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+//! Incremental BLOB I/O.
+//!
+//! Note that SQLite does not provide API-level access to change the size of a
+//! BLOB; that must be performed through SQL statements.
+//!
+//! There are two choices for how to perform IO on a [`Blob`].
+//!
+//! 1. The implementations it provides of the `std::io::Read`, `std::io::Write`,
+//! and `std::io::Seek` traits.
+//!
+//! 2. A positional IO API, e.g. [`Blob::read_at`], [`Blob::write_at`] and
+//! similar.
+//!
+//! Documenting these in order:
+//!
+//! ## 1. `std::io` trait implementations.
+//!
+//! `Blob` conforms to `std::io::Read`, `std::io::Write`, and `std::io::Seek`,
+//! so it plays nicely with other types that build on these (such as
+//! `std::io::BufReader` and `std::io::BufWriter`). However, you must be careful
+//! with the size of the blob. For example, when using a `BufWriter`, the
+//! `BufWriter` will accept more data than the `Blob` will allow, so make sure
+//! to call `flush` and check for errors. (See the unit tests in this module for
+//! an example.)
+//!
+//! ## 2. Positional IO
+//!
+//! `Blob`s also offer a `pread` / `pwrite`-style positional IO api in the form
+//! of [`Blob::read_at`], [`Blob::write_at`], [`Blob::raw_read_at`],
+//! [`Blob::read_at_exact`], and [`Blob::raw_read_at_exact`].
+//!
+//! These APIs all take the position to read from or write to from as a
+//! parameter, instead of using an internal `pos` value.
+//!
+//! ### Positional IO Read Variants
+//!
+//! For the `read` functions, there are several functions provided:
+//!
+//! - [`Blob::read_at`]
+//! - [`Blob::raw_read_at`]
+//! - [`Blob::read_at_exact`]
+//! - [`Blob::raw_read_at_exact`]
+//!
+//! These can be divided along two axes: raw/not raw, and exact/inexact:
+//!
+//! 1. Raw/not raw refers to the type of the destination buffer. The raw
+//! functions take a `&mut [MaybeUninit<u8>]` as the destination buffer,
+//! where the "normal" functions take a `&mut [u8]`.
+//!
+//! Using `MaybeUninit` here can be more efficient in some cases, but is
+//! often inconvenient, so both are provided.
+//!
+//! 2. Exact/inexact refers to to whether or not the entire buffer must be
+//! filled in order for the call to be considered a success.
+//!
+//! The "exact" functions require the provided buffer be entirely filled, or
+//! they return an error, whereas the "inexact" functions read as much out of
+//! the blob as is available, and return how much they were able to read.
+//!
+//! The inexact functions are preferable if you do not know the size of the
+//! blob already, and the exact functions are preferable if you do.
+//!
+//! ### Comparison to using the `std::io` traits:
+//!
+//! In general, the positional methods offer the following Pro/Cons compared to
+//! using the implementation `std::io::{Read, Write, Seek}` we provide for
+//! `Blob`:
+//!
+//! 1. (Pro) There is no need to first seek to a position in order to perform IO
+//! on it as the position is a parameter.
+//!
+//! 2. (Pro) `Blob`'s positional read functions don't mutate the blob in any
+//! way, and take `&self`. No `&mut` access required.
+//!
+//! 3. (Pro) Positional IO functions return `Err(rusqlite::Error)` on failure,
+//! rather than `Err(std::io::Error)`. Returning `rusqlite::Error` is more
+//! accurate and convenient.
+//!
+//! Note that for the `std::io` API, no data is lost however, and it can be
+//! recovered with `io_err.downcast::<rusqlite::Error>()` (this can be easy
+//! to forget, though).
+//!
+//! 4. (Pro, for now). A `raw` version of the read API exists which can allow
+//! reading into a `&mut [MaybeUninit<u8>]` buffer, which avoids a potential
+//! costly initialization step. (However, `std::io` traits will certainly
+//! gain this someday, which is why this is only a "Pro, for now").
+//!
+//! 5. (Con) The set of functions is more bare-bones than what is offered in
+//! `std::io`, which has a number of adapters, handy algorithms, further
+//! traits.
+//!
+//! 6. (Con) No meaningful interoperability with other crates, so if you need
+//! that you must use `std::io`.
+//!
