## GInputStream

GInputStream — Base class for implementing streaming input

## Synopsis

    #include <gio/gio.h>

                        GInputStream;
    gssize              g_input_stream_read                 (GInputStream *stream,
                                                             void *buffer,
                                                             gsize count,
                                                             GCancellable *cancellable,
                                                             GError **error);
    gboolean            g_input_stream_read_all             (GInputStream *stream,
                                                             void *buffer,
                                                             gsize count,
                                                             gsize *bytes_read,
                                                             GCancellable *cancellable,
                                                             GError **error);
    gssize              g_input_stream_skip                 (GInputStream *stream,
                                                             gsize count,
                                                             GCancellable *cancellable,
                                                             GError **error);
    gboolean            g_input_stream_close                (GInputStream *stream,
                                                             GCancellable *cancellable,
                                                             GError **error);
    void                g_input_stream_read_async           (GInputStream *stream,
                                                             void *buffer,
                                                             gsize count,
                                                             int io_priority,
                                                             GCancellable *cancellable,
                                                             GAsyncReadyCallback callback,
                                                             gpointer user_data);
    gssize              g_input_stream_read_finish          (GInputStream *stream,
                                                             GAsyncResult *result,
                                                             GError **error);
    void                g_input_stream_skip_async           (GInputStream *stream,
                                                             gsize count,
                                                             int io_priority,
                                                             GCancellable *cancellable,
                                                             GAsyncReadyCallback callback,
                                                             gpointer user_data);
    gssize              g_input_stream_skip_finish          (GInputStream *stream,
                                                             GAsyncResult *result,
                                                             GError **error);
    void                g_input_stream_close_async          (GInputStream *stream,
                                                             int io_priority,
                                                             GCancellable *cancellable,
                                                             GAsyncReadyCallback callback,
                                                             gpointer user_data);
    gboolean            g_input_stream_close_finish         (GInputStream *stream,
                                                             GAsyncResult *result,
                                                             GError **error);
    gboolean            g_input_stream_is_closed            (GInputStream *stream);
    gboolean            g_input_stream_has_pending          (GInputStream *stream);
    gboolean            g_input_stream_set_pending          (GInputStream *stream,
                                                             GError **error);
    void                g_input_stream_clear_pending        (GInputStream *stream);

## Object Hierarchy

      GObject
       +----GInputStream
             +----GFilterInputStream
             +----GFileInputStream
             +----GMemoryInputStream
             +----GUnixInputStream

## Known Derived Interfaces

GInputStream is required by GPollableInputStream.

## Description

GInputStream has functions to read from a stream (`g_input_stream_read()`), to close a stream (`g_input_stream_close()`) and to skip some content (`g_input_stream_skip()`).

To copy the content of an input stream to an output stream without manually handling the reads and writes, use `g_output_stream_splice()`.

All of these functions have async variants too.

## Details

### GInputStream

    typedef struct _GInputStream GInputStream;

Base class for streaming input operations.

### g_input_stream_read ()

    gssize              g_input_stream_read                 (GInputStream *stream,
                                                             void *buffer,
                                                             gsize count,
                                                             GCancellable *cancellable,
                                                             GError **error);

Tries to read `count` bytes from the stream into the buffer starting at `buffer`. Will block during this read.

If count is zero returns zero and does nothing. A value of `count` larger than `G_MAXSSIZE` will cause a `G_IO_ERROR_INVALID_ARGUMENT` error.

On success, the number of bytes read into the buffer is returned. It is not an error if this is not the same as the requested size, as it can happen e.g. near the end of a file. Zero is returned on end of file (or if `count` is zero), but never otherwise.

If `cancellable` is not NULL, then the operation can be cancelled by triggering the cancellable object from another thread. If the operation was cancelled, the error G_IO_ERROR_CANCELLED will be returned. If an operation was partially finished when the operation was cancelled the partial result will be returned, without an error.

On error -1 is returned and `error` is set accordingly.

`stream` : | a GInputStream.
`buffer` : | a buffer to read data into (which should be at least count bytes long).
`count` : | the number of bytes that will be read from the stream
`cancellable` : | optional GCancellable object, `NULL` to ignore. [allow-none]
`error` : | location to store the error occurring, or `NULL` to ignore
Returns : | Number of bytes read, or -1 on error

### g_input_stream_read_all ()

    gboolean            g_input_stream_read_all             (GInputStream *stream,
                                                             void *buffer,
                                                             gsize count,
                                                             gsize *bytes_read,
                                                             GCancellable *cancellable,
                                                             GError **error);

Tries to read `count` bytes from the stream into the buffer starting at `buffer`. Will block during this read.

This function is similar to `g_input_stream_read()`, except it tries to read as many bytes as requested, only stopping on an error or end of stream.

