miqt: pass all miqt_string by value, not by pointer

cmd/genbindings/emitcabi.go

@@ -9,7 +9,7 @@ import (
 func (p CppParameter) RenderTypeCabi() string {
 
 	if p.ParameterType == "QString" {
-		return "struct miqt_string*"
+		return "struct miqt_string"
 
 	} else if _, ok := p.QListOf(); ok {
 		return "struct miqt_array*"
@@ -146,7 +146,7 @@ func emitParametersCabi(m CppMethod, selfType string) string {
 
 	for _, p := range m.Parameters {
 		if p.ParameterType == "QString" {
-			tmp = append(tmp, "struct miqt_string* "+p.ParameterName)
+			tmp = append(tmp, "struct miqt_string "+p.ParameterName)
 
 		} else if t, ok := p.QListOf(); ok {
 			tmp = append(tmp, "struct miqt_array* /* of "+t.RenderTypeCabi()+" */ "+p.ParameterName)
@@ -197,9 +197,10 @@ func emitCABI2CppForwarding(p CppParameter, indent string) (preamble string, for
 	nameprefix := makeNamePrefix(p.ParameterName)
 
 	if p.ParameterType == "QString" {
-		// The CABI has accepted two parameters - need to convert to one real QString
+		// The CABI received parameter is a struct miqt_string, passed by value
-		// Create it on the stack
+		// C++ needs it as a QString. Create one on the stack for automatic cleanup
-		preamble += indent + "QString " + nameprefix + "_QString = QString::fromUtf8(&" + p.ParameterName + "->data, " + p.ParameterName + "->len);\n"
+		// The caller will free the miqt_string
+		preamble += indent + "QString " + nameprefix + "_QString = QString::fromUtf8(" + p.ParameterName + ".data, " + p.ParameterName + ".len);\n"
 		return preamble, nameprefix + "_QString"
 
 	} else if listType, ok := p.QListOf(); ok {
@@ -315,7 +316,11 @@ func emitAssignCppToCabi(assignExpression string, p CppParameter, rvalue string)
 			afterCall += indent + "QByteArray " + namePrefix + "_b = " + namePrefix + "_ret.toUtf8();\n"
 		}
 
-		afterCall += indent + assignExpression + "miqt_strdup(" + namePrefix + "_b.data(), " + namePrefix + "_b.length());\n"
+		afterCall += indent + "struct miqt_string " + namePrefix + "_ms;\n"
+		afterCall += indent + namePrefix + "_ms.len = " + namePrefix + "_b.length();\n"
+		afterCall += indent + namePrefix + "_ms.data = static_cast<char*>(malloc(" + namePrefix + "_ms.len));\n"
+		afterCall += indent + "memcpy(" + namePrefix + "_ms.data, " + namePrefix + "_b.data(), " + namePrefix + "_ms.len);\n"
+		afterCall += indent + assignExpression + namePrefix + "_ms;\n"
 
 	} else if t, ok := p.QListOf(); ok {
 

cmd/genbindings/emitgo.go

@@ -142,7 +142,7 @@ func (p CppParameter) RenderTypeGo(gfs *goFileState) string {
 
 func (p CppParameter) parameterTypeCgo() string {
 	if p.ParameterType == "QString" {
-		return "*C.struct_miqt_string"
+		return "C.struct_miqt_string"
 	}
 
 	if _, ok := p.QListOf(); ok {
@@ -256,11 +256,13 @@ func (gfs *goFileState) emitParameterGo2CABIForwarding(p CppParameter) (preamble
 		// Go: convert string -> miqt_string*
 		// CABI: convert miqt_string* -> real QString
 
-		gfs.imports["libmiqt"] = struct{}{}
+		gfs.imports["unsafe"] = struct{}{}
-		preamble += nameprefix + "_ms := libmiqt.Strdupg(" + p.ParameterName + ")\n"
+		preamble += nameprefix + "_ms := C.struct_miqt_string{}\n"
-		preamble += "defer C.free(" + nameprefix + "_ms)\n"
+		preamble += nameprefix + "_ms.data = C.CString(" + p.ParameterName + ")\n"
+		preamble += nameprefix + "_ms.len = C.size_t(len(" + p.ParameterName + "))\n"
+		preamble += "defer C.free(unsafe.Pointer(" + nameprefix + "_ms.data))\n"
 
-		rvalue = "(*C.struct_miqt_string)(" + nameprefix + "_ms)"
+		rvalue = nameprefix + "_ms"
 
 	} else if listType, ok := p.QListOf(); ok {
 		// QList<T>
@@ -359,9 +361,9 @@ func (gfs *goFileState) emitCabiToGo(assignExpr string, rt CppParameter, rvalue
 	} else if rt.ParameterType == "QString" {
 		gfs.imports["unsafe"] = struct{}{}
 
-		shouldReturn = "var " + namePrefix + "_ms *C.struct_miqt_string = "
+		shouldReturn = "var " + namePrefix + "_ms C.struct_miqt_string = "
-		afterword += namePrefix + "_ret := C.GoStringN(&" + namePrefix + "_ms.data, C.int(int64(" + namePrefix + "_ms.len)))\n"
+		afterword += namePrefix + "_ret := C.GoStringN(" + namePrefix + "_ms.data, C.int(int64(" + namePrefix + "_ms.len)))\n"
-		afterword += "C.free(unsafe.Pointer(" + namePrefix + "_ms))\n"
+		afterword += "C.free(unsafe.Pointer(" + namePrefix + "_ms.data))\n"
 		afterword += assignExpr + namePrefix + "_ret"
 		return shouldReturn + " " + rvalue + "\n" + afterword
 

libmiqt/libmiqt.cpp

@@ -1,8 +0,0 @@
-#include "libmiqt.h"
-
-struct miqt_string* miqt_strdup(const char* src, size_t len) {
-    struct miqt_string* ret = (struct miqt_string*)( malloc(len + sizeof(size_t)) );
-    ret->len = len;
-    memcpy(&ret->data, src, len);
-    return ret;
-}

libmiqt/libmiqt.go

@@ -0,0 +1,10 @@
+package libmiqt
+
+// SPDX-License-Identifier: MIT
+
+/*
+
+#include "libmiqt.h"
+
+*/
+import "C"

libmiqt/libmiqt.h

@@ -10,12 +10,12 @@ extern "C" {
 
 struct miqt_string {
     size_t len;
-    char data; // Data continues after this element, all in the same allocation
+    char* data;
 };
 
 struct miqt_array {
     size_t len;
-    void* data; // Separate, second allocation
+    void* data;
 };
 
 struct miqt_string* miqt_strdup(const char* src, size_t len);

libmiqt/strings.go

@@ -1,25 +0,0 @@
-package libmiqt
-
-// SPDX-License-Identifier: MIT
-
-/*
-
-#include "libmiqt.h"
-
-struct miqt_string* miqt_strdupg(_GoString_ gs) {
-	return miqt_strdup(_GoStringPtr(gs), _GoStringLen(gs));
-}
-
-*/
-import "C"
-
-import (
-	"unsafe"
-)
-
-// Strdupg will strdup a Go string into a miqt_string*.
-// It is typed as returning an unsafe.Pointer because Cgo types cannot be shared
-// across Go file boundaries.
-func Strdupg(s string) unsafe.Pointer {
-	return unsafe.Pointer(C.miqt_strdupg(s))
-}