Reduce binary footprint: minimal SQLite and selectable curl TLS backend

CMakeLists.txt

@@ -11,6 +11,16 @@ else()
 endif()
 message(STATUS "MATSDK_USE_VCPKG_DEPS: ${MATSDK_USE_VCPKG_DEPS}")
 
+# Build a private, feature-stripped copy of the vendored SQLite amalgamation
+# instead of linking an external SQLite. The SDK uses SQLite only for its offline
+# event-storage cache, so the minimal build (see lib/CMakeLists.txt
+# MATSDK_SQLITE_MINIMAL_DEFS) omits every optional SQLite subsystem the SDK does
+# not use, shrinking the SQLite code ~10% and removing the external sqlite3
+# dependency. Off by default to preserve the existing external/system-SQLite
+# behavior; the Android NDK path always bundles SQLite regardless.
+option(MATSDK_MINIMAL_SQLITE "Build a feature-stripped vendored SQLite instead of an external one" OFF)
+message(STATUS "MATSDK_MINIMAL_SQLITE: ${MATSDK_MINIMAL_SQLITE}")
+
 # Begin Uncomment for i386 build
 #set(CMAKE_SYSTEM_PROCESSOR i386)
 #set(CMAKE_C_FLAGS -m32)
@@ -363,10 +373,25 @@ if(PAL_IMPLEMENTATION STREQUAL "CPP11"
    AND NOT BUILD_APPLE_HTTP)
   set(MATSDK_NEEDS_CURL ON)
   add_definitions(-DHAVE_MAT_CURL_HTTP_CLIENT)
-  find_package(CURL REQUIRED)
   if(MATSDK_USE_VCPKG_DEPS)
+    # The TLS backend (OpenSSL/mbedTLS) is selected by the vcpkg port's
+    # curl-openssl (default) / curl-mbedtls features; the SDK just links libcurl.
+    # Force CONFIG mode so the vcpkg-provided CURLConfig (which defines the
+    # CURL::libcurl imported target) is used rather than the module FindCURL,
+    # which on some CMake versions does not define that target.
+    find_package(CURL CONFIG QUIET)
+    if(NOT TARGET CURL::libcurl)
+      message(FATAL_ERROR
+        "libcurl was not found. The vcpkg port provides the curl HTTP client "
+        "through the curl-openssl (default) or curl-mbedtls feature. Install "
+        "cpp-client-telemetry with its default features, or, under the [core,...] "
+        "form (which drops the default curl-openssl and system-sqlite features), "
+        "re-select a curl backend and a SQLite backend together, e.g. "
+        "[core,curl-openssl,system-sqlite] or [core,curl-mbedtls,minimal-sqlite].")
+    endif()
     list(APPEND LIBS CURL::libcurl)
   else()
+    find_package(CURL REQUIRED)
     # Prefer the imported target, which carries curl's include dirs and link
     # flags. Fall back to the find-module variables on CMake < 3.12, where
     # find_package(CURL) does not define CURL::libcurl.
@@ -383,10 +408,40 @@ endif()
 # Dependency resolution (vcpkg mode vs vendored)
 ################################################################################################
 if(MATSDK_USE_VCPKG_DEPS)
-  find_package(unofficial-sqlite3 CONFIG REQUIRED)
-  find_package(ZLIB REQUIRED)
-  find_package(nlohmann_json CONFIG REQUIRED)
-  message(STATUS "Using vcpkg-provided sqlite3, zlib, nlohmann-json")
+  if(APPLE)
+    # macOS/iOS ship libsqlite3 and libz as system libraries (the SDK's SPM
+    # distribution links them the same way), so the vcpkg sqlite3/zlib packages are
+    # not pulled there -- find the system ones via CMake's standard find modules.
+    find_package(SQLite3 REQUIRED)
+    find_package(ZLIB REQUIRED)
+    find_package(nlohmann_json CONFIG REQUIRED)
+    set(MATSDK_APPLE_SYSTEM_DEPS ON)
+    message(STATUS "Apple: using system SQLite3 + zlib; vcpkg-provided nlohmann-json")
+  else()
+    set(MATSDK_APPLE_SYSTEM_DEPS OFF)
+    # SQLite is provided by the private minimal build when MATSDK_MINIMAL_SQLITE is
+    # ON, so only require the external vcpkg sqlite3 package otherwise.
+    if(NOT MATSDK_MINIMAL_SQLITE)
+      find_package(unofficial-sqlite3 CONFIG QUIET)
+      if(NOT unofficial-sqlite3_FOUND)
+        message(FATAL_ERROR
+          "SQLite was not found and the minimal SQLite is not enabled. The vcpkg "
+          "port provides SQLite through one of two features: 'system-sqlite' "
+          "(default, links the external sqlite3 package) or 'minimal-sqlite' "
+          "(builds a private feature-stripped SQLite). Install "
+          "cpp-client-telemetry with its default features, or with "
+          "[core,system-sqlite] or [core,minimal-sqlite]. For a direct CMake build, pass "
+          "-DMATSDK_MINIMAL_SQLITE=ON or ensure unofficial-sqlite3 is discoverable.")
+      endif()
+    endif()
+    find_package(ZLIB REQUIRED)
+    find_package(nlohmann_json CONFIG REQUIRED)
+    if(MATSDK_MINIMAL_SQLITE)
+      message(STATUS "Using vcpkg-provided zlib, nlohmann-json; private minimal SQLite")
+    else()
+      message(STATUS "Using vcpkg-provided sqlite3, zlib, nlohmann-json")
+    endif()
+  endif()
 else()
   # Include repo root to allow includes of vendored sqlite, zlib, and nlohmann
   include_directories(${CMAKE_SOURCE_DIR})

