openpgp-ffi: Add a general writer interface.

4 files changed, 86 insertions, 0 deletions

diff --git a/openpgp-ffi/examples/Makefile b/openpgp-ffi/examples/Makefile
index f5dd0f8c..c8de2c1f 100644
--- a/openpgp-ffi/examples/Makefile
+++ b/openpgp-ffi/examples/Makefile
@@ -13,6 +13,7 @@ EXAMPLES = \
 	decrypt-with \
 	generate-key \
 	type-safety-demo use-after-free-demo immutable-reference-demo \
+	writer-cookie \
 
 CFLAGS  = -I../include -O0 -g -Wall -Werror
 LDFLAGS = -L$(CARGO_TARGET_DIR)/debug -lsequoia_openpgp_ffi
diff --git a/openpgp-ffi/examples/writer-cookie.c b/openpgp-ffi/examples/writer-cookie.c
new file mode 100644
index 00000000..b22f1fc3
--- /dev/null
+++ b/openpgp-ffi/examples/writer-cookie.c
@@ -0,0 +1,31 @@
+#include <assert.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <sequoia/openpgp.h>
+
+int
+main (int argv, char **argc)
+{
+  pgp_status_t rc;
+
+  /* First, generate the key.  */
+  pgp_cert_builder_t builder = pgp_cert_builder_new ();
+  pgp_cert_builder_set_cipher_suite (&builder, PGP_CERT_CIPHER_SUITE_CV25519);
+
+  pgp_cert_t cert;
+  pgp_signature_t revocation;
+  pgp_cert_builder_generate (NULL, builder, &cert, &revocation);
+  assert (cert);
+  assert (revocation);
+  pgp_signature_free (revocation);    /* Free the generated revocation.  */
+
+  /* As an example, use write(2) as the callback.  */
+  pgp_writer_t w = pgp_writer_from_callback ((pgp_writer_cb_t) write,
+					     (void *) 1);
+  rc = pgp_cert_serialize (NULL, cert, w);
+  assert (rc == PGP_STATUS_SUCCESS);
+
+  pgp_cert_free (cert);
+  pgp_writer_free (w);
+  return 0;
+}
diff --git a/openpgp-ffi/include/sequoia/io.h b/openpgp-ffi/include/sequoia/io.h
index 103116ae..8cce06c5 100644
--- a/openpgp-ffi/include/sequoia/io.h
+++ b/openpgp-ffi/include/sequoia/io.h
@@ -84,6 +84,18 @@ pgp_writer_t pgp_writer_from_bytes (uint8_t *buf, size_t len);
 pgp_writer_t pgp_writer_alloc (void **buf, size_t *len);
 
 /*/
+/// The callback type for the generic callback-based writer interface.
+/*/
+typedef ssize_t (*pgp_writer_cb_t) (void *cookie, const void *buf, size_t len);
+
+/*/
+/// Creates an writer from a callback and cookie.
+///
+/// This writer calls the given callback to write data.
+/*/
+pgp_writer_t pgp_writer_from_callback (pgp_writer_cb_t, void *);
+
+/*/
 /// Frees a writer.
 /*/
 void pgp_writer_free (pgp_writer_t writer);
diff --git a/openpgp-ffi/src/io.rs b/openpgp-ffi/src/io.rs
index f0314e19..e3488e07 100644
--- a/openpgp-ffi/src/io.rs
+++ b/openpgp-ffi/src/io.rs
@@ -228,6 +228,48 @@ impl Write for WriterAlloc {
     }
 }
 
+/// The callback type for the generic callback-based writer interface.
+type WriterCallbackFn = fn(*mut c_void, *const c_void, size_t) -> ssize_t;
+
+/// Creates an writer from a callback and cookie.
+///
+/// This writer calls the given callback to write data.
+#[::sequoia_ffi_macros::extern_fn] #[no_mangle] pub extern "C"
+fn pgp_writer_from_callback(cb: WriterCallbackFn,
+                            cookie: *mut c_void)
+                            -> *mut Writer {
+    let w: Box<dyn io::Write> = Box::new(WriterCallback {
+        cb, cookie,
+    });
+    w.move_into_raw()
+}
+
+/// A generic callback-based writer implementation.
+struct WriterCallback {
+    cb: WriterCallbackFn,
+    cookie: *mut c_void,
+}
+
+impl Write for WriterCallback {
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        let r =
+            (self.cb)(self.cookie, buf.as_ptr() as *const c_void, buf.len());
+        if r < 0 {
+            use std::io as stdio;
+            Err(stdio::Error::new(stdio::ErrorKind::Other,
+                                  "Unknown error in write callback"))
+        } else {
+            Ok(r as usize)
+        }
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        // Do nothing.
+        // XXX: Should we add a callback for that?
+        Ok(())
+    }
+}
+
 /// Writes up to `len` bytes of `buf` into `writer`.
 #[::sequoia_ffi_macros::extern_fn] #[no_mangle] pub extern "C"
 fn pgp_writer_write(errp: Option<&mut *mut crate::error::Error>,