On a successful read of `count` bytes, or if we reached the end of the stream, `TRUE` is returned, and `bytes_read` is set to the number of bytes read into `buffer`.

If there is an error during the operation `FALSE` is returned and `error` is set to indicate the error status, `bytes_read` is updated to contain the number of bytes read into `buffer` before the error occurred.

`stream` : | a GInputStream.
`buffer` : | a buffer to read data into (which should be at least count bytes long).
`count` : | the number of bytes that will be read from the stream
`bytes_read` : | location to store the number of bytes that was read from the stream. [out]
`cancellable` : | optional GCancellable object, `NULL` to ignore. [allow-none]
`error` : | location to store the error occurring, or `NULL` to ignore
Returns : | `TRUE` on success, `FALSE` if there was an error

### g_input_stream_skip ()

    gssize              g_input_stream_skip                 (GInputStream *stream,
                                                             gsize count,
                                                             GCancellable *cancellable,
                                                             GError **error);

Tries to skip `count` bytes from the stream. Will block during the operation.

This is identical to `g_input_stream_read()`, from a behaviour standpoint, but the bytes that are skipped are not returned to the user. Some streams have an implementation that is more efficient than reading the data.

This function is optional for inherited classes, as the default implementation emulates it using read.

If `cancellable` is not `NULL`, then the operation can be cancelled by triggering the cancellable object from another thread. If the operation was cancelled, the error `G_IO_ERROR_CANCELLED` will be returned. If an operation was partially finished when the operation was cancelled the partial result will be returned, without an error.

`stream` : | a GInputStream.
`count` : | the number of bytes that will be skipped from the stream
`cancellable` : | optional GCancellable object, `NULL` to ignore. [allow-none]
`error` : | location to store the error occurring, or `NULL` to ignore
Returns : | Number of bytes skipped, or -1 on error

### g_input_stream_close ()

    gboolean            g_input_stream_close                (GInputStream *stream,
                                                             GCancellable *cancellable,
                                                             GError **error);

Closes the stream, releasing resources related to it.

Once the stream is closed, all other operations will return `G_IO_ERROR_CLOSED`. Closing a stream multiple times will not return an error.

Streams will be automatically closed when the last reference is dropped, but you might want to call this function to make sure resources are released as early as possible.

Some streams might keep the backing store of the stream (e.g. a file descriptor) open after the stream is closed. See the documentation for the individual stream for details.

On failure the first error that happened will be reported, but the close operation will finish as much as possible. A stream that failed to close will still return `G_IO_ERROR_CLOSED` for all operations. Still, it is important to check and report the error to the user.

If `cancellable` is not NULL, then the operation can be cancelled by triggering the cancellable object from another thread. If the operation was cancelled, the error `G_IO_ERROR_CANCELLED` will be returned. Cancelling a close will still leave the stream closed, but some streams can use a faster close that doesn't block to e.g. check errors.

`stream` : | A GInputStream.
`cancellable` : | optional GCancellable object, `NULL` to ignore. [allow-none]
`error` : | location to store the error occurring, or `NULL` to ignore
Returns : | `TRUE` on success, `FALSE` on failure

### g_input_stream_read_async ()

    void                g_input_stream_read_async           (GInputStream *stream,
                                                             void *buffer,
                                                             gsize count,
                                                             int io_priority,
                                                             GCancellable *cancellable,
                                                             GAsyncReadyCallback callback,
                                                             gpointer user_data);

Request an asynchronous read of `count` bytes from the stream into the buffer starting at `buffer`. When the operation is finished `callback` will be called. You can then call `g_input_stream_read_finish()` to get the result of the operation.

During an async request no other sync and async calls are allowed on `stream`, and will result in `G_IO_ERROR_PENDING` errors.

A value of `count` larger than `G_MAXSSIZE` will cause a `G_IO_ERROR_INVALID_ARGUMENT` error.

On success, the number of bytes read into the buffer will be passed to the callback. It is not an error if this is not the same as the requested size, as it can happen e.g. near the end of a file, but generally we try to read as many bytes as requested. Zero is returned on end of file (or if `count` is zero), but never otherwise.

Any outstanding i/o request with higher priority (lower numerical value) will be executed before an outstanding request with lower priority. Default priority is `G_PRIORITY_DEFAULT`.

The asyncronous methods have a default fallback that uses threads to implement asynchronicity, so they are optional for inheriting classes. However, if you override one you must override all.

`stream` : | A GInputStream.
`buffer` : | a buffer to read data into (which should be at least count bytes long).
`count` : | the number of bytes that will be read from the stream
`io_priority` : | the I/O priority of the request.
`cancellable` : | optional GCancellable object, `NULL` to ignore. [allow-none]
`callback` : | callback to call when the request is satisfied. [scope async]
`user_data` : | the data to pass to callback function. [closure]

### g_input_stream_read_finish ()

    gssize              g_input_stream_read_finish          (GInputStream *stream,
                                                             GAsyncResult *result,
                                                             GError **error);

Finishes an asynchronous stream read operation.