cmake/MSTelemetryConfig.cmake.in

@@ -2,8 +2,14 @@
 
 include(CMakeFindDependencyMacro)
 
-# Re-find dependencies that consumers need
-find_dependency(unofficial-sqlite3 CONFIG)
+# Re-find dependencies that consumers need.
+# On Apple the SDK links the system libsqlite3 (SQLite::SQLite3); elsewhere it uses
+# the vcpkg sqlite3 package unless a private minimal SQLite is bundled.
+if(@MATSDK_APPLE_SYSTEM_DEPS@)
+  find_dependency(SQLite3)
+elseif(NOT @MATSDK_BUNDLE_SQLITE@)
+  find_dependency(unofficial-sqlite3 CONFIG)
+endif()
 find_dependency(ZLIB)
 find_dependency(nlohmann_json CONFIG)
 
@@ -14,7 +20,11 @@ find_dependency(nlohmann_json CONFIG)
 # because the macOS BUILD_APPLE_HTTP choice can't be inferred from
 # CMAKE_SYSTEM_NAME alone.
 if(@MATSDK_NEEDS_CURL@)
-  find_dependency(CURL)
+  # Force CONFIG mode so the vcpkg-provided CURLConfig (which defines the
+  # CURL::libcurl imported target referenced by MSTelemetryTargets.cmake) is
+  # used, rather than module-mode FindCURL, which on some CMake versions does
+  # not define that target.
+  find_dependency(CURL CONFIG)
 endif()
 
 # Pthreads are needed on Linux and Android (POSIX threading)

docs/building-with-vcpkg.md

@@ -145,10 +145,24 @@ The vcpkg port automatically resolves the following dependencies:
 
