refactor(errorsx): auto-generate syscall errors mapping (#429)

* refactor(errorsx): auto-generate syscall errors mapping

Part of https://github.com/ooni/probe/issues/1505

* fix: generate independently of the platform

internal/errorsx/generator/main.go

@@ -0,0 +1,175 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"time"
+
+	"golang.org/x/sys/execabs"
+)
+
+// ErrorSpec specifies the error we care about.
+type ErrorSpec struct {
+	// Errno is the error name as an errno value (e.g., ECONNREFUSED).
+	Errno string
+
+	// Failure is the error name according to OONI (e.g., FailureConnectionRefused).
+	Failure string
+}
+
+// TODO(kelmenhorst): find out if we need more system errors here. Currently
+// the code does not generate any mapping if Failure is empty.
+
+// Specs contains all the error specs.
+var Specs = []ErrorSpec{{
+	Errno:   "ECANCELED",
+	Failure: "Interrupted",
+}, {
+	Errno:   "ECONNREFUSED",
+	Failure: "ConnectionRefused",
+}, {
+	Errno:   "ECONNRESET",
+	Failure: "ConnectionReset",
+}, {
+	Errno:   "EHOSTUNREACH",
+	Failure: "HostUnreachable",
+}, {
+	Errno:   "ETIMEDOUT",
+	Failure: "GenericTimeoutError",
+}, {
+	Errno: "EAFNOSUPPORT",
+}, {
+	Errno: "EADDRINUSE",
+}, {
+	Errno: "EADDRNOTAVAIL",
+}, {
+	Errno: "EISCONN",
+}, {
+	Errno: "EFAULT",
+}, {
+	Errno: "EBADF",
+}, {
+	Errno: "ECONNABORTED",
+}, {
+	Errno: "EALREADY",
+}, {
+	Errno: "EDESTADDRREQ",
+}, {
+	Errno: "EINTR",
+}, {
+	Errno: "EINVAL",
+}, {
+	Errno: "EMSGSIZE",
+}, {
+	Errno: "ENETDOWN",
+}, {
+	Errno: "ENETRESET",
+}, {
+	Errno: "ENETUNREACH",
+}, {
+	Errno: "ENOBUFS",
+}, {
+	Errno: "ENOPROTOOPT",
+}, {
+	Errno: "ENOTSOCK",
+}, {
+	Errno: "ENOTCONN",
+}, {
+	Errno: "EWOULDBLOCK",
+}, {
+	Errno: "EACCES",
+}, {
+	Errno: "EPROTONOSUPPORT",
+}, {
+	Errno: "EPROTOTYPE",
+}}
+
+func fileCreate(filename string) *os.File {
+	filep, err := os.Create(filename)
+	if err != nil {
+		log.Fatal(err)
+	}
+	return filep
+}
+
+func fileWrite(filep *os.File, content string) {
+	if _, err := filep.WriteString(content); err != nil {
+		log.Fatal(err)
+	}
+}
+
+func fileClose(filep *os.File) {
+	if err := filep.Close(); err != nil {
+		log.Fatal(err)
+	}
+}
+
+func filePrintf(filep *os.File, format string, v ...interface{}) {
+	fileWrite(filep, fmt.Sprintf(format, v...))
+}
+
+func gofmt(filename string) {
+	cmd := execabs.Command("go", "fmt", filename)
+	if err := cmd.Run(); err != nil {
+		log.Fatal(err)
+	}
+}
+
+func writeSystemSpecificFile(kind string) {
+	filename := "errno_" + kind + ".go"
+	filep := fileCreate(filename)
+	fileWrite(filep, "// Code generated by go generate; DO NOT EDIT.\n")
+	filePrintf(filep, "// Generated: %+v\n\n", time.Now())
+	fileWrite(filep, "package errorsx\n\n")
+	filePrintf(filep, "import \"golang.org/x/sys/%s\"\n\n", kind)
+	fileWrite(filep, "const (\n")
+	for _, spec := range Specs {
+		filePrintf(filep, "\t%s = %s.%s\n", spec.Errno, kind, spec.Errno)
+	}
+	fileWrite(filep, ")\n\n")
+	fileClose(filep)
+	gofmt(filename)
+}
+
+func writeGenericFile() {
+	filename := "errno.go"
+	filep := fileCreate(filename)
+	fileWrite(filep, "// Code generated by go generate; DO NOT EDIT.\n")
+	filePrintf(filep, "// Generated: %+v\n\n", time.Now())
+	fileWrite(filep, "package errorsx\n\n")
+	fileWrite(filep, "//go:generate go run ./generator/\n\n")
+	fileWrite(filep, "import (\n")
+	fileWrite(filep, "\t\"errors\"\n")
+	fileWrite(filep, "\t\"syscall\"\n")
+	fileWrite(filep, ")\n\n")
+	fileWrite(filep, "// toSyscallErr converts a syscall error to the\n")
+	fileWrite(filep, "// proper OONI error. Returns the OONI error string\n")
+	fileWrite(filep, "// on success, an empty string otherwise.\n")
+	fileWrite(filep, "func toSyscallErr(err error) string {\n")
+	fileWrite(filep, "\t// filter out system errors: necessary to detect all windows errors\n")
+	fileWrite(filep, "\t// https://github.com/ooni/probe/issues/1526 describes the problem\n")
+	fileWrite(filep, "\t// of mapping localized windows errors.\n")
+	fileWrite(filep, "\tvar errno syscall.Errno\n")
+	fileWrite(filep, "\tif !errors.As(err, &errno) {\n")
+	fileWrite(filep, "\t\treturn \"\"\n")
+	fileWrite(filep, "\t}\n")
+	fileWrite(filep, "\tswitch errno {\n")
+	for _, spec := range Specs {
+		if spec.Failure != "" {
+			filePrintf(filep, "\tcase %s:\n", spec.Errno)
+			filePrintf(filep, "\t\treturn Failure%s\n", spec.Failure)
+		}
+	}
+	fileWrite(filep, "\t}\n")
+	fileWrite(filep, "\treturn \"\"\n")
+	fileWrite(filep, "}\n\n")
+	fileClose(filep)
+	gofmt(filename)
+}
+
+func main() {
+	writeSystemSpecificFile("unix")
+	writeSystemSpecificFile("windows")
+	writeGenericFile()
+}