+//! To generalize: the `std::io` traits are useful because they conform to a
+//! standard interface that a lot of code knows how to handle, however that
+//! interface is not a perfect fit for [`Blob`], so another small set of
+//! functions is provided as well.
+//!
+//! # Example (`std::io`)
+//!
+//! ```rust
+//! # use rusqlite::blob::ZeroBlob;
+//! # use rusqlite::{Connection, DatabaseName};
+//! # use std::error::Error;
+//! # use std::io::{Read, Seek, SeekFrom, Write};
+//! # fn main() -> Result<(), Box<dyn Error>> {
+//! let db = Connection::open_in_memory()?;
+//! db.execute_batch("CREATE TABLE test_table (content BLOB);")?;
+//!
+//! // Insert a BLOB into the `content` column of `test_table`. Note that the Blob
+//! // I/O API provides no way of inserting or resizing BLOBs in the DB -- this
+//! // must be done via SQL.
+//! db.execute("INSERT INTO test_table (content) VALUES (ZEROBLOB(10))", [])?;
+//!
+//! // Get the row id off the BLOB we just inserted.
+//! let rowid = db.last_insert_rowid();
+//! // Open the BLOB we just inserted for IO.
+//! let mut blob = db.blob_open(DatabaseName::Main, "test_table", "content", rowid, false)?;
+//!
+//! // Write some data into the blob. Make sure to test that the number of bytes
+//! // written matches what you expect; if you try to write too much, the data
+//! // will be truncated to the size of the BLOB.
+//! let bytes_written = blob.write(b"01234567")?;
+//! assert_eq!(bytes_written, 8);
+//!
+//! // Move back to the start and read into a local buffer.
+//! // Same guidance - make sure you check the number of bytes read!
+//! blob.seek(SeekFrom::Start(0))?;
+//! let mut buf = [0u8; 20];
+//! let bytes_read = blob.read(&mut buf[..])?;
+//! assert_eq!(bytes_read, 10); // note we read 10 bytes because the blob has size 10
+//!
+//! // Insert another BLOB, this time using a parameter passed in from
+//! // rust (potentially with a dynamic size).
+//! db.execute(
+//! "INSERT INTO test_table (content) VALUES (?)",
+//! [ZeroBlob(64)],
+//! )?;
+//!
+//! // given a new row ID, we can reopen the blob on that row
+//! let rowid = db.last_insert_rowid();
+//! blob.reopen(rowid)?;
+//! // Just check that the size is right.
+//! assert_eq!(blob.len(), 64);
+//! # Ok(())
+//! # }
+//! ```
+//!
+//! # Example (Positional)
+//!
+//! ```rust
+//! # use rusqlite::blob::ZeroBlob;
+//! # use rusqlite::{Connection, DatabaseName};
+//! # use std::error::Error;
+//! # fn main() -> Result<(), Box<dyn Error>> {
+//! let db = Connection::open_in_memory()?;
+//! db.execute_batch("CREATE TABLE test_table (content BLOB);")?;
+//! // Insert a blob into the `content` column of `test_table`. Note that the Blob
+//! // I/O API provides no way of inserting or resizing blobs in the DB -- this
+//! // must be done via SQL.
+//! db.execute("INSERT INTO test_table (content) VALUES (ZEROBLOB(10))", [])?;
+//! // Get the row id off the blob we just inserted.
+//! let rowid = db.last_insert_rowid();
+//! // Open the blob we just inserted for IO.
+//! let mut blob = db.blob_open(DatabaseName::Main, "test_table", "content", rowid, false)?;
+//! // Write some data into the blob.
+//! blob.write_at(b"ABCDEF", 2)?;
+//!
+//! // Read the whole blob into a local buffer.
+//! let mut buf = [0u8; 10];
+//! blob.read_at_exact(&mut buf, 0)?;
+//! assert_eq!(&buf, b"\0\0ABCDEF\0\0");
+//!
+//! // Insert another blob, this time using a parameter passed in from
+//! // rust (potentially with a dynamic size).
+//! db.execute(
+//! "INSERT INTO test_table (content) VALUES (?)",
+//! [ZeroBlob(64)],
+//! )?;
+//!
