Thank you Esteban for your fast answer. 1) NULL Pointer assignment: I have implemented your advise, and changed the attribute "abrufCode" to "ExternalAddress null"; >> fieldDesc #(myStruct uint32 version; ... void * abrufCode; ) The Structure has a NULL pointer assigned!? (see Inspector on MyStruct "MyStruct ( version: 2 zertifikatHandle: (void*)@ 16r7F8400000001 pin: (char*)@ 16r7F84FB7FE5A0 abrufCode: (void*)@ 16r00000000 )" But the problem is the same. I get the error: "attribute abrufCode must have the value NULL." Any ideas? 2) coercing problem: In my various tries I changed the whole structure to ExternalAddress null. (In some circumstances I have to set the whole Structure to NULL) Now I got an coercing error. I think, because ExternalAddress is not a FFIExternalStructure. " ^ self ffiCall: #(int BearbeiteVorgang(String daten, String version, int flags, ExternalAddress * druck, MyStruct * crypto, TransferHandle * transfer, RueckgabeHandle * rueckgabe, RueckgabeHandle * serverantwort)). " Is it possible, NOT to decide between (here 4: druck and crypto can be either Structures or NULL) ffi-calls? Thank you, Georg Am Do., 5. Sept. 2019 um 16:30 Uhr schrieb Esteban Lorenzano <estebanlm@gmail.com>:

On 5 Sep 2019, at 17:41, Georg Hagn <georg.hagn@gmail.com> wrote:

I have to implemet following external structure (extrakt from the german api Doku):

typedef struct { /**@brief MUST be always 2. */ uint32_t version;

/** @brief Pointer to KeyStore -- Verweis auf den KeyStore, see EricGetHandleToCertificate(). */ EricZertifikatHandle zertifikatHandle;

/** @brief PIN für den KeyStore.*/ const char *pin;

/** * @brief MUST be NULL in my context Dieser muss ... In allen anderen Fällen muss hier NULL übergeben werden. Der Parameter abrufCode besteht aus 2 x 5 Zeichen, die mit "-" verbunden sind. Beispiel: "K6FG5-RS32P" */ const char *abrufCode;

} eric_verschluesselungs_parameter_t;

My Problem is, that i have to assign a NULL - value to the attribute abrufCode. I have tried varies possibilities but I get always the error, that the attribute abrufCode must have the value NULL.

" Extract from log-file: 019-09-05 17:08:52,257709[0x00007fe036a2f050] ERROR: Für die übermittelte Datenart ist die Angabe eines Abrufcodes nicht zulässig, daher muss für den Abrufcode der Wert NULL übergeben werden. 610001029"

How do I assign a NULL value to an attribute in a FFIExternalStructure?

The problem is not that is an structure but that is a char *, which is converted to a String in Pharo. Ideally, a nil should be mapped to NULL in this cases, but this is not working (never implemented).

Easiest workaround, just map abrufCode to void * instead char * (pointers are always same size).

So you can have:

myStryct abrufCode: ExternalAddress null.

But of course, that will change the way you put the value there when *it is not* a NULL:

myStryct abrufCode: ‘hello’ utf8Encoded copyWith 0.

(The copyWith: 0 is to ensure the void * will receive something with proper \0 finalisation)

Esteban

Following my last attempt (extracted from the Pharo Booklet Colletion "Calling Foreign Functions with Pharo May 31,2018") I assign values not directly with the generated attributes but with "api???" attributes.

FFIExternalStructure subclass: #ERiCVerschluesselungsParameter instanceVariableNames: '' classVariableNames: 'OFFSET_ABRUFCODE OFFSET_PIN OFFSET_VERSION OFFSET_ZERTIFIKATHANDLE' package: 'Bajoras-ERiC'!

ERiCVerschluesselungsParameter class >> fieldsDesc [

"ERiCVerschluesselungsParameter rebuildFieldAccessors"

^ #( uint32 version; ERiCZertifikatHandle * zertifikatHandle; char * pin; char * abrufCode; ) ]

ERiCVerschluesselungsParameter >> initialize [

self apiVersion: 2; apiAbrufCode: nil; apiPin: 'mySecret'. ]

ERiCVerschluesselungsParameter >> accessorMethods for: pin, version, abrufCode, zertifikatHandle ("This method were automatically generated")

ERiCVerschluesselungsParameter >> apiAbrufCode: aCode [

| codeSize anAbrufCode |

codeSize := 11. anAbrufCode := FFIExternalArray externalNewType: 'char' size: codeSize. 1 to: codeSize do: [ :idx | anAbrufCode at: idx put: Character null ] .

aCode ifNotNil: [ aCode doWithIndex: [ :char :i | anAbrufCode at: i put: char ]. ].

self abrufCode: anAbrufCode.

]

ERiCVerschluesselungsParameter >> apiPin: aPin [

| newPin |

newPin := FFIExternalArray externalNewType: 'char' size: aPin size. aPin doWithIndex: [ :char :i | newPin at: i put: char ].

self pin: newPin. ]

ERiCVerschluesselungsParameter >> apiVersion: aVersion [

| cryptoVersion |

cryptoVersion := 2. self version: cryptoVersion.

]

Thanks, Georg Hagn