How do you get the output value of a C(CDELC) function defined in an external library as char** - progress-4gl

Question

I want to be able to use the following function defined in a shared object file (lib.so) :
int encrypt_data (char* buffer_in, int size_in, char** buffer_out, int* size_out)
Basically, i want to be able to pass the content of a file to this function (buffer_in) and write the output content (buffer_out) into another file. Here is what i've tried so far :
PROCEDURE encrypt_data EXTERNAL "lib.so" CDECL :
DEFINE INPUT PARAMETER buffer_in AS MEMPTR.
DEFINE INPUT PARAMETER size_in AS LONG.
DEFINE OUTPUT PARAMETER buffer_out AS MEMPTR.
DEFINE OUTPUT PARAMETER size_out AS LONG.
DEFINE RETURN PARAMETER returnvalue AS LONG.
END PROCEDURE.
PROCEDURE pi_encryptHash:
DEFINE INPUT PARAMETER ipc_fullPathToEncrypt AS CHARACTER NO-UNDO.
DEFINE VARIABLE lm_bufferIn AS MEMPTR NO-UNDO.
DEFINE VARIABLE li_sizeIn AS INT NO-UNDO.
DEFINE VARIABLE lm_bufferFakeOut AS MEMPTR NO-UNDO.
DEFINE VARIABLE lm_bufferOut AS MEMPTR NO-UNDO.
DEFINE VARIABLE li_sizeOut AS INT NO-UNDO.
DEFINE VARIABLE li_returnedCode AS INTEGER NO-UNDO.
/* make sure MEMPTR is sized correctly */
FILE-INFO:FILE-NAME = ipc_fullPathToEncrypt.
SET-SIZE(lm_bufferIn) = FILE-INFO:FILE-SIZE.
li_sizeIn = GET-SIZE(lm_bufferIn).
/* the actual read */
INPUT FROM VALUE(ipc_fullPathToEncrypt) BINARY NO-MAP NO-CONVERT.
IMPORT lm_bufferIn.
INPUT CLOSE.
/* Call the encrypt proc a first time to get the output lenght */
SET-SIZE(lm_bufferFakeOut) = 2.
RUN encrypt_data(INPUT lm_bufferIn, INPUT li_sizeIn, OUTPUT lm_bufferFakeOut, OUTPUT li_sizeOut, OUTPUT li_returnedCode).
/* Call it a second time with a buffer large enough to get the output value */
SET-SIZE(lm_bufferOut) = li_sizeOut.
RUN encrypt_data(INPUT lm_bufferIn, INPUT li_sizeIn, OUTPUT lm_bufferOut, OUTPUT li_sizeOut, OUTPUT li_returnedCode).
/* Write MEMPTR to file */
OUTPUT TO VALUE(ipc_fullPathToEncrypt + ".sha") BINARY NO-MAP NO-CONVERT.
EXPORT lm_bufferOut.
OUTPUT CLOSE.
SET-SIZE(lm_bufferIn) = 0.
SET-SIZE(lm_bufferOut) = 0.
DISPLAY li_returnedCode.
RETURN "".
END PROCEDURE.
I think my problem is that i can't read the data of char** buffer_out, from what i understand it is a pointer to a pointer so what i'm really exporting here EXPORT lm_bufferOut. is the pointer address of the data i would like to export? But how can i export the data instead?

