refactor(netxlite/errorsx): extract string-suffix classifier (#482)

This change makes the code more tidy and easier to read.

No functional change, though.

See https://github.com/ooni/probe/issues/1591.

internal/netxlite/errorsx/classify.go

@@ -11,11 +11,6 @@ import (
 	"github.com/ooni/probe-cli/v3/internal/scrubber"
 )
 
-// TODO (kelmenhorst, bassosimone):
-// Use errors.Is / errors.As more often, when possible, in this classifier.
-// These methods are more robust to library changes than strings.
-// errors.Is / errors.As can only be used when the error is exported.
-
 // ClassifyGenericError is the generic classifier mapping an error
 // occurred during an operation to an OONI failure string.
 //
@@ -58,6 +53,18 @@ func ClassifyGenericError(err error) string {
 		return FailureInterrupted
 	}
 
+	if failure := classifyWithStringSuffix(err); failure != "" {
+		return failure
+	}
+
+	formatted := fmt.Sprintf("unknown_failure: %s", err.Error())
+	return scrubber.Scrub(formatted) // scrub IP addresses in the error
+}
+
+// classifyWithStringSuffix is a subset of ClassifyGenericError that
+// performs classification by looking at error suffixes. This function
+// will return an empty string if it cannot classify the error.
+func classifyWithStringSuffix(err error) string {
 	s := err.Error()
 	if strings.HasSuffix(s, "operation was canceled") {
 		return FailureInterrupted
@@ -83,9 +90,7 @@ func ClassifyGenericError(err error) string {
 		// that we return here is significantly more specific.
 		return FailureDNSNXDOMAINError
 	}
-
-	formatted := fmt.Sprintf("unknown_failure: %s", s)
-	return scrubber.Scrub(formatted) // scrub IP addresses in the error
+	return "" // not found
 }
 
 // TLS alert protocol as defined in RFC8446. We need these definitions

internal/netxlite/errorsx/errno.go

@@ -1,5 +1,5 @@
 // Code generated by go generate; DO NOT EDIT.
-// Generated: 2021-09-07 20:26:06.502417 +0200 CEST m=+0.133209876
+// Generated: 2021-09-07 20:42:20.172357 +0200 CEST m=+0.135433792
 
 package errorsx
 
@@ -64,9 +64,6 @@ const (
 // proper OONI error. Returns the OONI error string
 // on success, an empty string otherwise.
 func classifySyscallError(err error) string {
-	// filter out system errors: necessary to detect all windows errors
-	// https://github.com/ooni/probe/issues/1526 describes the problem
-	// of mapping localized windows errors.
 	var errno syscall.Errno
 	if !errors.As(err, &errno) {
 		return ""

internal/netxlite/errorsx/errno_test.go

@@ -1,5 +1,5 @@
 // Code generated by go generate; DO NOT EDIT.
-// Generated: 2021-09-07 20:26:06.547786 +0200 CEST m=+0.178579584
+// Generated: 2021-09-07 20:42:20.217324 +0200 CEST m=+0.180405501
 
 package errorsx
 

internal/netxlite/errorsx/errno_unix.go

@@ -1,5 +1,5 @@
 // Code generated by go generate; DO NOT EDIT.
-// Generated: 2021-09-07 20:26:06.370246 +0200 CEST m=+0.001036417
+// Generated: 2021-09-07 20:42:20.037485 +0200 CEST m=+0.000558667
 
 package errorsx
 

internal/netxlite/errorsx/errno_windows.go

@@ -1,5 +1,5 @@
 // Code generated by go generate; DO NOT EDIT.
-// Generated: 2021-09-07 20:26:06.478577 +0200 CEST m=+0.109369751
+// Generated: 2021-09-07 20:42:20.147482 +0200 CEST m=+0.110557751
 
 package errorsx
 

internal/netxlite/errorsx/internal/generrno/main.go

@@ -198,9 +198,6 @@ func writeGenericFile() {
 	fileWrite(filep, "// proper OONI error. Returns the OONI error string\n")
 	fileWrite(filep, "// on success, an empty string otherwise.\n")
 	fileWrite(filep, "func classifySyscallError(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")