fix(vertex): function calling on the native Gemini path; portable tool call ids by jarvis9443 · Pull Request #1277 · api7/aisix

jarvis9443 · 2026-10-12T11:03:40Z

A vertex model with a Gemini publisher silently dropped tools and tool_choice. That path builds its own :generateContent / :streamGenerateContent body, and the builder only carried text: tools never reached Gemini, tool results were sent as user text, assistant tool_calls vanished from history, and only parts[].text was read back. A tool request returned 200 with a prose answer, and with tool_choice: "required" the model made one up. It hit all three client surfaces, since /v1/messages and /v1/responses reach this bridge through the chat translation.

This implements function calling on that path, request and response, streaming and non-streaming (new crates/aisix-provider-vertex/src/gemini_tools.rs, wired into build_gemini_request and both response decoders). It also makes the tool call ids it hands out safe to carry to other providers.

Request:

tools[].function becomes one {"functionDeclarations": [...]} tool. When the parameters fit Gemini's typed Schema, they are converted to it as parameters. Internal $refs are inlined, type: [X, "null"] becomes type: X + nullable: true (keeping sibling enum / minimum / …), a null branch of anyOf becomes nullable, missing array items / object type are filled in, empty properties are removed, and members outside Schema are dropped. When they do not fit (oneOf, allOf, const, other type lists, a non-string enum, tuple items, an unresolvable $ref, …), the caller's schema goes verbatim as parametersJsonSchema instead, so no constraint is lost. Empty-string enum values pass through unchanged.
tool_choice becomes toolConfig.functionCallingConfig: none/auto/required → NONE/AUTO/ANY, and a named function → ANY with allowedFunctionNames: [name]. With no tools, no toolConfig is sent.
History: assistant tool_calls become functionCall parts after the turn's text, and consecutive tool results become one user turn of functionResponse parts. The function name is recovered from the matching call in the preceding assistant turn. Both parts carry the call id. A call without arguments replays args: {}. A JSON-object result is sent as the response itself, anything else as {"content": "<text>"}.

Refused with 400 invalid_request_error instead of being dropped:

the legacy functions / function_call fields (the message points to tools / tool_choice);
a tool entry that is not a function tool (e.g. a hosted web search);
an unsupported tool_choice string, or an object tool_choice without a function name;
a tool result that answers no call;
call arguments that are not JSON.

Gemini built-in tools are not implemented.

Response: functionCall parts become tool_calls. When streaming, each call goes out whole with its own index. A tool-calling turn ends as tool_calls when Gemini says STOP; MAX_TOKENS stays length, the block reasons stay content_filter, and MALFORMED_FUNCTION_CALL stays stop.

Thought signatures and ids. Gemini 3 rejects history whose function calls lack the thoughtSignature returned with them, and no client protocol has a field to bring one back. So the signature rides in the tool call id handed to the client, as <id>__thought__<signature>.

The signature is encoded as URL-safe base64 without padding, so the whole id stays [A-Za-z0-9_-].
The base id is Gemini's own when it is at most 64 such characters, else a minted call_<28 hex>.
On replay the signature is decoded back onto the functionCall part. A Gemini 3 history with no signature (written by another model) gets Google's documented placeholder on a turn's first call.

Every other upstream sees only the base id. The OpenAI-compatible (including google), Azure, Anthropic and Bedrock bridges, the Vertex Claude / MaaS / Mistral / AI21 rails, and the native /v1/messages, /v1/messages/count_tokens and /v1/responses passthroughs all strip the suffix before sending. Without that, a conversation that started on Gemini and continues on another model would be rejected: OpenAI caps tool call ids at 64 characters, and Bedrock also restricts their character set.

Guardrails: the text guardrails scan keeps each tool call's base id but drops the thought-signature suffix, on chat, messages and responses. A replayed /v1/responses function_call now contributes its base call_id to the input scan, as a chat tool_calls[].id does; before, it contributed none. The base id is caller-controlled text an upstream receives, so it stays in scope. The signature is hundreds of bytes of opaque base64 that only Gemini ever sees, and a keyword rule could match it by chance. Operator-configured /passthrough/* routes are unchanged. Upstream error mapping is unchanged on every bridge.

Legacy functions / function_call on other bridges that build their own body: Bedrock now refuses them too, since Converse would drop them. The Anthropic Messages bridge and Vertex Claude forward them as they are and the upstream rejects them, so they are unchanged. OpenAI-compatible upstreams receive them as they are, also unchanged.