+//! // given a new row ID, we can reopen the blob on that row
+//! let rowid = db.last_insert_rowid();
+//! blob.reopen(rowid)?;
+//! assert_eq!(blob.len(), 64);
+//! # Ok(())
+//! # }
+//! ```
+use std::cmp::min;
+use std::io;
+use std::ptr;
+
+use super::ffi;
+use super::types::{ToSql, ToSqlOutput};
+use crate::{Connection, DatabaseName, Result};
+
+mod pos_io;
+
+/// Handle to an open BLOB. See
+/// [`rusqlite::blob`](crate::blob) documentation for in-depth discussion.
+pub struct Blob<'conn> {
+ conn: &'conn Connection,
+ blob: *mut ffi::sqlite3_blob,
+ // used by std::io implementations,
+ pos: i32,
+}
+
+impl Connection {
+ /// Open a handle to the BLOB located in `row_id`,
+ /// `column`, `table` in database `db`.
+ ///
+ /// # Failure
+ ///
+ /// Will return `Err` if `db`/`table`/`column` cannot be converted to a
+ /// C-compatible string or if the underlying SQLite BLOB open call
+ /// fails.
+ #[inline]
+ pub fn blob_open<'a>(
+ &'a self,
+ db: DatabaseName<'_>,
+ table: &str,
+ column: &str,
+ row_id: i64,
+ read_only: bool,
+ ) -> Result<Blob<'a>> {
+ let c = self.db.borrow_mut();
+ let mut blob = ptr::null_mut();
+ let db = db.as_cstring()?;
+ let table = super::str_to_cstring(table)?;
+ let column = super::str_to_cstring(column)?;
+ let rc = unsafe {
+ ffi::sqlite3_blob_open(
+ c.db(),
+ db.as_ptr(),
+ table.as_ptr(),
+ column.as_ptr(),
+ row_id,
+ if read_only { 0 } else { 1 },
+ &mut blob,
+ )
+ };
+ c.decode_result(rc).map(|_| Blob {
+ conn: self,
+ blob,
+ pos: 0,
+ })
+ }
+}
+
+impl Blob<'_> {
+ /// Move a BLOB handle to a new row.
+ ///
+ /// # Failure
+ ///
+ /// Will return `Err` if the underlying SQLite BLOB reopen call fails.
+ #[inline]
+ pub fn reopen(&mut self, row: i64) -> Result<()> {
+ let rc = unsafe { ffi::sqlite3_blob_reopen(self.blob, row) };
+ if rc != ffi::SQLITE_OK {
+ return self.conn.decode_result(rc);
+ }
+ self.pos = 0;
+ Ok(())
+ }
+
+ /// Return the size in bytes of the BLOB.
+ #[inline]
+ #[must_use]
+ pub fn size(&self) -> i32 {
+ unsafe { ffi::sqlite3_blob_bytes(self.blob) }
+ }
+
+ /// Return the current size in bytes of the BLOB.
+ #[inline]
+ #[must_use]
+ pub fn len(&self) -> usize {
+ use std::convert::TryInto;
+ self.size().try_into().unwrap()
+ }
+
+ /// Return true if the BLOB is empty.
+ #[inline]
+ #[must_use]
+ pub fn is_empty(&self) -> bool {
+ self.size() == 0
+ }
+
+ /// Close a BLOB handle.
+ ///
+ /// Calling `close` explicitly is not required (the BLOB will be closed
+ /// when the `Blob` is dropped), but it is available so you can get any
+ /// errors that occur.
+ ///
+ /// # Failure
+ ///
+ /// Will return `Err` if the underlying SQLite close call fails.
+ #[inline]
+ pub fn close(mut self) -> Result<()> {
+ self.close_()
+ }
+
+ #[inline]
+ fn close_(&mut self) -> Result<()> {
+ let rc = unsafe { ffi::sqlite3_blob_close(self.blob) };
+ self.blob = ptr::null_mut();
+ self.conn.decode_result(rc)
+ }
+}
+
+impl io::Read for Blob<'_> {
+ /// Read data from a BLOB incrementally. Will return Ok(0) if the end of
+ /// the blob has been reached.
+ ///
+ /// # Failure
+ ///
+ /// Will return `Err` if the underlying SQLite read call fails.
