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Data Checksums

Data Checksums — computes the checksum for data

Types and Values

Includes

#include <glib.h>

Description

GLib provides a generic API for computing checksums (or "digests") for a sequence of arbitrary bytes, using various hashing algorithms like MD5, SHA-1 and SHA-256. Checksums are commonly used in various environments and specifications.

GLib supports incremental checksums using the GChecksum data structure, by calling g_checksum_update() as long as there's data available and then using g_checksum_get_string() or g_checksum_get_digest() to compute the checksum and return it either as a string in hexadecimal form, or as a raw sequence of bytes. To compute the checksum for binary blobs and NUL-terminated strings in one go, use the convenience functions g_compute_checksum_for_data() and g_compute_checksum_for_string(), respectively.

Support for checksums has been added in GLib 2.16

Functions

g_checksum_type_get_length ()

gssize
g_checksum_type_get_length (GChecksumType checksum_type);

Gets the length in bytes of digests of type checksum_type

Parameters

checksum_type

a GChecksumType

 

Returns

the checksum length, or -1 if checksum_type is not supported.

Since 2.16


g_checksum_new ()

GChecksum *
g_checksum_new (GChecksumType checksum_type);

Creates a new GChecksum, using the checksum algorithm checksum_type . If the checksum_type is not known, NULL is returned. A GChecksum can be used to compute the checksum, or digest, of an arbitrary binary blob, using different hashing algorithms.

A GChecksum works by feeding a binary blob through g_checksum_update() until there is data to be checked; the digest can then be extracted using g_checksum_get_string(), which will return the checksum as a hexadecimal string; or g_checksum_get_digest(), which will return a vector of raw bytes. Once either g_checksum_get_string() or g_checksum_get_digest() have been called on a GChecksum, the checksum will be closed and it won't be possible to call g_checksum_update() on it anymore.

Parameters

checksum_type

the desired type of checksum

 

Returns

the newly created GChecksum, or NULL. Use g_checksum_free() to free the memory allocated by it.

[transfer full]

Since 2.16


g_checksum_copy ()

GChecksum *
g_checksum_copy (const GChecksum *checksum);

Copies a GChecksum. If checksum has been closed, by calling g_checksum_get_string() or g_checksum_get_digest(), the copied checksum will be closed as well.

Parameters

checksum

the GChecksum to copy

 

Returns

the copy of the passed GChecksum. Use g_checksum_free() when finished using it.

Since 2.16


g_checksum_free ()

void
g_checksum_free (GChecksum *checksum);

Frees the memory allocated for checksum .

Parameters

checksum

a GChecksum

 

Since 2.16


g_checksum_reset ()

void
g_checksum_reset (GChecksum *checksum);

Resets the state of the checksum back to its initial state.

Parameters

checksum

the GChecksum to reset

 

Since 2.18


g_checksum_update ()

void
g_checksum_update (GChecksum *checksum,
                   const guchar *data,
                   gssize length);

Feeds data into an existing GChecksum. The checksum must still be open, that is g_checksum_get_string() or g_checksum_get_digest() must not have been called on checksum .

Parameters

checksum

a GChecksum

 

data

buffer used to compute the checksum.

[array length=length][element-type guint8]

length

size of the buffer, or -1 if it is a null-terminated string.

 

Since 2.16


g_checksum_get_string ()

const gchar *
g_checksum_get_string (GChecksum *checksum);

Gets the digest as an hexadecimal string.

Once this function has been called the GChecksum can no longer be updated with g_checksum_update().

The hexadecimal characters will be lower case.

Parameters

checksum

a GChecksum

 

Returns

the hexadecimal representation of the checksum. The returned string is owned by the checksum and should not be modified or freed.

Since 2.16


g_checksum_get_digest ()

void
g_checksum_get_digest (GChecksum *checksum,
                       guint8 *buffer,
                       gsize *digest_len);

Gets the digest from checksum as a raw binary vector and places it into buffer . The size of the digest depends on the type of checksum.

Once this function has been called, the GChecksum is closed and can no longer be updated with g_checksum_update().

Parameters

checksum

a GChecksum

 

buffer

output buffer

 

digest_len

an inout parameter. The caller initializes it to the size of buffer . After the call it contains the length of the digest.

 

Since 2.16


g_compute_checksum_for_data ()

gchar *
g_compute_checksum_for_data (GChecksumType checksum_type,
                             const guchar *data,
                             gsize length);

Computes the checksum for a binary data of length . This is a convenience wrapper for g_checksum_new(), g_checksum_get_string() and g_checksum_free().

The hexadecimal string returned will be in lower case.

Parameters

checksum_type

a GChecksumType

 

data

binary blob to compute the digest of.

[array length=length][element-type guint8]

length

length of data

 

Returns

the digest of the binary data as a string in hexadecimal. The returned string should be freed with g_free() when done using it.

Since 2.16


g_compute_checksum_for_string ()

gchar *
g_compute_checksum_for_string (GChecksumType checksum_type,
                               const gchar *str,
                               gssize length);

Computes the checksum of a string.

The hexadecimal string returned will be in lower case.

Parameters

checksum_type

a GChecksumType

 

str

the string to compute the checksum of

 

length

the length of the string, or -1 if the string is null-terminated.

 

Returns

the checksum as a hexadecimal string. The returned string should be freed with g_free() when done using it.

Since 2.16


g_compute_checksum_for_bytes ()

gchar *
g_compute_checksum_for_bytes (GChecksumType checksum_type,
                              GBytes *data);

Computes the checksum for a binary data . This is a convenience wrapper for g_checksum_new(), g_checksum_get_string() and g_checksum_free().

The hexadecimal string returned will be in lower case.

Parameters

checksum_type

a GChecksumType

 

data

binary blob to compute the digest of

 

Returns

the digest of the binary data as a string in hexadecimal. The returned string should be freed with g_free() when done using it.

Since 2.34

Types and Values

enum GChecksumType

The hashing algorithm to be used by GChecksum when performing the digest of some data.

Note that the GChecksumType enumeration may be extended at a later date to include new hashing algorithm types.

Members

G_CHECKSUM_MD5

Use the MD5 hashing algorithm

 

G_CHECKSUM_SHA1

Use the SHA-1 hashing algorithm

 

G_CHECKSUM_SHA256

Use the SHA-256 hashing algorithm

 

G_CHECKSUM_SHA512

Use the SHA-512 hashing algorithm

 

Since 2.16


GChecksum

typedef struct _GChecksum GChecksum;

An opaque structure representing a checksumming operation. To create a new GChecksum, use g_checksum_new(). To free a GChecksum, use g_checksum_free().

Since 2.16

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