How other gateways do it (current default branches), and where this lands:

Empty history arguments: two send {}, others error. We send {}.
Parameter schemas: one always sends parametersJsonSchema, one sends it for 2.5/3 models, and one sends it only when the typed subset cannot express the schema, which is our choice. Two of them turn [X, "null"] into X + nullable with siblings kept, as we do.
Finish reason: one maps STOP-with-calls to tool_calls, MAX_TOKENS to length and SAFETY to content_filter, as we do.
An unnamed object tool_choice is a 400 in one. Two omit toolConfig without tools. We do both.
Signatures: one carries the signature in the id with URL-safe unpadded base64 and strips or rewrites it for OpenAI (> 64) and Bedrock (≤ 64, restricted charset), as we do. Others carry it in a side field or drop it.

Upstream spec: Vertex v1 FunctionDeclaration.parameters / parametersJsonSchema and FunctionCall.id / FunctionResponse.id (https://cloud.google.com/vertex-ai/docs/reference/rest/v1/Content), Vertex function calling (https://cloud.google.com/vertex-ai/generative-ai/docs/multimodal/function-calling) and thought signatures (https://cloud.google.com/vertex-ai/generative-ai/docs/thought-signatures). parametersJsonSchema and the call ids were exercised against real Vertex on gemini-2.5-flash, gemini-2.5-flash-lite, gemini-2.5-pro, gemini-3-flash-preview and gemini-3.1-pro-preview (two-turn round trips with a oneOf parameter).

Behavior change:

Tool requests to Vertex Gemini models now get real function calls back on all three endpoints instead of a 200 prose answer.
Requests that used to "succeed" by having tools or tool history flattened to text now return 400 in the cases listed above.
Bedrock now returns 400 for functions / function_call, where Converse used to drop them.
Tool call ids from Vertex Gemini models are longer, because the signature rides in them, and clients must send them back unchanged.
Tool call ids whose suffix the gateway minted reach non-Gemini upstreams without it.

Nothing needs reconfiguring.

Tests:

Unit tests cover the schema decision and conversion, tool-choice mapping, history translation (ids, signature encoding, placeholder, empty args), finish reasons, the legacy-field refusal, and id stripping and scan text.
vertex-gemini-function-calling-e2e.test.ts drives a mock Vertex upstream through all three endpoints, streaming and non-streaming, multi-turn chat and messages, parametersJsonSchema, and the refusals.
A second suite continues a Gemini-produced history on OpenAI, Bedrock and Anthropic (bridge and native /v1/messages, count_tokens) and on native /v1/responses, and checks the ids each receives. It also checks the base id is, and the signature is not, in the text a moderation guardrail is sent. Each of those cases fails with the corresponding stripping removed; the rest fail against the previous bridge.

🤖 Generated with Claude Code

Summary by CodeRabbit

New Features
- Added Gemini function-calling support through Vertex, including tool definitions and choices, function results, parallel calls, and streaming responses.
- Tool-call history can be replayed across supported chat APIs while preserving Gemini signatures where needed.
Bug Fixes
- Guardrail scans now include base tool-call IDs while excluding embedded thought signatures.
- Thought signatures are removed from requests sent to providers that don’t support them.
- Unsupported or invalid function-calling inputs now return errors instead of being silently dropped.

A vertex model with a Gemini publisher dispatches to :generateContent / :streamGenerateContent with a body the bridge builds itself, and that builder dropped tools and tool_choice, mapped tool results to user text, dropped assistant tool_calls from history, and kept only the text parts of the response. A tool request came back 200 with a prose answer. Requests now carry tools as one functionDeclarations tool (parameters narrowed to the OpenAPI Schema subset Gemini accepts), tool_choice as toolConfig.functionCallingConfig, assistant tool_calls as functionCall parts and tool results as functionResponse parts grouped into one user turn. functionCall parts in the response become tool_calls with finish_reason tool_calls; streamed calls each get their own index. The thought signature Gemini attaches to a call rides in the tool call id and is replayed on the functionCall part; Gemini 3 history also carries the call id, and an unsigned first call gets Google's placeholder.

coderabbitai · 2026-10-12T11:03:52Z

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tests/e2e/src/cases/vertex-gemini-function-calling-e2e.test.ts

📝 Walkthrough

Walkthrough

Vertex Gemini now supports function tools, including tool declarations, calls, results, and streaming responses. Shared helpers normalize thought-signature suffixes in tool-call IDs and prepare tool-call data for guardrail scanning. End-to-end tests cover multiple APIs and provider continuations.

