at each other via replace directives or via the Go 1.18+ workspace feature, though those are more complex workflows than placing everything for a given project in a single module.
Next steps
If you are new to Go modules, it is worthwhile to go through the official "Create a Go Module" tutorial from the Go project. This will likely save you time overall.
If you are stuck right now with an error message related to modules or import paths, there's a very good chance the error will make much more sense after completing the tutorial.
First you have to choose a name for your project and write it to go.mod file. This name belongs to root directory of the project. Each new package you create must be located inside its own subdirectory and its name should match directory name.
go.mod:
module myprojectname
or (preferred way, see #thepudd's answer for details)
module github.com/myname/myproject
Then import your project's packages like:
import myprojectname/stuff
or
import github.com/myname/myproject/stuff
Files of package stuff should be located inside project's stuff directory. You name these files as you like.
Also it's possible to create deeper project structure. For instance, you decided to separate source code files from other ones (like app configs, docker files, static files, etc...). Let's move stuff directory inside pkg, every go file inside pkg/stuff still have stuff package name. To import stuff package just write:
import myprojectname/pkg/stuff
Nothing stops you from creating more levels in the hierarchy like github.com/myuser/myproject/pkg/db/provider/postgresql, where:
github.com/myuser/myproject - project name.
postgresql - package name.
pkg/db/provider/postgresql - path to the package relative to project's root.
You can read more about go modules here: https://github.com/golang/go/wiki/Modules
Check out this repository to get useful information about various patterns used in project organizing: https://github.com/golang-standards/project-layout If you go inside pkg directory you will find out which open source projects use pkg directory in their structure.
How to setup project structure to produce library and cli with same name in
single repository?
Suppose my project name is project. I want to make it importable with name
project and have executable binary with name project when installed with
go get. My setup currently is like this:
host.com/project/
project/
main.go
core/
project.go
Then, when installed with:
go get host.com/project/project
it installs project as executable which pulls core as dependency. In
core/project.go file, the package has this:
package project
The problem is it is imported with:
import (
"host.com/project/core"
)
And it exports project as name space not core which violates go's convention.
How can I do this?
This isn't a convention, and you may do however you like, but it's a common practice to have a cmd folder in the project root, and all the executables go under that, each in is own folder.
So a good solution in your case could be simply:
host.com/project/
cmd/
project/
project.go
filea.go
fileb.go
In filea.go and fileb.go the package declaration should be:
package project
In cmd/project/project.go package and import declaration should be:
package main
import "host.com/project"
Of course if your project is more complex, you may create further packages under the project root, and it may have multiple commands (multiple main packages), e.g.:
host.com/project/
cmd/
project/
project.go
prjtool/
prjtool.go
packagex/
x.go
packagey/
y.go
filea.go
fileb.go
An example following this layout is the very popular Go Delve debugger (4.5k stars currently), available at https://github.com/derekparker/delve.
A very complex repository example is the golang.org/x/tools package which is a collection of multiple, essential Go tools, available at https://github.com/golang/tools/. Its cmd folder contains more than 20 subfolders (commands), many of the tools (main packages) even consist of multiple .go files (but each using package main declaration, forming a single package of the executable).
Also check out the following related question: What is a sensible way to layout a Go project
So I was developing a go application for the very first time. I came to know that there are two variables GOROOT and GOPATH which are used to maintain go packages. What I understand till now, is that GOROOT is for the go binary files and GOPATH is mainly for storing library and helper packages that is needed for projects.
Here is my current project structure -
/Users/john/work/project-mars
/Users/john/work/project-mars/main.go
/Users/john/work/project-mars/helper
/Users/john/work/project-mars/helper/helper.go
Content of main.go
package main
import (
"fmt"
"helper"
)
func main(){
fmt.Println("Hello")
}
Content of helper.go
package helper
import (
"fmt"
)
func SayWorld(){
fmt.Println("World")
}
And the go variables are -
GOROOT = /Users/john/apps/go
GOPATH = /Users/john/apps/go-packages
Problem:
Now when I perform the following command, I get this error -
mac-machine:project-mars john$ go build main.go
main.go:5:5: cannot find package "helper" in any of:
/Users/john/apps/go/src/helper (from $GOROOT)
/Users/john/apps/go-packages/src/helper (from $GOPATH)
I understand that GOPATH should be the project directory that I am working on. But I am concerned with keeping my projects and library packages in a modular way, so that when later I have a totally different project (i.e. project-aurora) which might use same github helper packages, that they are not downloaded two times, both in project-mars and project-aurora .
How can I avoid this redundancy while working on different projects ?
Update: It's not that I can not compile them. I can use the GOPATH as my project directory and use src,pkg,bin project layouts and also reorganize the files and finally get to compile the project. yeeeeppi. But my question is about resolving the redundancy of common package problem that appears in this single GOPATH way.
Please read How to Write Go Code carefully. It explains everything you need to know.
You don't use GOPATH as your project directory. Assuming you want to work with the standard Go tooling, your package source needs to be in the directory corresponding to its import path, just like any other package.
Your project should be located at $GOPATH/src/project-mars, which can be built via go install project-mars. The helper package should be located at $GOPATH/src/project-mars/helper, and imported via "project-mars/helper".
Rename your helper-lib folder to helper
Then move this folder from project-mars to the upper folder work
This should make your
import "helper"
statement in main.go work.