 | Dependency     | vcpkg Package   | CMake Target                      | Platforms          |
 | -------------- | --------------- | --------------------------------- | ------------------ |
-| SQLite3        | `sqlite3`       | `unofficial::sqlite3::sqlite3`    | All                |
-| zlib           | `zlib`          | `ZLIB::ZLIB`                      | All                |
+| SQLite3        | `sqlite3`       | `unofficial::sqlite3::sqlite3`    | Non-Apple (default; see `minimal-sqlite`). **macOS/iOS link the system `libsqlite3`** (`SQLite::SQLite3`) |
+| zlib           | `zlib`          | `ZLIB::ZLIB`                      | Non-Apple. **macOS/iOS link the system `libz`** |
 | nlohmann JSON  | `nlohmann-json` | `nlohmann_json::nlohmann_json`    | All                |
-| libcurl        | `curl[openssl]` | `CURL::libcurl`                   | Non-Windows, non-Apple |
+| libcurl        | `curl[openssl]` or `curl[mbedtls]` | `CURL::libcurl`          | Non-Windows, non-Apple (required; TLS backend selectable: OpenSSL default or mbedTLS) |
+
+On **macOS/iOS** the SDK links the OS-provided `libsqlite3` and `libz` (the same
+system libraries the SDK's Swift Package links), so the vcpkg `sqlite3` and `zlib`
+packages are not pulled there — those binaries carry no bundled SQLite/zlib.
+(`minimal-sqlite` therefore has no effect on Apple.)
+
+The external `sqlite3` package is provided by the default `system-sqlite`
+feature. The `minimal-sqlite` feature replaces it with a private, feature-stripped
+SQLite built from the SDK's vendored amalgamation — see
+[Build a private minimal SQLite](#build-a-private-minimal-sqlite-minimal-sqlite-feature).
+
+libcurl is provided by the default `curl-openssl` feature; `curl-mbedtls` swaps in
+the mbedTLS backend — see
+[Choose the HTTP client / TLS backend](#choose-the-http-client--tls-backend-largest-lever-on-linux).
 
 Windows and macOS/iOS use platform-native HTTP clients (WinInet and
 NSURLSession respectively). Android vcpkg consumers use native libcurl because
@@ -230,6 +244,54 @@ the stripping happens at your link. Keep the SDK a static dependency linked
 *into* your binary: if you re-export its API across your own DLL boundary, the
 export table pins its symbols and defeats `/OPT:REF`.
 
+### Choose the HTTP client / TLS backend (largest lever on Linux)
+
+On Linux/Android the built-in HTTP client is libcurl, and curl's TLS backend
+dominates the SDK's footprint. (Windows uses WinInet and Apple uses NSURLSession,
+so this section does not apply there.) The port exposes the TLS backend as two
+mutually-exclusive features; pick the one that matches what your application
+already has:
+
+| Feature | Transport | Approx. stripped size¹ | Use when |
+| ------- | --------- | ---------------------- | -------- |
+| `curl-openssl` (default) | libcurl + OpenSSL | ~10.6 MB | your app already links OpenSSL (share it) |
+| `curl-mbedtls` | libcurl + mbedTLS | ~4.4 MB | your app has no HTTP/TLS stack of its own |
+
+¹ Rough sizes of a minimal Linux consumer **without** consumer-side dead-stripping
+(worst case); enabling `-Wl,--gc-sections` at your link reduces them. Your numbers
+depend on triplet, dead-stripping, and what else shares those libraries.
+
+To select **mbedTLS**, two things are required in *your top-level* manifest:
+
+```json
+{
+  "dependencies": [
+    {
+      "name": "cpp-client-telemetry",
+      "default-features": false,
+      "features": [ "minimal-sqlite", "curl-mbedtls" ]
+    },
+    { "name": "curl", "default-features": false, "features": [ "mbedtls" ] }
+  ]
+}
+```
+
+1. `"default-features": false` (the `[core,...]` form) drops **all** of the SDK's
+   default features -- both `curl-openssl` *and* `system-sqlite` -- so the SDK no
+   longer *requests* OpenSSL. Because it also drops `system-sqlite`, you must
+   re-select a SQLite backend (`minimal-sqlite` above, or `system-sqlite`);
+   otherwise the SDK configure step fails with no SQLite feature selected.
+2. The explicit top-level `curl` entry is also needed because vcpkg honors curl's
+   own `"default-features": false` **only for top-level dependencies** — curl's
+   default `ssl` feature (which pulls OpenSSL on Linux) and `non-http` are
+   installed transitively otherwise. With both, curl resolves to `curl[core,mbedtls]`
+   and OpenSSL is not built; with only the feature, you get
+   `curl[mbedtls,ssl,openssl,non-http]` (mbedTLS *and* OpenSSL). This recipe is
+   verified with `vcpkg install --dry-run`.
+
+The default install (no features specified) keeps `curl-openssl` and works out of
+the box.
+
 ### Drop unused SQLite features (json1)
 