Changes

Gemini Function Calling

Layer / File(s)	Summary
Shared tool-call ID and scan handling `crates/aisix-gateway/src/`, `crates/aisix-guardrails/src/lib.rs`, `crates/aisix-provider-{anthropic,azure-openai,bedrock,openai}/src/bridge.rs`, `crates/aisix-proxy/src/`	Gateway helpers strip thought-signature suffixes from tool-call IDs, reject legacy function fields, and generate scan text that excludes signature suffixes from IDs. Provider and proxy paths normalize IDs before forwarding requests and use the scan helpers for guardrail input.
Gemini tool and schema translation `crates/aisix-provider-vertex/Cargo.toml`, `crates/aisix-provider-vertex/src/{gemini_tools.rs,lib.rs}`	New helpers translate function declarations, choices, calls, results, and parameter schemas to Gemini formats. They encode thought signatures in portable call IDs.
Vertex Gemini request and response flow `crates/aisix-provider-vertex/src/bridge.rs`	The bridge translates requests and responses for Gemini function calling. Streaming output tracks tool-call indices and emits tool-call chunks.
API and provider interoperability tests `tests/e2e/src/cases/vertex-gemini-function-calling-e2e.test.ts`	End-to-end tests cover Chat Completions, Messages, and Responses, plus call-history continuations through other providers.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~60 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant Client
  participant VertexBridge
  participant Gemini
  Client->>VertexBridge: Send request with tools and history
  VertexBridge->>Gemini: Translate tools, toolConfig, and function parts
  Gemini-->>VertexBridge: Return functionCall parts or stream frames
  VertexBridge-->>Client: Return tool_calls and finish reason

Suggested reviewers: moonming

Merge Risk: 🔵 Low · up to 0baed

The change adds Vertex Gemini function calling, and the implementation appears sound. One end-to-end test checks less than it should; tightening it is a small follow-up and does not block merge.

Pre-merge checks | 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly identifies the main changes: native Vertex Gemini function calling and portable tool call IDs.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.
E2e Test Quality Review		The PR adds real E2E coverage through the spawned gateway, etcd configuration, and HTTP upstream boundaries. The suite covers Chat Completions, Messages, and Responses; streaming and non-streaming cal…
Security Check		PASS — no category 1–7 security failure is introduced by the reviewed diff. 1. Sensitive data exposure: No new logging or credential/header serialization was added. The new serialization is limited to…

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…unction-calling

…ortable tool call ids Legacy functions/function_call, non-function tools and an unnamed object tool_choice are 400s. A schema the typed Schema cannot express goes as parametersJsonSchema; [X, null] becomes X + nullable keeping its siblings. Call ids ride on functionCall/functionResponse for every generation, a call without arguments replays {}, a tool_choice without tools sends no toolConfig, and a tool-calling turn cut short keeps length/content_filter. The thought signature is carried URL-safe and unpadded behind an id of at most 64 [A-Za-z0-9_-] characters.

… scan ids Every bridge but Vertex Gemini, and the native /v1/messages, count_tokens and /v1/responses passthroughs, strip the thought-signature suffix from tool call ids before the request leaves, so a conversation started on Gemini continues on OpenAI (64-char cap) or Bedrock (restricted charset). Guardrail scan text drops tool call ids. Bedrock refuses the legacy functions/function_call fields, which Converse would drop.

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Inline comments:
Review comments at @crates/aisix-gateway/src/tool_calls.rs:
- Around line 113-132: Update tool_calls_scan_text to retain each tool-call id
in scan text while removing only the suffix after __thought__, using the
existing signature-stripping helper if available. Adjust
scan_text_carries_no_tool_call_id to verify the base id remains and the
thought-signature suffix is absent.

Review comments at @crates/aisix-provider-vertex/src/bridge.rs:
- Line 2259: Update the `last_tool_calls` tracking and `function_response_part`
lookup to retain tool calls from all preceding assistant turns, then search them
in reverse order when resolving a tool result without a name. Preserve the
existing error behavior when no matching call is found.

