openpgp-ffi: Add a general reader interface.

4 files changed, 68 insertions, 0 deletions

diff --git a/openpgp-ffi/examples/Makefile b/openpgp-ffi/examples/Makefile
index c8de2c1f..faf6962d 100644
--- a/openpgp-ffi/examples/Makefile
+++ b/openpgp-ffi/examples/Makefile
@@ -14,6 +14,7 @@ EXAMPLES = \
 	generate-key \
 	type-safety-demo use-after-free-demo immutable-reference-demo \
 	writer-cookie \
+	reader-cookie \
 
 CFLAGS  = -I../include -O0 -g -Wall -Werror
 LDFLAGS = -L$(CARGO_TARGET_DIR)/debug -lsequoia_openpgp_ffi
diff --git a/openpgp-ffi/examples/reader-cookie.c b/openpgp-ffi/examples/reader-cookie.c
new file mode 100644
index 00000000..c9795fd1
--- /dev/null
+++ b/openpgp-ffi/examples/reader-cookie.c
@@ -0,0 +1,19 @@
+#include <assert.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <sequoia/openpgp.h>
+
+int
+main (int argv, char **argc)
+{
+  /* As an example, use read(2) as the callback.  */
+  pgp_reader_t r = pgp_reader_from_callback ((pgp_reader_cb_t) read,
+                                             (void *) 0);
+
+  pgp_cert_t cert = pgp_cert_from_reader (NULL, r);
+  assert (cert);
+
+  pgp_cert_free (cert);
+  pgp_reader_free (r);
+  return 0;
+}
diff --git a/openpgp-ffi/include/sequoia/io.h b/openpgp-ffi/include/sequoia/io.h
index 8cce06c5..81d0093a 100644
--- a/openpgp-ffi/include/sequoia/io.h
+++ b/openpgp-ffi/include/sequoia/io.h
@@ -29,6 +29,18 @@ pgp_reader_t pgp_reader_from_fd (int fd);
 pgp_reader_t pgp_reader_from_bytes (const uint8_t *buf, size_t len);
 
 /*/
+/// The callback type for the generic callback-based reader interface.
+/*/
+typedef ssize_t (*pgp_reader_cb_t) (void *cookie, const void *buf, size_t len);
+
+/*/
+/// Creates an reader from a callback and cookie.
+///
+/// This reader calls the given callback to write data.
+/*/
+pgp_reader_t pgp_reader_from_callback (pgp_reader_cb_t, void *);
+
+/*/
 /// Frees a reader.
 /*/
 void pgp_reader_free (pgp_reader_t reader);
diff --git a/openpgp-ffi/src/io.rs b/openpgp-ffi/src/io.rs
index e3488e07..afa3a74e 100644
--- a/openpgp-ffi/src/io.rs
+++ b/openpgp-ffi/src/io.rs
@@ -73,6 +73,42 @@ pub extern "C" fn pgp_reader_from_bytes(buf: *const u8,
     ReaderKind::Generic(Box::new(Cursor::new(buf))).move_into_raw()
 }
 
+/// The callback type for the generic callback-based reader interface.
+type ReaderCallbackFn = fn(*mut c_void, *const c_void, size_t) -> ssize_t;
+
+/// Creates an reader from a callback and cookie.
+///
+/// This reader calls the given callback to write data.
+#[::sequoia_ffi_macros::extern_fn] #[no_mangle] pub extern "C"
+fn pgp_reader_from_callback(cb: ReaderCallbackFn,
+                            cookie: *mut c_void)
+                            -> *mut Reader {
+    let r: Box<dyn io::Read> = Box::new(ReaderCallback {
+        cb, cookie,
+    });
+    ReaderKind::Generic(r).move_into_raw()
+}
+
+/// A generic callback-based reader implementation.
+struct ReaderCallback {
+    cb: ReaderCallbackFn,
+    cookie: *mut c_void,
+}
+
+impl Read for ReaderCallback {
+    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        let r =
+            (self.cb)(self.cookie, buf.as_mut_ptr() as *mut c_void, buf.len());
+        if r < 0 {
+            use std::io as stdio;
+            Err(stdio::Error::new(stdio::ErrorKind::Other,
+                                  "Unknown error in read callback"))
+        } else {
+            Ok(r as usize)
+        }
+    }
+}
+
 /// Reads up to `len` bytes into `buf`.
 #[::sequoia_ffi_macros::extern_fn] #[no_mangle]
 pub extern "C" fn pgp_reader_read(errp: Option<&mut *mut crate::error::Error>,