 The SDK uses SQLite only for offline event storage — plain tables and indexes,
@@ -256,6 +318,65 @@ If any package in your build (or your own code) needs SQLite's JSON functions,
 request `sqlite3[json1]` instead and the extension is restored for the whole
 graph.
 
+### Build a private minimal SQLite (`minimal-sqlite` feature)
+
+For a larger, self-contained reduction, the port can compile a private,
+feature-stripped SQLite directly from the SDK's vendored amalgamation instead of
+linking the external `sqlite3` package at all. The SDK uses SQLite only for its
+offline event-storage cache (plain tables and indexes, transactions, WAL,
+autovacuum/`VACUUM`, a few PRAGMAs, and one custom UTF-8 SQL function), so this
+build omits the unused SQLite subsystems — `SQLITE_OMIT_JSON` plus load-extension,
+shared-cache, deprecated APIs, authorization, EXPLAIN, introspection pragmas,
+deserialize, and more. The result is **~10% smaller SQLite code** (`.text`) and
+**~13% smaller** as a stripped object, and it drops the external `sqlite3`
+dependency from your graph entirely.
+
+Enable it through the vcpkg feature:
+
+```json
+{
+  "dependencies": [
+    {
+      "name": "cpp-client-telemetry",
+      "default-features": false,
+      "features": [ "minimal-sqlite", "curl-openssl" ]
+    }
+  ]
+}
+```
+
+Use the `[core,minimal-sqlite]` form (here, `"default-features": false` is the
+`[core]` part) so the default `system-sqlite` feature — and its `sqlite3`
+dependency — is dropped. Because `[core]` drops **all** defaults, the example
+also re-selects `curl-openssl`: on Linux/Android the built-in curl client
+requires a TLS backend, so omitting it would fail to configure (swap in
+`curl-mbedtls` for the smaller mbedTLS backend). Requesting `minimal-sqlite`
+*without* `[core]` still pulls in the default `system-sqlite`; that is harmless
+(the external `sqlite3` is installed but unused) but does not save the dependency.
+
+For a plain (non-vcpkg) CMake build, pass the option directly:
+
+```bash
+cmake -DMATSDK_MINIMAL_SQLITE=ON ..
+```
+
+The strip is **amalgamation-safe**: it changes no SQLite grammar/parser, so no
+code generation is required. All offline storage features the SDK relies on (WAL,
+autovacuum, `VACUUM`, PRAGMAs, the custom UTF-8 function, blobs, 64-bit integers,
+transactions) are retained, and the SDK's offline-storage unit tests pass
+unchanged against the minimal build.
+
+> **Caveat — symbol visibility when linking statically.** The private SQLite keeps
+> SQLite's default `sqlite3_*` symbol names. For a **shared** `mat`
+> (`mat.dll` / `libmat.so` / `libmat.dylib`), those symbols are hidden by the
+> SDK's `-fvisibility=hidden`, so there is no conflict. For a **static** `mat`,
+> the minimal SQLite is installed and exported as a separate
+> `MSTelemetry::sqlite3_bundled` archive that links into your binary; if **any**
+> part of the final static link — your own code *or another dependency* — also
+> pulls in SQLite, the duplicate `sqlite3_*` symbols will collide at link time. In
+> that case, prefer the default `system-sqlite` feature so the whole graph shares a
+> single SQLite.
+
 ## How It Works: MATSDK_USE_VCPKG_DEPS
 
 When the SDK detects it is being built via vcpkg (by checking for