Parity catch-up to upstream fastmcp v3.4.2 (F1–F8)#46
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F1 (Python fastmcp #4058, commit 24b594b1):
utilities/versions.py VersionSpec eq normalization. fastmcpp's
compare_versions already normalized {1, 1.0} via the default-zero
padding, but did not strip a leading 'v'/'V' prefix. After this
change, '�2.5.0' compares equal to '2.5.0' so version filters
match v-prefixed components consistently.
F2 (Python fastmcp #4061, commit 01b971d8):
resources/template.py FunctionResourceTemplate.create_resource()
was dropping annotations/meta/title/icons when materializing a
resource from a template. fastmcpp's ResourceTemplate::create_resource
had the same bug — only uri/name/description/mime_type/app/provider
propagated. Now title/annotations/icons/version/task_support also
carry through.
Tests:
- tests/providers/version_filter.cpp gains v_prefixed_tool case
(versioned 'v2.5.0', expected to fall in [2.0, 3.0)).
- tests/resources/template_metadata.cpp is a new focused test that
builds a ResourceTemplate with title/annotations/icons/version/
task_support set and asserts every field propagates through
create_resource().
ctest -R 'fastmcpp_(provider_version_filter|resources_template_metadata)':
2/2 passed.
Reference: fastmcp v3.4.2 (3b8538e2)
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Both findings are already-implemented in fastmcpp; these tests pin the
behavior explicitly so future regressions are caught.
F4 (Python fastmcp #4178, commit 834f96d4 + cosmetic #4023 / 7cfcaf22):
utilities/json_schema.py resolve_root_ref must preserve sibling
metadata (title/description/default/examples) when falling back to
a lookup for circular schemas. fastmcpp's dereference_node
(src/util/json_schema.cpp:152) already merges non- siblings
onto the resolved object. New test root_ref_metadata.cpp asserts
this for a root-level with title+description siblings.
F5 (Python fastmcp #4217, commit e242abee):
tools/base.py ToolResult.is_error so a tool can RETURN an error
(instead of raising), and proxy/caching round-trip is_error. At
the fastmcpp wire level, this already works:
- server-side: build_fastmcp_tool_result preserves isError when
a tool callback returns {"content": [...], "isError": true}
(handler.cpp:817)
- client-side: parse_call_tool_result reads isError into
CallToolResult (client.hpp:1043) and call_tool(raise_on_error=
false) returns without throwing
- ProxyApp passes the remote result through verbatim with
raise_on_error=false (proxy.cpp:268)
- CachingMiddleware caches list endpoints only — not tools/call
— so the Python CachableToolResult is_error round-trip concern
doesn't apply
Prior tests only covered the raise_on_error=true (throw) path
(interactions_part1.cpp test_call_tool_error_handling). New test
tool_result_is_error.cpp covers the no-throw F5 path and asserts
content + structuredContent are preserved (not collapsed).
ctest results (new tests only):
fastmcpp_schema_root_ref_metadata: PASS
fastmcpp_client_tool_result_is_error: PASS
Reference: fastmcp v3.4.2 (3b8538e2)
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
F7 (Python fastmcp #4227, commit 2bff3725):
AggregateProvider/FastMCPProxy gained provider_error_strategy
with values 'warn' (default — log + silently skip failed
providers) and 'raise' (propagate the first provider error).
fastmcpp ProxyApp's list_all_* previously hard-coded the
'warn' behavior (catch and continue with local-only). This
change introduces ProxyErrorStrategy enum (Warn|Raise) and
ProxyAppOptions surface, default Warn for back-compat. Under
Raise, list_all_tools/resources/templates/prompts re-raise
the first upstream exception so callers can fail fast.
F8 (Python fastmcp #4228, commit 140d96aa):
FastMCPProxy made validate_on_initialize always-on so the
proxy's MCP initialize forwards to the upstream and surfaces
connection failures as JSON-RPC errors immediately. fastmcpp
keeps this opt-in via ProxyAppOptions::validate_on_initialize
(default false) for back-compat with existing fastmcpp users
that construct proxies whose upstream may be lazily reachable.