+ #[inline]
+ fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+ let max_allowed_len = (self.size() - self.pos) as usize;
+ let n = min(buf.len(), max_allowed_len) as i32;
+ if n <= 0 {
+ return Ok(0);
+ }
+ let rc = unsafe { ffi::sqlite3_blob_read(self.blob, buf.as_mut_ptr().cast(), n, self.pos) };
+ self.conn
+ .decode_result(rc)
+ .map(|_| {
+ self.pos += n;
+ n as usize
+ })
+ .map_err(|err| io::Error::new(io::ErrorKind::Other, err))
+ }
+}
+
+impl io::Write for Blob<'_> {
+ /// Write data into a BLOB incrementally. Will return `Ok(0)` if the end of
+ /// the blob has been reached; consider using `Write::write_all(buf)`
+ /// if you want to get an error if the entirety of the buffer cannot be
+ /// written.
+ ///
+ /// This function may only modify the contents of the BLOB; it is not
+ /// possible to increase the size of a BLOB using this API.
+ ///
+ /// # Failure
+ ///
+ /// Will return `Err` if the underlying SQLite write call fails.
+ #[inline]
+ fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+ let max_allowed_len = (self.size() - self.pos) as usize;
+ let n = min(buf.len(), max_allowed_len) as i32;
+ if n <= 0 {
+ return Ok(0);
+ }
+ let rc = unsafe { ffi::sqlite3_blob_write(self.blob, buf.as_ptr() as *mut _, n, self.pos) };
+ self.conn
+ .decode_result(rc)
+ .map(|_| {
+ self.pos += n;
+ n as usize
+ })
+ .map_err(|err| io::Error::new(io::ErrorKind::Other, err))
+ }
+
+ #[inline]
+ fn flush(&mut self) -> io::Result<()> {
+ Ok(())
+ }
+}
+
+impl io::Seek for Blob<'_> {
+ /// Seek to an offset, in bytes, in BLOB.
+ #[inline]
+ fn seek(&mut self, pos: io::SeekFrom) -> io::Result<u64> {
+ let pos = match pos {
+ io::SeekFrom::Start(offset) => offset as i64,
+ io::SeekFrom::Current(offset) => i64::from(self.pos) + offset,
+ io::SeekFrom::End(offset) => i64::from(self.size()) + offset,
+ };
+
+ if pos < 0 {
+ Err(io::Error::new(
+ io::ErrorKind::InvalidInput,
+ "invalid seek to negative position",
+ ))
+ } else if pos > i64::from(self.size()) {
+ Err(io::Error::new(
+ io::ErrorKind::InvalidInput,
+ "invalid seek to position past end of blob",
+ ))
+ } else {
+ self.pos = pos as i32;
+ Ok(pos as u64)
+ }
+ }
+}
+
+#[allow(unused_must_use)]
+impl Drop for Blob<'_> {
+ #[inline]
+ fn drop(&mut self) {
+ self.close_();
+ }
+}
+
+/// BLOB of length N that is filled with zeroes.
+///
+/// Zeroblobs are intended to serve as placeholders for BLOBs whose content is
+/// later written using incremental BLOB I/O routines.
+///
+/// A negative value for the zeroblob results in a zero-length BLOB.
+#[derive(Copy, Clone)]
+pub struct ZeroBlob(pub i32);
+
+impl ToSql for ZeroBlob {
+ #[inline]
+ fn to_sql(&self) -> Result<ToSqlOutput<'_>> {
+ let ZeroBlob(length) = *self;
+ Ok(ToSqlOutput::ZeroBlob(length))
+ }
+}
+
+#[cfg(test)]
+mod test {
+ use crate::{Connection, DatabaseName, Result};
+ use std::io::{BufRead, BufReader, BufWriter, Read, Seek, SeekFrom, Write};
+
+ fn db_with_test_blob() -> Result<(Connection, i64)> {
+ let db = Connection::open_in_memory()?;
+ let sql = "BEGIN;
+ CREATE TABLE test (content BLOB);
+ INSERT INTO test VALUES (ZEROBLOB(10));
+ END;";
+ db.execute_batch(sql)?;
+ let rowid = db.last_insert_rowid();
+ Ok((db, rowid))
+ }
+
+ #[test]
+ fn test_blob() -> Result<()> {
+ let (db, rowid) = db_with_test_blob()?;
+
+ let mut blob = db.blob_open(DatabaseName::Main, "test", "content", rowid, false)?;
+ assert_eq!(4, blob.write(b"Clob").unwrap());
