GConverter: GIO Reference Manual

## GConverter GConverter — Data conversion interface |

## Functions

GConverterResult | g_converter_convert ()
void | g_converter_reset ()

## Types and Values

| GConverter
struct | GConverterIface
enum | GConverterResult
enum | GConverterFlags

## Object Hierarchy

        GInterface
        ╰── GConverter

## Prerequisites

GConverter requires GObject.

## Known Implementations

GConverter is implemented by GCharsetConverter, GZlibCompressor and GZlibDecompressor.

## Includes

    #include <gio/gio.h>

## Description

GConverter is implemented by objects that convert binary data in various ways. The conversion can be stateful and may fail at any place.

Some example conversions are: character set conversion, compression, decompression and regular expression replace.

## Functions

### g_converter_convert ()

    GConverterResult
    g_converter_convert (GConverter *converter,
                         const void *inbuf,
                         gsize inbuf_size,
                         void *outbuf,
                         gsize outbuf_size,
                         GConverterFlags flags,
                         gsize *bytes_read,
                         gsize *bytes_written,
                         GError **error);

This is the main operation used when converting data. It is to be called multiple times in a loop, and each time it will do some work, i.e. producing some output (in `outbuf` ) or consuming some input (from `inbuf` ) or both. If its not possible to do any work an error is returned.

Note that a single call may not consume all input (or any input at all). Also a call may produce output even if given no input, due to state stored in the converter producing output.

If any data was either produced or consumed, and then an error happens, then only the successful conversion is reported and the error is returned on the next call.

A full conversion loop involves calling this method repeatedly, each time giving it new input and space output space. When there is no more input data after the data in `inbuf` , the flag `G_CONVERTER_INPUT_AT_END` must be set. The loop will be (unless some error happens) returning `G_CONVERTER_CONVERTED` each time until all data is consumed and all output is produced, then `G_CONVERTER_FINISHED` is returned instead. Note, that `G_CONVERTER_FINISHED` may be returned even if `G_CONVERTER_INPUT_AT_END` is not set, for instance in a decompression converter where the end of data is detectable from the data (and there might even be other data after the end of the compressed data).

When some data has successfully been converted `bytes_read` and is set to the number of bytes read from `inbuf` , and `bytes_written` is set to indicate how many bytes was written to `outbuf` . If there are more data to output or consume (i.e. unless the `G_CONVERTER_INPUT_AT_END` is specified) then `G_CONVERTER_CONVERTED` is returned, and if no more data is to be output then `G_CONVERTER_FINISHED` is returned.

On error `G_CONVERTER_ERROR` is returned and `error` is set accordingly. Some errors need special handling:

`G_IO_ERROR_NO_SPACE` is returned if there is not enough space to write the resulting converted data, the application should call the function again with a larger `outbuf` to continue.

`G_IO_ERROR_PARTIAL_INPUT` is returned if there is not enough input to fully determine what the conversion should produce, and the `G_CONVERTER_INPUT_AT_END` flag is not set. This happens for example with an incomplete multibyte sequence when converting text, or when a regexp matches up to the end of the input (and may match further input). It may also happen when `inbuf_size` is zero and there is no more data to produce.

When this happens the application should read more input and then call the function again. If further input shows that there is no more data call the function again with the same data but with the `G_CONVERTER_INPUT_AT_END` flag set. This may cause the conversion to finish as e.g. in the regexp match case (or, to fail again with `G_IO_ERROR_PARTIAL_INPUT` in e.g. a charset conversion where the input is actually partial).

After `g_converter_convert()` has returned `G_CONVERTER_FINISHED` the converter object is in an invalid state where its not allowed to call `g_converter_convert()` anymore. At this time you can only free the object or call `g_converter_reset()` to reset it to the initial state.

If the flag `G_CONVERTER_FLUSH` is set then conversion is modified to try to write out all internal state to the output. The application has to call the function multiple times with the flag set, and when the available input has been consumed and all internal state has been produced then `G_CONVERTER_FLUSHED` (or `G_CONVERTER_FINISHED` if really at the end) is returned instead of `G_CONVERTER_CONVERTED`. This is somewhat similar to what happens at the end of the input stream, but done in the middle of the data.

This has different meanings for different conversions. For instance in a compression converter it would mean that we flush all the compression state into output such that if you uncompress the compressed data you get back all the input data. Doing this may make the final file larger due to padding though. Another example is a regexp conversion, where if you at the end of the flushed data have a match, but there is also a potential longer match. In the non-flushed case we would ask for more input, but when flushing we treat this as the end of input and do the match.

Flushing is not always possible (like if a charset converter flushes at a partial multibyte sequence). Converters are supposed to try to produce as much output as possible and then return an error (typically `G_IO_ERROR_PARTIAL_INPUT`).

#### Parameters

converter | a GConverter. |
inbuf | the buffer containing the data to convert. | [array length=inbuf_size][element-type guint8]
inbuf_size | the number of bytes in `inbuf` |
outbuf | a buffer to write converted data in. | [element-type guint8][array length=outbuf_size]
outbuf_size | the number of bytes in `outbuf` , must be at least one |
flags | a GConverterFlags controlling the conversion details |
bytes_read | will be set to the number of bytes read from `inbuf` on success. | [out]
bytes_written | will be set to the number of bytes written to `outbuf` on success. | [out]
error | location to store the error occurring, or `NULL` to ignore |

#### Returns

a GConverterResult, `G_CONVERTER_ERROR` on error.

Since: 2.24

### g_converter_reset ()

    void
    g_converter_reset (GConverter *converter);

Resets all internal state in the converter, making it behave as if it was just created. If the converter has any internal state that would produce output then that output is lost.

#### Parameters

converter | a GConverter. |

Since: 2.24

## Types and Values

### GConverter

    typedef struct _GConverter GConverter;

Seek object for streaming operations.

Since: 2.24

### struct GConverterIface

    struct GConverterIface {
      GTypeInterface g_iface;

      /* Virtual Table */

      GConverterResult (* convert) (GConverter *converter,
    				const void *inbuf,
    				gsize       inbuf_size,
    				void       *outbuf,
    				gsize       outbuf_size,
    				GConverterFlags flags,
    				gsize      *bytes_read,
    				gsize      *bytes_written,
    				GError    **error);
      void  (* reset)   (GConverter *converter);
    };

Provides an interface for converting data from one type to another type. The conversion can be stateful and may fail at any place.

#### Members

`convert` () | Converts data. |
`reset` () | Reverts the internal state of the converter to its initial state. |

Since: 2.24

### enum GConverterResult

Results returned from `g_converter_convert()`.

#### Members

G_CONVERTER_ERROR | There was an error during conversion. |
G_CONVERTER_CONVERTED | Some data was consumed or produced |
G_CONVERTER_FINISHED | The conversion is finished |
G_CONVERTER_FLUSHED | Flushing is finished |

Since: 2.24

### enum GConverterFlags

Flags used when calling a `g_converter_convert()`.

#### Members

G_CONVERTER_NO_FLAGS | No flags. |
G_CONVERTER_INPUT_AT_END | At end of input data |
G_CONVERTER_FLUSH | Flush data |

Since: 2.24

## See Also

GInputStream, GOutputStream