Struct hdbconnect::types::BLob

pub struct BLob(_);

LOB implementation for binary values that is used within HdbValue::BLOB instances coming from the database.

Bigger LOBs are not transferred completely in the first roundtrip, instead more data are fetched in subsequent roundtrips when they are needed.

BLob respects the Connection's lob read length (see Connection::set_lob_read_length), by transferring per fetch request lob_read_length bytes.

Implementations

impl BLob

pub fn into_bytes(self) -> HdbResult<Vec<u8>>

Converts the BLob into a Vec.

All outstanding data (data that were not yet fetched from the server) are fetched into this BLob object, before the complete data, as far as they were not yet read from this BLob object, are returned.

Example

 let mut resultset = connection.query(query)?;
 let mut blob = resultset.into_single_row()?.into_single_value()?.try_into_blob()?;

 let b = blob.into_bytes()?; // Vec<u8>, can be huge

Alternative

For larger objects, a streaming approach using the Read implementation of BLob might by more appropriate, to avoid total allocation of the large object.

Example

 std::io::copy(&mut blob, &mut writer)?;

Errors

Several variants of HdbError can occur.

pub fn read_slice(&mut self, offset: u64, length: u32) -> HdbResult<Vec<u8>>

Reads from given offset and the given length, in bytes.

Errors

Several variants of HdbError can occur.

pub fn total_byte_length(&self) -> u64

Total length of data, in bytes.

pub fn is_empty(&self) -> bool

Returns true if the BLob does not contain data.

pub fn max_buf_len(&self) -> usize

Returns the maximum size the internal buffers ever had, in bytes.

This method exists mainly for debugging purposes. With streaming, the returned value is not supposed to exceed lob_read_length (see Connection::set_lob_read_length) plus the buffer size used by the reader.

pub fn cur_buf_len(&self) -> usize

Current size of the internal buffer, in bytes.

pub fn server_usage(&self) -> ServerUsage

Provides information about the the server-side resource consumption that is related to this BLob object.

Trait Implementations

impl Clone for BLob

fn clone(&self) -> BLob

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for BLob

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Read for BLob

fn read(&mut self, buf: &mut [u8]) -> Result<usize>

Pull some bytes from this source into the specified buffer, returning how many bytes were read.

fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize, Error>

Like read, except that it reads into a slice of buffers.

fn is_read_vectored(&self) -> bool

🔬 This is a nightly-only experimental API. (can_vector)

Determines if this Reader has an efficient read_vectored implementation.

unsafe fn initializer(&self) -> Initializer

🔬 This is a nightly-only experimental API. (read_initializer)

Determines if this Reader can work with buffers of uninitialized memory.

fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize, Error>

Read all bytes until EOF in this source, placing them into buf.

fn read_to_string(&mut self, buf: &mut String) -> Result<usize, Error>

Read all bytes until EOF in this source, appending them to buf.

fn read_exact(&mut self, buf: &mut [u8]) -> Result<(), Error>

Read the exact number of bytes required to fill buf.

fn by_ref(&mut self) -> &mut Self

Creates a "by reference" adaptor for this instance of Read.

fn bytes(self) -> Bytes<Self>

Transforms this Read instance to an Iterator over its bytes.

fn chain<R>(self, next: R) -> Chain<Self, R> where
    R: Read, 

Creates an adaptor which will chain this stream with another.

fn take(self, limit: u64) -> Take<Self>

Creates an adaptor which will read at most limit bytes from it.