When enabled, make_mcp_handler(ProxyApp&) calls upstream
Client::initialize() on inbound initialize, and returns
jsonrpc_error(INTERNAL_ERROR, ...) on any std::exception.
API surface added:
enum class fastmcpp::ProxyErrorStrategy { Warn, Raise };
struct fastmcpp::ProxyAppOptions {
std::string name = "proxy_app";
std::string version = "1.0.0";
std::optional<std::string> instructions;
ProxyErrorStrategy error_strategy = ProxyErrorStrategy::Warn;
bool validate_on_initialize = false;
};
ProxyApp::ProxyApp(ClientFactory, ProxyAppOptions); // new
ProxyErrorStrategy ProxyApp::error_strategy() const;
bool ProxyApp::validate_on_initialize() const;
Files touched:
include/fastmcpp/proxy.hpp — enum, struct, ctor, accessors
src/proxy.cpp — new ctor + strategy check in
each list_all_* error handler
src/mcp/handler.cpp:2580 — F8 initialize-time upstream ping
in make_mcp_handler(ProxyApp&)
tests/proxy/error_strategy.cpp — 4 new test cases covering
Warn (default), Raise, and
both initialize paths
Verification:
ctest --test-dir build -C Debug -j 8:
107/107 passed (was 103/103 baseline + F1/F2/F4/F5 tests
+ this F7+F8 test = 107). No regressions.
Reference: fastmcp v3.4.2 (3b8538e2)
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
CMakeLists.txt project version and README.md headline updated to reflect the v3.4.2 parity catch-up for upstream fastmcp 3b8538e2. In-scope behavioral findings landed in this cycle: F1 — VersionSpec eq normalization (v-prefix strip) F2 — Resource-template metadata propagation F4 — JSON-schema root-ref metadata (verify-first; already correct) F5 — ToolResult is_error wire-level passthrough (verify-first; already correct) F7 — Proxy upstream error strategy (Warn|Raise; default Warn) F8 — Proxy initialize forwarding (opt-in via ProxyAppOptions) Deferred (documented in kb/sync/review_result.md): F3 — UTF-8 MCP config read (N/A: fastmcpp has no mcp_config equivalent) F6 — Pre-bound HTTP sockets (cpp-httplib limitation; revisit if user needs it) F9 — Proxy template query-params (N/A: fastmcpp passes URIs verbatim) F10 — OTEL spans on sampling (review-first: defer if no spans yet) F-NA-1 — Proxy ContextVar restore (N/A: no StatefulProxyClient in C++) Intentional divergences for the full v3.3.1..v3.4.2 delta (15 commits): - 11 auth/OAuth/JWT/joserfc/WorkOS/Azure/OIDC commits - 2 code-mode (Monty sandbox) commits - 1 fastmcp-remote bridge package - 1 'fastmcp dev apps' browser UI CLI Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Catch-up sync to upstream fastmcp
v3.4.2(3b8538e2) fromv3.3.1(d8dcc273). 56-commit delta triaged: 7 port-needed, 3 review, 15 intentional divergences (auth/OAuth/JWT/code-mode/fastmcp-remote/dev-apps), 29 N/A (docs/CI/deps/Python-only).Ported
compare_versionsstrips leadingvprefix (VersionSpec eq normalization) —src/providers/transforms/version_filter.cppsrc/resources/template.cppToolResultis_errorpassthrough via proxy/handler/cache (verified correct; interop test added)ProxyErrorStrategyenum (Warndefault,Raisepropagates upstream errors) —include/fastmcpp/proxy.hpp,src/proxy.cppinitializeforwarding (opt-invalidate_on_initialize) —src/mcp/handler.cppCMakeLists.txt,README.md)Deferred / N-A
mcp_configin C++), F6 deferred (cpp-httplib has no pre-bound socket API), F9 N/A (proxy passes URIs verbatim), F10 review-only (no existing sampling spans), F-NA-1 N/A (no StatefulProxyClient). Auth/OAuth/JWT/code-mode/fastmcp-remote/dev-apps remain intentional divergences.Verification
New tests:
tests/resources/template_metadata.cpp,tests/schema/root_ref_metadata.cpp,tests/client/tool_result_is_error.cpp,tests/proxy/error_strategy.cpp; extendedtests/providers/version_filter.cpp.