engine/ooapi: autogenerated API with login and caching (#234)

* internal/engine/ooapi: auto-generated API client

* feat: introduce the callers abstraction

* feat: implement API caching on disk

* feat: implement cloneWithToken when we require login

* feat: implement login

* fix: do not cache all APIs

* feat: start making space for more tests

* feat: implement caching policy

* feat: write tests for caching layer

* feat: add integration tests and fix some minor issues

* feat: write much more unit tests

* feat: add some more easy unit tests

* feat: add tests that use a local server

While there, make sure many fields we care about are OK.

* doc: write basic documentation

* fix: tweak sentence

* doc: improve ooapi documentation

* doc(ooapi): other documentation improvements

* fix(ooapi): remove caching for most APIs

We discussed this topic yesterday with @FedericoCeratto. The only
place where we want LRU caching is MeasurementMeta.

* feat(ooapi): improve handling of errors during login

This was also discussed yesterday with @FedericoCeratto

* fix(swaggerdiff_test.go): temporarily disable

Before I work on this, I need to tend onto other tasks.

* fix(ootest): add one more test case

We're going towards 100% coverage of this package, as it ought to be.

* feat(ooapi): test cases for when the probe clock is off

* fix(ooapi): change test to have 100% unittest coverage

* feat: sync server and client APIs definition

Companion PR: https://github.com/ooni/api/pull/218

* fix(ooapi): start testing again against API

* fix(ooapi): only generate each file once

* chore: set version to 3.7.0-alpha

While there, make sure we don't always skip a currently failing
riseupvpn test, and slightly clarify the readme.

* fix(kvstore): less scoped error message

internal/engine/ooapi/internal/generator/fakeapitest.go

@@ -0,0 +1,59 @@
+package main
+
+import (
+	"fmt"
+	"strings"
+	"time"
+)
+
+func (d *Descriptor) genNewFakeAPI(sb *strings.Builder) {
+	fmt.Fprintf(sb, "type Fake%s struct {\n", d.APIStructName())
+	if d.RequiresLogin {
+		fmt.Fprintf(sb, "\tWithResult %s\n", d.CallerInterfaceName())
+	}
+	fmt.Fprint(sb, "\tErr error\n")
+	fmt.Fprintf(sb, "\tResponse %s\n", d.ResponseTypeName())
+	fmt.Fprint(sb, "\tCountCall int32\n")
+	fmt.Fprint(sb, "}\n\n")
+
+	fmt.Fprintf(sb, "func (fapi *Fake%s) Call(ctx context.Context, req %s) (%s, error) {\n",
+		d.APIStructName(), d.RequestTypeName(), d.ResponseTypeName())
+	fmt.Fprint(sb, "\tatomic.AddInt32(&fapi.CountCall, 1)\n")
+	fmt.Fprint(sb, "\treturn fapi.Response, fapi.Err\n")
+	fmt.Fprint(sb, "}\n\n")
+
+	if d.RequiresLogin {
+		fmt.Fprintf(sb, "func (fapi *Fake%s) WithToken(token string) %s {\n",
+			d.APIStructName(), d.CallerInterfaceName())
+		fmt.Fprint(sb, "\treturn fapi.WithResult\n")
+		fmt.Fprint(sb, "}\n\n")
+	}
+
+	fmt.Fprint(sb, "var (\n")
+	fmt.Fprintf(sb, "\t_ %s = &Fake%s{}\n", d.CallerInterfaceName(),
+		d.APIStructName())
+	if d.RequiresLogin {
+		fmt.Fprintf(sb, "\t_ %s = &Fake%s{}\n", d.ClonerInterfaceName(),
+			d.APIStructName())
+	}
+	fmt.Fprint(sb, ")\n\n")
+}
+
+// GenFakeAPITestGo generates fakeapi_test.go.
+func GenFakeAPITestGo(file string) {
+	var sb strings.Builder
+	fmt.Fprint(&sb, "// Code generated by go generate; DO NOT EDIT.\n")
+	fmt.Fprintf(&sb, "// %s\n\n", time.Now())
+	fmt.Fprint(&sb, "package ooapi\n\n")
+	fmt.Fprintf(&sb, "//go:generate go run ./internal/generator -file %s\n\n", file)
+	fmt.Fprint(&sb, "import (\n")
+	fmt.Fprint(&sb, "\t\"context\"\n")
+	fmt.Fprint(&sb, "\t\"sync/atomic\"\n")
+	fmt.Fprint(&sb, "\n")
+	fmt.Fprint(&sb, "\t\"github.com/ooni/probe-cli/v3/internal/engine/ooapi/apimodel\"\n")
+	fmt.Fprint(&sb, ")\n")
+	for _, desc := range Descriptors {
+		desc.genNewFakeAPI(&sb)
+	}
+	writefile(file, &sb)
+}