Add provider lookup

provider.go

@@ -0,0 +1,84 @@
+package etw
+
+import (
+	"encoding/binary"
+	"fmt"
+	"unicode/utf16"
+	"unsafe"
+
+	"golang.org/x/sys/windows"
+)
+
+/*
+// MinGW headers are always restricted to the lowest possible Windows version,
+// so specify Win7+ manually.
+#undef _WIN32_WINNT
+#define _WIN32_WINNT _WIN32_WINNT_WIN7
+
+#include <windows.h>
+#include <tdh.h>
+ */
+import "C"
+
+//nolint:gochecknoglobals
+var (
+	enumerateProviders = tdh.NewProc("TdhEnumerateProviders")
+)
+
+type Provider struct {
+	Name string
+	GUID windows.GUID
+}
+
+func LookupProvider(name string) (Provider, error) {
+	providers, err := ListProviders()
+	if err != nil {
+		return Provider{}, err
+	}
+	for _, provider := range providers {
+		if provider.Name == name {
+			return provider, nil
+		}
+	}
+	return Provider{}, fmt.Errorf("provider not found")
+}
+
+func ListProviders() ([]Provider, error) {
+	var requiredSize uintptr
+	plainStatus, _, _ := enumerateProviders.Call(0, uintptr(unsafe.Pointer(&requiredSize)))
+	status := windows.Errno(plainStatus)
+	var buffer []byte
+	for status == windows.ERROR_INSUFFICIENT_BUFFER {
+		buffer = make([]byte, requiredSize)
+		plainStatus, _, _ := enumerateProviders.Call(
+			uintptr(unsafe.Pointer(&buffer[0])),
+			uintptr(unsafe.Pointer(&requiredSize)))
+		status = windows.Errno(plainStatus)
+	}
+	if status != windows.ERROR_SUCCESS {
+		return nil, status
+	}
+	enumerationInfo := (*C.PROVIDER_ENUMERATION_INFO)(unsafe.Pointer(&buffer[0]))
+	// Recast provider info array to escape golang boundary checks
+	providerInfoArray := (*[1 << 25]C.TRACE_PROVIDER_INFO)(unsafe.Pointer(&enumerationInfo.TraceProviderInfoArray))
+	var parsedProviders = make([]Provider, 0, enumerationInfo.NumberOfProviders)
+	for _, providerInfo := range providerInfoArray[:enumerationInfo.NumberOfProviders] {
+		parsedProviders = append(parsedProviders, Provider{
+			Name: parseUnicodeStringAtOffset(buffer, int(providerInfo.ProviderNameOffset)),
+			GUID: windowsGUIDToGo(providerInfo.ProviderGuid),
+		})
+	}
+	return parsedProviders, nil
+}
+
+func parseUnicodeStringAtOffset(buffer []byte, offset int) string {
+	var nameArray []uint16
+	for j := offset; j < len(buffer) - 1; j+=2 {
+		unicodeChar := binary.LittleEndian.Uint16(buffer[j:])
+		if unicodeChar == 0 {
+			break
+		}
+		nameArray = append(nameArray, unicodeChar)
+	}
+	return string(utf16.Decode(nameArray))
+}