Answer 1

Maybe not an answer to your original question but be aware that there are built functions in Progress for encryption. For instance you can do like this (in this example the encrypted value is base64-encoded so the result is "viewable"):
DEFINE VARIABLE cClearText AS CHARACTER NO-UNDO.
DEFINE VARIABLE rBinaryKey AS RAW NO-UNDO.
DEFINE VARIABLE rEncryptedValue AS RAW NO-UNDO.
DEFINE VARIABLE cEncryptedText AS CHARACTER NO-UNDO.
DEFINE VARIABLE cDecryptedText AS CHARACTER NO-UNDO.
ASSIGN
cClearText = "This is the clear text string to be encrypted.".
MESSAGE "Original message: " cCleartext
VIEW-AS ALERT-BOX INFO BUTTONS OK.
ASSIGN
SECURITY-POLICY:SYMMETRIC-ENCRYPTION-ALGORITHM = "AES_OFB_256"
rBinaryKey = GENERATE-RANDOM-KEY
SECURITY-POLICY:SYMMETRIC-ENCRYPTION-KEY = rBinaryKey
SECURITY-POLICY:SYMMETRIC-ENCRYPTION-IV = ?
rEncryptedValue = Encrypt (cClearText)
cEncryptedText = BASE64-ENCODE(rEncryptedValue)
.
MESSAGE "Encrypted Message:" cEncryptedText
VIEW-AS ALERT-BOX INFO BUTTONS OK.
ASSIGN
SECURITY-POLICY:SYMMETRIC-ENCRYPTION-KEY = rBinaryKey
cDecryptedText = GET-STRING(DECRYPT (rEncryptedValue),1).
MESSAGE "Decrypted Message: " cDecryptedText
VIEW-AS ALERT-BOX INFO BUTTONS OK.
This example is based on this knowledge base entry.
You can do:
MESSAGE SECURITY-POLICY:SYMMETRIC-SUPPORT VIEW-AS ALERT-BOX.
to see supported symmetric encryption algorithms supported.
Here's an SO question regarding different versions of AES algorithms:
How to choose an AES encryption mode (CBC ECB CTR OCB CFB)?

Answer 2

A solution has been found, below is the program used :
PROCEDURE pi_encryptDecrypt:
DEFINE INPUT PARAMETER ipc_inputFile AS CHARACTER NO-UNDO.
DEFINE INPUT PARAMETER ipc_outputFile AS CHARACTER NO-UNDO.
DEFINE INPUT PARAMETER ipi_codeOp AS INTEGER NO-UNDO.
DEFINE VARIABLE lm_bufferIn AS MEMPTR NO-UNDO.
DEFINE VARIABLE li_sizeIn AS INT NO-UNDO.
DEFINE VARIABLE lm_bufferFakeOut AS MEMPTR NO-UNDO.
DEFINE VARIABLE lm_bufferOut AS MEMPTR NO-UNDO.
DEFINE VARIABLE li_sizeOut AS INT NO-UNDO.
DEFINE VARIABLE li_returnedCode AS INTEGER NO-UNDO.
define variable mtarget as memptr.
/* make sure MEMPTR is sized correctly */
FILE-INFO:FILE-NAME = ipc_inputFile.
SET-SIZE(lm_bufferIn) = FILE-INFO:FILE-SIZE.
li_sizeIn = GET-SIZE(lm_bufferIn).
/* the actual read */
copy-lob from file ipc_inputFile to lm_bufferIn.
/* set a buffer large enough to get the output value */
SET-SIZE(lm_bufferOut) = 8.
if ipi_codeOp = 1 then
RUN encrypt_data(INPUT lm_bufferIn, INPUT li_sizeIn, OUTPUT lm_bufferOut, OUTPUT li_sizeOut, OUTPUT li_returnedCode).
else
RUN decrypt_data(INPUT lm_bufferIn, INPUT li_sizeIn, OUTPUT lm_bufferOut, OUTPUT li_sizeOut, OUTPUT li_returnedCode).
set-size(mtarget) = li_sizeOut.
SET-POINTER-VALUE(mtarget) = GET-INT64(lm_bufferOut, 1).
/* Write MEMPTR to file */
os-delete value(ipc_outputFile).
COPY-LOB FROM mtarget for /* FOR est SUPER IMPORTANT !! - ne pas enlever */ li_sizeOut TO FILE (ipc_outputFile).
SET-SIZE(lm_bufferIn) = 0.
SET-SIZE(lm_bufferOut) = 0.
set-size(mtarget) = 0.
/*DISPLAY li_returnedCode.
DISPLAY li_sizeOut.*/
RETURN "".
END PROCEDURE.
As i stated in my question, the problem was indeed that char** buffer_out returns a pointer to a pointer to the data in the memory.
The trick was to use a second MEMPTR (mtarget) that will point to the actual data, size it to be large enough with SET-SIZE and then sets it to the value of a particular memory location (using SET-POINTER-VALUE), which we get from GET-INT64(lm_bufferOut, 1).