glib & g_checksum_*

This is a discussion on glib & g_checksum_* within the Linux Programming forums, part of the Platform Specific Boards category; Though I am a glib fan, I really cannot use the g_checksum_* functions to obtain an MD5 string that is ...

  1. #1
    Registered User sbaginov's Avatar
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    glib & g_checksum_*

    Though I am a glib fan, I really cannot use the g_checksum_* functions to obtain an MD5 string that is compatible with the md5sum command.
    Code:
    gchar *get_hash(const gchar *filepath) {
    	FILE *fp;
    	if (NULL != (fp = fopen(filepath, "r+b"))) {
    		guchar buffer[65536];
    		gint read_bytes;
    		gchar *result;
    		GChecksum *checksum = g_checksum_new(hash_type);
    		while ((read_bytes = fread(buffer, sizeof(buffer), 1, fp)) > 0)
    			g_checksum_update(checksum, buffer, read_bytes);
    
    		fclose(fp);
    		result = (gchar *) g_checksum_get_string(checksum);
    		g_checksum_free(checksum);
    		return result;
    	}
    	return "";
    }
    Any idea on what is wrong with this code?
    Thanks in advance for any help and or suggestion
    Last edited by sbaginov; 01-26-2011 at 07:38 AM.

  2. #2
    and the hat of wrongness Salem's Avatar
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    I would say you need to make a COPY of the string returned by g_checksum_get_string(), before you call g_checksum_free()
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  3. #3
    Registered User sbaginov's Avatar
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    Yes, you are right.

    Code:
    gchar *get_hash(const gchar *filepath, GChecksumType hash_type) {
        FILE *fp;
        if (NULL != (fp = fopen(filepath, "r+b"))) {
            guchar buffer[65536];
            gint read_bytes;
            gchar *result;
            GChecksum *checksum = g_checksum_new(hash_type);
            while ((read_bytes = fread(buffer, sizeof(buffer), 1, fp)) > 0)
                g_checksum_update(checksum, buffer, read_bytes);
    
            fclose(fp);
            result = g_strdup((gchar *) g_checksum_get_string(checksum));
            g_checksum_free(checksum);
            return result;
        }
        return g_strdup("");
    }
    Unfortunately, the returned array contains a different hash value from that returned by md5sum

  4. #4
    and the hat of wrongness Salem's Avatar
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    Your fread parameters are the wrong way round.

    That is, if you're wanting to return the number of bytes, as opposed to the number of buffers.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  5. #5
    Registered User sbaginov's Avatar
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    Cool Solved

    ** Thank you so much!!
    Code:
    gchar *get_hash(const gchar *filepath, GChecksumType hash_type) {
    	FILE *fp;
    	if (NULL != (fp = fopen(filepath, "rb"))) {
    		guchar buffer[65536];
    		gint read_bytes;
    		gchar *result;
    		GChecksum *checksum = g_checksum_new(hash_type);
    		while ((read_bytes = fread(buffer, 1, sizeof(buffer), fp)) > 0)
    			g_checksum_update(checksum, buffer, read_bytes);
    
    		result = g_strdup((gchar *) g_checksum_get_string(checksum));
    
    		fclose(fp);
    		g_checksum_free(checksum);
    
    		return result;
    	}
    	return g_strdup("");
    }
    Last edited by sbaginov; 01-26-2011 at 08:22 AM. Reason: fopen mode fix

  6. #6
    and the hat of wrongness Salem's Avatar
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    > guchar buffer[65536];
    If you're stuck for choosing a buffer size, then the macro BUFSIZ (in stdio.h) is a good alternative.

    > result = g_strdup((gchar *) g_checksum_get_string(checksum));
    I can't see how this cast was necessary.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

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