refactor(golang): Use http provided constants for http methods

[mcristina422]

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\. If contributing template-only or documentation-only changes which will change sample output, be sure to build the project first.
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  @antihax @bvwells @grokify @kemokemo

Description of the PR

This modifies the golang client to use the http constants for method types as defined by RFC 7231 section 4.3. These are documented on:

https://golang.org/pkg/net/http/#pkg-constants

This does not require any new dependencies, as net/http is already imported.

Based on: #2983

[wing328]

CI reports the following errors:

SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
[ERROR] Error fetching link: /home/circleci/OpenAPITools/openapi-generator/modules/openapi-generator/home/circleci/OpenAPITools/openapi-generator/modules/openapi-generator-cli/target/apidocs. Ignored it.
# _/home/circleci/OpenAPITools/openapi-generator/samples/client/petstore/go/go-petstore
go-petstore/api_another_fake.go:17:2: imported and not used: "strings"
go-petstore/api_fake.go:17:2: imported and not used: "strings"
go-petstore/api_fake_classname_tags123.go:17:2: imported and not used: "strings"
FAIL	_/home/circleci/OpenAPITools/openapi-generator/samples/client/petstore/go [build failed]
[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.2.1:exec (go-test) on project Goswagger: Command execution failed. Process exited with an error: 2 (Exit value: 2) -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.

Looks like the strings import needs to be removed?

[mcristina422]

Oh, the edge case comes into play when the api file gets rendered with a path that includes a path parameter. Since sometimes this exists (or doesn't exist) for multiple operations, the logic of including this is not trivial.

Also fmt should probably also be moved into that block in
3deaa80 since fmt and strings both are only used in that case.

This is my first real interaction with mustache and this edge case seems more complex to handle than I initially thought.

Maybe the simplest solution is to always import it and hush the compiler with

// Linger please
var (
	_ context.Context
        _ strings.Replacer
)

Thoughts?

Also what does this do exactly? Maybe I'm misunderstanding something where this could be used

{{#imports}}	"{{import}}"
{{/imports}}

[wing328]

The imports is for importing models (e.g. Pet) defined in the endpoint/operation.

[wing328]

This is my first real interaction with mustache and this edge case seems more complex to handle than I initially thought.

Yup, that's another edge case that I've not yet encountered with other generators.

As a workaround, what about using "strings" somehow in the code so as to hardcode the import?

[mcristina422]

Ah, the import logic is handled here

openapi-generator/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractGoCodegen.java

Lines 364 to 371 in 2614670

	// this will only import "fmt" and "strings" if there are items in pathParams
	for (CodegenOperation operation : operations) {
	if (operation.pathParams != null && operation.pathParams.size() > 0) {
	imports.add(createMapping("import", "fmt"));
	imports.add(createMapping("import", "strings"));
	break; //just need to import once
	}
	}

so just adding strings to that was enough. No workarounds needed

[wing328]

Thanks again for the PR, which has been included in the v4.0.2 release: https://twitter.com/oas_generator/status/1141610197766426626