Re: [Pharo-users] uFFI Structure Problem

Sept. 9, 2019

      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 fÃ¼r den KeyStore.*/
    const char *pin;
/**
     * @brief MUST be NULL in my context
              Dieser muss ...
              In allen anderen FÃ¤llen muss hier NULL Ã¼bergeben
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: FÃ¼r die
Ã¼bermittelte Datenart ist die Angabe eines Abrufcodes nicht zulÃ¤ssig,
daher muss fÃ¼r den Abrufcode der Wert NULL Ã¼bergeben 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: âhelloâ 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