Add new entrypoint option to --load-extensions. (#1789)

Thanks, @asg017

tests/ext.c

@@ -0,0 +1,48 @@
+/*
+** This file implements a SQLite extension with multiple entrypoints.
+**
+** The default entrypoint, sqlite3_ext_init, has a single function "a".
+** The 1st alternate entrypoint, sqlite3_ext_b_init, has a single function "b".
+** The 2nd alternate entrypoint, sqlite3_ext_c_init, has a single function "c".
+**
+** Compiling instructions: 
+**     https://www.sqlite.org/loadext.html#compiling_a_loadable_extension
+**
+*/
+
+#include "sqlite3ext.h"
+
+SQLITE_EXTENSION_INIT1
+
+// SQL function that returns back the value supplied during sqlite3_create_function()
+static void func(sqlite3_context *context, int argc, sqlite3_value **argv) {
+  sqlite3_result_text(context, (char *) sqlite3_user_data(context), -1, SQLITE_STATIC);
+}
+
+
+// The default entrypoint, since it matches the "ext.dylib"/"ext.so" name
+#ifdef _WIN32
+__declspec(dllexport)
+#endif
+int sqlite3_ext_init(sqlite3 *db, char **pzErrMsg, const sqlite3_api_routines *pApi) {
+  SQLITE_EXTENSION_INIT2(pApi);
+  return sqlite3_create_function(db, "a", 0, 0, "a", func, 0, 0);
+}
+
+// Alternate entrypoint #1
+#ifdef _WIN32
+__declspec(dllexport)
+#endif
+int sqlite3_ext_b_init(sqlite3 *db, char **pzErrMsg, const sqlite3_api_routines *pApi) {
+  SQLITE_EXTENSION_INIT2(pApi);
+  return sqlite3_create_function(db, "b", 0, 0, "b", func, 0, 0);
+}
+
+// Alternate entrypoint #2
+#ifdef _WIN32
+__declspec(dllexport)
+#endif
+int sqlite3_ext_c_init(sqlite3 *db, char **pzErrMsg, const sqlite3_api_routines *pApi) {
+  SQLITE_EXTENSION_INIT2(pApi);
+  return sqlite3_create_function(db, "c", 0, 0, "c", func, 0, 0);
+}

tests/test_load_extensions.py

@@ -0,0 +1,65 @@
+from datasette.app import Datasette
+import pytest
+from pathlib import Path
+
+# not necessarily a full path - the full compiled path looks like "ext.dylib"
+# or another suffix, but sqlite will, under the hood, decide which file
+# extension to use based on the operating system (apple=dylib, windows=dll etc)
+# this resolves to "./ext", which is enough for SQLite to calculate the rest
+COMPILED_EXTENSION_PATH = str(Path(__file__).parent / "ext")
+
+# See if ext.c has been compiled, based off the different possible suffixes.
+def has_compiled_ext():
+    for ext in ["dylib", "so", "dll"]:
+        path = Path(__file__).parent / f"ext.{ext}"
+        if path.is_file():
+            return True
+    return False
+
+
+@pytest.mark.asyncio
+@pytest.mark.skipif(not has_compiled_ext(), reason="Requires compiled ext.c")
+async def test_load_extension_default_entrypoint():
+
+    # The default entrypoint only loads a() and NOT b() or c(), so those
+    # should fail.
+    ds = Datasette(sqlite_extensions=[COMPILED_EXTENSION_PATH])
+
+    response = await ds.client.get("/_memory.json?sql=select+a()")
+    assert response.status_code == 200
+    assert response.json()["rows"][0][0] == "a"
+
+    response = await ds.client.get("/_memory.json?sql=select+b()")
+    assert response.status_code == 400
+    assert response.json()["error"] == "no such function: b"
+
+    response = await ds.client.get("/_memory.json?sql=select+c()")
+    assert response.status_code == 400
+    assert response.json()["error"] == "no such function: c"
+
+
+@pytest.mark.asyncio
+@pytest.mark.skipif(not has_compiled_ext(), reason="Requires compiled ext.c")
+async def test_load_extension_multiple_entrypoints():
+
+    # Load in the default entrypoint and the other 2 custom entrypoints, now
+    # all a(), b(), and c() should run successfully.
+    ds = Datasette(
+        sqlite_extensions=[
+            COMPILED_EXTENSION_PATH,
+            (COMPILED_EXTENSION_PATH, "sqlite3_ext_b_init"),
+            (COMPILED_EXTENSION_PATH, "sqlite3_ext_c_init"),
+        ]
+    )
+
+    response = await ds.client.get("/_memory.json?sql=select+a()")
+    assert response.status_code == 200
+    assert response.json()["rows"][0][0] == "a"
+
+    response = await ds.client.get("/_memory.json?sql=select+b()")
+    assert response.status_code == 200
+    assert response.json()["rows"][0][0] == "b"
+
+    response = await ds.client.get("/_memory.json?sql=select+c()")
+    assert response.status_code == 200
+    assert response.json()["rows"][0][0] == "c"