`stream` : | a GInputStream.
`result` : | a GAsyncResult.
`error` : | a GError location to store the error occurring, or `NULL` to ignore.
Returns : | number of bytes read in, or -1 on error.

### g_input_stream_skip_async ()

    void                g_input_stream_skip_async           (GInputStream *stream,
                                                             gsize count,
                                                             int io_priority,
                                                             GCancellable *cancellable,
                                                             GAsyncReadyCallback callback,
                                                             gpointer user_data);

Request an asynchronous skip of `count` bytes from the stream. When the operation is finished `callback` will be called. You can then call `g_input_stream_skip_finish()` to get the result of the operation.

During an async request no other sync and async calls are allowed, and will result in `G_IO_ERROR_PENDING` errors.

A value of `count` larger than `G_MAXSSIZE` will cause a `G_IO_ERROR_INVALID_ARGUMENT` error.

On success, the number of bytes skipped will be passed to the callback. It is not an error if this is not the same as the requested size, as it can happen e.g. near the end of a file, but generally we try to skip as many bytes as requested. Zero is returned on end of file (or if `count` is zero), but never otherwise.

Any outstanding i/o request with higher priority (lower numerical value) will be executed before an outstanding request with lower priority. Default priority is `G_PRIORITY_DEFAULT`.

The asynchronous methods have a default fallback that uses threads to implement asynchronicity, so they are optional for inheriting classes. However, if you override one, you must override all.

`stream` : | A GInputStream.
`count` : | the number of bytes that will be skipped from the stream
`io_priority` : | the I/O priority of the request.
`cancellable` : | optional GCancellable object, `NULL` to ignore. [allow-none]
`callback` : | callback to call when the request is satisfied. [scope async]
`user_data` : | the data to pass to callback function. [closure]

### g_input_stream_skip_finish ()

    gssize              g_input_stream_skip_finish          (GInputStream *stream,
                                                             GAsyncResult *result,
                                                             GError **error);

Finishes a stream skip operation.

`stream` : | a GInputStream.
`result` : | a GAsyncResult.
`error` : | a GError location to store the error occurring, or `NULL` to ignore.
Returns : | the size of the bytes skipped, or `-1` on error.

### g_input_stream_close_async ()

    void                g_input_stream_close_async          (GInputStream *stream,
                                                             int io_priority,
                                                             GCancellable *cancellable,
                                                             GAsyncReadyCallback callback,
                                                             gpointer user_data);

Requests an asynchronous closes of the stream, releasing resources related to it. When the operation is finished `callback` will be called. You can then call `g_input_stream_close_finish()` to get the result of the operation.

For behaviour details see `g_input_stream_close()`.

The asyncronous methods have a default fallback that uses threads to implement asynchronicity, so they are optional for inheriting classes. However, if you override one you must override all.

`stream` : | A GInputStream.
`io_priority` : | the I/O priority of the request.
`cancellable` : | optional cancellable object. [allow-none]
`callback` : | callback to call when the request is satisfied. [scope async]
`user_data` : | the data to pass to callback function. [closure]

### g_input_stream_close_finish ()

    gboolean            g_input_stream_close_finish         (GInputStream *stream,
                                                             GAsyncResult *result,
                                                             GError **error);

Finishes closing a stream asynchronously, started from `g_input_stream_close_async()`.

`stream` : | a GInputStream.
`result` : | a GAsyncResult.
`error` : | a GError location to store the error occurring, or `NULL` to ignore.
Returns : | `TRUE` if the stream was closed successfully.

### g_input_stream_is_closed ()

    gboolean            g_input_stream_is_closed            (GInputStream *stream);

Checks if an input stream is closed.

`stream` : | input stream.
Returns : | `TRUE` if the stream is closed.

### g_input_stream_has_pending ()

    gboolean            g_input_stream_has_pending          (GInputStream *stream);

Checks if an input stream has pending actions.

`stream` : | input stream.
Returns : | `TRUE` if `stream` has pending actions.

### g_input_stream_set_pending ()

    gboolean            g_input_stream_set_pending          (GInputStream *stream,
                                                             GError **error);

Sets `stream` to have actions pending. If the pending flag is already set or `stream` is closed, it will return `FALSE` and set `error`.

`stream` : | input stream
`error` : | a GError location to store the error occurring, or `NULL` to ignore.
Returns : | `TRUE` if pending was previously unset and is now set.

### g_input_stream_clear_pending ()

    void                g_input_stream_clear_pending        (GInputStream *stream);

Clears the pending flag on `stream`.

`stream` : | input stream