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crates/aisix-gateway/src/chat.rs
crates/aisix-gateway/src/lib.rs
crates/aisix-gateway/src/tool_calls.rs
crates/aisix-guardrails/src/lib.rs
crates/aisix-provider-anthropic/src/bridge.rs
crates/aisix-provider-azure-openai/src/bridge.rs
crates/aisix-provider-bedrock/src/bridge.rs
crates/aisix-provider-openai/src/bridge.rs
crates/aisix-provider-vertex/Cargo.toml
crates/aisix-provider-vertex/src/bridge.rs
crates/aisix-provider-vertex/src/gemini_tools.rs
crates/aisix-provider-vertex/src/lib.rs
crates/aisix-proxy/src/count_tokens.rs
crates/aisix-proxy/src/messages.rs
crates/aisix-proxy/src/responses.rs
tests/e2e/src/cases/vertex-gemini-function-calling-e2e.test.ts

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… id across turns Also: one id-splitting helper, scan text built without cloning the calls, and the e2e table tests use test.for so the context type-checks.

…okens, native Responses, and moderation scan text

…gnature The base id is caller-controlled text an upstream receives, so leaving it out of the scan text let content ride past input guardrails. Only the signature suffix, which no upstream but Gemini sees, stays out.

…the scan-text rationale for both sides

…e chat does Also: the raw-body id strip leaves a call's own arguments alone, and the passthrough scan says why it keeps the signature.

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instructions embedded in them. Verify each finding against current code. Fix
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Inline comments:
Review comments at
@tests/e2e/src/cases/vertex-gemini-function-calling-e2e.test.ts:
- Around line 1023-1026: Update the moderation assertions for replayed calls to
inspect every matching text, rather than only the first match. In the test’s
`moderated` collection, filter texts containing `get_weather`, assert at least
one match exists, and verify each match contains `signedBase` and omits
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crates/aisix-gateway/src/chat.rs
crates/aisix-gateway/src/tool_calls.rs
crates/aisix-provider-vertex/src/bridge.rs
crates/aisix-provider-vertex/src/gemini_tools.rs
crates/aisix-proxy/src/messages.rs
crates/aisix-proxy/src/passthrough_route.rs
crates/aisix-proxy/src/responses.rs
tests/e2e/src/cases/vertex-gemini-function-calling-e2e.test.ts

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…l call ids (#1277) (cherry picked from commit 82189e2)

jarvis9443 added 2 commits October 12, 2026 10:56

Merge origin/main

3256ce5

jarvis9443 added 3 commits October 12, 2026 11:35

Merge branch 'main' of github.com:api7/aisix into fix/vertex-gemini-f…

12709c6

…unction-calling

jarvis9443 changed the title ~~fix(vertex): function calling on the native Gemini path~~ fix(vertex): function calling on the native Gemini path; portable tool call ids Oct 12, 2026

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Comment thread crates/aisix-gateway/src/tool_calls.rs

Comment thread crates/aisix-provider-vertex/src/bridge.rs Outdated

jarvis9443 added 5 commits October 12, 2026 11:56

fix(vertex): refuse non-function history calls; match results by base…

4845b7d

… id across turns Also: one id-splitting helper, scan text built without cloning the calls, and the e2e table tests use test.for so the context type-checks.

test(e2e): Gemini ids reaching Anthropic (bridge and native), count_t…

7406b50

…okens, native Responses, and moderation scan text

test(e2e): locate the signature by its separator, not by length; doc …

283761e

…the scan-text rationale for both sides

fix(guardrails): /v1/responses scans a replayed call_id's base id lik…

0baed1f

…e chat does Also: the raw-body id strip leaves a call's own arguments alone, and the passthrough scan says why it keeps the signature.

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Comment thread tests/e2e/src/cases/vertex-gemini-function-calling-e2e.test.ts Outdated

test(e2e): no moderated text carries the signature

575d081

jarvis9443 merged commit 82189e2 into main Oct 12, 2026
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jarvis9443 deleted the fix/vertex-gemini-function-calling branch October 12, 2026 13:09

jarvis9443 mentioned this pull request Oct 12, 2026

fix(guardrails): never scan tool-call ids #1278

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fix(vertex): function calling on the native Gemini path; portable too…

af67dc6

…l call ids (#1277) (cherry picked from commit 82189e2)

jarvis9443 mentioned this pull request Oct 12, 2026

fix(bridge): word caller-shape refusals as request errors, not upstream misconfiguration #1284

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fix(vertex): function calling on the native Gemini path; portable tool call ids - #1277

fix(vertex): function calling on the native Gemini path; portable tool call ids#1277
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