+ assert_eq!(6, blob.write(b"567890xxxxxx").unwrap()); // cannot write past 10
+ assert_eq!(0, blob.write(b"5678").unwrap()); // still cannot write past 10
+
+ blob.reopen(rowid)?;
+ blob.close()?;
+
+ blob = db.blob_open(DatabaseName::Main, "test", "content", rowid, true)?;
+ let mut bytes = [0u8; 5];
+ assert_eq!(5, blob.read(&mut bytes[..]).unwrap());
+ assert_eq!(&bytes, b"Clob5");
+ assert_eq!(5, blob.read(&mut bytes[..]).unwrap());
+ assert_eq!(&bytes, b"67890");
+ assert_eq!(0, blob.read(&mut bytes[..]).unwrap());
+
+ blob.seek(SeekFrom::Start(2)).unwrap();
+ assert_eq!(5, blob.read(&mut bytes[..]).unwrap());
+ assert_eq!(&bytes, b"ob567");
+
+ // only first 4 bytes of `bytes` should be read into
+ blob.seek(SeekFrom::Current(-1)).unwrap();
+ assert_eq!(4, blob.read(&mut bytes[..]).unwrap());
+ assert_eq!(&bytes, b"78907");
+
+ blob.seek(SeekFrom::End(-6)).unwrap();
+ assert_eq!(5, blob.read(&mut bytes[..]).unwrap());
+ assert_eq!(&bytes, b"56789");
+
+ blob.reopen(rowid)?;
+ assert_eq!(5, blob.read(&mut bytes[..]).unwrap());
+ assert_eq!(&bytes, b"Clob5");
+
+ // should not be able to seek negative or past end
+ assert!(blob.seek(SeekFrom::Current(-20)).is_err());
+ assert!(blob.seek(SeekFrom::End(0)).is_ok());
+ assert!(blob.seek(SeekFrom::Current(1)).is_err());
+
+ // write_all should detect when we return Ok(0) because there is no space left,
+ // and return a write error
+ blob.reopen(rowid)?;
+ assert!(blob.write_all(b"0123456789x").is_err());
+ Ok(())
+ }
+
+ #[test]
+ fn test_blob_in_bufreader() -> Result<()> {
+ let (db, rowid) = db_with_test_blob()?;
+
+ let mut blob = db.blob_open(DatabaseName::Main, "test", "content", rowid, false)?;
+ assert_eq!(8, blob.write(b"one\ntwo\n").unwrap());
+
+ blob.reopen(rowid)?;
+ let mut reader = BufReader::new(blob);
+
+ let mut line = String::new();
+ assert_eq!(4, reader.read_line(&mut line).unwrap());
+ assert_eq!("one\n", line);
+
+ line.truncate(0);
+ assert_eq!(4, reader.read_line(&mut line).unwrap());
+ assert_eq!("two\n", line);
+
+ line.truncate(0);
+ assert_eq!(2, reader.read_line(&mut line).unwrap());
+ assert_eq!("\0\0", line);
+ Ok(())
+ }
+
+ #[test]
+ fn test_blob_in_bufwriter() -> Result<()> {
+ let (db, rowid) = db_with_test_blob()?;
+
+ {
+ let blob = db.blob_open(DatabaseName::Main, "test", "content", rowid, false)?;
+ let mut writer = BufWriter::new(blob);
+
+ // trying to write too much and then flush should fail
+ assert_eq!(8, writer.write(b"01234567").unwrap());
+ assert_eq!(8, writer.write(b"01234567").unwrap());
+ assert!(writer.flush().is_err());
+ }
+
+ {
+ // ... but it should've written the first 10 bytes
+ let mut blob = db.blob_open(DatabaseName::Main, "test", "content", rowid, false)?;
+ let mut bytes = [0u8; 10];
+ assert_eq!(10, blob.read(&mut bytes[..]).unwrap());
+ assert_eq!(b"0123456701", &bytes);
+ }
+
+ {
+ let blob = db.blob_open(DatabaseName::Main, "test", "content", rowid, false)?;
+ let mut writer = BufWriter::new(blob);
+
+ // trying to write_all too much should fail
+ writer.write_all(b"aaaaaaaaaabbbbb").unwrap();
+ assert!(writer.flush().is_err());
+ }
+
+ {
+ // ... but it should've written the first 10 bytes
+ let mut blob = db.blob_open(DatabaseName::Main, "test", "content", rowid, false)?;
+ let mut bytes = [0u8; 10];
+ assert_eq!(10, blob.read(&mut bytes[..]).unwrap());
+ assert_eq!(b"aaaaaaaaaa", &bytes);
+ Ok(())
+ }
+ }
+}